1.2.5 Group 1: The Alkali Metals

Physical and Chemical Properties

All metals look dull on the outside due to the formation of a layer of oxide.
Over time, this layer of oxide makes the metal look dull.
The inside of every metal is shiny.
It is possible to cut every metal with a knife.
Alkali metals are kept in oil to prevent them from reacting with oxygen and moisture in the air.
They have low density, so most alkali metals float.
Their boiling point and melting point are lower than many other metals.

All Group 1 metals have 1 electron in their outer shell, making them very reactive as they bond by losing this electron.
Reactivity increases down the group because the outer electron is more easily lost, as it's further from the nucleus.

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Reaction with Oxygen to Form Oxides:

\text{metal} + \text{oxygen} \rightarrow \text{metal oxide}

Example (Potassium): $potassium+oxygen→potassium oxide$

4K(s)+O2(g)→2K2O(s)

The oxide layer that makes the metal look dull forms more quickly as you move down the group.

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Reaction with Water to Form Hydroxides (Alkalis):

\text{metal} + \text{water} \rightarrow \text{metal hydroxide} + \text{hydrogen}

Example (Lithium):

2Li_{(s)} + 2H_2O{_{(l)}} \rightarrow 2LiOH{_{(aq)}} + H_2{_{(g)}}

The metals create an alkali as they react with water (e.g., turning purple with a universal indicator).
The reaction produces hydrogen gas.
The metal floats, moves, and fizzes on the water's surface.
Sodium: Moves quicker and forms a ball shape.
Potassium: Moves quickly and has a lilac flame.