2.8 Group 1 (Alkali Metals)

Question 1

What do alkali metals have to be stored in?

Answer 1

Oil - and handled with forceps

Question 2

Why do alkali metals have to be stored in oil?

Answer 2

They react vigorously with water

Question 3

Are the alkali metals soft or hard?

Answer 3

Soft

Question 4

Do the alkali metals have low or high density?

Answer 4

Low

Question 5

What is special about the first 3 alkali metals in group 1 of the periodic table?

Answer 5

They are less dense than water

Question 6

What are the trends for the alkali metals as you go down the group? (5)

Answer 6

• Increasing reactivity
• Lower melting and boiling points
• Higher relative atomic mass
• Higher density
• Decrease in hardness

Question 7

Describe the structure of group 1 metals (3)

Answer 7

• Group 1 metals form regular structures held together with metallic bonds. In these bonds, the outer electron of each atom is free to move around (delocalised). There are strong attractions between these electrons and positively charged nuclei
• As you go down Group 1, the atoms get bigger - the nucleus is further away from the free electrons, so the attractions get weaker
• This means that less energy is needed to break the metallic bonds and turn the solid metal into a liquid then a gas - so melting and boiling points decrease down the group

Question 8

Describe why Group 1 metals are very reactive (3)

Answer 8

• The Group 1 metals readily lose their single outer electron to form a +1 ion with a stable electronic structure
• The more readily a metal loses its outer electrons, the more reactive it is - so the Group 1 metals are very reactive
• As you go down Group 1, the alkali metals get more reactive. The negatively charged outer electron is less strongly attracted to the positively charged nucleus. This is because it is further away (there are more electron shells) - so its more easily lost, as less energy is needed to remove it

Question 9

How do group 1 elements easily form iconic compounds with non-metals?

Answer 9

• E.g. A metal atom, like Sodium donates an electron to a non-metal like Chlorine so that both of them have full outer shells. As these two atoms are now oppositely charged ions, they become attracted to each other by electrostatic forces (ionic bond) and so together they make an ionic compound

Question 10

Regardless of what alkali metal is used to form an ionic compound, how do they generally look like? (2)

Answer 10

• White solids
• Tend to dissolve in water to form colourless solutions

Question 11

How does an alkali metal react with water?

Answer 11

Reacts vigorously to produce a metal hydroxide + hydrogen gas, e.g. sodium + water —> sodium hydroxide + hydrogen

Question 12

What happens when alkali metals from potassium downwards react with water?

Answer 12

Their reactivity is really high so they release more energy when they react with water; so much energy is released that it ignites the hydrogen gas that is produced, we can see this in the form of flames

Question 13

Except from water, which gas do the group 1 elements react vigorously with?

Answer 13

Chlorine gas

Question 14

What happens when the alkali metals react with oxygen?

Answer 14

They form metal oxides

Question 15

When sodium and oxygen react together, which two metal oxides can they form?

Answer 15

• Sodium oxide
• Sodium peroxide

Question 16

When potassium and oxygen react, which two metal oxides can they form?

Answer 16

• Potassium peroxide
• Potassium superoxide

Question 17

Explain why the reactivity of group 1 metals increases as you go down the group

Answer 17

The reactivity of group 1 elements increases as you go down the group because the atoms become larger, which means that the outer electron becomes further from the nucleus. This in turn means that the electrostatic attraction between the positive nucleus and outer negative electron decreases in strength. As a result the outer electron will be lost more easily, and so the element will be more reactive

Question 18

How do you calculate the reaction speeds of group 1 elements with water?

Answer 18

• You put universal indicator and water in a shallow bowl, and place a lump of the element inside. You time how long it takes for the water to become purple, this means it has becomes alkaline