Structure_of_Matter_-___________Science_Lesson_3_G10.pdf

👨🏻‍🎓 Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 Tags https://youtu.be/86_6ntKEtKU?si=GFsr3VV8WiVKHo2I Structure of Matter Matter(පදාර්ථ ) is composed of tiny particles called atoms(පරමාණුව), which are the fundamental building blocks of all substances. Atoms consist of three main subatomic particles: Protons - positively charged particles found in the nucleus Neutrons - neutral particles also found in the nucleus Electrons - negatively charged particles that orbit the nucleus in shells Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 1 The number of protons determines what element the atom is. For example, an atom with 6 protons is a carbon atom, while an atom with 8 protons is an oxygen atom. Atoms can combine in various ways to form molecules, which are the smallest units of a compound that still retain the compound's properties. Molecules are formed when atoms bond together, either by sharing electrons (covalent bonds) or by transferring electrons (ionic bonds). The three fundamental states of matter - solid, liquid, and gas - are determined by the arrangement and motion of atoms and molecules. In solids, atoms are closely packed and vibrate in fixed positions. In liquids, atoms are still close together but can move around each other. In gases, atoms are far apart and move randomly. The structure of matter can be further classified into pure substances and mixtures. Pure substances contain only one type of atom or molecule, while mixtures contain multiple substances physically combined. Understanding the structure of matter at the atomic and molecular level is fundamental to explaining the properties and behavior of all materials in the universe. This knowledge forms the basis for the fields of chemistry, materials science, and condensed matter physics. Classification of Matter 1. Based on Composition රසායනික සංයුතිය අනුව A. Pure Substances Definition: Matter that has a uniform and definite composition. Types: Elements: Substances that cannot be broken down into simpler substances by chemical means. Examples: Hydrogen (H), Oxygen (O), Gold (Au). Compounds: Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 2 Substances formed when two or more elements chemically combine in fixed ratios. Examples: Water (H₂O), Carbon Dioxide (CO₂), Sodium Chloride (NaCl). B. Mixtures Definition: Matter that consists of two or more substances physically combined, which can be separated by physical means. Types: Homogeneous Mixtures (Solutions): Mixtures that have a uniform composition throughout. Examples: Saltwater, air, vinegar. Heterogeneous Mixtures: Mixtures that do not have a uniform composition and can be easily separated. Examples: Salad, soil, and oil and water mixtures. 2. Based on Physical State A. Solids Have a definite shape and volume. Particles are closely packed and vibrate in fixed positions. B. Liquids Have a definite volume but take the shape of their container. Particles are close together but can move past one another. C. Gases Have neither a definite shape nor volume. Particles are far apart and move freely. 3. Based on Properties Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 3 A. Physical Properties Characteristics that can be observed or measured without changing the substance's composition. Examples: Color, melting point, boiling point, density. B. Chemical Properties Characteristics that describe how a substance interacts with other substances and changes into new substances. Examples: Reactivity with acids, flammability, oxidation states. Summary Table Classification Subcategories Examples Based on Composition Pure Substances Elements (O, H), Compounds (H₂O) Mixtures Saltwater, salad Based on Physical State Solids Ice, wood Liquids Water, oil Gases Oxygen, carbon dioxide Based on Properties Physical Properties Color, density Chemical Properties Reactivity, flammability Structure of Matter Chart Category Details The basic units of matter, consisting of protons, neutrons, and Atoms electrons. Subatomic Particles - Protons: Positively charged, found in the nucleus. - Neutrons: Neutral, also found in the nucleus. - Electrons: Negatively charged, orbit the nucleus in shells. Types of Bonds - Covalent Bonds: Atoms share electrons. - Ionic Bonds: Atoms transfer electrons, resulting in charged ions. States of Matter - Solid: Atoms are closely packed and vibrate in fixed positions. - Liquid: Atoms are close but can move around each other. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 4 - Gas: Atoms are far apart and move randomly. Classifications of - Pure Substances: Contain only one type of atom or molecule Matter (e.g., elements, compounds). - Mixtures: Contain two or more substances physically combined (e.g., air, salad). Structure of Matter 1. Atoms The basic units of matter. Composed of: Protons: Positively charged particles located in the nucleus. Neutrons: Neutral particles also found in the nucleus. Electrons: Negatively charged particles that orbit the nucleus in shells. 2. Subatomic Particles Protons: Determine the element (e.g., 6 protons = carbon). Neutrons: Contribute to the atomic mass and stability. Electrons: Involved in bonding and chemical reactions. 3. Types of Bonds Covalent Bonds: Atoms share electrons to form molecules. Ionic Bonds: Atoms transfer electrons, resulting in charged ions that attract each other. 4. States of Matter Solid: Atoms are closely packed. Vibrate in fixed positions. Liquid: Atoms are close but can move around each other. Have a definite volume but take the shape of their container. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 5 Gas: Atoms are far apart and move randomly. Have neither a definite shape nor volume. 