Juniour chemistry

1. The atom

3. Atoms
• Democritus 460BC – 370BC cutting
copper wire in half, last bit atom
• Atoms are thought of as the smallest part
of an element
• They are formed from three different sub-
atomic particles

4. The sub-atomic particles
Particle Charge Mass
Proton +1 1
Electron -1 /1850
1
Neutron 0 1
Complete the
following table

5. The Atom
This is one
electron
Electrons are
It contains all
This is the always present
the protons
nucleus in shells
and neutrons

6. Atomic Number
This is carbon
This is the
elements
12
C
symbol
6 This is the
All elements on elements
the periodic table atomic
are shown like this number

7. What does the atomic number tell
us?
• The atomic number tells us how many protons
an element’s atom has. This is the same as the
number of electrons
• So carbon has 6 electrons
• Sodium’s atomic number is 11. So it has 11
electrons
• Oxygen has an atomic number of 8. how many
electrons does it have?
• How many electrons does chlorine have
• Which has more electrons bromine or calcium?

8. Electron Shells
The first
The second
electron shell
The third
electron shell
can have up to
can have shell
electron up to
two electrons
eighthave up to
can electrons
eight electrons

9. Carbon’s Electron Shells
Carbon has 6
electrons
The electron
configuration is
written as 2. 4
Two electrons
These can go
There are
four electrons
can go in2nd
into the the
first shell
shell
left

10. The outer shell
• The number of electrons in the outer shell
of an atom is the same as the group of the
atom
• For example, carbon has four electrons in
its outer shell and it is in group four

11. Question Time
How many protons do the
following elements contain?
23 56 119 19 27
Na Fe Sn F Al
11 26 50 9 13
11 26 50 9 13

12. Question Time

13. Question Time
Make your own atom