Elements and Reactivity Revision Notes Elements There are just over 100 elements in the Periodic Table. Elements are made up of one type of atom. Every element has a name, atomic number and symbol. Element Symbols Each element can be represented by a one or two letter symbol. The first letter is always a capital letter, if there is a second letter in the symbol it is lower case. e.g. C is the symbol for carbon ; Cl is the symbol for chlorine Arrangement of Elements in the Periodic Table Elements can be sorted in different ways: metals and non-metals solids, liquids and gases naturally occurring and man-made Metals and Non-Metals Metals Examples: Copper, Tin and Lithium Most elements in the Periodic Table are metals and they are found to the left-hand side. Non-Metals Examples: Nitrogen and Carbon Poor conductors of heat and electricity Low melting and boiling points Solids, Liquids and Gases Examples of solids: Magnesium, Carbon and Sulphur Examples of Liquids: Mercury and Bromine Examples of Gases: Oxygen, Nitrogen and Helium Natural and Man-Made Examples of Natural: Copper and Hydrogen Examples of Man-made: Californium and Einsteinium 1
Groups in the Periodic Table Elements with similar properties are found in the same vertical column. This is called a group. Group 1- The Alkali Metals These elements are very reactive and so are stored under oil. They all react quickly with water releasing hydrogen gas and forming an alkaline solution. As you go down Group 1 the metals become more reactive. Group 7- The Halogens These elements have coloured vapours and are very reactive. As you go down the group the elements become less reactive and the melting and boiling points get higher. Group 8/0- The Noble Gases These elements are very unreactive (inert). Argon is used in filament lamps Helium is lighter than air and used in balloons Structure of the Atom All atoms have a small central nucleus containing protons and neutrons Particles called electrons orbit the nucleus Protons, neutrons and electrons have different masses and charges Particle Charge Location Mass Proton +1 Found inside the nucleus 1 Electron -1 Found in energy levels around the nucleus ~0 Neutron 0 Found inside the nucleus 1 2
Atomic Number All elements in the Periodic Table are listed in order of increasing atomic number. The atomic number is the number of protons there are in the nucleus of an atom. In an atom, the number of negative electrons always equals the number of positive protons. Atoms therefore do not have an overall electrical charge- they are neutral. Molecules, Mixtures and Compounds Molecules Molecules are small groups of atoms are joined together. Molecules of an element contain only one type of atom e.g. an oxygen molecule contains only oxygen atoms. Compounds Compounds are new substances formed when atoms of two or more elements chemically join together. Molecules of a compound contain two or more types of atom e.g. H 2 O is a molecule of water. Mixtures A mixture is a collection of two or more substances, elements or compounds, which are not chemically joined. Air is an example of a mixture of gases: 79% Nitrogen 20% Oxygen 1% Other Gases. 3
Chemical Formulae The chemical formula of a substance tells us the elements that present and how many atoms of each element there are in a molecule of the substance. e.g. the formula for carbon dioxide is CO 2. It contains one carbon atom and two oxygen atoms. Substance Formul a Name and type of atoms in molecule Element or Compound Water H O 2 2 Hydrogen atoms 1 Oxygen atom Compound Hydrogen H 2 2 Hydrogen atoms Element Methane CH 4 1 Carbon atom 4 Hydrogen atoms Compound Naming compounds Compounds with a name ending in -ide contain the two elements indicated in the name. A compound ending ite or ate means that the compound contains three elements, one of which is oxygen. Examples Sodium Sulphate contains the elements Sodium, Sulphur and Oxygen. Lead nitrite contains the elements Lead, Nitrogen and Oxygen. Copper chloride contains the elements Copper and Chlorine. 4
Breaking up Compounds Breaking up compounds into their elements is usually much more difficult than making compounds. Some compounds can be broken up using Electrolysis Electrolysis uses electricity to breakdown a compound into its elements. Electrolysis of Copper Chloride Copper chloride is a compound that can be broken up into its elements, copper and chlorine, by passing an electric current through a solution of it. This is called electrolysis. Brown copper metal forms at the negative electrode and bubbles of chlorine gas form at the positive electrode. Chemical Reactions When a chemical reaction occurs a new substance is always formed. Signs of a Chemical Reaction When a chemical reaction occurs a new substance is always formed. Some signs that show that a chemical reaction has occurred include: a gas being given off a solid forming a colour change a temperature change in the reaction mixture 5
Metal Ores Most metals have to be extracted from naturally occurring compounds in the earth s crust called metal ores. The more reactive a metal is the more difficult it is to extract from its compounds. Breaking up Copper oxide and Silver oxide Copper metal can be extracted from the compound copper oxide by heating it with carbon powder. copper oxide + carbon copper + carbon dioxide Silver is a very unreactive metal. Silver can be obtained from silver oxide by heating alone. silver oxide silver + oxygen Rates of Reaction Three factors which can affect the speed of a chemical reaction are: particle size of reactants temperature concentration of reactants When two reactions are compared only one variable should be changed to make the comparison fair. Particle Size of Reactants As the particles size of the reactants decreases, the speed of the reaction increases. This is because when smaller particles are used, there is a larger surface area. 6
Concentration of Reactants As the concentration of reactants increases, the speed of the reaction also increases. Temperature of Reactants As the temperature of the reactants increases, the speed of the reaction also increases. 7