Chemical Formula
Some chemical formulae are fancy, can you match them to the substance? acetylsalicylic acid C 9 H 8 O 4 sodium hydrogen carbonate NaHCO 3 glycerol C 3 H 5 (OH) 3 Ethanol C 2 H 6 O aluminum chlorohydrate Al 2 Cl(OH) 5 ethanoic acid C 2 H 4 O 2 1,4-dichlorobenzene C 10 H 8 Ferric ferrocyanide Fe 7 (CN) 18 14 H 2 O sucrose C 12 H 22 O 11
Starter a) How many atoms? b) How many atoms of each type? c) Formula if not given? 5. H 2 O 6. NaCl 7. HNO 3 8. Mg(NO 3 ) 2
Aim Understand the link between chemical formula and chemical structure. Explain how to work out the chemical formula of a compound Key words Product Reactants Conserved - ions (positive and negative) - group
Have you ever wondered The bigger picture Where do we use formula in everyday life?
Can you solve the puzzle? 1. Calcium Chloride 2. Magnesium Oxide 3. Magnesium Chloride 4. Potassium Sulphide 5. Calcium Oxide 6. Aluminium Oxide 7. Iron (III) Oxide MgCl 2 CaO Fe 2 O 3 CaCl 2 MgO K 2 S Al 2 O 3 Using the cards to help in front of you, work out the chemical symbols for the compounds on the left.
How do we know that calcium has 2 hooks and Chlorine has one? Ca 2 + Cl - Ca 2 + Cl - Cl - CaCl 2
Ions An ion is an atom (or group of atoms) that has a positive or negative electrical charge.
Positive ions Metal atoms, such as sodium, magnesium and iron, form positive ions. Positive ions have a small + symbol and a number by this to indicate how many electrons have been lost. This number is usually the same as the number of electrons in the atom s outer shell. For example: lithium atom in group 1 lithium ion [ 1 ] magnesium atom group 2 magnesium ion [ 2 ] = Mg 2+ aluminium atom group 3 aluminium ion [ 3 ] = Li + = Al 3+
Negative ions Non-metal atoms, such as chlorine, oxygen and nitrogen, form negative ions. Negative ions have a small - symbol and a number by this to indicate how many electrons have been gained to fill their outer shell. For example: chlorine atom Group 7 chloride ion [ 1 to make 8] = Cl - oxygen atom Group 6 oxide ion [ 2 to make 8 ] = O 2- nitrogen atom Group 5 nitride ion [ 3 to make 8 ] = N 3-
Summary The group 1 3 tells how many electrons are being lost This is written as positive, as we now have less negative charge The group 5 8 tells how many electrons need to be gained to make 8 This is written as negative, as we now have more negative charge The electrons can be written as hooks
Magnesium oxide Mg 2+ O 2- Mg 2+ O 2- Magnesium: Group 2 2 hooks Oxygen: Group 6 need to electrons to make 8 2 hooks MgO
Magnesium chloride Mg 2+ Cl - Mg 2+ Cl - Magnesium: Group 2 2 hooks Chlorine: group 7 need one electron to make 8 1 hook Cl - MgCl 2
Sodium sulphide Na + Na + S 2- S 2- Na + Sodium : Group 1 1 hooks Sulphur: Group 6 need two electrons to make 8 2 hooks Na S 2
Calcium oxide Ca 2+ O 2- Ca 2+ O 2- Magnesium: Group 2 2 hooks Oxygen: Group 6 need two electrons to make 8 2 hooks CaO
Aluminium oxide O Al 2-3+ O Al 2-3+ Aluminium: group 3 3 hooks Oxygen: Group 6 need two electrons to make 8 2 hooks Al 3+ O 2- O 2- Al O 2 3
Iron (III) oxide O 2- Fe 3+ Fe 3+ O 2- Iron is given to be in group 3 3 hooks Oxygen: Group 6 need two electrons to make 8 2 hooks Fe 3+ O 2- O 2- Fe O 2 3
Balancing equations Left Right Mg 1 2 1 O 2 1 2 2
Activity Go around the room in pairs and balance the equations. Some you need to find the chemical formula. Include your working and proof it is balanced as we have just done.
Balanced equations? On you whiteboards, write down your answers to the following chemical equations you balanced around the room.
Chemical Formula? On you whiteboards, write down your answers to the following chemical formula you worked out around the room.
Brackets Ca(OH) 2 Calcium Hydroxide How many Ca, O and H atoms are there in this molecule? O Ca O H H
Plenary Balance these equations on your whiteboards FeO + PdF 2 FeF 2 + PdO 1 FeO + 1 PdF 2 1 FeF 2 + 1 PdO
Plenary Balance these equations on your whiteboards CaF 2 + Li 2 SO 4 CaSO 4 + LiF 1 CaF 2 + 1 Li 2 SO 4 1 CaSO 4 + 2 LiF
Plenary Balance these equations on your whiteboards PbBr 2 + HCl HBr + PbCl 2 1 PbBr 2 + 2 HCl 2 HBr + 1 PbCl 2
Plenary Balance these equations on your whiteboards P 4 + Br 2 PBr 3 1 P 4 + 6 Br 2 4 PBr 3
Plenary Balance these equations on your whiteboards AlBr 3 + K KBr + Al 1 AlBr 3 + 3 K 3 KBr + 1 Al
Plenary Balance these equations on your whiteboards CoBr 3 + CaSO 4 CaBr 2 + Co 2 (SO 4 ) 3 2 CoBr 3 + 3 CaSO 4 3 CaBr 2 + 1 Co 2 (SO 4 ) 3
Key words Products - The substances that result from this recombination of atoms are called the products of the reaction. Reactants - a substance that takes part in and undergoes change during a reaction. Conserved maintain at a constant level Positive Ions atoms have lost electrons Negative Ions atoms have gained electrons Group a column down in the periodic table