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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

2.1.1 Atomic structure and isotopes

Atomic structure and isotopesRelative mass

Atomic Structure and Isotopes

Specification Reference 2.1.1 (a)–(b)

Quick Notes

  • Isotopes
    • Atoms with the same number of protons but different numbers of neutrons
    • Chemically identical, different masses and physical properties
  • Atomic Structure
    • Proton: +1 charge, relative mass = 1
    • Neutron: 0 charge, relative mass = 1
    • Electron: –1 charge, negligible mass (~1/1836)
    • Atoms: number of protons = number of electrons
    • Ions: adjust electron number according to charge

Full Notes

Isotopes

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have the same atomic number but different mass numbers. This difference in neutron number means that isotopes have different physical properties (like mass or rate of diffusion), but the same chemical properties.

For Example: Carbon isotopes

Carbon contains naturally occurring isotopes including Carbon-12, Carbon-13 and Carbon-14.

OCR (A) A-Level Chemistry diagram showing Carbon-12, Carbon-13 and Carbon-14 isotopes with equal 6 protons but different neutron numbers.

All have 6 protons.

C-12 has 6 neutrons, C-13 has 7 neutrons and C-14 has 8 neutrons.

Atomic Structure

Atoms consist of protons, neutrons, and electrons. With protons and neutrons making up a nucleus in the centre of an atom.

OCR (A) A-Level Chemistry schematic of an atom showing a central nucleus of protons and neutrons with electrons around it.

Protons have a +1 charge and a relative mass of 1.

Neutrons have no charge and a relative mass of 1.

Electrons have a –1 charge and a negligible mass (~1/1836).

Comparison of Subatomic Particles

Particle Relative Charge Relative Mass Location
Proton +1 1 Nucleus
Neutron 0 1 Nucleus
Electron –1 ~1/1836 Shells/energy levels

Atomic Number, Mass Number & Isotopes

The Atomic Number (Z) represents the number of protons in an atom.

The Mass Number (A) is the total number of protons and neutrons.

OCR (A) A-Level Chemistry diagram labelling atomic number Z as proton count and mass number A as total protons plus neutrons.

In a neutral atom, the number of protons equals the number of electrons.

In ions, the number of electrons is different:

Examples:
A Na+ ion has 11 protons and 10 electrons.
An O2− ion has 8 protons and 10 electrons.

Summary