Everything Science Grade 11

1.11 CHAPTER 1. ATOMICCOMBINATIONS

Step 2 : Determine the oxidation number for each atom

Oxygen (group 16) willhave an oxidation number of− 2. The oxidation number

of sulphur at this stage is uncertain.

Step 3 : Determine the oxidation number of sulphur byusing the fact that the oxidation

numbers of the atoms must add up to the chargeon the molecule

In the polyatomic SO^24 −ion, the sum of the oxidation numbers must be− 2.

Since there are four oxygen atoms in the ion, thetotal charge of the oxygen is− 8.

If the overall charge of the ion is− 2 , then the oxidation number of sulphur must

be +6.

Exercise 1 - 7

1. Give the oxidation numbers for each element in the following chemical compounds:

(a) NO 2

(b) BaCl 2

(c) H 2 SO 4

2. Give the oxidation numbers for the reactantsand products in each ofthe following reactions:

(a) C + O 2 → CO 2

(b) N 2 + 3H 2 → 2 NH 3

(c) Magnesium metal burns in oxygen

More practice video solutions or help at http://www.everythingscience.co.za

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Chapter 1 — Summary

See the summary presentation ( Presentation: VPgyp at http://www.everythingscience.co.za)

• Achemicalbond is the physical process that causes atoms and molecules to be attracted together
  and to be bound in newcompounds.


• Atoms are more reactive, and therefore more likely to bond, when theirouter electron orbitals
  are not full. Atoms are less reactive when theseouter orbitals contain the maximum number of
  electrons. This explainswhy the noble gases donot combine to form molecules.


• There are a number of forces that act between atoms: attractive forces between the positive
  nucleus of one atom andthe negative electrons ofanother; repulsive forcesbetween like-charged
  electrons, and repulsionbetween like-charged nuclei.


• Chemical bonding occurs when the energy of the system is at its lowest.


• Bond length is the distance betweenthe nuclei of the atomswhen they bond.