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OCR B (Salters) AS level Chemistry
UNIT 2 ­ F332

Elements from the sea
Halogens and Halides (group 7 chemistry)

Halogen is the elemental molecule, eg/ Cl, Br
Halide is in a compound, eg/ KBr, KCl

Fluorine Chlorine Bromine Iodine
Appearance Pale yellow Green gas Dark red Shiny black

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Element Oxidation number
Fluorine -1
Oxygen -2 (unless with Fluorine)
Chlorine -1 (unless with Fluorine or Oxygen, then +1)
Hydrogen +1

Working out oxidations states is really just simple maths.

Ion Oxidation state of Name of ion
ClO +1 Chlorate (I)
ClO +3 Chlorate (III)
ClO +5 Chlorate (V)…

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Needs to be covalently bonded.
One element has to be more electronegative then the other.
Has to have a delta negative end and delta positive end according to
the shape of the molecule.


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Nucleophillic substitution
`A nucleophile is a species which is strongly attracted to a region of positive
charge in another molecule, and can donate an electron pair'

SN2 mechanism


The Nu ion represents the attacking nucleophile
Curley arrows show the movement of electron pairs
The nucleophile is attracted to the…

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The first ionisation energy is the energy required to remove the most loosely
held electron from one mole of gaseous atoms to produce 1 mole of gaseous
ions each with a charge of 1+.
This is more easily seen in symbol terms.

It is the energy needed to carry out…

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Last calculations
Number of moles = Volume (dm³) x Molarity (mol dm³)
% uncertainty = (total error range) / (volume) x 100





really helpful, thanks

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