1. Atomic Structure

2. Copyright © 2006-2011 Marshall Cavendish
What are atoms made of?
Atoms are made of small particles
called protons, electrons and neutrons.
These particles are called sub-atomic
particles.

3. Copyright © 2006-2011 Marshall Cavendish
Where in the atoms are these sub-atomic
particles found?
Protons and neutrons are
known as nucleons.
Protons and neutrons are found in
the nucleus.
Electrons circle the atoms in areas called shells.

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Structure of an Atom - Electron
Carries a charge of -1
Found in shells which
surround the atom
Represented by the symbol, eRepresented by the symbol, e
Has negligible mass or
relative mass of 1840
1

5. Copyright © 2006-2011 Marshall Cavendish
Structure of an Atom - Neutron
Carries no charge (charge = 0)
Has relative mass of 1
Represented by the symbol, nRepresented by the symbol, n
Found in the nucleus which
is in the centre of an atom

6. Copyright © 2006-2011 Marshall Cavendish
Structure of an Atom - Proton
Carries a charge of +1
Has relative mass of 1
Represented by the symbol, pRepresented by the symbol, p
Found in the nucleus which
is in the centre of an atom

7. Copyright © 2006-2011 Marshall Cavendish
The Proton Number and Nucleon
Number
An atom contains
an equal number of
positively charged protons
and
negatively charged electrons.
All atoms are electrically neutral.

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The Proton Number and Nucleon
Number
The proton number is represented by the symbol Z.
The proton number can also tell us the number of
electrons in the atom (since atoms are neutral).
It is also known as the atomic number.
The number of protons in an atom is called the
proton number.

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An example
For example, the proton number of nitrogen is 7.
Hence, we can deduce that a nitrogen atom has
seven protons and seven electrons.

10. Copyright © 2006-2011 Marshall Cavendish
Different atoms have different proton
numbers
Atoms of different elements have different numbers of
protons.
Carbon, for example, has a proton number of 6.
Any atom with 6 protons must be a carbon atom.
Each element has a unique proton number.

11. Copyright © 2006-2011 Marshall Cavendish
Nucleon Number
It is represented by the letter A.
Nucleon number is the total number of protons and
neutrons in an atom.
Nucleon number (A)Nucleon number (A)
= number of protons= number of protons ++ number of neutronsnumber of neutrons

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Nucleon Number
The nucleon number is also called the mass number.
This is because the mass of an atom depends on
the number of protons and neutrons in an atom.

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Representing Proton and Nucleon
Numbers
The nucleon and proton numbers can be included
when representing an element in symbols.
An element is represented using only the nucleon
number e.g. sodium-23 or 23-Na.
Nucleon number in
superscript, left of
symbol
Na
23
11
Proton number in subscript, left of symbol
Chemical symbol