5. Classifications of Matter Pure Substances: Contain only one type of atom or molecule. Examples: Elements (like gold, oxygen) and compounds (like water, carbon dioxide). Mixtures: Contain two or more substances physically combined. Examples: Air (a mixture of gases), salad (a mixture of vegetables). Structure of Atoms Atoms are the fundamental building blocks of matter, consisting of three main subatomic particles: protons, neutrons, and electrons. The structure of an atom can be described as follows: Nucleus Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 6 The nucleus is the dense, central core of an atom. It contains protons and neutrons. Protons are positively charged particles. The number of protons determines the element. Neutrons are neutral particles that add to the atomic mass. Electron Shells Electrons are negatively charged particles that orbit the nucleus in shells or energy levels. The number of electrons equals the number of protons in a neutral atom. Electrons occupy most of an atom's volume but have very little mass compared to protons and neutrons. Atomic Number and Mass Number The atomic number is the number of protons in the nucleus of an atom. The mass number is the sum of the number of protons and neutrons in the nucleus. Atoms of the same element have the same atomic number but can have different mass numbers due to varying numbers of neutrons. Isotopes Isotopes are atoms of the same element with the same atomic number but different mass numbers. Isotopes have the same chemical properties but may have different physical properties and stabilities. Atomic Structure and Bonding The arrangement and number of protons, neutrons, and electrons determine an atom's properties and how it interacts with other atoms. Atoms can form chemical bonds by sharing or transferring electrons to achieve a stable configuration. The type of bonds formed depends on the atoms involved and their positions in the periodic table. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 7 Understanding the structure of atoms is crucial for explaining the behavior of matter at the most fundamental level. It forms the basis for understanding chemical reactions, the formation of molecules, and the properties of elements and compounds. Structure of Atom K, L, M, and N refer to the electron shells in an atom, which are layers where electrons are found around the nucleus. Each shell can hold a specific maximum number of electrons, and they are designated as follows: Electron Shells K Shell: The first shell, closest to the nucleus. L Shell: The second shell. M Shell: The third shell. N Shell: The fourth shell. Maximum Number of Electrons in Each Shell The maximum number of electrons that can be accommodated in each shell is given by the formula $$2n^2$$, where $$n$$ is the shell number: Shell Name Shell Number (n) Max Electrons K 1 2 Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 8 L 2 8 M 3 18 N 4 32 Summary K Shell (n=1): Can hold up to 2 electrons. L Shell (n=2): Can hold up to 8 electrons. M Shell (n=3): Can hold up to 18 electrons. N Shell (n=4): Can hold up to 32 electrons. This structure is fundamental in understanding how electrons are arranged in atoms and how they influence chemical properties and reactions. The Scientists who is involved in this 1. Ernest Rutherford: Conducted the gold foil experiment in 1909, leading to the discovery of the atomic nucleus. 2. Niels Bohr: Proposed the Bohr model of the atom in 1913, which introduced the concept of quantized electron shells. Niels Bohr introduced the concept of quantized electron shells in 1913 through his model of the atom. This model fundamentally changed the understanding of atomic structure by proposing that electrons orbit the nucleus in specific, discrete energy levels rather than in a continuous range of distances. Key Features of Bohr's Model 1. Quantized Orbits: Electrons are restricted to certain allowed orbits or energy levels, known as "stationary states." Each orbit corresponds to a specific energy level. 2. Energy Absorption and Emission: Electrons can move between these quantized orbits by absorbing or emitting energy in discrete amounts (quanta). When an electron absorbs energy, it jumps to a higher energy level (excited state), and Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 9 when it loses energy, it falls back to a lower level, emitting a photon of light in the process. 3. Angular Momentum Quantization: Bohr proposed that the angular momentum of an electron in its orbit is quantized, meaning it can only take on specific values. This is expressed mathematically as: $$ L = n\frac{h}{2\pi} $$ where $$L$$ is the angular momentum, $$n$$ is a positive integer (the principal quantum number), and $$h$$ is Planck's constant. 4. Spectral Lines: The quantization of energy levels explains the discrete spectral lines observed in atomic spectra. Each transition between energy levels corresponds to a specific wavelength of light, resulting in distinct spectral lines. Implications Bohr's introduction of quantized electron shells provided a framework for understanding the behavior of electrons in atoms, particularly for hydrogen. This model was pivotal in the development of quantum mechanics and laid the groundwork for future theories regarding atomic structure and chemical bonding. Although later models refined and expanded upon Bohr's ideas, his concept of quantized orbits remains a fundamental principle in atomic physics. The atomic number is defined as the number of protons present in the nucleus of an atom. It is a fundamental characteristic of each chemical element, determining its identity and position in the periodic table. Key Points about Atomic Number: 1. Symbol: The atomic number is represented by the letter Z. 2. Element Identification: Each element has a unique atomic number. For example, hydrogen has an atomic number of 1 (one proton), while carbon has an atomic number of 6 (six protons). 3. Neutral Atoms: In a neutral atom, the number of protons equals the number of electrons. Therefore, the atomic number also indicates the Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 10 number of electrons in a neutral atom. 4. Periodic Table Organization: The elements in the periodic table are arranged in order of increasing atomic number, which reflects their increasing number of protons. 5. Mass Number Relation: The atomic number is distinct from the mass number, which is the sum of protons and neutrons in the nucleus. Isotopes of an element have the same atomic number but different mass numbers due to varying numbers of neutrons. 