Chapter summary
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12.1 Atoms and compounds
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Chapter summary
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The smallest unit of matter is the atom. Atoms can combine to form compounds.
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A compound is a group of two or more different atoms that are attracted to each other by relatively strong forces or bonds. The atoms are combined in definite proportions.
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In a compound, atoms are held together by chemical bonds. Covalent bonds, ionic bonds and metallic bonds are examples of chemical bonds.
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A covalent bond exists between non-metal atoms. An ionic bond exists between non-metal and metal atoms and a metallic bond exists between metal atoms.
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Covalent molecular structures interact and exist as separate molecules.
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Network structures exist as giant repeating lattices. Network structures can consist of covalent, ionic or metallic compounds.
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A chemical formula is an abbreviated (shortened) way of describing a compound.
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The molecular formula is a concise way of expressing information about the atoms that make up a particular covalent molecular compound. The molecular formula gives the exact number of each type of atom in the molecule.
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The empirical formula is a way of expressing the relative number of each type of atom in a chemical compound. The empirical formula does not show the exact number of atoms, but rather the simplest ratio of the atoms in the compound.
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The structure of a compound can be represented by stick, ball-and-stick or space-filling models.
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A stick model use coloured sticks to represent compounds.
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A ball-and-stick model is a 3-dimensional molecular model that uses “balls” to represent atoms and “sticks” to represent the bonds between them.
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A space-filling model is also a 3-dimensional molecular model. The atoms are represented by spheres.
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12.1 Atoms and compounds
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