Elements and Compounds Elements are materials made up of one type of atom only. Hydrogen molecule contains two hydrogen atoms bonded together, so the formula is H2. It follows that compounds contain two or more types of atom. The water molecule contains two hydrogen atoms bonded to one oxygen atom, so the formula is H2O.

Compounds: Water Compounds are produced when elements combine. For example, water is produced in the following reaction. +  Two water molecules react with one oxygen molecule to give water. Word Equation Hydrogen + Oxygen  Water

Compounds – not mixtures The atoms in compounds are NOT mixed together. A mixture of hydrogen and oxygen would look like: They become bonded together during a chemical reaction. Because of this compounds have properties that are very different to the elements that they are made from. HYDROGEN Flammable gas. OXYGEN Gas in which many substances burn. WATER Liquid that extinguishes most fires. + 

Compounds – not mixtures Black solid used as barbecue fuel Gas in which many substances burn Gas used in fizzy drinks and fire extinguishers carbon + oxygen  carbon dioxide

Naming Simple compounds. It is easy to name simple compounds of metals and non-metals. Write down the name of the metal Write down the name of the non-metal but change the ending to “ide.” 1) magnesium 2) oxygen = magnesium oxide 1) sodium 2) chlorine = sodium chloride oxygen calcium sulphur silver bromine copper Name of compound Element 2 Element 1 copper bromide silver sulphide calcium oxide

Naming Simple compounds. Name the compound formed from these elements nitrogen lithium sulphur zinc iodine nickel bromine aluminium oxygen tin chlorine sodium magnesium iron Name of compound Element 2 Element 1 iron sulphide magnesium nitride sodium chloride tin oxide aluminium bromide nickel iodide zinc sulphide lithium nitride

Naming more complicated Compounds Many compounds contain more than two elements. Naming them can get complicated but for those containing two elements plus oxygen the name ending usually changes to –ate. oxygen bromine aluminium sulphur copper Element 3 nitrogen sodium magnesium nitrate magnesium nickel sulphate nickel Name of compound Element 2 Element 1 sodium nitrate copper sulphate aluminium bromate

The composition of compounds. Compounds are very different to the elements from which they are made but there is another way in which compounds are different to mixtures. In a mixture you can add any amount of the ingredients. Compounds always contain a definite amount of each element. They have a fixed composition. This is not really surprising as looking at the word equations you will have seen they always have a definite number of element atoms joined together. Na Cl O H O C Mg O

The formula of compounds This means that every compound can have a formula that tells us how many of each type of atom are present. We include small slightly dropped numbers if there are more of one atom than the other. Carbon dioxide One carbon atom Two oxygen atoms Formula CO2 O C Water One oxygen atom Two hydrogen atoms Formula H2O O H

The formula of compounds Activity The formula of compounds What is the formulae of each of the compounds shown? (As with names, put the metal first.) 1. Titanium oxide ? titanium atom ? oxygen atoms Formula Ti O 1 titanium atom Formula TiO2 2 oxygen atoms 2. Lithium Oxide Li O ? oxygen atom ? lithium atoms Formula ? 3. Aluminium chloride ? aluminium atom ? chlorine atoms Formula Al Cl 2 lithium atoms 1 aluminium atom Formula Li2O 1 oxygen atom Formula AlCl3 3 chlorine atoms

The formula of compounds Activity The formula of compounds Silicon chloride ? silicon atom ? chlorine atoms Formula Cl What is the formulae of each of the compounds shown? Cl Si Cl 1 silicon atom Cl 4 chlorine atoms Formula SiCl4 Aluminium oxide Manganese oxide O O O O Mn O Al Al 1 manganese atom ? manganese atom 2 aluminium atom ? aluminium atom Formula Al2O3 Formula Formula MnO2 Formula ? oxygen atoms 2 oxygen atoms 3 oxygen atoms ? oxygen atoms

Word Equations Word equations can be used to describe any chemical change. (i.e. any process where the atoms become joined (bonded) in different ways). The steps are: Write down the name of the reactant(s) linking them with a + sign if there is more than one. Write down an arrow Write down the names of the products linking them with a + sign if there is more than one

Word Equations Write out word equations for this reaction Activity Word Equations Write out word equations for this reaction Lead reacts with oxygen to form lead oxide Lead + oxygen  lead oxide Lead Lead oxide It hasn’t just mixed. It has reacted and atoms are joined differently. Why is lead oxide so different to both lead and oxygen?

Word Equations Write out word equations for the following reactions. Activity Word Equations Write out word equations for the following reactions. Limestone (calcium carbonate) is heated to make calcium oxide and carbon dioxide. Magnesium reacts with hydrochloric acid to make magnesium chloride and hydrogen. Methane is burnt to make carbon dioxide and water. calcium carbonate  calcium oxide +carbon dioxide magnesium + hydrochloric acid  magnesium chloride + hydrogen methane + oxygen  carbon dioxide + water

sea water: a mixture of salts and water Mixtures Mixtures are, as the name indicates, mixed rather than reacted together. This means that, unlike compounds: 1 They do not have to have any particular proportions of the various ingredients. 2 Their properties are often “an average” of the properties of their ingredients. (eg. a mixture of a black and white powder is grey!) sea water: a mixture of salts and water 3 They are mixed, not bonded, and so are usually not too hard to separate back into their ingredients. (For example, it is easy to get salt from sea water.)

Separating Mixtures  Immiscible liquids Immiscible means “doesn’t mix” and so we are talking about “mixtures” like water with cooking oil or water with petrol. On a small scale you can simply remove the top layer using a pipette. oil  water oil water

Separating Mixtures Miscible liquids Miscible means “does mix” and so we are talking about mixtures like water and alcohol or petrol with kerosine. These are separated by boiling them as it is unlikely that they will boil at exactly the same temperature. In order to “get back” the liquids we use a condenser. This is a tube that has cold water circulating through the outside. It cools down vapours and condenses them back to a liquid. Substances with low boiling points collect first, while those with higher boiling points collect later.

Distillation Equipment Miscible liquids Distillation Equipment thermometer condenser water in water out electric heater collection beaker

Separations Mixture Wanted Method Glass and water glass Sea water salt How would you get this? Mixture Wanted Method Glass and water glass Sea water salt water Cooking oil & water cooking oil Alcohol and water alcohol filter evaporate distil pipette distil

Separation Experiment John has been given a mixture of salt, sand and water. He needs to separate them but cannot remember how. Can you help him? Write an experimental plan for John to follow so that he can have the sand, salt and water in separate containers. Make sure you start off by telling him what equipment he will need. Then he will need a step by step plan that is easy to follow.

Summary activities A drag and drop activity

1. Which of these is a compound? bromine copper carbon dioxide uranium

Which of these best describes a compound? Two or more atoms bonded together. Two or more elements mixed together. Two or elements bonded together. Two or more types of molecule mixed together.

Which of these could best describe compounds? Substances that: are similar to the elements that they are made from. can be formed when elements react together. can be formed when elements decompose into two or more new substances. substances with symbols in the Periodic Table.

What would be the name of a compound formed from sulphur, oxygen and zinc? sulphur zincide sulphur zincate zinc sulphide zinc sulphate

What would be the formula of a compound containing two aluminium atoms for every three sulphur atoms? A. Al2S3 B. Al3S2 C. Al2S3 D. Al3S2

How would you separate a mixture of water and alcohol How would you separate a mixture of water and alcohol. (Two miscible liquids) filtering chromatography evaporation distillation

What is the main technique you would use when separating a mixture of salt and sand? filtering chromatography evaporation distillation

Use the chromatogram to decide which dyes are in the ink. A B C D Ink