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Basic Atomic Information

Matter - consists of particles

Atoms are the fundamental particles of matter. Evidence of this can be seen in:

Subdivision
Gases Mixing
Crystals Growing
Sugar, etc. Dissolving

Atomic Structure

There are 3 types of sub-atomic particles.

Protons - relatively large, have a positive charge.
Neutrons - approx. same mass as proton, no charge.
Electrons - small ( ~ 1/2000 mass of proton), negative charge.

Nucleus

Contains protons and neutrons
Makes up most of the mass of an atom.
Small part of atoms volume.

Electron Cloud

Space in which electrons orbit the nucleus at high speed.
Large part of atoms volume.
Subdivided into Energy Levels or Shells.
Electrons occupy the lowest energy levels. for energy level n; maximum number of electrons = 2n².

This table shows the maximum number of electrons for the first 4 energy levels.

Energy Level	Max. No. of electrons
1	2
2	8
3	18
4	32

This table shows the electron shell configuration for the first 18 elements.

Atomic Number	Element	Symbol	Electron configuration
1	Hydrogen	H	1
2	Helium	He	2
3	Lithium	Li	2,1
4	Beryllium	Be	2,2
5	Boron	B	2,3
6	Carbon	C	2,4
7	Nitrogen	N	2,5
8	Oxygen	O	2,6
9	Fluorine	F	2,7
10	Neon	Ne	2,8
11	Sodium	Na	2,8,1
12	Magnesium	Mg	2,8,2
13	Aluminium	Al	2,8,3
14	Silicon	Si	2,8,4
15	Phosphorous	P	2,8,5
16	Sulphur	S	2,8,6
17	Chlorine	Cl	2,8,7
18	Argon	Ar	2,8,8

Atomic Terms

Atomic Number

The number of protons in the atom.
The number of electrons = the number of protons, hence the overall charge in an atom is 0.

Mass Number

The number of protons in the nucleus + the number of neutrons in the nucleus, ie the total number of particles in the nucleus.

Element

Consists of atoms all having the same atomic numbers.

Isotopes

Atoms which have the same atomic number but different mass numbers.
ie, belong to the same element but have different number of neutrons.

eg¹²₆C + ¹⁴₆C

--> top number = mass number

--> bottom number = atomic number

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