Ocr A As Chemistry Unit 1 Definitions

Front 1

Atomic Number

Back 1

the number of protons in the nucleus of an atom

Front 2

mass number

Back 2

the number of particles (protons and neutrons) in the nucleus

Front 3

Isotopes

Back 3

Atoms of the same element with different number of neutrons

Front 4

Ion

Back 4

A positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion)

Front 5

Relative isotopic mass

Back 5

The mass of an atom of an isotope compared with 1/12th the mass of an atom of carbon 12

Hint 5

atom of an isotope

Front 6

Relative atomic mass

Back 6

the weighted mean mass of an atom of an element compared with 1/12th the mass of an atom of carbon 12

Front 7

Relative molecular mass (Mr)

Back 7

the weighted mean mass of a molecule compared with 1/12th the mass of an atom of carbon 12

Front 8

Relative Formula Mass

Back 8

the weighted mean mass of a formula unit compared with 1/12th the mass of an atom of carbon 12

Hint 8

formula unit

Front 9

Shell

Back 9

A group of atomic orbitals with the same principle quantum number (main energy level)

Hint 9

group of orbitals

Front 10

Principle quantum number

Back 10

Number representing overall energy of each orbital which increases with the distance from the nucleus. sets of orbitals with same n value are referred to as electron shell or energy level

Hint 10

overall energy of each orbital

Front 11

atomic orbital

Back 11

a region within an atom that can hold up to two electrons with opposite spins

Front 12

sub-shell

Back 12

a group of the same atomic orbitals within a shell

Front 13

Electron configuration

Back 13

arrangement of electrons within an atom

Front 14

Octet rule

Back 14

the tendency for atoms to combine so that each has 8 electrons in its outer shell, either through sharing or transferring electrons. results in noble gas configuration

Front 15

compound

Back 15

substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula

Front 16

ionic compound

Back 16

a compound in which electrons are transferred from one element to another to form an ionic bond. usually between a metal and a non-metal

Front 17

ionic bond

Back 17

the electrostatic attraction between oppositely charged ions

Front 18

giant ionic lattice

Back 18

a giant ionic lattice is a three-dimensional structure of oppositely charged ions, held together by strong ionic bonds.

strong electrostatic forces of attraction between oppositely charged ions

Front 19

Electronegativity

Back 19

an atom bonding electrons in a covalent bond

Front 20

Polar bond

Back 20

a covalent bond where a difference in electronegativity has caused a shift in electron density

Front 21

polar molecule

Back 21

a molecule containing polar bonds that are arranged so that the dipoles don't cancel each other out, causing the overall dipole to be created across the molecule

Front 22

intermolecular forces

Back 22

an attractive (electrostatic) force between neighboring molecules

Front 23

permanent dipole-dipole forces

Back 23

a weak attractive force between permanent dipoles in neighboring polar molecules

Front 24

van der Waals' forces

Back 24

attractive forces between induced attractions in neighboring molecules

Front 25

hydrogen bonds

Back 25

a hydrogen bond is a strong dipole-dipole attraction between:

an electron-deficient hydrogen atom on one molecule and a lone pair of electrons on, O, F, N on a different molecule

Front 26

Enthalpy, H

Back 26

the heat content that is stored in a chemical system

Front 27

chemical system

Back 27

the reactants and products

Front 28

surroundings

Back 28

what is outside the chemical system

Front 29

exothermic

Back 29

a reaction in which the enthalpy of the product is smaller than the enthalpy of the reactants

Front 30

Endothermic

Back 30

a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants resulting in heat being taken in from the surroundings

Front 31

enthalpy profile diagram

Back 31

a diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products

Front 32

Activation energy, Ea

Back 32

the minimum energy required to start a reaction by the breaking of bonds

Front 33

standard enthalpy change of reaction

Back 33

the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical reaction under standard conditions, all reactants and products being in their standard states

Front 34

standard enthalpy change of combustion

Back 34

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states

Front 35

standard enthalpy of formation

Back 35

the enthalpy change that takes place when one mole of a compound is formed from ints constituent elements in their standard states in standard conditions, the enthalpy change of formation for an element is 0 kJ/mol

Front 36

standard conditions

Back 36

a pressure of 100 kPa a stated temperature, usually 25 degrees celsius or 298 K and a concentration of 1.0 mol/dm-3

Front 37

standard state

Back 37

the physical state of a substance under the standard conditions

Front 38

specific heat capacity

Back 38

the energy required to raise the temperature of 1g of a substance by 1 degree celsius

Front 39

standard enthalpy change of neutralisation

Back 39

the enthalpy change when 1 mole of water is formed in the reaction between an acid and a base in their standard states and conditions

Front 40

bond enthalpy

Back 40

the enthalpy change required to break and separate 1 mole of bonds in the molecules if a gas so that the resulting gaseous (neutral) particles exert no force on each other

Front 41

average bond enthalpy

Back 41

the average enthalpy change that takes place when breaking by homolytic fission 1 mole of a given type of bond in the molecule of a gaseous species

Front 42

hess' law

Back 42

if a reaction can take place by more than one route and the initial and final conditions are the sane, the total enthalpy change is the same for each route

Front 43

hess cycle

Back 43

a diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using hess' law