A level Chemistry

Question 1

Element

Answer 1

A substance which cannot be broken down by any chemical process. All the atoms within it have the same atomic number (a material with only one type of atom).

Question 2

Ion

Answer 2

An electrically charged particle formed from an atom or group of atoms which have lost or gained electrons.

Question 3

Mass Number

Answer 3

The number of protons + the number of neutrons in the nucleus.

Question 4

Atomic Number

Answer 4

The number of protons in an atom

Question 5

Isotopes

Answer 5

Atoms which have the same number of protons but different numbers of neutrons. They have the same atomic number but different neutron numbers.

Question 6

Relative Isotopic Mass

Answer 6

The mass of an atom of a particular isotope of an element relative to 1/12 of the mass of carbon–12 atom, defined as 12 exactly.

Question 7

Relative Atomic Mass

Answer 7

The weighted average mass of atoms of an element in their natural relative isotopic abundance compared to the carbon 12 isotope taking the mass of 12 C =
12.0000.

Question 8

Ionic Bond

Answer 8

An electrostatic attraction between oppositely charged positive cations and negative anions. It is usually formed by electron transfer from a metal atom to a non metal.

Question 9

Covalent Bond

Answer 9

A shared pair of electrons one from each donor atom

Question 10

Covalent Bonding

Answer 10

The electrostatic attraction between the nuclei and the bonding pair of electrons which holds the 2 nuclei together.

Question 11

Bond Length

Answer 11

The distance between the nuclei of the two atoms that are covalently bonded together.

Question 12

Double Covalent Bond

Answer 12

A covalent bond in which two pairs of electrons are shared between two atoms.

Question 13

Dative Covalent Bond

Answer 13

Is a shared pair of electrons both from one donor atom

Question 14

Allotropes

Answer 14

Two or more forms of the same element in which the atoms or molecules are arranged in different ways

Question 15

Metallic Bonding

Answer 15

The electrostatic attractions between positive metal

cations and the delocalised electrons.

Question 16

Valence Shell Electron Pair Repulsion (VSEPR) Theory

Answer 16

• Bonding pairs of electrons around a central atom repel each other and arrange themselves as far apart around the central atom to minimise repulsion
• lone pairs of electrons are held more closely to the central atom and so exert a greater repelling effect than bonding pairs. This reduces the bond angle by approx 2 o per lone pair.

Question 17

Bond Angle

Answer 17

The angle between two covalent bonds in a molecule or giant covalent structure

Question 18

Bond Length

Answer 18

The distance between the nuclei of two atoms linked by one or more covalent bonds.

Question 19

Polar Covalent Bond

Answer 19

A covalent bond where the bonding pair of electrons are not shared equally by the two atoms in the bond.The shared electrons are attracted towards the atom with the stronger pull from the nucleus which is described as more electronegative The bonds have a slightly positive pole  + at one end and a negative one  - at the other.

Question 20

Electronegativity

Answer 20

A measure of its ability to attract the shared pair of

electrons in a covalent bond. It is a comparative scale based on Fluorine = 4.0

Question 21

Hydrogen Bond

Answer 21

A particularly strong permanent dipole-permanent dipole attraction between the lone pair of electrons on a very electronegative atom (N, O or F) and a hydrogen atom directly covalently bonded to another very electronegative N, O or F atom.

Question 22

Atom

Answer 22

The smallest uncharged particle of an element.

Question 23

Compound

Answer 23

Made up of two or more elements chemically joined together

Question 24

Mole

Answer 24

The amount of substance containing the Avogadro number of atoms, molecules or groups of ions. Where Avogadro’s number is 6.023 * 10^23 mol -1. Or The amount of substance containing as many particles as there are carbon atoms in 12g of 12 C

Question 25

Empirical Formula

Answer 25

The simplest whole number ratio of the atoms of each element in the substance. It is also the simplest whole number ratio of moles of atoms in a substance.

Question 26

Molecular Formula

Answer 26

Shows the number of atoms of each element in | the compound.

Question 27

Parts per Million

Answer 27

The mass of solute per million grams of solvent.

Question 28

Relative Formula Mass

Answer 28

The weighted mean mass of a formula unit compared to the carbon-12 isotope taking 12 C = 12.0000.

Question 29

Molar Mass

Answer 29

The mass of one mole of any substance in g/mol.

Question 30

Avogadro Constant

Answer 30

The number of atoms in exactly 12g of 12 C which is 6.02 * 10^23 .

Question 31

Experimental Error

Answer 31

An inaccuracy in the results of the experiment which | is caused by a limitation of the method or equipment being used.

Question 32

Measurement Errors

Answer 32

These are the inaccuracies of any measurement taken which involves a piece of measuring equipment and their size depends on the equipment used.

Question 33

Procedural Errors

Answer 33

These are due to the problems with the method used which affect the results but cannot be measured.

Question 34

Molar Volume of a Gas

Answer 34

The volume occupied by 1 mole of the gas under specified conditions of temperature and pressure.

