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Chemistry
for Secondary Schools

environments, making certain elements suitable for deep-sea applications and
industrial machineries.
(b) Density also increases down a group as atomic mass increases more
significantly than the atomic volume. Heavier elements tend to have stronger
structural properties, making them valuable in industries that require durability
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and strength. These elements play crucial roles in construction and aerospace
engineering, where materials must withstand extreme conditions.
(c) Melting points for metals generally decrease down a group due to weaker
metallic bonding. As atomic sizes increase, the attraction between metal
atoms weakens, reducing the energy required to melt the substances. This
trend is significant in the design of alloys for safety devices such as fuses,
which need to melt easily to prevent electrical hazards.
(d) Ionisation energy decreases down a group in the periodic table. This is because
as atomic sizes increase, the outermost electrons are farther from the nucleus.
As a result, the attractions between the nucleus and outer electrons become
weaker, making it easier for metals to lose electrons. The trend in ionisation
energy influences an element’s reactivity, the types of compounds it forms, its
electrical conductivity, and its role in biological and industrial processes such
as metallurgy, battery design, and semiconductor manufacturing.

Trends in chemical properties down a group
(a) Electronegativity decreases down a group. This is because, as atomic size
increases, the outer electrons are farther from the nucleus. This condition
reduces the attractions between the nucleus and electrons, making atoms less
able to attract electrons in a chemical bond.
(b) Metallic character increases down a group. These properties are crucial in
selecting metals for use in catalysts and chemical processing industries.
Reactivity trends differ between metals and non-metals as you move down
a group. Metals become more reactive because they are more likely to lose
electrons, which is advantageous in processes such as metal extraction from
ores. In contrast, non-metals become less reactive because their ability to
attract electrons weakens. This behaviour is applied in industries where
reactive metals facilitate the breakdown of substances as in cleaning agents,
while non-metals help stabilise compounds to prevent undesired reactions.

Trends in selected groups
Groups I, II, and VII elements exhibit distinct physical and chemical properties
due to their unique positions in the periodic table. Group I (alkali metals) and

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