Ideas from an On-line Educator

Outcome: Students will be able to give the order of reactivity of the alkali metals with reasons.

Read through these notes and complete the questions.

Introduction to the Group 1 Alkali Metals 

The Alkali Metals form Group 1 of The Periodic Table, and called so because they form oxides and hydroxides that dissolve in water to give alkaline solutions.

Alkali metals form the first element of a period, with one outer electron, in any period from period 2 onwards. This outer electron similarity makes them behave in a chemically similar way and in a particularly reactive way.

Although Alkali Metals all have one outer electron and so similar physical and chemical properties, a characteristic of a periodic table group, BUT always watch out for trends down a group too.

Alkali Metals are so reactive that they must be stored under oil in a well sealed glass container to minimise reaction with the oxygen or water vapour in air.

Note: Oil is a water repellent and a physical barrier towards air and moisture BUT the alkali metals still gradually corrode as traces of oxygen and water diffuse through the oil to reach the very reactive lumps of alkali metal!

Alkali metals are many typical metallic properties: e.g. good conductors of heat and electricity, high boiling points, silvery grey surface (but rapidly tarnished by air oxidation).

When an alkali metal atoms reacts, it loses an electron (oxidation) to form a singly positively charged ion eg Na ==> Na⁺ + e^-. In terms of electrons 2.8.1 ==> 2.8 and so forming a stable ion with a noble gas electron arrangement.

They tend to readily react with most non-metals to form ionic compounds which are usually soluble white solids.

Important trends down Group 1 with increase in atomic number (proton number), for the Alkali Metals ...

What are the group trends in melting point, boiling point, reactivity, size of atom (atomic radius), density and physical strength as you go down the group 1 alkali metals as the atomic/proton number increases?

the melting point and boiling point generally decrease down Group 1 Alkali Metals 

the element gets more reactive down Group 1 Alkali Metals with increase in atomic number

the atoms get bigger down Group 1 Alkali Metals 

generally the density increases down Group 1 Alkali Metals although the atom gets bigger, there is a greater proportional increase in the atomic mass 

generally the hardness decreases down Group 1 Alkali Metals, this suggests the metallic bonding gets weaker down the group

Questions 

1. What is the common name for the family of metals in Group 1 of the periodic table?

2. Rank the alkali metals from most to least reactive. Why have you decided on this order?

3. Look up potassium on the periodic table. Based on its position, would you predict it is more or ess reactive than sodium. Why?