Question 35

Limiting Reagent

Answer 35

The substance that determines the theoretical yield of a product in a reaction.

Question 36

Percentage Yield

Answer 36

Is defined as % yield = (actual yield/theoretical yield) x 100

Question 37

% atom economy

Answer 37

(mass of desired product from equation/total mass of products from equation)x 100

Question 38

Standard Solution

Answer 38

A solution with an accurately known concentration. A standard solution is prepared by taking a known mass of solute and making this up to a known volume of solution in a volumetric flask.

Question 39

Concentration/Molarity in mol/dm^3

Answer 39

number of moles *(1000cm^3/volume in cm^3)

Question 40

Oxidation

Answer 40

When a species loses one or more electrons

Question 41

Reduction

Answer 41

When a species gains one or more electrons

Question 42

Redox

Answer 42

Reactions which involve transfer of electrons

Question 43

Oxidising agent

Answer 43

Brings about an oxidation. It itself is reduced

Question 44

Reducing agent

Answer 44

Brings about a reduction. It itself is oxidised

Question 45

Oxidation Numbers

Answer 45

The charge the species in a molecule or ion would have if the bonding was 100% ionic

Question 46

Disproportionation

Answer 46

The simultaneous oxidation and reduction of atoms of the same elements

Question 47

First ionisation Energy

Answer 47

The first ionisation energy is defined as the energy required to remove one mole of electrons from one mole of gaseous neutral atoms to form one mole of gaseous ions with a charge of +1

Question 48

Periodic Properties

Answer 48

Properties which show a gradual change/trend across a period which repeats from period to period. It due to this repeating pattern from left to right that the table in known as the periodic table

Question 49

Hydrocarbons

Answer 49

Compounds containing carbon and hydrogen atoms only

Question 50

Homologous series

Answer 50

A family of compounds with the same functional group, which differ in formula by CH 2 from the next member.

Question 51

Functional Group

Answer 51

The atom or group of atoms responsible for the chemical behaviour of the molecule

Question 52

Aliphatic Compounds

Answer 52

Are made up of chains of carbon atoms which may be straight or branched (i.e. they do not contain rings)

Question 53

Alicyclic/Cyclic Compounds

Answer 53

Are made up of closed rings of carbon atoms.

Question 54

Saturated Compounds

Answer 54

Contain only single covalent bonds. They have the maximum number of hydrogen atoms.

Question 55

Unsaturated Compounds

Answer 55

Contain double or triple bonds which can add more | hydrogen atoms to form additional C-H bonds.

Question 56

Structural Isomerism

Answer 56

Occurs when two or more compounds have the same molecular formula but different structural formulae.

Question 57

Cracking

Answer 57

Cracking is the breakdown of molecules into | shorter ones by heating with a catalyst.

Question 58

Reforming

Answer 58

The conversion of straight chained hydrocarbons into branched and cyclic hydrocarbons by heating with a platinum catalyst.

Question 59

Homolytic Fission

Answer 59

Is the term used to describe the breaking of a covalent bond so that the bonding electrons are shared equally between the atoms involved. It is represented using half-headed curly arrows.

Question 60

Half Headed Curly Arrows

Answer 60

Show the movement of one electron precisely from | the covalent bond to the atom to which the electron moves.

Question 61

Free Radicals

Answer 61

Molecular fragments or atoms with one unpaired electron. They are highly reactive.

Question 62

Substitution Reaction

Answer 62

Where one atom or group of atoms replaces another atom or group of atoms

Question 63

Hazard

Answer 63

Something that could cause harm depending on circumstances

Question 64

Risk

Answer 64

The chance or probability that harm will occur

Question 65

Addition Reaction

Answer 65

Where one or more groups are added onto a molecule to give a single product (It usually converts an unsaturated compound into a saturated compound.)

Question 66

Electrophile

Answer 66

An electron deficient species with a vacant orbital. They are often positively charged. They react by accepting a pair of electrons forming a new covalent bond.

Question 67

Heterolytic Bond Fission

Answer 67

This results in the production of two different (hetero) species. A: B ---> A: - + B + or A :B ---> A + + :B - The covalent bond breaks so that both the bonding electrons go to either A or B. It results in the formation of oppositely charged ions.

Question 68

Hydrolysis

Answer 68

A reaction in which water or a hydroxide group replace an atom in a molecule with an -OH group

Question 69

Elimination Reaction

Answer 69

The removal of one or more groups or atoms from adjacent C atoms forming an unsaturated molecule.

Question 70

Dehydration

Answer 70

The removal of a water molecule – water is the only inorganic product formed in the reaction

Question 71

Enthalpy Change

Answer 71

The heat change when the reaction is carried | out at constant pressure. It is given the symbol ΔH

Question 72

Specific Heat Capacity

Answer 72

The enthalpy in joules/KJ which heats 1g/Kg of the substance by 1 o C/K

Question 73

Standard Enthalpy of Combustion

Answer 73

The heat energy released when one mole of a substance in its standard state is completely burned in excess oxygen under standard conditions (1atm. 298K)