Atomic Structure
Structure of the atom
Elements
Mixtures
Compounds
What does an Atom Look Like?
An atom consists of a nucleus
surrounded by electrons.
Structure of Atoms
The atom was once thought to be the smallest particle you could get.
We now know that atoms consist of three smaller particles.
Neutron
The protons and neutrons are found in the
middle of the atom, this is called the nucleus.
Proton
Electron
The electrons orbit around the
outside of the nucleus.
Lithium atom
The Differences between the Particles
The protons and neutrons are roughly the same mass, but the
electron has a mass that is negligible by comparison.
The proton has a positive electrostatic charge. The electron has
a negative electrostatic charge. The neutron has no charge, it is
neutral.
For a neutral atom there are always the same number of protons as
electrons. Lithium has three protons, so it must have three electrons.
Proton
Neutron Electron
Charge
+1
none
-1
Relative mass
1
1
1/1840th
Exercise 1: Particles
1. Which three particles make up an atom?
Neutron, proton and electron.
2. Which two particles are found in the nucleus?
Proton and neutron.
3. Which particle has no electrostatic charge?
The neutron.
4. Which particle has a negative charge?
The electron.
Exercise 2: Atoms
1. Which letter represents the nucleus?
B
2. Which letter represents the electron?
A
3. Which particle has a positive charge?
The proton
4. How many protons has the atom shown?
Four
A
Beryllium atom
B
Elements, Mixtures and Compounds
An ELEMENT is the simplest type of substance.
A COMPOUND is when you have two or more different
elements joined (bonded) together.
A MOLECULE is when you have two or more atoms joined
together (they may be the same element, they may not).
A MIXTURE is when you have different elements or
compounds together, but not chemically joined (bonded).
You need to be able to interpret particle diagrams and deduce
whether the diagram represents an element, a compound, a
molecule or a mixture.
Exercise 3: Link the Definitions and Diagrams
Mixture
Compound
Element
Exercise 4: Complete the Table
1. For the substances shown below, say which is a compound,
which is a mixture and which is an element.
Sand
Rust
Air
Oxygen
Sea water
Salt
Gold
Steel
Sulphur
Helium
Element
Mixture
Compound
Oxygen
Air
Sand
Gold
Sulphur
Helium
Sea water
Steel
Rust
Salt
Compounds
A compound is two or more elements joined together. Water
is a compound made from the elements oxygen and hydrogen.
What does a molecule of water look like?
Oxygen atom
WRONG!
Hydrogen atom
You know elements have symbols. In the same way we can
represent compounds using a chemical formula which is a
combination of the symbols of the elements from which it is made.
This chemical formula tells you how many atoms of each element
are present.
The chemical formula is H2O, this means
that every molecule of water has two
hydrogen atoms joined to one oxygen
atom.
Exercise 5: What Elements?
1. For the compounds below, write down the names of
the elements present.
a) NH3
Nitrogen and hydrogen
b) CH4
Carbon and hydrogen
c) H2SO4
Hydrogen, sulphur and oxygen
d) CaCl2
Calcium and chlorine
e) CO
Carbon and oxygen
f)
Sodium and chlorine
NaCl
g) SiO2
Silicon and oxygen
h) Fe2O3
Iron and oxygen
Exercise 6: How Many?
1. For the compounds below, write down the names of
the elements present and how many atoms of each
there are.
a) NH4OH
Nitrogen(1), oxygen (1) and hydrogen(5)
b) C6H12O6 Carbon(6), hydrogen(12) and oxygen(6)
c) AlCl3
Aluminium(1) and chlorine(3)
d) CO2
Carbon(1) and oxygen(2)
e) CuO
Copper(1) and oxygen(1)
f)
Hydrogen(1) and chlorine(1)
HCl
g) MgCl2
Magnesium(1) and chlorine(2)
h) ZnCO3
Zinc(1), carbon(1) and oxygen(3)
Exercise 7: Draw the Structures
1. For the compounds below, draw the simple structures.
a) NH3
b) CH4
c) CO2
Naming Compounds
You can often use the chemical formula for a
compound to deduce the name of the compound. (This
does not always work though!)
MgCl2 - Magnesium chloride
Chlorine  chloride
NaBr - Sodium bromide
Bromine  bromide
KI
- Potassium Iodide
Iodine  iodide
So, when the halogens form compounds, the
ending –ine changes to –ide.
Exercise 8: Naming Halides
1. For the compounds below, write down their names.
a) ZnCl2
Zinc chloride
b) ZnBr2
Zinc bromide
c) MgBr2
Magnesium bromide
d) CaCl2
Calcium chloride
e) NaI
Sodium iodide
f)
Silver bromide
AgBr
g) KCl
Potassium chloride
More Common Names for Compounds
MgSO4
…….. Magnesium sulphate
NaNO3
…….. Sodium nitrate
CaCO3
…….. Calcium carbonate
KOH
…….. Potassium Hydroxide
…..(SO4)

Sulphates
…..(NO3)

Nitrates
…..(CO3)

Carbonates
…..(OH)

Hydroxides
Exercise 9: Naming Compounds
1. For the compounds below, write down their names.
a) Na2SO4
Sodium sulphate
b) CaSO4
Calcium sulphate
c) CuCO3
Copper carbonate
d) AgNO3
Silver nitrate
e) NaOH
Sodium hydroxide
f)
Ca(NO3)2 Calcium nitrate
g) Mg(OH)2 Magnesium hydroxide