Page 42 - Chemistry_Form_2

Chemistry
for Secondary Schools

Group II (alkaline earth metals) are highly reactive metals, while Group VII
(halogens) consists of reactive non-metals. Their physical properties, such
as atomic radius, ionisation energy, density, and melting points, exhibit clear
trends within each group, as shown in Tables 2.6 and 2.7. Chemically, they
differ in reactivity and electronegativity, reflecting variations in their electronic
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configurations. Understanding these properties provides valuable insights into
their behaviour and applications in chemistry and other fields.

Group I: Alkali metals
Group I consists of metals such as lithium (Li), sodium (Na), potassium (K),
rubidium (Rb), and caesium (Cs) as shown in the Table 2.6. The data from this
table show that the physical and chemical properties of these elements generally
increase or decrease down the group. Each of these elements has one electron in
its outermost shell. Lithium, sodium and potassium react very readily with water
or air and are stored in oil.

Table 2.6: Trends in Group I
Name Atomic Electronic Atomic 1 ionisation Melting Density Electro-
st
number radius energy 3
(Symbol) (z) configuration (picometres) (kJ /mol) point (°C) (g/cm ) negativity
Lithium 3 2:1 152 526 180 0.54 1.0
(Li)
Sodium 11 2:8:1 186 504 98 0.97 0.9
(Na)
Potassium 19 2:8:8:1 231 425 64 0.86 0.8
(K)
Rubidium 37 2:8:18:8:1 244 410 39 1.5 0.8
(Rb)
Caesium 55 2:8:18:18:8:1 262 380 29 1.9 0.7
(Cs)

Note: 1. Francium (Fr) is also an alkali metal but is rarely discussed or
experimented in the discussion or experiments involving Group I
elements due to its radioactive nature. It is also among the rarest
naturally occurring elements.

2. The way electronic configurations of rubidium and caesium are written,
is above the scope of this book. However, for the sake of understanding
this section, the electronic configurations are written to show the period
number, group number, and their relations to the trends.

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