OCR a level chemistry

• Chemical bonding is the process by which atoms are held together in compounds.
• A redox reaction is a chemical reaction that involves the transfer of electrons between species.
• An atom is the smallest unit of matter that retains the chemical properties of an element.
• Equilibrium is a state in a chemical reaction where the rate of the forward reaction is equal to the rate of the reverse reaction.
• An acid is a substance that donates a proton (H+) in a chemical reaction.
• Energetics is the study of energy changes in chemical reactions.
• Kinetics is the study of the rates of chemical reactions and the factors that affect them.
• Periodicity refers to the repeating pattern of chemical and physical properties of elements as they are arranged in the periodic table.
• The Group 2 elements in the periodic table are also known as the alkaline earth metals.
• The Group 7 elements in the periodic table are known as the halogens.
• An atom consists of a nucleus, which contains protons and neutrons, and electrons that orbit the nucleus.
• Protons have a positive charge and are located in the nucleus of an atom.
• Neutrons have no charge and are located in the nucleus of an atom.
• Electrons have a negative charge and are located in energy levels or shells around the nucleus.
• The atomic number of an element is equal to the number of protons in the nucleus of an atom of that element.
• There are three main types of chemical bonding: ionic bonding, covalent bonding, and metallic bonding.
• Ionic bonding occurs between a metal and a non-metal, where electrons are transferred from the metal to the non-metal.
• Covalent bonding occurs between non-metals, where electrons are shared between atoms.
• Metallic bonding occurs between metal atoms, where electrons are delocalized and shared among all the atoms.
• Ionic compounds have high melting and boiling points, and conduct electricity when dissolved in water or molten.
• The species that loses electrons is said to be oxidized, while the species that gains electrons is said to be reduced.
• Oxidation involves an increase in oxidation state, while reduction involves a decrease in oxidation state.
• The oxidation state of an element in its elemental form is always zero.
• The sum of the oxidation states of all the atoms in a neutral compound is zero.
• The sum of the oxidation states of all the atoms in a polyatomic ion is equal to the charge of the ion.
• A base is a substance that accepts a proton (H+) in a chemical reaction.
• The pH scale is a measure of the acidity or alkalinity of a solution, ranging from 0 to 14.
• A pH value below 7 indicates acidity, while a pH value above 7 indicates alkalinity.
• Strong acids completely dissociate in water, releasing all of their hydrogen ions.
• Weak acids only partially dissociate in water, releasing some of their hydrogen ions.
• The unit of energy used in chemistry is the joule (J).
• Endothermic reactions absorb energy from the surroundings, while exothermic reactions release energy to the surroundings.
• The enthalpy change (∆H) is the heat energy transferred in a reaction at constant pressure.
• Standard conditions for enthalpy changes are 298K (25°C) and 1 atmosphere pressure.
• The enthalpy change of a reaction can be measured using a calorimeter.
• Le Chatelier's principle states that when a system at equilibrium is subjected to a change, it will adjust to minimize the effect of that change.
• The equilibrium constant (Kc) is a ratio of the concentrations of products to the concentrations of reactants at equilibrium.
• If the value of Kc is greater than 1, the equilibrium lies to the right and the reaction favors the formation of products.
• If the value of Kc is less than 1, the equilibrium lies to the left and the reaction favors the formation of reactants.
• The reaction quotient (Q) is calculated in the same way as the equilibrium constant, but it can be calculated at any point during the reaction, not just at equilibrium.