Chemistry F332 Summary

 mole of gaseous substance = 24dm3 

The number of molecules in one mole of gas is always = 6x10²³

Sructure of an Ionic Lattice: Sodium Chloride 

• Ions are held together by attractions between the oppositely charged ions. So the giant ionic lattice is built up. 
• Electrostatic bonds hold all ionic lattices together. 
• The lattice structure of sodium chloride is said to be simple cubic. 

Some Ionic crystals contain some water molecules:                                                               The water molecules sit inside the ion lattice : Water of Crystallisation  These crystals are said to by hydralysed. 

1. All Nitrates are soluble in water 

2. All Chlorides are soluble in water (except AgCl and PbCl^2) 

3. All Sulfates are soluble in water (except BaSO^4, PbSO^4 and SrSO^4) 

4. All Na, K, and Ammonium SALTS are soluble in water 

5. All Carbonates are insoluble in water (except (NH^4)^2CO^3 and group 1.) 

O xidation 

I s

L oss 

R eduction 

I s 

G ain 

an element is oxidised when its oxidation state increases 

an element is reduced when its oxidation state decreases 

• Atoms in an element, oxidation state = 0
• Compounds, Oxidation state is assigned to each ion or ion. 
  • when compound has no charge atoms must add to 0
  • when compound is an ion must add to the charge 

• F = -1 
• O = -2 ( except in O^2- and OF-)
• H = +1 
• Cl = -1 (except when combined with O or F)

FeO = iron(II) oxide 

Fe^2O^3 = iron (III) oxide 

the number in the brackets is the charge. 

e.g. 

2Na + Cl^2 --> 2NaCl 

written as two half equations 

2Na --> 2Na+ + 2e- (this is oxidation as there is a loss of electrons) 

Cl^2 + 2e- --> 2Cl- (this is reduced as there is a gain of electrons) 

REDOX CHANGES WITH HALIDE IONS 

Displacement reactions!! 

Fluorine:  - pale yellow gas at room temp.                                                                                                                           - reacts with water                                                                                                                                               - soluble in organic solvents 

Chlorine: - green gas at room temp.                                                                                                                                - slightly soluble in water to give a pale green solution                                                                            - soluble in organic substances to give a pale green solution 

Bromine:      - dark red liquid at room temp which quickly forms a brown gas on warming                               - slightly soluble to give a red/brown solution in water                                                                         - soluble to give a red solution in organic substances 

Iodine:     - Shiny black solid sublimes on warming to give a purple vapour                                                        - barely soluble in water but gives a brown solution                                                                           - soluble in organic substances to give a purple solution 

most reactive - fluorine 

chlorine                               (reactivity decreases down the group) 

bromine 

least reactive - iodine 

Halide ions and Silver ions 

chlorine + silver --> silver chloride / white precipitate 

bromine + silver --> silver bromide / cream precipitate 

iodine + silver --> silver iodide / yellow precipitate 

General reaction (X- = halide ion) 

Ag+(aq) + X-(aq) --> AgX(s) 

REDOX REACTION INVOLVING HALOGENS - 

Fluorine is the strongest oxidising agent in group7. Fluorine atoms are small and the attraction of a fluorine nucleus for an electron is very strong. As the halogen atoms get bigger, the nucleus is further from the outer shell into which an electron will fit, and the attraction decreases. 

ELECTROLYSIS OF SOLUTIONS CONTAINING HALIDE IONS 

electric current passed through a solution of sodium chloride, chlorine gas bubbles off at the anode. This reaction is the basis of the industrial manufacture of chlorine. Chloride ions lose electrons to the anode and become oxidised:

2Cl- --> Cl^2 + 2e-

STORAGE AND TRANSPORT OF HALOGENS 

• Fluorine far to reactive to store. So made in situ by electrolysing liquid hydrogen fluoride. 
• Chlorine is a very toxic, so it is transported as a liquid 
• Bromine transported in lead lined lorries, supported by metal frames and routes are planned. 

's' = 2 electrons 

'p' = 6 electrons 

'd' = 10 electrons 

A dipole arises when a charge is not shared equally between two molecules, causing a slightly positive and slightly negative end. This molecule is said to be polarised. 

Permanent Dipoles

• These occur when two atoms bonded to each other have significantly different electronegativities.
• Hydrogen has a lower electronegativity than chlorine, and so when chlorine bonds with hydrogen, a dipole is formed.

Instantaneous Dipoles

• Atoms with similar/same electronegativities do not have permanenet dipoles; however they do have instantaneous dipoles due to the constant movement of the electrons.

Induced Dipole (for example a Br₂ molecule is polarised next to a C=C bond)

• If an unpolarised molecule finds itself next to a polar molecule, the unpolarised molecule may get a dipole induced in it. This happens when hydrogen chloride comes into contact with a chlorine molecule:

• Permanent Dipole- Permanent Dipole: Two or more permanent dipoles are attracted to each other, for example in HCl.

• Permanent Dipole- Induced Dipole: a permanent dipole induces a dipole in another molecule, this causes an attraction between the molecules, for example between HCl and Cl₂

• Instantaneous Dipole Induced Dipole (Van der Waals forces / London forces / Dispersion): where an instantaneous dipole induces a dipole in another molecule, for example between Cl₂ molecules. These attractions occur between all molecules.

The degree to which an atom of an element attracts electrons is called its electronegativity. 

The more electronegative an atom is the greater its attraction for electrons 

The order of electronegativity of the common elements is: 

F > O > Cl > Br and N > I > S > C > H