8.2 Group I properties
- Syllabus
- 0620–2026–2027
- Topic
- 8.2
- Level
- —
Learning objectives
8.2.1Group I alkali metals, lithium, sodium• Describe Group I alkali metals, lithium, sodium and potassium, as relatively soft metals with general trends down the group, (a) decreasing melting point (b) increasing density (c) increasing reactivity8.2.2Predict the properties of other• Predict the properties of other elements in Group I, given information about the elements
Describe the Group I trends
Lithium, sodium and potassium are Group I alkali metals. They are relatively soft metals and can be cut more easily than typical transition metals.
| Going down Group I | Trend | Lithium → sodium → potassium |
|---|---|---|
| melting point | decreases | highest → intermediate → lowest |
| density | generally increases | lowest → higher → generally higher |
| reactivity | increases | least reactive → more reactive → most reactive |
The increasing reactivity is seen in increasingly vigorous reactions. With water, each metal forms an alkaline metal hydroxide solution and hydrogen; potassium reacts more vigorously than sodium, which reacts more vigorously than lithium.
Keep the directions separate: down the group, melting point decreases, but density and reactivity increase. These are general trends; do not reverse density simply because melting point falls.
Predict properties of another Group I element
An unfamiliar Group I element should continue the pattern shown by the known elements, unless the supplied data reveal an exception.
| Step | Action | Example for rubidium below potassium |
|---|---|---|
| locate | place the unknown relative to known Group I elements | rubidium is below potassium |
| set direction | read the trend for each requested property | melting point ↓; density ↑; reactivity ↑ |
| bound | compare rather than invent unsupported precision | lower melting point and generally higher density than potassium |
| predict behaviour | extend the qualitative pattern | reacts more vigorously than potassium |
| check | apply every supplied datum and unit | a numerical estimate must fit the surrounding values |
If an unknown lies between two known elements, predict a value between their values. If it lies below the last known element, extrapolate in the established direction and use an approximate value only when the question asks for one.
Do not assume that every physical property rises or falls together. Make a separate prediction for melting point, density and reactivity, and justify each one from the given trend.