OCR A-Level Chemistry: Definitions Part 1
This flashcard set explains key terms related to atomic structure, including the definitions of isotopes, atomic and mass numbers, ions, and relative isotopic mass. It provides foundational knowledge essential for understanding atomic theory and chemical calculations.
Isotope
Atoms with the same number of protons but a different number of neutrons
Key Terms
Isotope
Atoms with the same number of protons but a different number of neutrons
Atomic Number
Number of protons in the nucleus
Mass Number
Number of protons and neutrons in the nucleus
Ion
A positively or negatively charged single atom or covalently bonded group of atoms
Relative Isotopic Mass
The mass of an atom of an isotope compared with one twelfth of the mass of carbon-12
Relative Atomic Mass
The weighted mean mass of an atom of an element compared to one twelfth of the mass of carbon-12
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| Term | Definition |
|---|---|
Isotope | Atoms with the same number of protons but a different number of neutrons |
Atomic Number | Number of protons in the nucleus |
Mass Number | Number of protons and neutrons in the nucleus |
Ion | A positively or negatively charged single atom or covalently bonded group of atoms |
Relative Isotopic Mass | The mass of an atom of an isotope compared with one twelfth of the mass of carbon-12 |
Relative Atomic Mass | The weighted mean mass of an atom of an element compared to one twelfth of the mass of carbon-12 |
Avogadro’s Constant | The number of atoms per mole of the carbon-12 isotope |
Mole | The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope |
Relative Formula Mass | The weighted mean mass of the formula unit of a compound compared with one twelfth of an atom of carbon-12 |
Empirical Formula | The simplest whole number ratio of atoms of each element present in a compound |
Molecular Formula | The actual number of atoms of each element in a molecule |
Molar Volume | The volume per mole of a gas At rtp it is 24 dm^3/mol |
Concentration of a solution | The amount of solute in mol, dissolved in 1dm^3 of solution |
Stoichiometry | The molar relationship between the relative quantities of substances taking part in a reaction |
% Yield | Actual Yield / Theoretical Yield |
Atom Economy | Molar mass of desired products / Sum of molar masses of all products |
Aufbau Principle |
|
Hund’s Rule | Within a sub level, the orbitals are first occupied singly by unpaired electrons |
Ionic Bonding | The electrostatic attraction between positive and negative ions |
Covalent Bonding | The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms |
Bond Length | The distance between the nuclei of two bonded atoms |
Bond Angle | The angle between two covalent bonds |
Electronegativity | The measure of its tendency to attract the electron pair(s) from a covalent bond |
Permanent Dipole | A small charge difference that does not change across a bond, with partial charges on the bonded atoms |
Hydrogen Bonding | A strong dipole-dipole attraction between a hydrogen atom bonded to O, N or F and a lone pair on O, N or F |
First Ionisation Energy | The energy required to remove one mole of electrons from one mole of gaseous atoms |
Oxidation Number | A measure of the number of electrons that an atom uses to bond with atoms of another element |
Oxidation | Loss of electrons or an increase in oxidation number |
Reduction | Gain of electrons or a decrease in oxidation number |
Oxidising Agent | A reagent that oxidises another species |
Reducing Agent | A reagent that reduces another species |
Disproportionation | A redox reaction in which the same element is both oxidised and reduced |
| Energy cannot be created or destroyed, just converted from one form to another |
Enthalpy | The heat content that is stored in a chemical system |
Enthalpy Change | The heat exchanged with the surroundings during a chemical reaction |
Exothermic | A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings |
Endothermic | A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken out of the surroundings |
Standard State | The state an element or compound will exist in at standard temperature and pressure |
Standard Enthalpy Change of Combustion | The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all the reactants and products in their standard state |
Standard Enthalpy Change of Reaction | The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states |
Standard Enthalpy Change of Neutralisation | The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions, with all the reactants and products in their standard states |
Average Bond Enthalpy | Energy required to break one mole of a specific type of bond in a gaseous molecule |
Hess' Law | If a reaction can take place by more than one route and the initial and final concentrations are the same, the total energy is the same for each route |
Enthalpy Change of Formation | The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states |
Reaction Rate | The change in concentration of a reactant or product in a given time |