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CHEMISTRY FORM FOUR STUDY NOTES TOPIC 1: NON METALS AND THEIR COMPOUNDS & TOPIC 2: ORGANIC CHEMISTRY

TOPIC 1: NON METALS AND THEIR COMPOUNDS
General Chemical Properties of Non Metals
The non-metals are very reactive and most of them react with other elements to form different compounds.
The
following are important chemical properties of non-metals which are
connected with their tendency towards electron gain in the course of
formation of compounds:
1.
The oxide of a non-metal is either acidic or neutral but never basic.
The oxide of a non-metal is a covalent compound. Being acidic, it
combines with water to form an acid, e.g.
2.
A non-metal never replaces hydrogen in an acid to form a salt. This is
because replacement of hydrogen in an acid is due to the fact that H+ accepts electrons supplied by a metallic atom.
A non-metal is an electron acceptor and so cannot release electrons to hydrogen ions in solution.
3. Non-metals form covalent chlorides, for example, the behaviour of phosphorus forming its chlorides is well known.
A covalent chloride like this is usually a volatile liquid, a non electrolyte, and rapidly hydrolysed by water.
These properties are characteristic of non metallic chlorides (except CCl4 which is not hydrolysed by water).
4.
Non-metals combine with hydrogen to form many hydrides. A covalent
compound is formed by equal sharing of electrons between or among the
combining atoms. For example, methane ammonia, hydrogen chloride and
hydrogen sulphide are the covalent compounds.
5.
Non-metals are oxidizing agents As discussed early, non-metals accept
electrons from other substances. Therefore, they are called oxidizing
agents because, upon accepting the electrons, the substances donating
these electrons are oxidized. So they act as the agents for oxidation of
other substances.
The Oxidizing Properties of Non-metals
Explain the oxidizing properties of non-metals
Non-metals
react by gaining electrons to become negative ions. A univalent
non-metal accepts one electron while a divalent one accepts two
electrons. The ion formed carries the corresponding number of negative
charges, but they rarely exceed two and never exceed three.
When a substance loses electron(s), it becomes oxidized, i.e. its oxidation number increases. This is called oxidation.
Due to the fact that non-metals accept the electrons(s) donated by
other substances, particularly metals, they are, therefore, termed as oxidizing agents. This is because by accepting the electrons, they help oxidize the electron donors.
Those substances or metals which donated the electrons are called reducing agents. This is because the electrons they donate reduce the oxidation number of non-metals. This process is called reduction. In this respect, non-metals act as oxidizing agents while metals act as reducing agents.
Strong and weak oxidants
As
we have already seen, non-metals ionize by electron gain. In all cases,
the extra electron(s) accepted lead to the formation of negative ions.
The easiness of formation of negative ions depends on the ability of an
element to accept the electrons. The ability of accepting electrons is
called electronegativity of an element. Some elements are more electronegative than others.
The
order of electronegativity of some non-metals is as follows: Fluorine
< Chlorine > Bromine > Iodine > Nitrogen > Carbon
The
degree of electronegativity indicates reactivity and hence oxidizing
power of the element. Elements with higher electronegativity will
displace those elements with lower electronegativity from their
compounds.
Referring
to the series above, fluorine will displace all the rest of the
elements from their compounds as it is more electronegative than any
other element in the series. Likewise, chlorine can displace bromine,
iodine and nitrogen from their compounds. The displacement reaction
occurs in the manner:
Where X is more electronegative than Y
The
higher the electronegativity the stronger the oxidant. For example,
bromine is a stronger oxidant than iodine, nitrogen and carbon.
The Displacement of Non-metals by another Non-metal from a Compound
Describe the displacement of non-metals by another non-metal from a compound
Non-metals in the reactivity series
It is useful to placecarbonandhydrogeninto the reactivity series because these elements can be used to extract metals.
Here is the reactivity series including carbon and hydrogen:
Note
that zinc and iron can bedisplacedfrom theiroxidesusing carbon but not
using hydrogen. However, copper can be extracted using carbon or
hydrogen.
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