6. Charge and Ions: If an atom has a different number of electrons than protons, it becomes an ion, carrying a positive or negative charge. In summary, the atomic number is crucial for defining the properties of elements and their behavior in chemical reactions. It serves as a unique identifier for each element in the periodic table. The mass number (symbol A) is the total number of protons and neutrons in the nucleus of an atom. It provides an approximation of the atom's mass and is crucial for distinguishing between different isotopes of an element. Key Points about Mass Number: 1. Definition: Mass number is defined as: A = Number of Protons+ Number of Neutrons Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 11 2. Protons and Neutrons: Protons are positively charged particles, while neutrons have no charge. Together, they are known as nucleons. 3. Isotopes: Different isotopes of the same element have the same atomic number (number of protons) but different mass numbers due to varying numbers of neutrons. For example, carbon-12 (¹²C) has 6 protons and 6 neutrons, while carbon-14 (¹⁴C) has 6 protons and 8 neutrons. 4. Notation: The mass number is typically written as a superscript to the left of the element symbol. For example, the notation for carbon-12 is written as: 12 Mass Number 6 Atomic Number C Here, 12 is the mass number, and 6 is the atomic number (number of protons). 5. Whole Numbers: The mass number is always a whole number because it counts discrete particles (protons and neutrons). 6. Relation to Atomic Mass: While the mass number is an integer, the atomic mass (average mass of an atom) can be a fraction due to the presence of different isotopes and their relative abundances. 7. Importance: The mass number is essential in nuclear chemistry and physics, as it helps in understanding nuclear stability, radioactive decay, and the behavior of isotopes. In summary, the mass number is a fundamental concept in atomic structure, providing insight into the composition of an atom's nucleus and its isotopes. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 12 💡 Example ( The mass number of sodium (Na) is 23. Its atomic number is 11. A 23 X Na Z 11 A - mass number atomic number - 11 Z - atomic number mass number - 23 Electronic Configuration Electronic configuration refers to the arrangement of electrons in an atom or molecule, distributed among atomic or molecular orbitals. This concept is fundamental in understanding the structure of matter, particularly in atomic physics and quantum chemistry. Definition and Importance The electronic configuration of an atom is expressed by listing the occupied orbitals in order of increasing energy, with the number of electrons in each orbital indicated by superscripts. For example, the electron configuration of neon is written as $$1s^2 2s^2 2p^6$$, meaning that the 1s, 2s, and 2p orbitals are filled with two, two, and six electrons, respectively. Understanding electronic configurations is crucial because they help explain various properties of elements, including their chemical behavior and bonding characteristics. For instance, elements in the same group of the periodic table exhibit similar chemical properties due to their analogous electronic configurations, particularly in their outermost electron shells, known as valence electrons. Quantum Mechanical Model In the quantum mechanical model, electrons are not viewed as particles in fixed orbits but rather as moving independently in orbitals, which are regions of space around the nucleus where the probability of finding an electron is Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 13 high. Each orbital can hold a specific number of electrons: 2 for s orbitals, 6 for p orbitals, 10 for d orbitals, and 14 for f orbitals. The filling of these orbitals follows the Aufbau principle, which states that electrons occupy the lowest energy orbitals first. This is complemented by the Pauli Exclusion Principle, which asserts that no two electrons can have the same set of quantum numbers within an atom, and Hund's Rule, which states that electrons will fill degenerate orbitals singly before pairing up. Applications Knowledge of electronic configurations allows scientists to predict and explain the chemical reactivity of elements, the formation of ions, and the types of bonds they can form. For example, when sodium (Na) loses an electron to form a cation (Na⁺), its electron configuration changes from $$1s^2 2s^2 2p^6 3s^1$$ to $$1s^2 2s^2 2p^6$$, resembling that of the noble gas neon, which is more stable. In summary, electronic configuration is a key concept in the structure of matter, providing insights into the behavior and properties of atoms and molecules. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 14 💡 Easiest way to remember Periodic Table හායි(h) හිලී(he) ලිලීගෙ(li) බෙල්ල(be) බල්ලො(b) කාලා(c) නන්ගි(n) ඔතන(o) ෆයිට්(f) නේද(ne) නංගි(na) මගේ(mg) අල්ල(al) සි(si) ප(p) සනසන(s) කෙල්ල(cl) අර(ar) කොල්ලට(k) කැමති.(ca) Modern Periodic Table The modern periodic table is an organized arrangement of chemical elements based on their atomic numbers, electron configurations, and recurring chemical properties. Here are some key features and historical insights regarding the modern periodic table: Key Features Arrangement: Elements are arranged in rows called periods and columns known as groups. The table is structured so that elements with similar properties are grouped together in the same column, allowing for easy identification of trends and relationships among elements. Atomic Number: The modern periodic law states that when elements are arranged in order of increasing atomic number, there is a periodic recurrence of their properties. This is a shift from earlier models that were based on atomic mass. Blocks: The table is divided into blocks (s, p, d, f) based on the electron configurations of the elements. This classification helps in understanding the chemical behavior of the elements. Trends: Several trends can be observed in the periodic table, such as metallic character increasing