Physical-Science-Lecture-Quarterly-Assessment.docx

Lecture for Physical Science Quarterly Assessment **Lesson 1: The Atom and Its Models, Theories, and Applications** **Atom -- The smallest unit of matter as recognized by chemical properties of molecules.** **The Subatomic Particles:** 1. **Protons -- positively charged** 2. **Electrons -- n...

Lecture for Physical Science Quarterly Assessment **Lesson 1: The Atom and Its Models, Theories, and Applications** **Atom -- The smallest unit of matter as recognized by chemical properties of molecules.** **The Subatomic Particles:** 1. **Protons -- positively charged** 2. **Electrons -- negatively charged particles** 3. **Neutrons -- neutrally charged particles** **Early days of the Atomic Theory:** - **5th Century BC** - **Greek Philosophers hypothesized about the composition of matter** - **Some ideas were accepted than the others** **Ancient Greek** **Democritus -- He was among the first to suggest the existence of atoms. Everything is made up of small indivisible and indestructible particles known as atomos (Greek word meaning "not to be cut"). His atomic model was called "solid sphere model".** **Leucippus -- He was a teacher of Democritus. Pioneered the ideas of composition and change in matter. Both Democritus and Leucippus were the first Greek scholars who believed in atomism.** **According to Atomism:** - **Matter is composed of atomos and void (no existence).** - **The atomos may combine to form clusters in the void.** - **Change can happen when some atoms collide with each other in the void.** **Aristotle -- Did not believe in Atomism. Aristotle thought the idea of the atom goes against ex nihilo and it limits the power of the gods.** **Aristotle's nature elements:** 1. **Earth** 2. **Fire** 3. **Air** 4. **Water** **John Dalton -- An English Chemist in the early 1800s who performed a number of experiments that eventually led to the acceptance of the idea of atoms.** **Dalton's Atomic Theory** - **Matter is made up of indivisible atoms. Atoms of the same elements have the same properties.** - **Atoms cannot be created nor destroyed. These can only be combined, separated or rearranged.** - **Atoms of the same or different elements may combine with each other in a fixed, whole number ratio.** **Laws Used by Dalton** - **Law of Definite Proportion** - **Law of Multiple Proportion** - **Law of Conservation of Mass and Energy** **J.J. Thomson -- An English scientist who created the Plum Pudding Model. He found out that an atom consists of a positive and negative charge. The Plum Pudding Model is a sphere with a uniformly distributed positive charge and enough embedded electrons to neutralize the positive charge. Discovered atoms have negative particles (electrons) using a cathode ray tube.** **Ernest Rutherford -- He is a student of Thomson's, who was among many who studied radioactivity. He concluded that radioactivity occurred due to changes on a subatomic level, or changes within the atom itself. Thomson's laboratory where he distinguished two kinds of radiation based on their penetrating power: α (alpha) and β (beta). Used the Gold Foil Experiment and created the Nuclear model which stated that the atom is composed of positive and negatively charged particles. The nucleus is at the center of the atom and this is where the mass of the atom is concentrated.** **Niels Bohr - Bohr proposed that the electrons existed only at fixed distances from the nucleus at set "energy levels," or quanta. Quanta was first conceptualized mathematically by Max Planck by absorbing or releasing discrete amounts of energy. Bohr's model of a hydrogen atom.** **James Chadwick** - **Proved the existence of neutrons which are neutral particles in the nucleus of the atom by bombarding alpha particles on beryllium. His discovery of neutrons solved the mystery on how protons clump themselves together in the nucleus.** **Erwin Schrodinger -- Electron cloud model or the quantum mechanical model.** **Modern Atomic Theory:** 1. **Matter is composed of atoms.** 2. **Atoms of the same elements generally have the same properties. However, there are isotopes which are atoms of the same element differing in the number of neutrons.** 3. **Atoms cannot be created nor destroyed. These can only be combined, separated, or rearranged.** 4. **Atoms of the same or different elements may combine with each other in a fixed, whole number ratio.** **As the structure of the atom began to be understood, scientists were able to observe the significance of the subatomic particles and how these were able to influence atomic properties.** **Elements:** - **Elements are composed of just one atom with different properties.** - **Jöns Jacob Berzelius made use of symbols to represent elements.** - **Johann Dobereiner grouped elements by three's and named them "triads".** - **John Newlands grouped them by eight's and named them "octaves".** - **Dmitri Ivanovich Mendeleev was able to propose a working periodic table giving a pattern brought about by increasing atomic weights. He is also considered as the Father of the Periodic Table.** - **Henry Moseley modified the periodic table by looking at the pattern brought about by increasing the atomic number. He made use of spectroscopic data that lead him to arrange elements by increasing atomic number.** **Atomic Number:** - **The atomic number is also known as the Z number. The Z came from the German word, \"Zahl.\" It means number.** - **The atomic number corresponds to the number of protons.** - **The number of protons gives the identity of the atom.** **Nuclear Transmutation Reactions Was Possible:** - **Knowledge of the atomic number introduced nuclear reactions.