Chemistry spec

• The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram, for example, for sodium chloride.
• Theories of bonding explain how atoms are held together in these structures.
• The transition elements have melting points, densities, strength, hardness and reactivity with oxygen, water and halogens that are different from those of the elements in Group 1.
• There are three types of strong chemical bonds: ionic, covalent and metallic.
• Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts.
• Non-metal atoms gain electrons to become negatively charged ions.
• Metal atoms lose electrons to become positively charged ions.
• Covalent bonding occurs in most non-metallic elements and in compounds of non-metals.
• The transition elements are metals with similar properties which are different from those of the elements in Group 1.
• The properties of these materials may offer new applications in a range of different technologies.
• Ionic bonding occurs in compounds formed from metals combined with non-metals.
• The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).
• An ionic compound is a giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions.
• When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred.
• Scientists use this knowledge of structure and bonding to engineer new materials with desirable properties.
• Students should be able to explain chemical bonding in terms of electrostatic forces and the transfer or sharing of electrons.
• Metallic bonding occurs in metallic elements and alloys.
• Students should be able to use ratios, fractions and percentages.
• Students should be able to balance an equation given the masses of reactants and products.
• One mole of magnesium reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride and one mole of hydrogen gas.
• The masses of reactants and products in a chemical equation can be calculated from the balanced symbol equation.
• Students should be able to calculate the masses of reactants and products from the balanced symbol equation and the mass of a given reactant or product.
• Students should be able to calculate the masses of substances shown in a balanced symbol equation.
• The balancing numbers in a symbol equation can be calculated from the masses of reactants and products by converting the masses in grams to amounts in moles and converting the numbers of moles to simple whole number ratios.
• Students should be able to change the subject of a mathematical equation.
• Students should be able to substitute numerical values into algebraic equations using appropriate units for physical quantities.
• Students should be able to calculate the mass of solute in a given volume of solution of known concentration in terms of mass per given volume of solution.
• In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used.
• The atom economy (atom utilisation) is a measure of the amount of starting materials that end up as useful products.
• Chemical equations can be interpreted in terms of moles.
• The reactant that is completely used up in a chemical reaction is called the limiting reactant because it limits the amount of products.
• The concentration of a solution can be measured in mass per given volume of solution, eg grams per dm 3 (g/dm 3 ).
• Students should be able to use the relative formula mass of a substance to calculate the number of moles in a given mass of that substance and vice versa.
• The minimum amount of energy that particles must have to react is called the activation energy.
• According to collision theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
• The rate of a chemical reaction can be found by measuring the quantity of a reactant used or the quantity of product formed over time.
• The units of rate of reaction may be given as g/s or cm 3 /s.
• In industry, chemists and chemical engineers determine the effect of different variables on reaction rate and yield of product.
• Students should be able to draw, and interpret, graphs showing the quantity of product formed or quantity of reactant used up against time.
• Hydrogen fuel cells are compared with rechargeable cells and batteries.