C4.1 - Predicting Chemical Reactions

Question 1

Why are group 1 metals called the alkali metals?

Answer 1

Group 1 metals are called the alkali metals because they react with water to form alkaline solutions.

Question 2

What are some properties of the alkali metals?

Answer 2

• Have some typical properties of metals.
• Shiny when freshly cut.
• Good conductors of electricity.
• Solid state at room temperature.
• Group 1 elements are soft enough to cut
  with a knife.
• Each alkali metal is softer as you go down
  the group.

Question 3

What are the trends of group 1 metals?

Answer 3

• Going down the group - Their density increases,
  although sodium is denser than expected.
• Going down the group - Their melting point
  decreases.
• Going down the group - Their reactivity increases.

Question 4

Why are the alkali metals stored in oil?

Answer 4

The alkali metals are stored in oil because they react rapidly with the 1oxygen in the air and with water.

Question 5

What happens when an alkali metal reacts with water?

Answer 5

Alkali metal + Water -> Metal hydroxide + Hydrogen

Question 6

Describe the reaction of the alkali metals and water.

Answer 6

• Lithium fizzes steadily and slowly disappears.
• Sodium melts to form a silvery ball, fizzes
  vigorously, and quickly disappears.
• Potassium immediately ignites, burns with a lilac
  flame, and very quickly disappears.

Question 7

Why do group 1 elements have similar chemical properties?

Answer 7

All group 1 elements atoms have 1 electron in their outer shell which they lose in a reaction to leave a complete outer shell forming ions with a single positive charge.

Question 8

Why does the reactivity of alkali metals increase as you go down the group?

Answer 8

- There is an increased distance between the 
  electron and nucleus.
- More shielding.
- It is easier to lose an electron.
- Therefore it is more reactive.

Question 9

Why does density increase as you go down an elements group?

Answer 9

• There are more protons and neutrons as you go
  down the group.
• Even though the atoms are bigger, the mass
  increases even more.
• Therefore, there is a greater mass per unit volume
  which means a higher density.

Question 10

Why does melting point decrease as you go down the group 1?

Answer 10

• Metallic bonds are weaker.
• Because there is a greater distance between
  the nucleus and the electrons.
• Therefore, less energy is needed to break the
  bonds between the atoms.

Question 11

Give the three symbol equations with reactions relating to alkali metals.

Answer 11

• 2M + 2H2O -> 2MOH + H2
• 4M + O2 -> 2M2O
• M -> M+ + e-

Question 12

What are group 7 elements known as are what are their properties?

Answer 12

• Group 7 elements are known as the halogens.
• They have typical properties of non -
  metals.
• Brittle in solid state.
• Poor conductors of electricity.

Question 13

How do group 7 elements exist?

Answer 13

• Diatomic molecules.
• Weak intermolecular forces.
• Coloured or form coloured vapours.
• Occur in different states at room temperature.

Question 14

What are the colours and states (at room temperature) for the group 7 elements?

Answer 14

• Fluorine is a pale yellow gas.
• Chlorine is a green gas.
• Bromine is an orange-brown liquid that
  vaporises easily.
• Iodine is a shine grey-black crystalline solid that
  sublimes to form a purple vapour.

Question 15

What are the trends going down group 7?

Answer 15

• Density increases.
• Melting and boiling points increase.
• Reactivity decreases.

Question 16

Why does the melting and boiling points of the halogens increase as you go down the group?

Answer 16

• The molecules are bigger.
• Therefore the intermolecular forces are stronger
  and more energy is required to break them.

Question 17

Why do the halogens all have similar chemical properties?

Answer 17

• All halogens have 7 electrons in their outer
  shell.
• They all gain an electron in their outer shell
  forming ions with a single negative charge.

Question 18

Why does reactivity decrease as you go down group 7?

Answer 18

• Halogens are trying to gain an electron to
  complete its outer shell.
• As you go down the group, it is harder to gain
  an electron because the nuclear attraction is
  weaker as there is more shielding.

