IGCSE Double Award Extended Coordinated Science

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1 IGCSE Double Award Extended Coordinated Science Chemistry Chemical Formulae and Equations - the chemical symbols for the first 20 elements - And the charges of the ions they form - And use them to name and write the chemical symbols for different compounds Naming Cations You need to know how to name cations Metal cations that only form one type of ion are just the element name - Lithium -> lithium ion ( Li + ) - Calcium -> calcium ion ( Ca 2+ ) - Aluminium -> aluminium ion ( Al 3+ ) Some metal elements can form multiple ions with different charges (transition metals) - In this case, we have two methods: 1. Put the charge of the ion in brackets and in roman numerals - This method is most often used. 2. Use the latin method (not often used): - Latin name + suffix -ous for the ion with lower charge - Latin name + suffix -ic for the ion with higher charge Iron -> - Iron (II) ion / ferrous ion : Fe 2+ Copper -> - Iron (III) ion / ferric ion : Fe 3+ - Copper (I) ion : Cu + - Copper (II) ion : Cu 2+

2 Naming Anions Anions formed from single atoms are named by adding the suffix -ide - Chlorine -> chloride ion ( Cl - ) - Oxygen -> oxide ion ( O 2- ) Anions formed from multiple atoms ( polyatomic ions ) have special names with some rules - Polyatomic ions that include oxygen are named - Suffix -ate : for the higher number of oxygen (or the only ion) - Suffix -ite : for the lower number of oxygen - Sulph ate ion ( SO 4 2- ), sulph ite ion ( SO 3 2- ) - Nitrate ion ( NO 3 - ), nitrite ion ( NO 2 - ) - Carbonate ion ( CO 3 2- ) Common Ions You should to know the names the charges these ions: Hydrogen ion H + Beryllium ion Be 2+ Boron ion B 3+ Oxide ion O 2 - Hydride ion H - Lithium ion Li + Magnesium ion Mg 2+ Aluminium ion Al 3+ Sulphide ion S 2- Fluoride ion F - Sodium ion Na + Calcium ion Ca 2+ Chloride ion C l - Potassium ion K + Iodide ion I - Iron (II) ion Fe 2+ Iron (III) ion Fe Carbonate ion CO 3 - Bicarbonate ion HCO 3 Copper (I) ion Cu + Copper (II) ion Cu Phosphate ion PO 4 2- Sulphate ion SO 4 Hydroxide ion OH - + Ammonium ion NH 4 - Nitrate ion NO 3

3 Ionic Compounds - Ionic compounds are named by - The name of the cation + name of anion - NaCl : Sodium ion + chloride ion = Sodium Chloride - KOH : Potassium ion + hydroxide ion = Potassium Hydroxide - NaHCO 3 : Sodium ion + bicarbonate (or hydrogen carbonate) ion = Sodium Bicarbonate - Even if there are multiple ions, we just write it same as before - MgCl 2 : Magnesium ion + 2 chloride ions = Magnesium Chloride - Li 2 O : 2 Lithium ions + oxide ion = Lithium Oxide - How to write the chemical formula from the names of ionic compounds - If given a compound, like sodium chloride. 1. Determine the ions and the charges - sodium ion (1+) and chloride ion (1-) 2. We know that all compounds are neutral in charge - This means that all the charges must cancel out 3. If we have one of each ion, Na + and Cl -, (1+) + (1-) = 0 - This is neutral (equalling to zero) 4. This means the ratio is 1:1, so the formula for hydrogen chloride is: - NaCl - In the case of calcium hydroxide, - Calcium ion (2+) and hydroxide ion (1-) - We need two hydroxide ions for every calcium ion for a neutral charge. - (2+) + 2(1-) = 0 - So the chemical formula would be Ca(OH) 2 - In the case of aluminium oxide, - Aluminium ion (3+) and oxide ion (2-) - We need three oxide ions for every two aluminium ion - 2(3+) + 3(-2) = 0 - So the chemical formula would be Al 2 O 3

4 Covalent Compounds - Covalent compounds are named by - Nonmetal cation + nonmetal (polyatomic) anion - This is same as ionic compounds, but one thing is different - If any of these ions are in multiples, we add the prefixes - 1 : mono (mono is not often used) - 2 : di - 3: tri - 4 : tetra - Etc. - NO : nitrogen mono xide - CO 2 : carbon di oxide - SO 3 : sulphur tri oxide - N 2 O 4 : di nitrogen tetr oxide - How to write the chemical formula from the names of covalent compounds - For covalent compounds, this is easier, - Number of the ions are given as prefixes - Carbon mono xide - If there are no suffixes, assume mono- - CO - Di nitrogen tri oxide - Two nitrogens, three oxygens. - N 2 O 3 Try for yourself: - Lithium oxide - Calcium carbonate - Potassium carbonate - Sodium hydroxide - Copper (II) phosphate - Aluminium chloride - Calcium nitrate - Dihydrogen Monoxide - Nitrogen dioxide - Sulphur dioxide - Carbon tetrachloride - Hydrogen nitrate (nitric acid) - Hydrogen chloride (hydrochloric acid) - Hydrogen sulphate (sulphuric acid)

5 Balancing Equations You need to know how to write word and balanced symbolic equations for chemical reactions Word equations simply state the reactants (on the left) and products (on the right). - nitrogen + oxygen -> nitrogen monoxide - Sulphur dioxide + oxygen -> sulphur trioxide - Glucose + oxygen -> carbon dioxide + water Word equations are only useful in terms of what chemicals are involved in the reaction - The relative amounts (ratio of chemicals used) are not shown To show the relative amounts, we use the balanced chemical equation 1. the names of chemicals are written in symbols (N, O, CO etc.) 2. Like any math equation, the left side must equal the right side - This means the number of atoms for each element on the left must must equal to the right side - For example, Na + Cl -> NaCl is balanced, - because there are one Na and one Cl on each side. - However, H 2 + O 2 -> H 2 O is no t balanced, - There are two oxygen atoms on the left, but there is only one oxygen on the right - In this case we need to balance it by multiplying a molecule by a number - This number is called the coefficient - You cannot put the coefficient in the middle of a compound, only in front. - The coefficient multiplies all the atoms of the molecule - If we wrote: 2( H 2 )+ O 2 -> 2(H 2 O) - There are 4 H and 2 O on the left, and 4 H and 2 O on the right. - Now it is balanced, but in chemical multiplications, we don t need to write in the brackets - (like a variable in algebra, instead of 2(a), you would write 2a) - 2 H 2 + O 2 -> 2H 2 O - This gets easier by practice, so just keep balancing many equations. The syllabus says you should be able to, (SO check if you can): - Use the symbols of the elements to write the formulae of simple compounds. - Deduce the formula of a simple compound from the relative numbers of atoms present. - Deduce the formula of a simple compound from a model or a diagrammatic representation. - Determine the formula of an ionic compound from the charges on the ions present. - Construct and use word equations. - Construct and use symbolic equations with state symbols, including ionic equations. - Deduce the balanced equation for a chemical reaction, given relevant information.