2.1.2Inorganic Chemistry
Group 1: Reactivity and Electronic Configurations — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions
5 min read 5 parts Lesson 16 of 23 Unit quiz
Section 1 of 5Electronic Configurations
The number of outer electrons gives the group; the number of shells gives the period.
Lithium
- Lithium has the configuration 2,1, with a single electron in its outer shell.
Sodium
- Sodium has the configuration 2,8,1, so its outer electron is in the third shell.
Potassium
- Potassium has the configuration 2,8,8,1, so its outer electron is in the fourth shell.
Common pattern
- All Group 1 atoms have one outer electron, which is why they form 1+ ions and behave similarly.
Section 2 of 5Reactivity Increases Down the Group
Reactivity Increases Down the Group
Distance
- Going down, the outer electron is in a shell further from the nucleus, so the attraction to it is weaker.
Shielding
- More inner shells of electrons shield the outer electron from the positive nucleus.
Easier loss
- Because the outer electron is lost more easily, the metal forms a 1+ ion more readily and is more reactive.
Evidence
- Reactions with water and oxygen become more vigorous from lithium to sodium to potassium.
| Metal | Observations with water |
|---|---|
| Lithium | Fizzes steadily and moves on the surface |
| Sodium | Melts into a ball, fizzes vigorously and moves rapidly |
| Potassium | Reacts very vigorously and the hydrogen burns with a lilac flame |
Section 3 of 5Equations
Equations
With water
- 2M(s) + 2H₂O(l) → 2MOH(aq) + H₂(g), where M is Li, Na or K.
Sodium example
- 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g), giving an alkaline solution.
With oxygen
- 4Li(s) + O₂(g) → 2Li₂O(s), and sodium and potassium form Na₂O and K₂O in the same ratio.
Alkali test
- Universal indicator turns purple in the solution, showing the hydroxide is strongly alkaline.
Section 4 of 5Physical Trends and Predictions
Physical Trends and Predictions
Softness
- The metals are soft and can be cut with a knife, getting softer down the group.
Density
- Lithium, sodium and potassium are less dense than water, so they float.
Melting points
- Melting points fall down the group as the attraction between the outer electrons and the positive ions weakens.
Prediction
- Rubidium and caesium would react even more vigorously than potassium and have lower melting points.
Section 5 of 5Exam Checklist & Tips
2.1.2 – Key Points for the Exam
- Alkali metal A Group 1 metal, so called because it forms an alkaline hydroxide in water.
- Outer shell The highest occupied energy level of an atom.
- Shielding Reduction in the nuclear attraction felt by outer electrons due to inner shells.
- Ion An atom or group of atoms that has gained or lost electrons.
Common Mistakes
- Saying the metals become more reactive because they have more outer electrons; they all have one.
- Writing the product of the water reaction as a metal oxide instead of hydroxide.
- Forgetting that hydrogen, not oxygen, is the gas produced with water.
- Explaining reactivity with 'bigger atoms' without mentioning distance and shielding.
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