down a group and decreasing across a period, while non-metallic character increases from left to right. Historical Development Dmitri Mendeleev: The first widely accepted periodic table was created by Mendeleev in 1869. He organized elements by atomic mass and left gaps Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 15 for undiscovered elements, predicting their properties. Modernization: The modern periodic table evolved significantly with the discovery of atomic numbers and advancements in quantum mechanics. Glenn T. Seaborg's work in the mid-20th century further refined the table, particularly the placement of actinides and lanthanides. Recognition: The periodic table is celebrated for its significance in science, with the United Nations declaring 2019 as the International Year of the Periodic Table to honor its 150th anniversary. The modern periodic table is not only a fundamental tool in chemistry but also a vital reference in physics and other scientific disciplines, aiding in the understanding of elemental properties and their interactions. Dividing Elements into Periods Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Period 1 1 2 H He 2 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 3 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 4 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 55 56 * 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 87 88 * 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 Fr Ra * Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og * 57 58 59 60 61 62 63 64 65 66 67 68 69 70 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb * 89 90 91 92 93 94 95 96 97 98 99 100 101 102 * Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No The periodic table is organized into horizontal rows called periods and vertical columns known as groups. Here’s a breakdown of how elements are divided into periods: Periods in the Periodic Table Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 16 Total Number of Periods: There are seven periods in the modern periodic table, each corresponding to the number of electron shells that the elements in that period possess. Elements in Each Period: Period 1: Contains 2 elements (Hydrogen and Helium). Period 2: Contains 8 elements (Lithium to Neon). Period 3: Contains 8 elements (Sodium to Argon). Period 4: Contains 18 elements (Potassium to Krypton). Period 5: Contains 18 elements (Rubidium to Xenon). Period 6: Contains 32 elements (Cesium to Radon), including the lanthanides. Period 7: Contains 32 elements (Francium to Oganesson), including the actinides. Characteristics of Periods Electron Shells: All elements in a given period have the same number of electron shells. For example, all elements in Period 2 have two electron shells. Increasing Atomic Number: As you move from left to right across a period, the atomic number increases, meaning each subsequent element has one more proton and electron than the previous one. Metallic to Non-metallic Character: Generally, elements become less metallic and more non-metallic as you move from left to right across a period. For example, sodium (a metal) is on the left, while chlorine (a non- metal) is on the right. Chemical Properties: Elements within the same period do not exhibit similar chemical properties; this similarity is more pronounced within groups (vertical columns) rather than periods. Understanding the structure of periods in the periodic table is essential for predicting the behavior and properties of elements based on their position in the table. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 17 Dividing Elements into groups Here’s a breakdown of the first 20 elements of the periodic table organized into groups I to VIII (or 0 for noble gases): Group Number Group Name Elements in Group (1-20) H (Hydrogen), Li (Lithium), Na (Sodium), K I Alkali Metals (Potassium) Alkaline Earth II Be (Beryllium), Mg (Magnesium), Ca (Calcium) Metals III Boron Group B (Boron), Al (Aluminum) IV Carbon Group C (Carbon), Si (Silicon) V Nitrogen Group N (Nitrogen), P (Phosphorus) VI Chalcogens O (Oxygen), S (Sulfur) VII Halogens F (Fluorine), Cl (Chlorine) VIII/0 Noble Gases He (Helium), Ne (Neon), Ar (Argon) Summary of Groups for the First 20 Elements Group I: Alkali Metals (H, Li, Na, K) Group II: Alkaline Earth Metals (Be, Mg, Ca) Group III: Boron Group (B, Al) Group IV: Carbon Group (C, Si) Group V: Nitrogen Group (N, P) Group VI: Chalcogens (O, S) Group VII: Halogens (F, Cl) Group VIII/0: Noble Gases (He, Ne, Ar) This classification provides a clear view of how the first 20 elements fit into the traditional groupings of the periodic table. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 18 Isotopes Isotopes are variants of a chemical element that have the same number of protons but differ in the number of neutrons within their atomic nuclei. This difference in neutron count results in variations in atomic mass while maintaining the same chemical properties. For example, carbon has three stable isotopes: Carbon-12 (with 6 neutrons), Carbon-13 (with 7 neutrons), and Carbon-14 (with 8 neutrons). Key Characteristics of Isotopes Atomic Number: All isotopes of an element share the same atomic number, which is determined by the number of protons. This means they occupy the same position in the periodic table. Mass Number: The mass number, which is the sum of protons and neutrons, varies between isotopes. For instance, Carbon-12 has a mass number of 12, while Carbon-14 has a mass number of 14. Types of Isotopes: Isotopes can be classified as stable or radioactive. Stable isotopes do not undergo radioactive decay, while radioactive isotopes (or radioisotopes) are unstable and decay over time, emitting radiation. Examples of radioactive isotopes include Carbon-14 and Uranium-238. