SC17 - Groups in the Periodic Table ✓

Question 1

SC17a - What are the physical properties of the alkali metals (group 1)

Answer 1

• Malleable
• Good conductors of electricity
• Relatively low melting points
• Soft/easily cut

Question 2

SC17a - Why are alkali metals stored in oil?

Answer 2

They are incredibly reactive and would react with the oxygen and moisture in air otherwise.

Question 3

SC17a - When you cut an alkali metal, a layer of tarnish forms. What is this called and what is the equation for this?

Answer 3

This is oxidation.

4x(s) + O₂(g) -> 2x₂O(s) Metal + Oxygen → Metal Oxide

[Where x is any alkali metal]

Question 4

SC17a - How does the melting point of the alkali metals change as you go down?

Answer 4

It decreases

Question 5

SC17a - What is the equation for the reaction that takes place when an alkai metal reacts with water?

Answer 5

2x(s) + 2H₂O(l) → 2xOH(aq) + H₂(g)

Question 6

SC17a - What would you observe when you put lithium, sodium and potassium in water that contains universal indicator?

Answer 6

• Li: Bubbling fiercely on the surface and moves around a bit. Water turns purple
• Na: Melts into a ball and fizzes about the surface Water turns purple
• K: Bursts into flames and flies about the surface. Water turns purple.
• Effervesance/bubbling indicates the presence of a gas (hydrogen)
• Water turns purple becuase it is alkali.
• Increased speed indicates a higher rate of reaction

Question 7

SC17a - What happens to the reactivity of alkali metals as you go down?

Answer 7

It increases.

Question 8

SC17a - The reactivity of alkali metals increases as you go down the table. Explain why this is using Lithium and Potassium as examples.

Answer 8

• Both Lithium and Potassium want to loose their only outer shell electron to gain a full outer shell and become stable
• Potassium has more shells of electrons and so there are more shells between its positive nucleus and its outer most electron
• The shells in between shield the positive charge
• Additionally it is urther away from the nucleus
• The positive charge from Lithium’s outermost electron is shielded by less shells and so the electrostatic forces of attraction to its outer shell electron are stronger
• As Potassium has weaker electrostatic forces of attraction to its outer shell electron, this electron can be los tmore easily
• This means Potassium will be more willing to loose its electron to form an ion making it more reactive.
• Thus as you go down the group, every extra layer of electron shells makes the element more reactive

Question 9

SC17b - What is the name for group 7 elements and what is key about their natural state?

Answer 9

• The halogens.
• They exist covalently bonded as diatomic atoms.

Question 10

SC17b - What is fromed when a halogen reacts with a metal (e.g. Chlorine and Magnesium)?

Answer 10

• It forms a halide salt.
• Cl₂(g) + Mg(s) → MgCl₂(s)

Question 11

SC17b - What happens to the name of a halogen once it it becomes an ion?

Answer 11

• It changes from -ine to -ide
• e.g. BromiNe atom to BromiDe ion

Question 12

SC17b - What is the trend in mp/bp and density of halogens as you go down the group?

Answer 12

It increases.

Question 13

SC17b - What are the appearances of Chlorine, Bromine and Iodine at room temperature?

Answer 13

• Cl: Green gas
• Br: Brown liquid
• I:Purple/grey solid

Question 14

SC17b - What are the properties of Halogen gases?

Answer 14

• Non-metals
• Diatomic
• Toxic
• Corrosive
• Brittle when solid
• Low mp/bp
• Poor conductors of electricity and heat
• Coloured vapours

Question 15

SC17b - What is the common use for all the halogens?

Answer 15

As disinfectancs/bleaches as they can kill microorganisms and remove stains.

Question 16

SC17b - Using Hydrogen and Chlorine as examples explain how halogen gases cna be used to from acidic solutions.

