1. Structure of Matter
The atomic model
During the ppt, click the atom for answers to questions& to return back again

2. Brainstorm . . .
What do we know about the structure of an atom?

3. Brainstorm . . .
What do we know about the structure of an atom?
comprised of protons, neutrons and electrons
protons are positively charged
electrons are negatively charged
very small
mostly empty space
protons and neutrons form nucleus
electrons found in space surrounding
the nucleus

4. Inside an Atom
Electric Relative Position in
charge mass (to atom
each other)
Lithium atom

5. Inside an Atom
Electric Relative Position in
charge mass (to atom
each other)
proton +1 1 nucleus
Lithium atom
neutron 0 1
nucleus
Energy
1 levels
electron –1
1840 around
nucleus

6. Atom Models in History
The last 200 years have seen ideas
about the atom develop from
Dalton’s “indivisible atom” where it
is the smallest thing possible; to the
discovery of sub-atomic particles
(electrons, protons & neutrons); to
sophisticated understandings about
where these particles are found and
how they behave.
Each model has allowed
hypothesises to be made &
predictions tested. This has lead to
the development of our knowledge
as the technology has improved.
video link

7. Relative Sizes in an Atom
atoms are really small!
The space electrons occupy is most of the space in an atom.
(if the atom was 1 km across, the nucleus would be 1 cm across)

8. The scanning
tunnelling
microscope (a
recent
invention) lets
us “see” atoms
for the first time.
Nickel atoms – showing the regular
arrangement of “particles” in a solid
Note: the colours are artificially
added by computer – nickel atoms
aren’t blue!

9. Review of Building
Atoms Exercise

10. Atomic Number
Lithium atom
Atoms from different elements differ in their number of protons.
Atomic Number = number of protons
In a neutral atom, number of protons = number of electrons

11. Mass Number
Mass number = number of protons + neutrons
Number of neutrons = Mass number – Atomic number
In this Helium Atom: 4
Atomic number = 2
Mass number = 4 2 He
number of protons = 2
Helium atom number of electrons = 2
number of neutrons = (4 – 2) = 2

12. Ions
Ions are atoms that have lost or gained electrons.
Ions have an electrical charge:
losing electrons makes positive ions
(more protons than electrons)
gaining electrons makes negative ions
(more electrons than protons)
Ex Chlorine atoms gain 1 electron → Chloride ions Cl–1
Ex Sodium atoms lose 1 electron → Sodium ions Na+1
Ex Oxygen atoms gain 2 electrons → Oxide ions O–2
Ex Magnesium atoms gain 2 electrons → Magnesium ions Mg+2