** - **Transformation of one element or isotope into another element.** - **The reaction includes protons and neutrons.** **Ernest Rutherford did the First Nuclear Transmutation Reaction using an Alpha Particle:** **Nuclear Transmutation Reactions:** - **Alpha particles are positively charged and the nucleus will repel it.** - **Neutrons were then used in lieu of the alpha particle.** **Particle Accelerators** -- To overcome the repulsion between the nucleus and alpha particles, particle accelerators were used. The alpha particles were made to move in a very fast way which will overcome repulsive forces. A **cyclotron** is a particle accelerator that uses alternating electric field to accelerate particles that move in a spiral path in the presence of a magnetic field. **Lesson 2: Polarity of Molecules** **Let's begin with electronegativity --- an important concept that determines the type of bond atoms form and the behavior of molecules. But as we go along, I want you to think of real-life examples. Have you ever wondered why oil and water don't mix, or why salt dissolves in water but not in oil? We're going to explore those questions today.** 1. **What is Electronegativity?** **Electronegativity is essentially an atom's ability to attract electrons towards itself in a chemical bond. Think of it as a game of tug-of-war between two atoms. The stronger atom pulls the electrons closer, giving it more control.** **Example: Imagine a molecule like hydrogen chloride (HCl). Chlorine is much more electronegative than hydrogen, so it pulls the shared electrons toward itself. In this \"tug-of-war,\" chlorine wins and becomes partially negative (δ-), leaving hydrogen partially positive (δ+).** **Now, who developed this idea? Linus Pauling created a scale that measures electronegativity, making it easier for chemists to understand how strongly atoms pull on electrons.** **Periodic Trends:**  **Electronegativity increases as you move from left to right across a period.\ It decreases as you move from top to bottom in a group.\ This is why fluorine, at the top right of the periodic table, is the most electronegative element.** 2. **Electronegativity vs. Electron Affinity** **While electronegativity describes how atoms pull electrons in a bond, electron affinity is about how much energy an atom releases when it gains an electron. The two are similar, but electron affinity applies to individual atoms, not bonds.** **Example: Think about when you snap a magnet to a fridge. There's a tiny energy release, right? That\'s what happens when an atom gains an electron.** **Fun Fact: Neil Bartlett discovered the first noble gas compound, XeF₄, because he realized that xenon, despite being a noble gas, could still attract electrons under certain conditions.** **3. Electronegativity Difference and Bond Types** **Now, let's discuss the electronegativity difference (Δχ) between two atoms, which helps determine what type of bond they form.** **Type of Chemical Bond** **Electronegativity difference range (∆)** --------------------------- -------------------------------------------- nonpolar covalent bond 0 to 0.4 polar covalent bond 0.4 to 1.7 ionic bond greater than 1.7 **Example: In the HCl molecule, the electronegativity difference between hydrogen and chlorine is significant, so the bond is polar. In contrast, in Cl₂ (a molecule with two chlorine atoms), the electronegativity difference is zero, so the bond is nonpolar.**  **4. Understanding Polarity and Dipole Moments** **Now, let's talk about polarity. When a molecule has an uneven distribution of electrons, we call it polar. This happens when one atom pulls harder on the electrons than the other, creating partial charges (δ+ and δ-). The measure of this separation is called the dipole moment, which can be visualized as a vector pointing from the positive to the negative side.** **Example: In a water molecule (H₂O), oxygen pulls electrons towards itself, leaving the hydrogen atoms slightly positive. This gives water a dipole moment and makes it a polar molecule. Polar molecules tend to stick together, which is why water has such a high boiling point.** **5. Molecular Geometry and Its Impact on Polarity** **But wait! It's not just about bond polarity --- the overall shape of the molecule matters too.** **Nonpolar molecules: If the molecule\'s shape is symmetrical, even if the bonds are polar, the dipoles cancel each other out.** **Example: Carbon dioxide (CO₂) is linear and symmetrical, so it's nonpolar.** **\ Polar molecules: When the shape is asymmetrical, the dipoles don't cancel, making the molecule polar.** **Example: Water (H₂O) has a bent shape, making it polar.** **6. Real-World Applications: Solubility\ Let's answer the question: Why does sugar dissolve in water but not in oil?** **It's all about the rule \"like dissolves like\". Polar substances dissolve in polar solvents, and nonpolar substances dissolve in nonpolar solvents.** **Water is polar, so it dissolves other polar substances like sugar.\ Oil is nonpolar, so it doesn\'t mix with water but can dissolve other nonpolar substances.** **Soaps and Detergents are a great example of this concept. They are amphiphilic, meaning they have both a polar (hydrophilic) end and a nonpolar (hydrophobic) end. When you use soap, the nonpolar end sticks to grease and dirt, while the polar end interacts with water, allowing the dirt to be washed away.** **7. Properties of Polar and Nonpolar Molecules\ The polarity of a molecule affects important properties like boiling point, melting point, and solubility.** **Boiling and Melting Points: Polar molecules have stronger attractions between them, so they require more heat to break apart. This is why water (a polar molecule) has a higher boiling point than methane (a nonpolar molecule).