SC17 - Groups in the Periodic Table ✓ Flashcards Preview

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Flashcards in SC17 - Groups in the Periodic Table ✓ Deck (29)
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1

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

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

2

SC17a - Why are alkali metals stored in oil?

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

3

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

This is oxidation.

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

[Where x is any alkali metal]

4

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

It decreases

5

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

2x(s) + 2H2O(l) → 2xOH(aq) + H2(g)

6

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

  • Li: Bubbling fiercely on the surface and moves around a bit. Water turns purple
  • Na: Moderate effervesance (fizzing) on the surface. Moves about quicker. Might have a yellow spark. Water turns purple
  • K: Lots of effervesance (fizzing) on the surface. Moves about very fast. Lilac flame produced. 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

7

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

It increases.

8

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

  • 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

9

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

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

10

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

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

11

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

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

12

SC17b - What is the trend in mp/bp and density of halogens as you go down group 7 ?

It increases.

13

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

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

14

SC17b - What are the properties of Halogen gases?

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

15

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

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

16

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

  • Hydrogen and a halogen bond to from hydrogen halide.
  • This is dissolved in water to from an acidic solution. For example:
  • Hydrogen + Chlorine → Hydrogen Chloride
  • This can dissolved in water to form Hydrochloric acid

17

SC17b - What is the test for chlorine?

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

18

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

  • 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.

19

SC17c - What is a displacement reaction?

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

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. Bromine + Potassium iodide

  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

21

SC17c - Why is displacement a redox reaction?

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

22

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

  • 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

23

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

Group 8 / Noble gases

24

SC17d - What are the properties of the noble gases?

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

25

SC17d - What is the trend in m.p/b.p and density as you go down the group 0?

It increases

26

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

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

27

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

  • 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

28

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

  • 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.

29

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

  • 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 elctron may transfer over.