Building Blocks

Particle and Kinetic Theory Substances are made up of particles. The state of the substance depends on the arrangement of the particles. The Three States of Matter Solid Particles held tightly Very close together Regular arrangement Vibrate Can’t move from place to place Liquid Particles held weakly Very close together Random arrangement Vibrate Constantly move past each other Gas No attraction between particles Far apart Random arrangement Vibrate Move quickly in all directions

Atoms and Elements Elements consist of only one type of particle. We call these particles atoms. They cannot be split into simpler, smaller particles by chemical methods. There are about 109 elements known at the moment (2004). Don’t worry, you don’t have to learn them all! The elements each have a name and a symbol. By the end of year 9, you must know the first twenty elements off by heart, so it is a good idea to start learning them now!

The First Twenty Elements Atomic Number Symbol Name 1 H hydrogen 11 Na sodium 2 He helium 12 Mg magnesium 3 Li lithium 13 Al aluminium 4 Be beryllium 14 Si silicon 5 B boron 15 P phosphorus 6 C carbon 16 S sulphur 7 N nitrogen 17 Cl chlorine 8 O oxygen 18 Ar argon 9 F fluorine 19 K potassium 10 Ne neon 20 Ca calcium

Arranging the Elements As you know, the elements are arranged in the Periodic Table. The elements were first arranged in this way by Dmitri Mendeleev, a professor at St. Petersburg University, in 1869. His arrangement was based on atomic mass. When Mendeleev was setting out the table, only 63 elements had been discovered. His big idea was to leave gaps for yet to be discovered elements. He was able to predict the properties of some of these elements, including silicon and boron. When his predictions were shown to be accurate his table became accepted, and it is the basis of the one we use today. ‘Maybe one day we’ll understand why Dmitri always lays out his blocks this way!’

Non- Metals Metals Arranging the Elements : Metals and Non-Metals Most of the elements are metals. The non-metals are found to the top right of the periodic table. The metals and non-metals are separated by a sort of ‘stair case’. Non- Metals Metals

Arranging the Elements : Groups and Periods The columns of the periodic table are called Groups. Elements in a group have similar properties. Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group Group 2 : Alkaline earth metals Group 1 : Alkali metals Group 0 : Noble gases Group 7 : Halogens Transition metals The horizontal rows are called Periods.

X Properties of Metals Metals have the following properties : They conduct electrical energy well They conduct thermal energy well They are shiny They are malleable (can be hammered into shape) They are ductile (can be drawn out into wires) They are sonorous (make a ringing sound when hit) All except mercury are solids at room temperature X Only a few metals are magnetic. Magnetism is not a property of most metals!

Properties of Non-Metals Non-metals have the following properties : They are poor conductors of electrical energy They are poor conductors of thermal energy Many of them are gases They are brittle if they are solid Both a diamond and a pencil ‘lead’ are made of the same element – carbon.

Elements, Molecules and Compounds Some elements, such as the noble gases, exist as individual atoms. Often, elements consist of two or more atoms joined together. We call these molecules. If more than one type of atom is in a molecule, we call it a compound.

Mixtures This is a mixture of elements made up of atoms, elements made up of molecules, and compounds. In a mixture, the particles are not joined together. Atom, molecule or compound? (click for answer) atom Atom, molecule or compound? (click for answer) molecule Atom, molecule or compound? (click for answer) compound

Naming Compounds If we heat copper in air, it reacts with the oxygen to make a new compound. We call this compound copper oxide. We can write a word equation for this : copper + oxygen  copper oxide Most metals will react with oxygen to form an oxide. For example : magnesium + oxygen  (click for answer) magnesium + oxygen  magnesium oxide When metals react with oxygen we often say they are corroding. Iron is a very common metal (steel is mostly made of iron), and it reacts with oxygen to make the compound iron oxide. This is such a common reaction that we give the compound iron oxide a common name – rust! Iron is the only metal that rusts. The correct term to use for other metals is that they corrode.

More Oxygen Compounds Oxygen also reacts with some non-metals to form compounds. When carbon burns, the following reaction happens : carbon + oxygen  carbon dioxide C + O2  CO2 A molecule of carbon dioxide – one atom of carbon and two atoms of oxygen And of course, oxygen reacts with hydrogen to form a very common compound! hydrogen + oxygen  water 2H2 + O2  2H2O A molecule of water – one atom of oxygen and two atoms of hydrogen

More Compounds Naming compounds is quite straightforward when you get used to it. When metals react with chlorine, they form chlorides. sodium + chlorine  sodium chloride Salt (sodium chloride) crystals are made up of millions of sodium and chlorine atoms. lithium + chlorine  lithium chloride lithium + chlorine  (click for answer) With sulphur, sulphides are formed. iron + sulphur  iron sulphide magnesium + sulphur  (click for answer) magnesium + sulphur  magnesium sulphide

Element or Compound? methane, CH4 sulphur, S8 compound element (Click for answer) (Click for answer) hydrogen peroxide, H2O2 sulphuric acid, H2SO4 compound compound (Click for answer) (Click for answer) oxygen (ozone), O3 carbon (buckyball), C60 element element (Click for answer) (Click for answer)

Testing for Gases In some chemical reactions, gases are given off. There are several simple tests we can do to find out which element or compound a gas is. Here are two of them. Carbon dioxide Bubble the gas through lime water. If the lime water turns milky, the gas is CO2. Oxygen Hold a glowing splint in the gas. If the splint relights, the gas is O2.