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 19 Applications of Isotopes Isotopes have various applications in fields such as medicine, archaeology, and environmental science. For example, Carbon-14 dating is used to determine the age of ancient organic materials, while radioactive isotopes are employed in medical imaging and cancer treatment. In summary, isotopes are crucial for understanding the behavior of elements in different contexts, from chemical reactions to applications in technology and research. Examples for isotopes Hydrogen has three isotopes. They are called protium, deuterium and tritium Chlorine has two isotopes. They are, Chlorine-35 Chlorine-37 Patterns Seen in the Periodic Table Periodic trends refer to specific patterns observed in the properties of elements as they are arranged in the periodic table. These trends arise due to the Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 20 similarities in electron configurations among elements within the same group or period. To study those patterns, let's consider the following properties of the elements. First ionization energy Electronegativity First ionization Energy First ionization energy refers to the energy required to remove the most loosely bound electron from a neutral gaseous atom, resulting in the formation of a cation with a +1 charge. This energy is crucial in understanding the reactivity and chemical behavior of elements. Trends in First Ionization Energy 1. Across a Period: Increase in Ionization Energy: As you move from left to right across a period in the periodic table, the first ionization energy generally increases. This is due to: Increasing Nuclear Charge: The number of protons in the nucleus increases, enhancing the positive charge and the attraction between the nucleus and the electrons. Decreasing Atomic Radius: The atomic size decreases because the added electrons enter the same energy level, and the increased nuclear charge pulls the electrons closer to the nucleus, making them harder to remove. 2. Down a Group: Decrease in Ionization Energy: As you move down a group, the first ionization energy generally decreases. This is attributed to: Increasing Atomic Radius: Additional electron shells are added, increasing the distance between the nucleus and the outermost electron, which reduces the nuclear attraction. Increased Shielding Effect: More inner electron shells result in greater shielding, which diminishes the effective nuclear charge felt by the outermost electron, making it easier to remove. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 21 Exceptions to the Trend There are notable exceptions to the general trends in ionization energy: Group 2 to Group 3 Transition: For example, the first ionization energy of boron is lower than that of beryllium, despite boron having a higher nuclear charge. This is because boron's outer electron is in a higher energy 2p subshell, which is further from the nucleus and experiences more shielding than the 2s electron in beryllium. Half-Filled and Fully Filled Subshells: Elements with half-filled or fully filled subshells may exhibit lower ionization energies due to electron-electron repulsion being alleviated when an electron is removed. For instance, oxygen has a lower ionization energy than nitrogen, as removing an electron from oxygen reduces the repulsion between paired electrons in its p subshell. Summary of Trends Property Across a Period Down a Group First Ionization Energy Increases Decreases Understanding these trends in first ionization energy helps predict the reactivity of elements and their tendency to form ions, which is fundamental in chemistry. The formation of a unipositive gaseous ion by removing an electron from an atom in the gaseous state can be represented by a chemical equation as follows. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 22 Mole - මවුල What is a Mole? Definition: A mole is a unit used in chemistry to measure the amount of a substance. Avogadro's Constant: One mole contains 6.022 x 10²³ particles. This number is called Avogadro's number and it can refer to atoms, molecules, Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 23 ions, or other entities. Why Use Moles? Counting Particles: Just like a dozen means 12 items, a mole is a way to count a large number of tiny particles (like atoms or molecules) in a manageable way. Connecting Mass and Particles: The mole helps chemists relate the mass of a substance to the number of particles it contains. For example, 1 mole of water (H₂O) weighs about 18 grams and contains approximately 6.022 x 10²³ water molecules. Everyday Example Baking: If you think of a recipe that calls for 2 dozen eggs, you know you need 24 eggs. Similarly, if a chemical reaction needs 1 mole of a substance, it means you need 6.022 x 10²³ of those particles to make it work. Summary In short, a mole is a convenient way to count and measure substances in chemistry, making it easier to work with the tiny particles that make up everything around us! Electronegativity Electronegativity means the ability of an atom of an element to attract the electrons of a bond towards itself when it is bonded to an atom of another element. Key Points About Electronegativity Definition: Electronegativity is the ability of an atom to attract bonding electrons towards itself when forming a chemical bond. The higher the electronegativity value, the stronger the atom's attraction for electrons. Measurement: The most commonly used scale for electronegativity is the Pauling scale, where fluorine is assigned the highest value of 4.0, indicating it is the most electronegative element. Values range down to around 0.7 for the least electronegative elements, such as cesium and Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 24 francium. Pauling scale does not assign electronegativity values to noble gases Trends in the Periodic Table: Across a Period: Electronegativity increases from left to right across a period. This is due to the increasing nuclear charge (more protons in the nucleus), which enhances the atom's ability to attract electrons. Down a Group: Electronegativity decreases as you move down a group. This is because the atomic size increases, and the outer electrons are further from the nucleus, resulting in a weaker attraction. Importance of Electronegativity Chemical Bonding: Electronegativity is crucial in determining the nature of chemical bonds. A large difference in electronegativity between two bonded atoms can lead to ionic bonds, while a small difference typically results in covalent bonds. For example, the bond between hydrogen and chlorine (with differing electronegativities) is polar covalent. Predicting Molecular Behavior: Understanding electronegativity helps predict how molecules will behave in reactions, their polarity, and their overall chemical properties. In summary, electronegativity is a fundamental concept in chemistry that influences how atoms bond and interact with each other, playing a key role in the structure and behavior of molecules. