2. PART 2 STRUCTURE AND
BONDING
FORMULAE AND
EQUATIONS
3.7 CHEMICAL FORMULAE
3.8 WORKING OUT THE FORMULAE
3.9WORKING OUT FORMULA FOR
IONIC COMPOUND
3.10 Polymers
3.11 Alloys
3. 3.7 CHEMICAL FORMULAE • CHEMICAL SYMBOLS
• EVERY ELEMENT HAS ITS OWN CHEMICAL
SYMBOL
• SULFUR IS S OXYGEN IS O AND BROMINE IS BR.
• MANY SYMBOLS ARE NOT OBVIOUS .THIS IS
BECAUSE THEY COME FROM LATIN,GREEK OR ARABIC
WORDS. FOR EXAMPLE IRON IS FE AND POTASSIUM
IS K
• FIRST LETTER IS CAPITAL AND THE SECOND IS SMALL
4. FORMULAE
• WE CAN WORK OUT THE FORMULA OF A
COMPOUND BY KNOWING THE VALENCIES OR
COMBINING POWERS OF THE ELEMENT IT
CONTAIN .
• YOU CAN USUALLY WORK OUT THE VALENCIES
FROM THE GROUP OF THE PERIODIC TABLE TO
WHICH THE ELEMENT BELONGS.
• YOU CAN SEE THAT THE VALENCIES OF YHE
NON METALS ON THE RIGHT HAND SIDE OF
THE PERIODIC TABLE IN GROUP 5 TO 0 ARE
FOUND BY TAKING THE GROUP NO. AWAY
FROM 8.
5. FORMULA
THREE POINTS YOU SHOULD BARE
IN MIND WHILE WRITING
FORMULAE;
1.YOU CAN NOT PERDICT THE
VALENCY OF THE TRANSITION
ELEMENTS.
2.THE FORMULAE OF SOME
COMPOUNDS CONTAINING ONLY
NON METALS ARE NOT SIMPLIFIED
BY CANCELLINHG OUT E.G
HYDROGEN PEROXIDE IS H2O2
3.SOME NON METALS FORM OXIDES
WITH DIFFERENT FORMULAE.FOR
EXAMPLE CO IS CARBON
MONOXIDEAND CO2 IS CARBON
DIOXID;SO2 IS SULFUR DIOXIDE AND
SO3 IS SULFUR TRIOXIDE.
6. SIMPLE RULES FOR NAMEING COMPOUNDS
• NAMING COMPOUNDS OF TWO ELEMENTS
1. IF THE COMPOUND CONTAINS A METAL AND A NON METAL,THE METAL IS PUT FIRST AND THE
ENDING OF THE NON METAL CHANGES TO –IED.THE COMPOUND OF CHLORINE AND MAGNESIUM
IS NAMED MAGNESIUM CHLORIDE
2. IF A COMPOUND COMPOUND CONTAINS TWO NON METALS,NAMING BECOMES COMPLICATED.IF
THE COMPOUND CONTAINS HYDROGEN THIS COMES FIRST.IF NOT THEN NON METAL WITH LOWER
GROUP NO.COMES FIRST FOR EXAMPLE IN NITROGEN DIOXIDE- NITROGEN IS IN GROUP 5 SO IT
COMES FIRST THEN OXYGEN WHICH IS IN GROUP 6.
3. IF THE NON METALS BELONG TO THE SAME GRPOUP THEN FURTHER DOWN THE GROUP COMES
FIRST.E.G IN SULFUR DIOXIDE SULFUR IS LOWER THEN OXYGEN IN GROUP 6 SO IT COMES FIRST
4. SOME COMPOUND HAVE BEING KNOWN FOR A LONG TIME ARE CALLED BY THEIR COMMON NAMES
E.G H2O IS WATER AND NH3 IS AMMONIA.
7. NAMING COMPOUNDS WITH THREE ELEMENTS
• YOU SHOULD BE ABLE TO RECOGNISE THE FOLLOWING GROUPS WHICH CONTAINS OXYGEN AS
WELL AS ANOTHER ELEMENT.
• OH HYDROXIDE NAOH SODIUM HYDROXIDE
• NO3 NITRATE MG{NO3}2 MAGNESIUM NITRATE
• SO4 SULFATE CASO4 CALCIUM SULPHATE
• CO3 CARBONATE NA2CO3 SODIUM CARBONATE
9. 3.9WORKING OUT FORMULA OF AN IONIC COMPOUND
FROM DIAGRAM
• YOU CAN WORK OUT THE FORMULA OF AN IONIC
COMPOUND FROM DIAGRAM BY
• 1.COUNTING UP THE NO. OF POSITIVE IONS
• 2.COUNTING UP THE NO. OF NEGATIVE IONS
• 3.CANCELLING THE NO.DOWN TO THE SIMPLEST
WHOLE NO, RATIO.
