Page 40 - Chemistry_Form_2

Chemistry
for Secondary Schools

elements found in Groups V to VIII, such as nitrogen (N₂), oxygen (O₂),
and neon (Ne), exist as simple molecules with low melting and boiling
points. These are commonly used in gas form; for example, oxygen is
used in hospitals for respiration, nitrogen in food preservation, and neon in
lighting systems.
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(e) Increase in ionisation energy
Ionisation energy increases from left to right across a period due to stronger
nuclear attraction, making it harder to remove electrons from an atom.
Elements with high ionisation energy, such as noble gases, are used in
lighting and insulation due to their chemical stability.

Trends in chemical properties across periods
The following are changes in chemical properties across periods:

(a) Increase in electronegativity
Electronegativity increases from left to right across a period, with non-
metals attracting electrons more strongly. This is due to the stronger
nuclear attraction resulting from the increasing number of protons in the
nucleus. This trend is particularly crucial in various applications, such as
semiconductor technology, where elements like silicon and germanium are
widely used in electronic devices.
(b) Decrease in metallic character
Metallic characters decrease, and non-metallic characters increase across a
period. Metals tend to lose electrons, while non-metals gain electrons. This
trend is important in various applications such as battery production, where
metals act as electron donors.
(c) Variations in chemical reactivity

Metals on the left are highly reactive and lose electrons easily, while non-metals
on the right become more reactive in gaining electrons. For metals, reactivity
decreases from left to right, while for non-metals, reactivity increases from
left to right. This trend plays crucial roles in different activities such as drug
formulation and material design, ensuring the stability and effectiveness of
compounds in pharmaceuticals and engineering.

Trends in physical properties down a group

(a) Atomic size increases down a group as more electron shells are added. This
expansion causes atoms to become larger, affecting their physical behaviour.
Larger atomic size influences material performance under high-pressure

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