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 25 Metals, Non - metals and Metalloids - ලෝහ අලෝහ ලෝහාලෝහ Metals, non-metals, and metalloids are three broad categories used to classify elements based on their physical and chemical properties. Here’s a concise overview of each category: Metals Physical Properties: Typically hard, shiny, and have a metallic luster. (ලෝහක දිස්නය ) Good conductors of heat and electricity. Malleable (ආහන්‍යතාව )(can be hammered into sheets) and ductile(තන්‍යතාව ) (can be drawn into wires). Most metals are solid at room temperature (except mercury, which is liquid). Have high melting and boiling points, though some, like gallium, can melt at low temperatures. Examples: Iron (Fe), Copper (Cu), Gold (Au), and Aluminum (Al). Chemical Properties of Metals Metals form positive ions or cations by losing electrons. They combine with oxygen to form basic oxides. (භාස්මික ඔක්සයිඩ ) The oxides when dissolved in water form basic solutions. (භාස්මික ද්‍රාවණ ) Some of the metals Sodium Sodium (Na) is a highly reactive metallic element classified in Group I of the Periodic Table. It is never found in its native form due to its reactivity and primarily exists in various compounds, the most notable being sodium chloride (NaCl), commonly found in seawater. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 26 Physical Properties Appearance: Sodium is a soft, silvery-white metal that exhibits a bright metallic luster. Density: It has a density of approximately 0.97 g/cm³, allowing it to float on water. Melting and Boiling Points: Sodium has a melting point of 97.794°C and a boiling point of 882.940°C. Reactivity: Sodium tarnishes quickly when exposed to air, forming sodium oxide. It is a good conductor of heat and electricity and can be easily cut with a knife. Chemical Properties Reactivity with Water: Sodium reacts vigorously with cold water, producing sodium hydroxide (NaOH) and hydrogen gas. Reactivity with Oxygen: It reacts rapidly with oxygen in the air, forming sodium oxide. Reactivity with Acids: Sodium reacts violently with dilute acids(තනුක අම්ලය), producing salt and hydrogen gas. Uses of Sodium Chemical Production: Sodium is used in the production of sodium cyanide for gold and silver extraction, sodium amalgam(සෝඩියම් සරංසය) as a reducing agent in organic chemistry, and in the extraction of metals like titanium and zirconium. Dyes and Lighting: It is also involved in the production of indigo dye for denim and is used in street lamps that emit a characteristic yellow glow. Sodium's high reactivity necessitates careful handling and storage, typically under oil or inert gases to prevent unwanted reactions with moisture and air. Magnesium Magnesium (Mg) is a light, reactive metal that does not occur in its native form in nature. Instead, it is primarily found as magnesium chloride in Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 27 seawater. When exposed to air, magnesium tarnishes, obscuring its luster, but cleaning it reveals a shiny surface. Physical Properties Density: Magnesium has a density of 1,740 kg/m³, which is higher than that of water. Conductivity: It is an excellent conductor of heat and electricity. Appearance: The metal is silvery-white and can be polished to reveal its luster after cleaning. Chemical Properties Reactivity with Air: When heated in air, magnesium burns with a bright white flame, forming magnesium oxide. Reactivity with Water: Magnesium does not react with cold water but reacts with hot water to produce magnesium hydroxide and hydrogen gas. When heated in steam, it forms magnesium oxide and hydrogen gas. Reactivity with Acids: It reacts rapidly with dilute acids, producing magnesium salts and hydrogen gas. Uses of Magnesium Alloys: Magnesium is mixed with aluminum to create an alloy called magnelium, which is strong and corrosion-resistant, making it suitable for the aircraft and automotive industries. Medicines: It is used in the production of medications, such as milk of magnesia, which is used to treat various health conditions. Corrosion Prevention: Magnesium serves as a sacrificial anode to prevent the corrosion of iron. Magnesium's properties and reactivity make it valuable in various industrial applications, particularly in manufacturing and medicine. Non-Metals Physical Properties: Generally lack the properties of metals; they are poor conductors of heat and electricity. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 28 Brittle(භංගුරතාවය ) in solid form and not malleable or ductile. Can exist in various states at room temperature: gases (like oxygen), solids (like sulfur), and liquids (like bromine). Typically have lower melting and boiling points compared to metals. Examples: Oxygen (O), Carbon (C), Nitrogen (N), and Sulfur (S). Chemical Properties of Non – metals Non - metals form negative ions (anions). Many oxides formed by non – metals with oxygen are acidic. Mostly these exist in the gaseous state. They easily dissolve in water and form acids. අම්ල Nitrogen Nitrogen (N₂) is a colorless, odorless gas that constitutes about 78.1% of the Earth's atmosphere by volume. It is essential for life, forming a key component of proteins in both plants and animals, and is also found in soil, organic matter, and various nitrogen compounds. Physical Properties Appearance: Nitrogen is colorless and odorless. Density: It is lighter than air and has a density of approximately 1.2506 grams per liter. Solubility: Nitrogen is slightly soluble in water. Chemical Properties Reactivity: Nitrogen is a non-supporter of combustion and exhibits low reactivity under normal conditions. However, at high temperatures, it can react with non-metals (like oxygen and hydrogen) and metals (such as magnesium and aluminum). Formation of Compounds: Nitrogen reacts with oxygen in the atmosphere when subjected to a strong electric arc, forming nitric oxide (NO), which can further react to produce nitrogen dioxide (NO₂). This process can also occur naturally during lightning. