Chemical Structure and Bonding

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Bonding and structure

The physical properties of substances are dependent on its structure and type of bonding. Atoms bond with each other because of the need to have a full outer shell of electrons to be stable. There are three main types of bonding; covalent bonding, ionic bonding and metallic. In covalent bonding, atoms of non-metals share pairs of electrons in their outer shells in order to obtain a full outer shell. Ionic bonding occurs between a metal and a non-metal, where one atom loses one or more electrons to the other atom, and both atoms end up with full outer shells. Metallic bonding occurs between two metals, where the metal atoms lose their outer electrons to form metal cations, and a “sea” of electrons that flow around them. The attraction between the cations and electrons(electrostatic forces) is called a metallic bond, and is what holds the particles together.

Covalent bonding can form simple molecules of elements (H2) and compounds (HCl), or giant molecules of elements (diamond) and compounds (SiO2).

Although the covalent bonds between atoms in a simple molecule are very strong, the molecules are held together by relatively weak intermolecular forces, which can be easily broken. As a result, simple molecular substances have low melting and boiling points, and are not very hard or strong. Simple molecular substances do not usually dissolve in water, and do not conduct electricity due to a lack of ions. An example of a simple molecule is methane. Methane has low melting and boiling points and exists as a gas at room temperature. It is also insoluble and does not conduct electricity.

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Molecule of methane

Silicon dioxide (SiO2) is an example of a giant molecular structure. The bonding between the atoms goes on and on in three dimensions. The covalent bonds that exist between the atoms are very strong, and as a result these substances are hard, with high melting and boiling points. Giant covalent molecules generally do not conduct electricity, with the exception of graphite, and are insoluble in water. In a silicon dioxide molecule, each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms.

Molecules of SiO2

When an atom loses ...

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