10. FORMULA FOR IONIC COMPOUNDS
What the formula of an ionic substance means
The formula of an ionic substance represents the
ratio of the ions in the lattice. For example, in
sodium chloride the formula NaCl means that
the ratio of sodium (Na+) ions to (Cl−) chloride
ions in the lattice is 1 : 1. In aluminium oxide, the
formula Al2O3 means that the ratio of aluminium
(Al3+) ions to oxide (O2−) ions in the lattice is 2 :
3.
Working out the formula of an ionic substance
In an ionic substance the total number of
positive charges must equal the total number of
negative charges. This allows us to work out the
formula of ionic substances.
Some ions contain atoms of different elements.
Examples include sulfate (SO4)-2
, hydroxide (OH−) and nitrate (NO3−). If you
need to write
more than one of these in a formula, then those
ions should be placed in a bracket.
EXAMPLES
Sodium chloride Na+ (1+ charge) Cl− (1− charge)
NaCl
Magnesium chloride Mg2+ (2+ charges) Cl− (2−
charges)MgCl2
Magnesium sulfide Mg2+ (2+ charges) S2− (2−
charges) MgS
Copper(II) sulfate Cu2+ (2+ charges) SO4
2− (2− charges) CuSO4
Sodium carbonate 2 Na+ (2+ charges) CO3 2− (2−
charges) Na2CO3
Ammonium sulfate 2 (NH4)+ (2+ charges)
(SO4)2− (2− charges) (NH4)2SO4
Calcium nitrate Ca2+ (2+ charges) 2 (NO3)− (2−
charges)
−
Ca(NO3)2
Aluminium oxide 2 Al3+ (6+ charges) 3 O2− (6−
charges)
Al2O3
11. 3.10 POLYMERS
• THERE ARE MANY DIFFERENT TYPES OF POLYMER (PLASTICS), INCLUDING POLYTHENE
PVC, PERSPEX, TEFLON AND POLYSTYRENE. POLYMERS CONTAIN VERY LARGE
MOLECULES,OFTEN WITH HUNDREDS OR THOUSANDS OR ATOMS. WITHIN EACH
MOLECULE, THE ATOMS ARE JOINED TO EACH OTHER BY COVALENT BOND.
• POLYMERS CONTAIN VERY LARGE MOLECULES, WITHIN WHICH ATOMS ARE
JOINEDTOGETHER BY COVALENT BONDS.
• THERMOSOFTENING POLYMERS SOFTEN OR MELT WHEN HEATED. IN
THERMOSOFTENING POLYMERS, THE MOLECULES ARE NOT JOINED
TOGETHER.HOWEVER, BECAUSE THE MOLECULES ARE VERY LARGE THE FORCES
BETWEEN THE POLYMER MOLECULES ARE RELATIVELY STRONG. THIS MEANS THAT THEY
ARE SOLIDS AT ROOM TEMPERATURE, ALTHOUGH THEY WILL MELT QUITE EASILY IF
HEATED.
12. 3.11 ALLOYS
• PURE METALS ARE VERY MALLEABLE. THIS CAN MAKE THEM TOO SOFT FOR MOSTUSES AS THEY
LOSE THEIR SHAPE EASILY. METALS CAN BE MADE MORE USEFUL BY MAKING THEM INTO ALLOYS.
• AN ALLOY IS A MIXTURE OF A METAL WITH SMALL AMOUNTS OF OTHER ELEMENTS,USUALLY OTHER
METALS. PURE METALS SUCH AS ALUMINIUM, IRON, COPPER AND GOLD ARE RARELY USED, AND
ALLOYS OF THESE METALS ARE USED INSTEAD.
FOR EXAMPLE, STEELS ARE ALLOYS MADE FROM IRON.
ALLOYS OF GOLD ARE USED FOR MAKING JEWELLERY AS PURE GOLD WOULD LOSE ITS SHAPE TOO
EASILY.
• ALLOYS ALSO HAVE METALLIC STRUCTURES. HOWEVER, SOME OF THE ATOMS IN THE ALLOY ARE A
DIFFERENT SIZE TO THOSE OF THE METAL. THIS DISTORTS THE LAYERS IN THE STRUCTURE AND
MAKES IT MUCH MORE DIFFICULT FOR THE LAYERS OF ATOMS TO SLIDE OVER EACH OTHER.