Answer 16

• Hydrogen and chlorine molecules collide and the covalent bonds holding the atoms together break
• Covalent bonds form between hydrogen and chlorine atoms, making a new compound of hydrogen chloride
• When hydrogen chloride dissolves in water, the molecules break up into two ions, H+ and Cl-. The formation of H+ ions makes solution acidic

Question 17

SC17b - What is the test for chlorine?

Answer 17

Damp blue litmus paper will turn red and bleach white in the presence of chlorine gas.

Question 18

SC17c - What observations will you make when you heat halogens with iron wool and what does this tell you about the reactivity trend?

Answer 18

• Fluorine: Bursts into flames
• Chlorine: Glows brightly
• Bromine: Glows dull red
• Iodine: Changes colour
• As the reaction gets less violent as you go down the group you can tell that they get less reactive.

Question 19

SC17c - What is a displacement reaction?

Answer 19

A reaction in which a more reactive element displaces a less reactive metal from a compound producing the less reactive metal

Question 20

SC17c - State what observation you would make in each of these reactions signifying that displacement has taken place:

1. Fluorine + Potassium chloride
2. Chlorine + Potassium bromide
3. Potassium bromide+ iodide

Answer 20

1. Solution turns yellow showing that chlorine has been produced
2. Solution turns orangey-brown showing that bromine has been produced
3. Solution turns dark brown showing that iodine has been produced

Question 21

SC17c - Why is displacement a redox reaction?

Answer 21

• Because both oxidation and reduction occur at the same time.
• e.g 2Cl^- + F₂ → Cl₂ + F^-
• The chlorine looses electrons at the same time that the fluorine gains electrons and so it is a redox reaction

Question 22

SC17c - Using Fluorine and Iodine as examples explain why the reactivity of halogens decreases as you go down the group?

Answer 22

• Both Fluorine and Iodine want to gain one outer shell electron to have a full outer shell and become stable
• Iodine has more shells of electrons and so there are more shells between its positive nucleus and its outer most electron
• The shells in between shield the positive charge
• Additionally it is further away from the nucleus
• The positive charge from Fluorine’s outermost electron is shielded by less shells and so the electrostatic forces of attraction to its outer shell electron are stronger
• As Fluorine has stronger electrostatic forces of attraction to its outer shell electron, the last needed electron is attracted more easily
• This means Fluorine will be more willing to gain an electron to form an ion making it more reactive.
• Thus as you go down the group, every extra layer of electron shells makes the element less reactive as there is more shielding and it’s harder to gain an electron

Question 23

SC17d - What is another name for the group 0 elements?

Answer 23

Group 8 / Noble gases

Question 24

SC17d - What are the properties of the noble gases?

Answer 24

• Colourless
• Have very low m.p/b.p
• Poor conductros of heat and electricity
• Inert/unreactive

Question 25

SC17d - What is the trend in m.p/b.p and density as you go down the group?

Answer 25

It increases

Question 26

SC17d - Why weren’t the noble gases discovered until the late 19th century?

Answer 26

They don’t form compounds and are in very small amounts in our atmosphere and so are hard to detect.

Question 27

SC17d - What are the uses for each of the noble gases from helium to krypton?

Answer 27

• He: Used for weather ballons/airships as it is non-flammable and has a low density
• Ne: Used in electrical signs for its orange-red glow when electricity passes through
• Ar: Used in the space above wine to preserve it as its denser than air will stop the wine from reacting
• Kr: Used in photography lighting for its brilliant white light when electricity passes through

Question 28

SC17d - Describe, in terms of their electron configuration, why halogen gases are inert?

Answer 28

• Halogen gases have complete outer shells (e.g. 2 in helium or 8 in neon).
• This means that they are stable as their energy levels are full.
• Thus they ahve no need to loose any electrons.

Question 29

SC17d - Explain why, despite being a noble gas, Xenon can still form compounds?

Answer 29

• Xenon has many shells of electrons.
• These shield the positive charge form the nucleus meaning that the positive electrostatic force of attraction acting on its outer layer is weaker.
• Thus if it is near to an atom with few shells (such as fluorine) and is close to the positive charge from that nucleus, the electron may transfer over.