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 29 Ammonia Production: Under specific conditions, nitrogen gas can react with hydrogen gas to form ammonia (NH₃), which is used in fertilizers and explosives. Uses of Nitrogen Industrial Applications: Nitrogen gas is primarily used in the production of ammonia, fertilizers, and other nitrogen compounds. Inert Atmosphere: Due to its inert nature, nitrogen is used to fill electric bulbs and thermometers, preventing oxidation and maintaining a stable environment in electronic device manufacturing. Food Preservation: Nitrogen is utilized in packaging to preserve perishable goods by delaying spoilage and preventing oxidation. Cryogenics: Liquid nitrogen serves as a coolant in various applications, including cryopreservation of biological samples and in cryotherapy. Tire Inflation: Nitrogen is used to fill vehicle tires, as it helps maintain consistent pressure and reduces moisture-related issues. Nitrogen's abundance and non-reactive properties make it invaluable across various industries, from agriculture to electronics and food preservation. Sulfur Sulfur (S) is a non-metallic element that exists in various allotropic forms in nature. It is a poor conductor of electricity and insoluble in water, but highly soluble in carbon disulfide. Physical Properties Appearance: Sulfur occurs as a yellow, brittle solid and can also be found as a white amorphous(අස්ඵටිකරූපි) powder. Solubility: While insoluble in water, sulfur is slightly soluble in organic solvents and highly soluble in carbon disulfide. Chemical Properties Combustion: Sulfur burns with a blue flame in air, producing sulfur dioxide gas. Reactivity with Metals: When heated with sulfur, many metals form metal sulfides. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 30 Uses of Sulfur Industrial Applications: Sulfur is used in the production of sulfuric acid, vulcanization of rubber, and the manufacture of calcium and magnesium sulfites for bleaching wood pulp. Chemical Production: It is used to produce paints containing sulfides, solvents like carbon disulfide, sulfur dioxide gas, matches, crackers, and gunpowder. Agriculture and Medicine: Sulfur is used in the production of vine, beer, and medicines, and as a fungicide. Sulfur's unique properties and wide range of applications make it an important element in various industries, from agriculture to chemical manufacturing. Carbon Carbon is a versatile(බහුරූපි) non-metal element that exists in various allotropes(බහුරූපි), primarily diamond and graphite, each exhibiting distinct physical and chemical properties. Physical Properties Allotropic Forms: Carbon can exist in crystalline(ස්ඵටික ආකාර) forms (diamond, graphite, fullerenes) and amorphous(asස්ඵටික ආකාර) forms (charcoal, lamp soot, coal). Color and State: Except for diamond, which is colorless, other forms of carbon are typically black and exist as solid materials. Density: Diamond has the highest density among carbon allotropes, while other forms, like graphite, have lower densities. Conductivity: Diamond is a poor conductor of electricity, whereas graphite is a good conductor due to the presence of delocalized electrons. Charcoal has absorptive properties, allowing it to trap gases. Chemical Properties Reactivity: Carbon is generally low in reactivity. It combines with oxygen at high temperatures but does not react with acids, bases, or chlorine under normal conditions. However, amorphous forms like charcoal can undergo chemical reactions. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 31 Combustion: When ignited, charcoal reacts with oxygen to produce carbon dioxide. Carbon can also react with calcium oxide at high temperatures to form calcium carbide. Uses of Carbon Different allotropes of carbon have various applications: Form of Carbon Uses Amorphous Carbon Production of black ink, vulcanizing rubber Coal Fuel source Used in pencils, electrodes for electrochemical cells, and as a Graphite lubricant Jewelry, cutting glass and gems, and as pivots in machinery Diamond due to its hardness Charcoal Absorbing gases, purifying water Carbon Fibers and Reinforcement in goods, lightweight and strong materials Tubes Carbon's unique properties and various allotropes make it essential in numerous industrial, technological, and everyday applications, showcasing its versatility as a fundamental element in chemistry and materials science. Metalloids Physical Properties: Have intermediate properties between metals and non-metals. Can exhibit a metallic luster but are brittle and not malleable. Often behave as semiconductors, meaning they can conduct electricity under certain conditions, making them useful in electronics. Can form alloys with metals and may gain or lose electrons in chemical reactions. Examples: Silicon (Si), Germanium (Ge), Arsenic (As), and Boron (B). Summary of Classification Category Properties Examples Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 32 Shiny, good conductors, malleable, Metals Iron, Copper, Gold ductile Non-Metals Dull, poor conductors, brittle Oxygen, Carbon, Nitrogen Silicon, Germanium, Metalloids Intermediate properties, semiconductors Arsenic This classification is essential for understanding the behavior of elements in chemical reactions and their applications in various fields. Silicon Silicon (Si) is the second most abundant element in the Earth's crust, following oxygen. It occurs in both crystalline and amorphous forms, with notable examples including quartz(තිරුවානා), sand, and gemstones like emerald for crystalline silicon, while clay represents its amorphous form. Silicon has a melting point of 1,410°C. Uses of Silicon Electronics: Silicon is essential in