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Atomic Structure
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What are atoms?
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What are atoms made of?
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What particles are atoms made of?
protons neutrons electrons
Atoms are made up of three smaller particles:
The electrons are spread out around the edge of the atom. They orbit the nucleus in layers called shells (energy levels).
The protons and neutrons exist in a dense core at the centre of the atom. This is called the nucleus.
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There are two properties of protons, neutrons and electrons that are especially important:
mass
electrical charge.
The atoms of an element contain equal numbers of protons and electrons and so have no overall charge.
-1almost 0electron
01neutron
+11proton
chargemassparticle
Mass and electrical charge
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Properties of the particles of the atom
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Summary: the atom so far
The nucleus is:
made up of protons and neutrons
positively charged because of the protons
dense because it contains all the mass of the atom in a tiny space.
Electrons are:
very small and light, and negatively charged
able to be lost or gained in chemical reactions
found thinly spread around the outside of the nucleus, orbiting in layers called shells (energy levels).
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Discovering atomic structure
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Atomic (proton) number and mass number
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How many protons?
Each element has a definite and fixed number of protons. All the atoms of a particular element always contain the same number of protons. For example:
The number of protons in an atom is known as the atomic number or proton number.
It is the smaller of the two numbers shown in most periodic tables.
hydrogen atoms always contain 1 proton
carbon atoms always contain 6 protons.
If the number of protons changes, then the atom becomes a different element.
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The atomic number (proton number)
What are the atomic (proton) numbers of these elements?
11
26
50
9
tin
iron
sodium
fluorine
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What is mass number?
Electrons have a mass of almost zero, which means that the mass of each atom results almost entirely from the number of protons and neutrons in the nucleus.
The sum of the protons and neutrons in an atom’s nucleus is the mass number.
1413aluminium
43lithium
01hydrogen
neutronsprotonsatoms mass number
27
7
1
It is the larger of the two numbers shown in most periodic tables.
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mass number = number of protons + number of neutrons
What’s the mass number?
What is the mass number of these atoms?
3227
3529
22
59
64
4
cobalt
copper
helium
NeutronsProtonsAtoms Mass number
iodine
germanium
53
32
74
41 73
127
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Building a nucleus
Needs fixing – in the spreadsheet
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What are the missing numbers?
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Summary activities
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Glossary
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Atoms – true or false?
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Multiple-choice quiz
