1. 2.1.2 The simple Atomic Structure of the First Twenty Elements in the Periodic Table

2. List the elements or their symbols Give their atomic number
Let us revise the atomic structure of these elements by drawing a table
[In the back of your practical books - see next slide]
List the elements or their symbols
Give their atomic number
Then their atomic mass
Then their number of protons
Then their number of neutrons
Then the numbers of electrons
The finally their electron patterns

3. Atomic
Number
Element 1
Hydrogen 2
Helium 3
Lithium 4
Beryllium 5
Boron 6
Carbon 7
Nitrogen 8
Oxygen 9
Fluorine 10
Neon 11
Sodium 12
Magnesium 13
Aluminium 14
Silicon 15
Phosphorus 16
Sulphur 17
Chlorine 18
Argon 19
Potassium 20
Calcium

4. Next comes the atomic mass
Compare the atomic mass number to the atomic number
Is there a pattern?
In many tables there are decimal points – ignore these

5. Atomic
Number
Atomic
Mass
Element 1 1
Hydrogen 2 4
Helium 3 7
Lithium 4 9
Beryllium 5 11
Boron 6 12
Carbon 7 14
Nitrogen 8 16
Oxygen 9 19
Fluorine 10 20
Neon 11 23
Sodium 12 24
Magnesium 13 27
Aluminium 14 28
Silicon 15 31
Phosphorus 16 32
Sulphur 17 35
Chlorine 18 40
Argon 19 39
Potassium 20 40
Calcium

6. What did you notice?
Atomic mass gets bigger as the atomic number increases – as a general rule
But K lighter than Argon
The atomic mass is roughly twice the atomic number

7. Proton Number
Atomic
Number
Atomic
Mass
Element 1 1 1
Hydrogen 2 4 2
Helium 3 7 3
Lithium 4 9 4
Beryllium 5 11 5
Boron 6 12 6
Carbon 7 14 7
Nitrogen 8 16 8
Oxygen 9 19 9
Fluorine 10 20 10
Neon 11 23 11
Sodium 12 24 12
Magnesium 13 27 13
Aluminium 14 28 14
Silicon 15 31 15
Phosphorus 16 32 16
Sulphur 17 35 17
Chlorine 18 40 18
Argon 19 39 19
Potassium 20 40 20
Calcium

8. What did you notice?
The number of protons equals the atomic number
It is the atomic number that determines what the element is.
If the atomic number changes then the element becomes a different element

9. Proton Number
Neutron Number
Atomic
Number
Atomic
Mass
Element 1 1 1
Hydrogen 2 4 2 2
Helium 3 7 3 4
Lithium 4 9 4 5
Beryllium 5 11 5 6
Boron 6 12 6 6
Carbon 7 14 7 7
Nitrogen 8 16 8 8
Oxygen 9 19 9 10
Fluorine 10 20 10 10
Neon 11 23 11 12
Sodium 12 24 12 12
Magnesium 13 27 13 14
Aluminium 14 28 14 14
Silicon 15 31 15 16
Phosphorous 16 32 16 16
Sulphur 17 35 17 18
Chlorine 18 40 18 22
Argon 19 39 19 20
Potassium 20 40 20 20
Calcium

10. What did you notice?
The number of neutrons is the atomic mass minus the atomic number
The number of neutrons is roughly the same as the number of protons

11. Proton Number
Neutron Number
Electron Number
Atomic
Number
Atomic
Mass
Element 1 1 1 1
Hydrogen 2 4 2 2 2
Helium 3 7 3 4 3
Lithium 4 9 4 5 4
Beryllium 5 11 5 6 5
Boron 6 12 6 6 6
Carbon 7 14 7 7 7
Nitrogen 8 16 8 8 8
Oxygen 9 19 9 10 9
Fluorine 10 20 10 10 10
Neon 11 23 11 12 11
Sodium 12 24 12 12 12
Magnesium 13 27 13 14 13
Aluminium 14 28 14 14 14
Silicon 15 31 15 16 15
Phosphorus 16 32 16 16 16
Sulphur 17 35 17 18 17
Chlorine 18 40 18 22 18
Argon 19 39 19 20 19
Potassium 20 40 20 20 20
Calcium

12. What did you notice?
Number of electrons is equal to the number of protons
This is why atoms are neutral [positive protons and negative electrons cancel out]
The number of electrons is also equal to the atomic number

13. Proton Number
Neutron Number
Electron Number
Atomic
Number
Atomic
Mass
Electron Pattern
Element k l m n 1 1 1 1 1
Hydrogen 2 4 2 2 2 2
Helium 3 7 3 4 3 2 1
Lithium 4 9 4 5 4 2 2
Beryllium 5 11 5 6 5 2 3
Boron 6 12 6 6 6 2 4
Carbon 7 14 7 7 7 2 5
Nitrogen 8 16 8 8 8 2 6
Oxygen 9 19 9 10 9 2 7
Fluorine 10 20 10 10 10 2 8
Neon 11 23 11 12 11 2 8 1
Sodium 12 24 12 12 12 2 8 2
Magnesium 13 27 13 14 13 2 8 3
Aluminium 14 28 14 14 14 2 8 4
Silicon 15 31 15 16 15 2 8 5
Phosphorus 16 32 16 16 16 2 8 6
Sulphur 17 35 17 18 17 2 8 7
Chlorine 18 40 18 22 18 2 8 8
Argon 19 39 19 20 19 2 8 8 1
Potassium 20 40 20 20 20 2 8 8 2
Calcium

14. What did you notice? Shells fill from inside outwards
When outer shell becomes full something different happens - shown by shading
Atoms become very stable
Octet rule because usually when there are eight electrons in outer shell
Helium is an exception

15. Summary

16. Atomic number is a series
Atomic number tells number of protons
Number of protons determines what the element is.
Atomic Mass is about twice atomic number
Number of neutrons calculated by atomic mass – atomic number

17. Number of electrons = number of protons = atomic number Electrons fill shells from inside out
2,8,8,(2) is maximum – brackets because not full
If an outer shell is full the atom is very stable
Usually 8 electrons fill the outer shell – Octet rule
Helium is one exception