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Flashcards in A level Chemistry Deck (73):
1

Element

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).

2

Ion

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

3

Mass Number

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

4

Atomic Number

The number of protons in an atom

5

Isotopes

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

6

Relative Isotopic Mass

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.

7

Relative Atomic Mass

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.

8

Ionic Bond

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.

9

Covalent Bond

A shared pair of electrons one from each donor atom

10

Covalent Bonding

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

11

Bond Length

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

12

Double Covalent Bond

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

13

Dative Covalent Bond

Is a shared pair of electrons both from one donor atom

14

Allotropes

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

15

Metallic Bonding

The electrostatic attractions between positive metal
cations and the delocalised electrons.

16

Valence Shell Electron Pair Repulsion (VSEPR) Theory

- 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.

17

Bond Angle

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

18

Bond Length

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

19

Polar Covalent Bond

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.

20

Electronegativity

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

21

Hydrogen Bond

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.

22

Atom

The smallest uncharged particle of an element.

23

Compound

Made up of two or more elements chemically joined together

24

Mole

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

25

Empirical Formula

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.

26

Molecular Formula

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

27

Parts per Million

The mass of solute per million grams of solvent.

28

Relative Formula Mass

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

29

Molar Mass

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

30

Avogadro Constant

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

31

Experimental Error

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

32

Measurement Errors

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

33

Procedural Errors

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

34

Molar Volume of a Gas

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

35

Limiting Reagent

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

36

Percentage Yield

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

37

% atom economy

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

38

Standard Solution

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.

39

Concentration/Molarity in mol/dm^3

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

40

Oxidation

When a species loses one or more electrons

41

Reduction

When a species gains one or more electrons

42

Redox

Reactions which involve transfer of electrons

43

Oxidising agent

Brings about an oxidation. It itself is reduced

44

Reducing agent

Brings about a reduction. It itself is oxidised

45

Oxidation Numbers

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

46

Disproportionation

The simultaneous oxidation and reduction of atoms of the same elements

47

First ionisation Energy

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

48

Periodic Properties

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

49

Hydrocarbons

Compounds containing carbon and hydrogen atoms only

50

Homologous series

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

51

Functional Group

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

52

Aliphatic Compounds

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

53

Alicyclic/Cyclic Compounds

Are made up of closed rings of carbon atoms.

54

Saturated Compounds

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

55

Unsaturated Compounds

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

56

Structural Isomerism

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

57

Cracking

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

58

Reforming

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

59

Homolytic Fission

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.

60

Half Headed Curly Arrows

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

61

Free Radicals

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

62

Substitution Reaction

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

63

Hazard

Something that could cause harm depending on circumstances

64

Risk

The chance or probability that harm will occur

65

Addition Reaction

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.)

66

Electrophile

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.

67

Heterolytic Bond Fission

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.

68

Hydrolysis

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

69

Elimination Reaction

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

70

Dehydration

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

71

Enthalpy Change

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

72

Specific Heat Capacity

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

73

Standard Enthalpy of Combustion

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)