Group 1 and group 2: the reactive metals · Chemistry Class 9–10 | StemPy Lab
Course 9.3·Lesson 1 of 3
Group 1 and group 2: the reactive metals
Group 1 has the alkali metals. They are soft, they have one outer electron, and they react with water to give hydrogen and an alkali. They become more reactive down the group. Group 2 has the alkaline earth metals, with two outer electrons. They are harder and less reactive than their neighbours in group 1.
about 25 min1 simulation2 practice questions
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Group 1: the alkali metals
Lithium, sodium, potassium, rubidium, caesium and francium are the alkali metals. Hydrogen is not in the family, though it is at the top of the group.
They have one outer electron, so the valency is 1 and they make M+ ions.
They are soft, silvery, and they have low melting points. A knife can cut sodium.
They are very reactive, so sodium and potassium are stored under kerosene.
With water:
2Na+2H2O→2NaOH+H2
The product is an alkali, which is why the family has this name. Lithium reacts slowly. Sodium reacts quickly. Potassium reacts so fast that the hydrogen burns with a lilac flame.
Reactivity increases down the group
Electron shell diagrams of lithium with the arrangement 2, 1, sodium with 2, 8, 1 and potassium with 2, 8, 8, 1. Each atom has one electron in the outer shell. The atoms get bigger down the group, the outer electron is farther from the nucleus, and the reactivity increases.
Lithium has 2 shells, sodium has 3 and potassium has 4. Each time, the outer electron is farther from the nucleus, and the electrons in the inner shells shield it. So it is lost more easily.
Element
Li
Na
K
Rb
Cs
Shells
2
3
4
5
6
Melting point (K)
454
371
337
312
302
Down the group, the atoms are bigger, the melting point falls, and the reactivity rises.
You should find that the melting point falls all the way down the group, while the radius grows.
Group 2: the alkaline earth metals
Beryllium, magnesium, calcium, strontium, barium and radium have two outer electrons. The valency is 2 and they make M2+ ions.
They are harder than the alkali metals, and they melt at higher temperatures.
They are less reactive than the group 1 metal of the same period. Magnesium is less reactive than sodium. Calcium is less reactive than potassium.
Magnesium burns in air with a bright white flame and makes magnesium oxide, a white powder.
Calcium reacts with cold water, slowly: Ca+2H2O→Ca(OH)2+H2. It sinks, and the bubbles of hydrogen carry it up.
Their oxides and hydroxides are basic. Lime, CaO, and slaked lime, Ca(OH)2, are used in building, and in farming.
Down group 2, the reactivity rises, just as in group 1.
Why is magnesium less reactive than sodium?
A magnesium atom has to lose two electrons, and it has a bigger nuclear charge, +12 against +11. So it holds its electrons more strongly.
Practise with new numbers
Try it in Python
This program lists the atomic radius and the melting point of group 1.
Remember these
Group 1: one outer electron, soft metals, they react with water to give an alkali and hydrogen. Stored under kerosene.
Reactivity increases down the group. The melting point falls.
Group 2: two outer electrons, harder and less reactive than their neighbours in group 1.
Check yourself
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
What colour does the hydrogen burn with when potassium reacts with water?
Which is more reactive, magnesium or sodium? Why?
What valency does strontium, below calcium in group 2, have?
What is slaked lime, and what is it used for?
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