Summary
Summary Periodic table and tests
This is a summary of the periodic table, its rows and groups. Also has decomposition and other topics covered to do with gases or metals
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Unit 2Periodic table
Group 1 (Alkali Metals)
Group 1 metals, Li to K
Belong to ‘alkali’ metals because in water they form alkaline
solutions.
Properties:
o Soft
o Very reactive
As soon as exposed to the air, they react with the oxygen in are and
become dull as the metal oxide forms
Relatively low melting and boiling points + densities.
Reactivities and properties of the alkali metals are similar because
they all have 1 outer electron
Reactions with water
Elements in Gr1 react easily with water to form a hydroxide and
hydrogen gas.
General equation for a group 1 metal (call it X for now) with water
is:
o 2X(s) + 2H2O (l) → 2XOH(aq) + H2(g)
Relative reactivities of Group 1 Metals
Reactivity of the alkali metals increases down group 1
The increasingly violent reaction of group 1 metals with water as we
go down the group, demonstrates their increasing reactivities: the
outer electron is more easily lost because it is further from the
nucleus.
Trends in reactivity can also be seen with other reactions of the
alkali metals and also in their physical properties; melting and
boiling points decrease down the group while densities increase.
Group 7 (Halogens)
Halogen means salt forming.
Properties
o Toxic
o Non-metal elements
o Low melting and boiling points
o Exist as diatomic molecules
o Brittle when solid
,Relative reactivities explained.
In gr1 we saw that the elements differ because each has an
additional shell of electrons, down the group the atoms get bigger
Same for Halogens. Examples:
o Fluorine has 2 shells; its outer electrons are close to the
nucleus. There are 7 outer electrons, very tightly attracted by
the protons in the nucleus. The nucleus acts as a strong
magnet to attract another electron to complete the shell.
o Chlorine has 3 shells and so the outer electron is a little
further away from the nucleus than the outer electron in the
fluorine atom. The electrons are therefore less strongly
attracted to the nucleus and the nucleus is not as strong a
magnet, so not as able to attract an electron.
o Bromine has its outer electron in the 4th shell and so there is
not much attraction between the nucleus and the outer
electrons.
The further away the outer electrons are from the nucleus, the less
strongly the nucleus attracts an extra electron into the shell
Because gr7 elements need to gain an electron, the less strongly
the nucleus attracts the electrons, the less able it is to attract
another electron and so the reactivity of the halogens decreases
down group 7
Reactivity of the halogens decreases down group 7
Displacement reactions of the halogens
The decreasing reactivity of the halogens can be demonstrated by
looking at their displacement reactions.
A more reactive halogen will displace (take the place of) a less
reactive halogen from a solution of it salts.
Halogen means salt forming and we call halogen salts ‘halides’,
Reacting bromine with chloride and iodide ions
Bromine is less reactive than chlorine so it cant displace chloride
ions
, Bromine is more reactive than iodine so will displace the iodine ions
no
Br2(aq) + 2NaCl(aq) →
reaction
(colourles (stays
(orange)
s) orange)
Br2(aq) + 2NaI(aq) → 2NaBr(aq) + I2(g)
(dark
reddis
(colourles (colourles
(orange) h
s) s)
brown
)
Experiment to test for chlorine :
o Use a damp blue litmus paper
The chlorine will turn it to red and then white as it
bleaches it.
o Also use damp starch-iodide paper
Hold it in the gas being released and loo for a colour
change
Paper will go a black-blue if chlorine is present
Experiment to test for Ammonia
o Use indicator paper
Damp litmus red paper and it will turn blue with
ammonia
Displacement reactions as REDOX reactions
Oxidations and reduction happen together; if one element is
reduced (gains electrons) another has to be oxidised (lose electrons)
hence we have (REDuction + Oxidation)
When a halogen forms a halide it gains an electron, therefore its
reduced
Reactions of the Halogens with Hydrogen
The halogens react with hydrogen to form hydrogen halides: hydrogen
fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide.
Remember from the last unit that the non-metals change their endings
when they form a compound; hence when the halogens react they
become ‘halides.’
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