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C1 pages 96-99 (compounds (compounds can be represented by formulas…
C1 pages 96-99
compounds
when elements react, atoms combine with other atoms to form compounds
they are substances formed from two or more elements, the atoms of each are in fixed proportions throughout the compound and are held together by chemical bonds
it is usually difficult to separate the original elements out again because a chemical reaction is needed
making bonds involves atoms giving away, taking or sharing electrons. only the electrons are involved and the nuclei aren't affected
ionic boding
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the metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions. the opposite charges of the ions mean that they're strongly attracted to each other
examples of compounds that bond ionically include sodium chloride, magnesium oxide and calcium oxide
covalent bonding
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examples of compounds that are bonded covalently include hydrogen chloride gas, carbon monoxide and water
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atoms
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Atoms contain protons, neutrons and electrons
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elements
an element is a substance made up of atoms that all have the same number of protons in their nucleus (same atomic number)
Atoms can have different numbers of protons, neutrons and electrons but its the number of protons that decides what type of atom it is. for example an atom with one proton in its nucleus is hydrogen and an atom with two protons is helium
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so all atoms of a particular element have the same number of protons and different elements have atoms with different numbers of protons
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chemical equations
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one way to show a chemical reaction is to write a word equation (it is not as quick as chemical symbols and you cant tell straight away what's happened to each of the atoms)
the molecules on the left-hand side of the equation are called reactants (because they react with each other)
the molecules on the right-hand side are called the products (because they have been produced from the reactants)
symbol equations
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they need to be balanced meaning there must always be the same number of atoms on both sides (they cant just disappear)
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1) find an element that doesn't balance and pencil in a number and try and sort it out
2) see where it gets you. it may create another imbalance, but if so, pencil in another number
3)carry on chasing imbalanced elements and it will sort itself out quickly