SC17 - Groups in the Periodic Table ✓ Flashcards
SC17a - What are the physical properties of the alkali metals (group 1)
- Malleable
- Good conductors of electricity
- Relatively low melting points
- Soft/easily cut
SC17a - Why are alkali metals stored in oil?
They are incredibly reactive and would react with the oxygen and moisture in air otherwise.
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]
SC17a - How does the melting point of the alkali metals change as you go down?
It decreases
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)
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
SC17a - What happens to the reactivity of alkali metals as you go down?
It increases.
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
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.
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)
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
SC17b - What is the trend in mp/bp and density of halogens as you go down group 7 ?
It increases.
SC17b - What are the appearances of Chlorine, Bromine and Iodine at room temperature?
- Cl: Green gas
- Br: Brown liquid
- I:Purple/grey solid
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
SC17b - What is the common use for all the halogens?
As disinfectancs/bleaches as they can kill microorganisms and remove stains.