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C4 Revision Cards Hope you find these useful -V Protons: • Positive charge • Mass = 1 Neutrons • No charge • Mass = 1 Electrons: • Negative charge • Mass = 0.0005 2 protons + 2 electrons = neutral charge. 56 Fe 26 neutron number = mass number – atomic number So for the example above: Neutron number is 56-26 = 30 neutrons A normal, neutral Lithium atom An ion is an atom with a charge If it loses an electron, there is one more proton overall – so the atom is now charged (an ion) This helium atom has a full 1st shell: 2 This neon atom has a full 2nd shell: 2,8 This argon atom has a full 3rd shell: 2,8,8 • A sodium atom will give up it’s outer electron to become a Na+ ion. • A chlorine atom will pick up that electron, becoming a Cl- ion. • The now oppositely charged ions are strongly attracted to each other. • They bond together – ionically. Non-metal atoms can share electrons in order to simulate full outer shells. Dot-cross diagrams can be used to show how the electrons are shared. Each pair of shared electrons represents one covalent bond. A hydrogen molecule (H2) consists of two H atoms sharing a pair of electrons. They ‘feel’ as if their 1st shell is full. A CO2 molecule consists of a carbon atom covalently bonded to two oxygen atoms. The carbon, with 4 electrons in it’s outer shell, shares 2 electrons with each oxygen atom. Periods The rows are known as periods. Groups The columns are known as groups. The group number is the same as the number of electrons in the outer shell. EG: Group 1 elements all have one outer electron. The period that an element is in, indicates how many electron shells it has. If an element is in period 2, it will have 2 electron shells. Elements in the same groups or period have similar chemical properties. For example, group 1 elements all react in a similar way with water. alkali metal + water --> hydroxide + hydrogen lithium + water --> lithium hydroxide + hydrogen potassium + water --> potassium hydroxide + hydrogen lithium + water --> lithium hydroxide + hydrogen (word) Li + H2O --> LiOH + H2 (symbol) 2Li + 2H2O --> 2LiOH + H2 (balanced) • When flame tests are carried out on alkali metal compounds, the flame changes colour: Alkali Metal Lithium Colour of Flame Red Sodium Potassium Yellow Lilac Take a break! mmmm…. break EG: lithium + chlorine lithium chloride potassium + bromine potassium bromide sodium + chlorine sodium chloride 3 different metal halides Balanced: 2Li + Cl2 2LiCl 2K + Br2 2KBr 2Na + Cl2 2NaCl Use the group 1 + 7 elements to think of other combinations and write out the reactions. chlorine + potassium bromide potassium chloride + bromine Cl2 + 2KBr 2KCl + Br2 Transition metal compounds are often coloured: • Copper compounds are often blue. • Iron(II) compounds are pale green. • Iron(III) compounds are orange/brown. Transition metals are often used as catalysts in reactions: • Iron in the Haber Process. • Nickel in Margarine Production. FeCO3 decomposes into Iron Oxide and CO2 On CuCO3 decomposes into Copper Oxide and CO2 heating… MnCO decomposes into Manganese Oxide and CO 3 2 ZnCO3 decomposes into Zinc Oxide and CO2 Precipitation is a reaction between solutions that make an INSOLUBLE SOLID. • In other words, when you mix two solutions, a cloud of solid particles appears. • If transition metal compounds are mixed with sodium hydroxide, precipitation reactions occur. • Colourful clouds of Transition Metal Compound Colour solids form: Copper Blue Iron (II) Pale Green Iron (III) Orange/Brown It’s the sea of delocalised (free) electrons that give metals most of their properties. It’s important to understand that the electrons can move. Their delocalised nature means: 1. They can conduct electricity. 2. They allow the metal to bend (malleable) 3. They allow the formation of strong metallic bonds, giving metals very high melting and boiling points. Superconductors do not have a magnetic field. They repel permanent magnets and cause them to levitate. The potential benefits of superconductors…. Loss-free power transmission Super-fast electronic circuits Powerful electromagnets At the moment, superconductors have to be kept very cold with the help of liquid nitrogen. Maglev trains are kept levitating above the track with help of very powerful superconducting electromagnets. This eliminates contact friction, allowing very high speeds. • Water in a river is rarely pure and needs to be purified before we can drink it. • It may contain the following: 1. 2. 3. 4. Salts and minerals Pollutants Insoluble materials Microorganisms 1. Sedimentation Solid particles and bacteria settle out from the water. 2. Filtration Very fine particles are filtered using sand and gravel 3. Chlorination The water in treated with chlorine to kill microbes • Seawater is completely undrinkable, and requires processes such as distillation to remove dissolved substances. 1. Adding barium chloride to water will produce a white precipitate if sulphate ions are present. 2. To test for chloride, bromide or iodide ions, add silver nitrate: If chloride ions are present, a white precipitate will form. If bromide ions are present, a cream precipitate will form. If iodide ions are present, a yellow precipitate will form. These cards are for revision purposes. They were made in a single night! Some of the content has been condensed! Make sure you check out anything you don’t understand by looking at your revision guide or using the internet. Good luck.