Gggggggggggg PDF - Chemistry Notes

1.1. Description of Matter The matter is the term for any material that has mass and volume. There are three basic states of matter: solid, liquid, and gas. Examples: Wood, stones, and metals and their molecules or atoms are all classified as matter. The atom is the smallest particle of an element...

1.1. Description of Matter The matter is the term for any material that has mass and volume. There are three basic states of matter: solid, liquid, and gas. Examples: Wood, stones, and metals and their molecules or atoms are all classified as matter. The atom is the smallest particle of an element that retains the unique properties of that element. There are different types of atoms (e.g., carbon, hydrogen, and oxygen atoms). Each type of atom is the building block of a certain chemical element. Mass and Weight: Mass is the amount of matter in an object. Weight is the force that gravity exerts on an object. The mass of an object does not depend on location; it is constant everywhere and does not change when an object's location changes. While the weight changes with the location because gravity changes. Note; Unit of mass is Kilogram (Kg), while weight is expressed in Newton (N). For example; An astronaut whose mass is 120 kg weighs 1200 N on earth but 200 N on the moon due to the gravitational force. [ 1.2. Classification of Matter 5 Substances are pure forms of matter that consist of only one entity. There are two types of pure substances: elements and compounds. Elements are pure substances made up of one kind of atom-atom cannot be broken down into simpler substances by chemical means. Examples of elements include; hydrogen (H2), carbon (C), oxygen (O2), and sodium (Na). Compounds are substances consisting of atoms or ions of two or more different elements in definite proportions and joined by chemical bonds. They can be broken down into simpler substances by chemical methods. The newly formed entities (broken down substances) will have completely different properties than the original compound. Examples of compounds include; Water (H2O), table salt (NaCl), and methane (CH4). [ The various materials (matters) we see around us are substances or mixtures of substances. Mixtures are two or more substances mixed without chemical reaction and can be separated physically into their original components. There are two types of mixtures: Homogeneous mixtures are those whose components cannot be distinguished by the naked eye. Examples include; rainwater, tap water, air, aqueous sugar solution, etc. Heterogeneous mixtures are those whose components can be distinguished by the naked eye. Examples include; salads, sand in water, concrete, etc. 6 The various separation techniques for mixtures include the following: Distillation, Filtration, Evaporation, and Magnetic separation. 1.3. Properties of Matter Physical Properties  A property that can be observed and measured without changing the material's composition. It can be observed due to physical changes in a material.  Examples: Melting Point, Boiling Point, Solubility, Temperature, Mass, Volume, Density, Viscosity, Electrical conductivity, Thermal conductivity, etc. Chemical Properties - A property that can only be observed by changing the composition of the material. It can be observed due to chemical changes in a material. - Examples: Flammability, Combustibility, Corrosion, Toxicity, Reactivity, Acidity, Basicity, etc.  Physical change: A change in the visible appearance, without changing the composition of the material.  Chemical change: A change in the composition of the material and a new form of matter is formed. Chemical changes are also known as chemical reactions. 7 1.4. States (Phases) of Matter Matter exists in three fundamental states, and their interchange depends on the temperature and pressure to which the matter is subjected. Under normal conditions, these three distinct states of matter are solids, liquids, and gases. For example, water exists as ice (solid water), as liquid water, and as steam (gaseous water). 1.4.1. Solids  Solids have definite shapes and definite volumes.  The molecules in a solid matter are close together and connected by strong bonding forces.  Solids can be crystalline or amorphous. 1.4.2. Liquids  Liquids have indefinite shapes but definite volumes. They assume the shape of their containers, such as a drink in a can.  The molecules in a liquid matter are far from each other and connected by weak bonding forces. 