Question 19

Why are group 7 elements called the halogens?

Answer 19

• They react with metals to produce salts.
• They also react vigorously with group 1 metals,
  particularly if the metal is heated first.

Question 20

Give the two symbol equations relating to the halogens.

Answer 20

• 2M + X2 -> 2MX

- X2 + 2e- -> 2X-

Question 21

What is a halide and halide ions?

Answer 21

• A halide is a compound of a group 7 element and
  one other element (usually a hydrogen or metal).
• A halide ion is a negative ion formed by a group 7
  element.

Question 22

Describe what is a halogen displacement reaction and which halogens displace which.

Answer 22

• A halogen will displace a less reactive halogen
  from its halide ions in solution.
• Chlorine displaces bromine from bromides, and
  iodine from iodides.
• Bromine displaces iodine from iodides but not
  chlorine from chlorides.
• Iodine cannot displace chlorine from chlorides or
  bromine from bromides.

Question 23

Describe the steps to carry out a halogen displacement reaction.

Answer 23

• Wearing eye protection place a small volume of
  potassium chloride, potassium bromide, and
  potassium iodide in each all 9 spaces of a three
  by three spotting tile.
• Add a few drops of chlorine solution across the
  first row, a few drops of bromine across the
  second row and a few drops of iodine across
  the third row.
• Note your observations in a table.
• Asthmatics should take particular care not to
  breathe in any chemical fumes.

Question 24

What are group 0 elements called and why?

Answer 24

The elements in group 0 are called the noble gases because they are so unreactive.

Question 25

What are the properties and trends of noble gases?

Answer 25

• Non-metals.
• All gases at room temperature.
• Boiling point increases as you do down the
  group.
• Density increases as you go down the group

Question 26

Why do noble gases have very low boiling points?

Answer 26

• The noble gases are monatomic.
• Exist as single atoms with very weak forces of
  attraction between them.
• These forces are easily overcome and need very
  little energy to overcome them.
• Hence, noble gases have really low boiling points
  and are gasses at room temperature.

Question 27

Why are noble gases so unreactive?

Answer 27

• The atoms of Group 0 elements have complete
  outer electron shells.
• This means that they have no tendency to lose or
  gain electrons in reactions.

Question 28

What are the transition metals?

Answer 28

• The transition metals are placed between groups
  two and three of the periodic table.
• They are all metals and their properties are typical
  of metals.

Question 29

Compared to the alkali metals in group 1, the transition metals…

Answer 29

• Are stronger and harder.
• Have higher densities.
• Have higher melting points (except mercury
  which is in the liquid state at room temperature).

Question 30

How reactive are the transition metals?

Answer 30

• The transition metals are less reactive than the
  alkali metals and react slowly if at all,
• Iron reacts slowly with water to produce hydrated
  iron(III) oxide.
• Gold, platinum and iridium do not react with water
  or oxygen at all.

Question 31

What coloured ionic compounds do alkali metals and the transition metals make?

Answer 31

The alkali metals produce white or colourless ionic compounds, but the transition metals produce coloured ionic compounds.

Question 32

What are transition metals often good for?

Answer 32

Catalysts - Increase the rate of reactions without being used up.

Question 33

What does a metal have to be in order for it to react with water?

Answer 33

The metal has to be more reactive than hydrogen.

Question 34

When a metal reacts with water or an acid, what does more vigorous bubbling tell you?

Answer 34

• The greater the rate of hydrogen production.

- The more reactive the metal.

Question 35

When measuring the reactivity of metals, what should you do if you can’t see any bubbling?

Answer 35

• Gently warm the water to see if bubbling starts.
• Don’t boil the water or acid as it will bubble and
  you wouldn’t be able to tell if the bubbles were
  due to a reaction.

Question 36

Describe what a metal displacement reaction is.

Answer 36

• A more reactive metal can displace a less reactive
  metal from solutions of its compounds.
• Displacement reactions are also examples of
  redox reactions.