Topic 6 Flashcards
Explain why some elements can be classified as alkali metals (group 1), halogens (group 7) or noble gases (group 0), based on their position in the periodic table
Groups (columns) in the periodic table can be classified in specific groups as e.g. alkali metals, halogens or noble gases, because they have the same number of
electrons in their outer shell (position in the periodic table determines this), therefore they have the same chemical properties
Describe alkali metals
Alkali metals are soft and have relatively low melting points
Describe the reactions of lithium, sodium and potassium with water
Lithium, sodium and potassium in group one react vigorously with water to create an alkaline metal hydroxide and hydrogen.
Describe the pattern in reactivity of the alkali metals, lithium, sodium and potassium, with water
- lithium fizzes steadily
- sodium melts into a ball then fizzes quickly
- potassium gives off sparks and hydrogen burns with a lilac flame
How can you use this pattern to predict the reactivity of
other metals ?
● as shown by the way the reactions with water become more vigourous down the group, the reactivity of all alkali metals increases down the group
Explain this pattern in reactivity in terms of electronic configurations
(alkali metals)
● Down the group – easier to lose electrons and form positive metal ions (cations) (these are formed when metals react)
● It is easier to lose electrons due to the increase in electron shells as you go down the group. This means there is more electron shielding and so decrease in
attraction between the positively charged nucleus and the negatively charged outer shell electrons, which can then be lost more easily
Recall the colours and physical states of chlorine, bromine and iodine at room temperature
● Chlorine is a yellow-green gas
● Bromine is a red-brown liquid
● Iodine is a grey solid
Describe the pattern in the physical properties of the halogens( chlorine,bromine and iodine) and use this pattern to predict the physical properties of other halogens
● There is a trend in state from gas to liquid to solid down the group
● this is because the melting and boiling points increase as you go down the group
● from this, you can predict that any halogens above chlorine will be gases (their boiling points will be even lower), and any below iodine will be solids (their melting points will be even greater)
●they get darker as they go down the group
Describe the chemical test for chlorine
When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white
Describe the reactions of the halogens, chlorine, bromine and iodine, with metals to form metal halides, and use this pattern to predict the reactions of other halogens
● They react with metals to form ionic compounds in which the halide ion carries a -1 charge. e.g. NaCl or MgBr2 (as Mg has a +2 charge so you need two Br to cancel this out)
● Reaction is less vigorous as you move down group 7, but they still all react to form metal halides
What halides (which dissolve in water to form acidic solutions) do halogens, chlorine, bromine and iodine form
● halogen + hydrogen → hydrogen halide (HCl, HBr, HI)
● reaction becomes less vigorous down group: chlorine reacts in sunlight, but bromine will react in a flame (higher temperature)
● hydrogen halides dissolve in water to produce acidic solutions- in solution the hydrogen halide will fully dissociate into H+ and halide ions
Describe the relative reactivity of the halogens by their displacement reactions with halide ions in aqueous
solution
● A more reactive halogen can displace a less reactive in an aqueous solution of its salt.
● chlorine will displace bromine and iodine
● bromine will displace iodine but not chlorine
● iodine can replace neither chlorine or iodine
Why does this displacement of halogens occur?
● This happens because as you go down the group, the reactivity of halogens decreases.
● The halogens react by gaining an electron in their outer shell, as you go down the group:
o outer shell becomes further from the nucleus
o electron shielding increases
o attraction decreases between nucleus and outer electrons
o electrons are gained less easily
o halogens become less reactive
Explain why these displacement reactions are redox reaction
● OILRIG- oxidation is loss, reduction is gain (of electrons)
● More reactive halogen which displaces the less reactive one, forms a negative ion itself, therefore being reduced as it has gained electrons
● The less reactive halogen that is displaced is oxidised as it gains these electrons to go from a negative ion to an atom with 0 charge
Explain the relative reactivity of the halogens in terms of electronic configurations
● electronic configurations of the halogens:
○ fluorine: 2,7
○ chlorine: 2,8,7
● these show clearly the extra shell of electrons gained as you move down group 7, which lead to greater shielding and weaker attraction, leading to reduced reactivity