1.4.3. Gases  Gases have indefinite shapes and indefinite volumes.  The molecules in a gaseous matter are very far from each other and connected by very weak bonding forces.  The volume of gases strongly depends on their temperature and pressure.  Gases have a unique property: compressibility (opposite to expansibility). 8 1.5. Physical Processes for Matter Matter can often change from one physical state to another through a physical change. For example, liquid water can be heated to form a gas called steam or cooled to form liquid water. However, such changes in the state do not affect the chemical composition of the substance. Key Definitions: Phase transition is the transformation of a system from one state of matter (phase) to another one by either change in the system heat or pressure. Phase transition occurs via the following physical processes. 9 Physical Processes:  Melting is a physical process (phase transition) in which the substance changes from a solid to a liquid by heating. o The temperature at which a solid melts and changes to a liquid is termed melting point (m.p.).  Boiling or Vaporization is when the substance changes from liquid to gas by heating. o The temperature at which liquid boils or the temperature at which liquid changes to a gas is termed boiling point (b.p.).  Sublimation is when the substance changes from solid to gas by heating without becoming a liquid.  Freezing or Solidification is a process in which the substance changes from liquid to solid by cooling. It is the reverse of melting. o The temperature at which a liquid freezes and changes to a solid is termed the freezing point (f.p.).  Condensation is when the substance changes from gas to liquid by cooling. It is the reverse of boiling.  Deposition is when the substance changes from gas to solid by cooling without becoming a liquid. It is the reverse of sublimation. Physical processes at which matter changes from one phase to another. 10 1.6. Solutions The solution is a homogeneous mixture of two or more substances, consisting of ions or molecules. Solute and Solvent The terms solute and solvent refer to the components of a solution. o Solute is the component of a solution in smaller amounts. o Solvent is the component of a solution in greater amounts. Example: Sodium chloride is dissolved in water. Sodium chloride is the solute and, water is the solvent. Solutions may exist in any of the three states of matter; that is, they may be gases, liquids, or solids (according to the state of the solvent). Examples: – Gaseous solution: Air (O2, N2, others) – Liquid solution: Ethanol in water, CO2 in water, NaCl in water. – Solid solution: Gold-silver alloy, Dental-filling alloy, K-Na alloy. 11  Study Tips Mole & Avogadro's Constant:  Avogadro’s number: is the number of units in one mole of any substance, equal to 6.02 × 1023. The units may be atoms, ions, electrons, or molecules.  no. of units = no. of moles x Avogadro’s no. Example: How many molecules do 4 grams of sodium hydroxide (NaOH) contain? The molar mass of NaOH is 40 g/mol = 4 g / 40 g/mol = 0.1 mol No. of molecules = no. of moles X Avogadro’s no. = 0.1 × 6.02 × 1023 = 6.02 × 1022 molecules Practice questions 1. Which of the following changes are examples of a chemical change? a. Crushing rock salt. b. Melting an ice cube c. Burning wood d. Dissolving sugar and water 2. Which of the following options is a homogeneous mixture? a. Pure water b. Apple juice c. Soil d. Copper metal 3. The melting of ice to liquid water is classified as: a) A chemical change [ b) A physical change 12 4. Which of the following options is a chemical property of matter? a. Volume change b. Density c. Freezing point d. Flammability 5. Which one of the following substances is a compound? a. Iron (Fe) b. Oxygen (O2) c. Copper (Cu) d. Water (H2O) 6. Calculate the mass of 2 moles of sodium hydroxide (NaOH), the molar mass of NaOH is 40 g/mol a. 80 g b. 40 g c. 0.05 g d. 2 g 7. Aqueous alcohol is classified as: a. Compound b. Homogeneous mixture c. Element d. Heterogeneous mixture 8. What is the physical process in which the substance changes from a solid to a gas by heating? a. Sublimation b. Melting c. Solidification d. Boiling HOMEWORK ACTIVITY 1. The process by which a solid transforms into a liquid is termed….......... 2. The process by which a solid transforms directly to a gas is termed…........... 