** **Example: Compare methanol (CH₃OH) and methane (CH₄). Methanol, being polar, has a higher boiling point than methane because it has stronger intermolecular forces (hydrogen bonding).** **Solubility: Polar molecules dissolve in polar solvents, and nonpolar molecules dissolve in nonpolar solvents. This principle explains why sugar dissolves in water and why oil does not.** **\ ** **Lesson 3: Intermolecular Forces\ In nature, forces of attraction and repulsion govern interactions at various scales, from the macroscopic to the microscopic. For instance, small insects can walk on water due to these forces, demonstrating how even the tiniest particles interact. Similarly, in chemistry, attractive forces play a crucial role in the behavior of molecules. These forces are essential for understanding various physical properties of substances.** **1. Intermolecular Forces of Attraction (IMFA)** Intermolecular forces are attractive forces present between molecules. These forces determine many physical properties of substances and can be classified into several types. **Types of Intermolecular Forces:** 1. London Dispersion Forces (LDF) 2. Dipole-Dipole Forces 3. Ion-Dipole Forces 4. Hydrogen Bonding **2. London Dispersion Forces (LDF)** - London Dispersion Forces are the weakest type of IMFA and exist between all electrically neutral molecules, whether polar or nonpolar. - These forces arise from fluctuations in the electron distribution within atoms or molecules, leading to temporary dipoles. - Example: Bromine (Br₂) exhibits stronger LDF compared to chlorine (Cl₂) because Br₂ has more electrons, making its electron cloud more polarizable. This increased LDF in Br₂ results in a higher boiling point than Cl₂. **3. Dipole-Dipole Forces** - These forces occur between polar molecules, where the partially positive end of one molecule is attracted to the partially negative end of another.  - Example: In hydrogen chloride (HCl), the positive end of one HCl molecule is attracted to the negative end of another HCl molecule, leading to dipole-dipole interactions. **4. Ion-Dipole Forces** - Ion-dipole forces result from the electrostatic attraction between an ion and a polar molecule. Ions are atoms that contain an uneven number of protons and electrons which result in an overall positive or negative charge. Cations are atoms that contain positive charge. Anions are atoms that contain negative charge. - The strength of ion-dipole forces increases with the charge of the ion and the dipole moment of the molecule. - Example: The interaction between sodium ions (Na⁺) and water molecules (H₂O) is an example of ion-dipole forces. **5. Hydrogen Bonding** - Hydrogen bonding is a special type of dipole-dipole interaction and is one of the strongest IMFA. It occurs when hydrogen is bonded to highly electronegative atoms like fluorine (F), oxygen (O), or nitrogen (N). - Example: Water (H₂O) forms hydrogen bonds between its molecules, leading to its unique properties such as a higher boiling point compared to hydrogen sulfide (H₂S), which does not form hydrogen bonds. **6. Physical States of Matter** - Matter exists in three primary states---solids, liquids, and gases. - The state of matter depends on the balance between intermolecular forces and temperature. - Solids and Liquids: Molecules with strong IMFA tend to be in solid or liquid states at room temperature. - Gases: Molecules with weak IMFA are typically in the gaseous state. Example: Mothballs (naphthalene) sublime at room temperature due to its weak IMFA. 6 Facts you should know about Naphthalene Moth Balls -- Ceylon Organic **7. IMFA and Properties of Molecules** **Solubility:** - \"Like dissolves like\" means that substances with similar intermolecular forces are more likely to dissolve in each other. - Hydrophilic vs. Hydrophobic: Hydrophilic substances interact well with water, while hydrophobic substances do not. - Example: Salt (sodium chloride) is hydrophilic and dissolves in water, whereas oil is hydrophobic and does not. **Melting Points and Boiling Points:** - Melting Point: The temperature at which a substance changes from solid to liquid. - Boiling Point: The temperature at which a substance changes from liquid to gas. - Influence of IMFA: Stronger IMFA result in higher melting and boiling points because more energy is required to overcome these forces. - Example: Water has a higher boiling point (100°C) compared to hydrogen sulfide (H₂S), which boils at -60°C, due to stronger hydrogen bonding in water. **Surface Tension:** - The tendency of a liquid to minimize its surface area. - Cohesive Forces: Attractive forces between molecules of the same kind. - Adhesive Forces: Attractive forces between different types of molecules, such as a liquid and a solid surface. - Example: Water has high surface tension due to strong hydrogen bonding, which leads to a concave meniscus in a glass container. **Viscosity:** - The measure of a fluid's resistance to flow. - Effect of IMFA: Stronger IMFA results in higher viscosity because it is harder for molecules to slide past one another. - Example: Honey has higher viscosity compared to water due to stronger intermolecular forces. **Vapor Pressure:** - The pressure exerted by a vapor in equilibrium with its liquid phase in a closed system. Vapor is diffused matter (such as smoke or fog) suspended floating in the air - Effect of IMFA: Molecules with stronger IMFA have lower vapor pressure because they are less likely to escape into the gas phase. - Example: Acetone is a volatile liquid with high vapor pressure compared to water.