Group 1

Alkali metals are quite different from the "typical" metals you might think of (like iron or copper).

Physical Properties

Melting Points:

The melting point decreases down the group because the metallic bonds become weaker as atomic radius increases.

Why They're Called "Alkali" Metals

When alkali metals react with water, they form alkaline solutions (metal hydroxides with pH > 7). That's where the name comes from.

All alkali metals have one electron in their outermost shell:

This single outer electron is the key to understanding their reactivity. To achieve a stable, full outer shell, alkali metals need to lose just one electron, forming a +1 ion:

$\text{Na} \rightarrow \text{Na}^+ + e^-$

This makes them very reactive.

3.1 Reaction with Water

All alkali metals react vigorously with water to produce a metal hydroxide and hydrogen gas:

$2\text{M} + 2\text{H}_2\text{O} \rightarrow 2\text{MOH} + \text{H}_2$

where M represents any alkali metal.

Specific examples:

$2\text{Li} + 2\text{H}_2\text{O} \rightarrow 2\text{LiOH} + \text{H}_2$

$2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2$

$2\text{K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2$

Observations for each element:

The solution produced is alkaline (pH > 7). You can test this with universal indicator (turns purple) or phenolphthalein (turns pink).

3.2 Reaction with Oxygen

Alkali metals react with oxygen to form metal oxides:

$4\text{Li} + \text{O}_2 \rightarrow 2\text{Li}_2\text{O}$

$4\text{Na} + \text{O}_2 \rightarrow 2\text{Na}_2\text{O}$

This is why freshly cut alkali metals tarnish quickly — they react with oxygen and moisture in the air. They must be stored under oil to prevent this.

3.3 Reaction with Chlorine

Alkali metals react with chlorine to form metal chlorides (white solids):

$2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}$

$2\text{K} + \text{Cl}_2 \rightarrow 2\text{KCl}$

The metal chlorides dissolve in water to form colourless solutions.

Reactivity increases as you go down Group 1:

$\text{Li} < \text{Na} < \text{K} < \text{Rb} < \text{Cs}$

Why Does Reactivity Increase?

As you go down the group:

1. More electron shells → the atom is larger
2. The outer electron is further from the nucleus
3. There is more shielding from inner electrons
4. The attraction between the nucleus and the outer electron is weaker
5. The outer electron is easier to lose
6. Therefore, the element is more reactive

Key exam phrase: "Going down Group 1, the outer electron is further from the nucleus and is more shielded by inner electrons. The electrostatic attraction between the nucleus and the outer electron decreases, so the electron is lost more easily."

Going Down Group 1:

Alkali metals must be handled with care:

• Stored under oil (to prevent reaction with air and moisture)
• Never touched with bare hands (react with moisture on skin)
• Cut with a knife in a dry environment
• Safety screens used when reacting with water (especially K, Rb, Cs)

• When explaining reactivity trends, always mention: distance from nucleus, shielding, and ease of losing the outer electron
• Know the observations for Li, Na, and K with water — they're commonly tested
• Be ready to predict properties of Rb and Cs based on the trends
• In equations, alkali metals always form +1 ions and hydroxides with water
• Don't forget: the products with water are a hydroxide and hydrogen gas

• Group 1 metals have one outer electron and form +1 ions
• They are soft, low density, and have low melting points
• They react with water to form metal hydroxides + hydrogen: $2\text{M} + 2\text{H}_2\text{O} \rightarrow 2\text{MOH} + \text{H}_2$
• Reactivity increases down the group because the outer electron is easier to lose
• They are stored under oil to prevent reaction with air and water