C2aL7 Alkali Metals

Key Words

Alkali metals - a family of metals in Group 1 of the periodic table.

Group 1 - the first column of the periodic table

Ionic compounds - compounds held together by ionic bonds

Reactive - readily takes part in chemical reactions.

Salts - compounds formed by reactions between metals and non-metals.

Tarnish - shiny surface goes dull due to reaction with oxygen in the air.

Grade E

The alkali metals form a family at the extreme left of the periodic table, the first column.

They are also called the Group 1 metals.  They all have 1 outer shell electron.

Hydrogen (a gas) is often put on top of the Group 1 as it has one outer shell electron.  Under extremely high pressure, hydrogen can exist as a metal.

The family consists of:

• Lithium (Li);

• Sodium (Na);

• Potassium (K);

• Rubidium (Rb);

• Caesium (Cs);

• Francium (Fr).

They all react readily with water to form hydroxides that are very alkaline.

Their physical properties are:

• Soft;

• Good thermal and electrical conductors;

• Have low melting points;

• Tarnish quickly when exposed to air.

With non-metals, Group 1 metals form salts.  The metal ions have a single (+1) positive charge.

Grade C

The reactions of Group 1 metals are similar:

Sodium + chlorine ® sodium chloride

Caesium + chlorine ® caesium chloride

They all form positive ions with a single positive charge.

The alkali metals become more reactive as we go down the group:

• Lithium fizzes with water;

• Sodium fizzes and may burn with an orange flame;

• Potassium reacts more violently, burning with a purple flame;

• Rubidium reacts very violently, burning with a bright flash;

• Caesium explodes on contact with water.

• Francium would explode even more violently with water.

Click on the link to see the Braniac demonstration:

http://www.youtube.com/watch?v=eCk0lYB_8c0

Francium is actually highly radioactive with a half-life of 22 minutes.  So no sample has been prepared.  While it occurs naturally, it is estimated that there is no more than 30 g at any time in the entire crust of the Earth.  Even if you did get to mine the entire Earth's surface, the Francium will have decayed away.

The reason for this is that the outer shell electrons get further away from the nucleus as we go down the group.  Therefore they are held less strongly, making the elements more reactive.

Grade A

Alkali metals are too reactive to be found as pure metals in nature.  Sodium and potassium are very abundant on the Earth, but it is difficult to extract these metals from their compounds.  They can only be extracted using electrolysis.