formula & calculations

• Some compounds have meaningful names where they have prefixes.
• five - Penta
• For these chemical formulas, we write the formula as it says.
• If there is no prefix in front of the element, we assume it is “1”.
• Examples of chemical formulas include carbon tetrachloride – CCl 4 and boron trisulfide – BS 3.
• The valency of an atom can be described as the number of bonds an atom can make.
• Elements in the same group of the Periodic Table have the same valency.
• To work out the chemical formula the letter SVSDF is used (or “swap and drop”).
• In the process of working out the chemical formula, the symbol is written first, followed by the valency of each element underneath the symbol.
• The process of working out the chemical formula involves swapping the valency.
• The valency is simplified, if possible, by dividing by the smaller of the two numbers.
• The formula for the compound is written at the end of the process of working out the chemical formula.
• Compounds ending in –ate or –ite contain 3 elements.
• One of these elements is always oxygen.
• These compounds are referred to as “group ions”.
• The hydroxide and ammonium ion are also group ions.
• The name of the formula doesn’t help you with the chemical formula – you find the formula and valency of group ions on page 21 of the data booklet.
• Once you have the formula and valency of the group ion, you apply the (SVSDF) method to work out the chemical formula.
• The transition metals have no fixed valency.
• Roman numerals are used to show the valency for each compound.
• The same method and valency and group ions is applied to work out the chemical formula of transition metals.
• One - I
• Two - II
• Three - III
• Four - IV
• A chemical equation can be used to describe a reaction, showing the chemicals which react (reactants) and the chemicals which are produced (products).
• Reactants are transformed into products in a chemical reaction.
• State symbols of the reactants and products are often included in the equation.
• Solids can be represented by the state symbol 's'.
• Liquids can be represented by the state symbol 'l'.
• Gases can be represented by the state symbol 'g'.
• Aqueous solutions can be represented by the state symbol 'aq'.
• The reaction of lithium with water to produce lithium hydroxide and hydrogen can be represented by the word equation 'Lithium + Water -> Lithium hydroxide + Hydrogen'.
• The chemical equation for the reaction 'Li + H 2 O -> LiOH + H 2' can also be used to represent the reaction.
• State symbols can be used in the chemical equation 'Na(s) + H 2 O(l) -> LiOH(aq) + H 2 (g)'.
• N = C x V
• N = Number of moles (mol) This is a measurement of how many particles are in a substance.
• C = Concentration = mol l -1
• V = Volume (l)
• MUST be in litres! If in cm 3 divide by 1000 to convert to litres.