Group I metals

Last time

Before we start: last time, in Acids, bases and the pH scale, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

A metal you can cut with a knife

Most metals are hard. But sodium is soft enough to cut with a knife, it floats on water, and it fizzes round on the surface, giving off hydrogen. Sodium belongs to Group I, the alkali metals, and the whole group follows a pattern you can predict.

Where they are

Group I is the first column: lithium, sodium and potassium are the three you need to know. Each has one outer electron: lithium 2,1, sodium 2,8,1 and potassium 2,8,8,1. They each lose that electron to form a plus one ion. That explains their chemistry.

Physical properties

They are soft and can be cut with a knife. They are shiny when freshly cut, but quickly go dull. They have low melting points and low densities, and lithium, sodium and potassium all float on water. They are good conductors of heat and electricity, like all metals.

The trend down the group

Going down the group, the melting point decreases. Lithium melts at 181, sodium at 98, potassium at 63 degrees. The metals become softer going down. The density increases going down, though potassium is less dense than sodium in practice.