the production of transistors and diodes, forming the backbone of modern electronic devices. Solar Cells: Silicon is widely used in the manufacturing of solar cells due to its semiconducting properties. Computer Equipment: It is a critical material in the production of various computer components and integrated circuits. Silicon's unique properties and abundance make it vital for a range of technological applications, particularly in electronics and renewable energy. Boron Boron is a metalloid element that occurs as a black, crystalline solid. It has a high melting point of 2,200°C and a density of 3,300 kg/m³. Boron exhibits relatively low reactivity and does not react even when heated to high temperatures in air. However, at very high temperatures, amorphous boron can react with substances like oxygen, nitrogen, nitric acid, concentrated sulfuric acid, carbon, and sulfur to form the corresponding compounds. Uses of Boron Welding Metals: Boron is used in welding processes to join metals together. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 33 Skin Creams: Boron compounds are used in the production of certain skin creams and cosmetic products. Heat-Resistant Glass: Boron is used in making glass that can withstand high temperatures without breaking or deforming. Acidic, basic and amphoteric(උභයගුණී) nature of oxides Oxides are chemical compounds formed by the combination of elements with oxygen. In Period 3 of the periodic table, the oxides exhibit a clear pattern of acidic, basic, and amphoteric properties as follows: Oxides of Period 3 Elements Element Oxide Acidic/Basic Nature Sodium Na₂O Strongly basic Magnesium MgO Weakly basic Aluminum Al₂O₃ Amphoteric Silicon SiO₂ Weakly acidic Phosphorus P₂O₅ Acidic Sulfur SO₃ Strongly acidic Chlorine Cl₂O₇ Very strongly acidic Trends in Acidic and Basic Properties Basicity Decreases: As you move from left to right across Period 3, the basicity of the oxides decreases. Sodium oxide is strongly basic, while magnesium oxide is weakly basic. Acidity Increases: Conversely, the acidity of the oxides increases from left to right. For instance, aluminum oxide is amphoteric, meaning it can act as both an acid and a base, while silicon dioxide is weakly acidic. Amphoteric Oxides Amphoteric oxides, like aluminum oxide (Al₂O₃), can react with both acids and bases to form salts and water, demonstrating both acidic and basic properties. This dual behavior is characteristic of elements that are near the metalloid line in the periodic table. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 34 Summary In summary, the oxides of Period 3 elements display a trend where basicity decreases and acidity increases from sodium to chlorine. This pattern highlights the transition from strongly basic oxides to strongly acidic ones, with aluminum oxide acting as an amphoteric oxide that can exhibit properties of both acids and bases. Chemical Formulae A chemical formula is a symbolic representation that indicates the composition of a chemical compound, detailing the types and quantities of atoms present. It utilizes chemical element symbols along with numerical subscripts to convey the proportions of each element in the compound. Valency(සංයුජතාව) Valency, also spelled valence, refers to the combining capacity of an atom, indicating how many other atoms it can bond with to form a chemical compound. It is determined by the number of electrons in the outermost shell of an atom, which can be gained, lost, or shared during chemical reactions. Key Points about Valency Definition: Valency is the number of hydrogen atoms that can combine with or displace one atom of a particular element in forming compounds. For example, carbon has a valency of 4, meaning it can form four bonds with other atoms. Types of Valency: Monovalent: Atoms that can form one bond (e.g., hydrogen). Divalent: Atoms that can form two bonds (e.g., oxygen). Trivalent: Atoms that can form three bonds (e.g., nitrogen). Quadrivalent: Atoms that can form four bonds (e.g., carbon). Reactivity: The valency of an element influences its reactivity and the types of compounds it can form. Elements with higher valency typically form stronger bonds. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 35 Applications: Understanding valency is crucial in predicting how different elements will interact in chemical reactions, which is fundamental in fields such as organic chemistry, biochemistry, and materials science. In summary, valency is a fundamental concept in chemistry that helps explain the behavior of atoms in forming compounds, guiding predictions about chemical reactions and the properties of various substances. Writing Formulae using Valency Compounds are formed by the attachment of atoms or ions of elements by chemical bonds. Valences of elements is shown below Writing Formulae Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 36 Polyatomic Ions (Radicals) Polyatomic ions are groups of atoms that are bonded together and carry an overall positive or negative charge. They act as a single unit during chemical reactions. Some key points about polyatomic ions: They are made up of two or more atoms that are covalently bonded together. The atoms in a polyatomic ion are tightly held together and behave as a single entity. Polyatomic ions can have a positive charge (cation) or a negative charge (anion). Examples of common polyatomic ions include: Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 37 Nitrate (NO₃⁻) Sulfate (SO₄²⁻) Phosphate (PO₄³⁻) Ammonium (NH₄⁺) The charge on a polyatomic ion is determined by the total number of protons and electrons in the group of atoms. Polyatomic ions are different from free radicals, which are highly reactive species with unpaired electrons. In summary, polyatomic ions are charged groups of atoms that behave as a single unit during chemical reactions. Understanding their composition and charges is important for writing chemical formulas and equations. Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 38 Summery Structure of Matter - පදාර්ථවල වියූහය Science Lesson 3 G10 39

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