3. How many molecules are present in 18 grams of glucose? The molar mass of glucose is 180g/mol 4. How many moles do 37.3 grams of Potassium chloride (KCl) contain? The molar mass of KCl is 74.6 g/mol 5. 13 In this chapter, you will find out about: 2.1. Atomic structure and its components 2.2. Isotopes 2.3. Energy levels (Shells), subshells, and, atomic orbitals 2.4. Quantum numbers 2.5. Electronic configuration 2.6. Methods of writing electronic configuration 2.7. Valence Electrons 14 2.1. Atomic structure and its components Atomic structure: Atom consists of: 1. Nucleus: A tiny and dense central nucleus containing: a. Positively charged particles called protons (p+) b. Neutral particles (has no charge) called neutrons (n) 2. Electrons (e-) are negatively charged particles that surround the nucleus and rotate around it, at a very high speed, in one or more levels called energy levels or shells. Why is the atom electrically neutral? Atoms are neutral because they have equal numbers of electrons and protons, and hence the overall charge is zero. 15 If electrons are lost from or added to a neutral atom, the atom will be charged and is called an ion, which may be a cation or anion. o Cations (positive ions) are formed when a neutral atom loses one or more electrons. So, the number of electrons is lower than the number of protons. o Anions (negative ions) are formed when a neutral atom gains one or more electrons. So, the number of electrons is higher than the number of protons. A specific atom is described by two numbers; atomic number and mass number Atomic number, Z: is the number of protons in the atom's nucleus Atomic number (Z) = number of protons = number of electrons In the neutral atom: the number of protons inside the nucleus is the same number of electrons around the nucleus. The mass number, A: It is equal to the sum of neutrons and protons inside the atom's nucleus. Mass number (A) = number of protons + number of neutrons Number of neutrons = Mass number (A) - Atomic number (Z) The shown figure illustrates the universal way of symbolizing atoms and their atomic and mass numbers. Example: A=23 Sodium, Na, has atomic number 11. Na Number of protons = number of electrons = 11 Z=11 Number of neutrons = A - Z Number of neutrons = 23 - 11 = 12 16 Question: How many protons, electrons, and neutrons are present in the shown elements? Note: The identity of an element is controlled by its atomic number (the number of protons in the nucleus). Every element has its unique atomic number. 2.2. Isotopes All the atoms of a given element have the same atomic number. For example, all carbon atoms contain 6 protons, gold atoms contain 79 protons, and lead atoms contain 82 protons. But they can have different mass numbers, depending on how many neutrons they contain. Isotopes are atoms of the same element with the same number atomic number but different mass numbers due to containing different numbers of neutrons. Isotope No of Protons No of Electrons No of Neutrons 12 C 6 6 6 13 C 6 6 7 14 C 6 6 8 17 2.3. Energy levels (Shells), subshells, and, atomic orbitals Electrons are arranged in energy levels, also called shells. The numbers of shells in the heaviest atoms are seven; designated as K, L, M, N, O, P & Q, or 1, 2, 3, 4, 5, 6 & 7 respectively. Shell No. 1 is the nearest to the nucleus and has the lowest energy. As the order of the shell is increased, its energy is increased and electrons are less tightly bound to the nucleus. The outermost energy level is called the valence level and its electrons are called valence electrons.  Atoms can exist in specific energy states, and in each energy state, the atom has a definite energy. When an atom has its electrons in their lowest possible energy levels, the atom is in its ground state (Lowest energy state). When the atom absorbs energy, one or more electrons will jump to a higher energy level (promotion of electrons) and the atom changes its energy state to the excited state (highest energy state). 18 Energy levels or shells contain energy sublevels or subshells. The number of subshells per a certain energy level is equal to the order of the energy level. This is applicable until the fourth energy level. So, energy level # 1 has only one subshell (1s) energy level # 2 has two subshells (2s & 2p) energy level #3 has three subshells (3s ,3p & 3d) energy level #4 has four subshells (4s, 4p, 4d, 4f) The s subshell is the lowest energy subshell and the f subshell is the highest energy subshell. s