Atoms And Elements Worksheet Page 13
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18Practice 2-6
For the element sulfur:
a) write the electron configuration,
b) draw the orbital diagrams,
c) how many unpaired electrons are in the sulfur atom?
Answer
2
2
6
2
4
a) S: 1s
2s
2p
3s
3p
b) ↑↓
↑↓
↑↓
↑↓ ↑↓
↑↓
↑↓ ↑
↑
2
2
6
2
4
1s
2s
2p
3s
3p
c) Two unpaired electrons in 3p orbitals.
Shorthand Electron Configurations
An electron configuration can also be written in an abbreviated (shorthand) configuration.
In this method the electron configuration of the preceding noble gas is replaced by
writing its symbol inside brackets.
2
1
B: [He]2s
2p
2
2
Si: [Ne]3s
3p
2
Ca: [Ar]4s
1
Cs: [Xe]6s
2.6 Valence Electrons and Lewis Structures
The electrons in the highest energy level of an atom are called Valence electrons . For
2
2
6
2
3
example, phosphorous, which has the electron configuration: 1s
2s
2p
3s
3p
, has
electrons in the first, second, and the third energy level. The third energy level, the
2
3
highest energy level, has a total of five electrons (3s
3p
), so phosphorous has five
valence electrons.
For all group A elements, the number of valence electrons is equal to the group number.
For example, the elements in Group IIA such as Be, Mg, Ca, Sr, and Ba, all have two
electrons in the highest energy level.
2
2
Be: 1s
2s
2
2
6
2
3s
Mg: 1s
2s
2p
2
2
6
2
6
2
Ca: 1s
2s
2p
3s
3p
4s
2
2
6
2
6
2
10
6
2
Sr: 1s
2s
2p
3s
3p
4s
3d
4p
5s
2
2
6
2
6
2
10
6
2
10
6
2
Ba: 1s
2s
2p
3s
3p
4s
3d
4p
5s
4d
5p
6s
2-13
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