Chemistry - Bonding

  • Formation of Ions
  • Ionic Compounds
  • Covalent Bonding
  • Covalent Compounds/Covalent Molecular Substances
  • Giant Covalent Structures
  • Metallic Substances
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Formation of Ions

Ionic bonding occurs between a metal and non-metal atom.

  •        Atoms have equal numbers of protons and electrons and therefore no overall charge.
  •       Atoms with incomplete electron shells are unstable.
  •       They can obtain full outer shells by losing or gaining electrons.

Positive Ions - Formed when an atom loses one or more electrons, meaning it has an overall positive charge.

  •       Occurs when an atom has a nearly empty outer shell and so loses its outer shell electrons to become stable.

Negative Ions - Formed when an atom gains one or more electrons, meaning it has an overall negative charge.

  •       Occurs when an atom has a nearly full outer shell and so gains electrons to become stable.
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Ionic Compounds

Ionic compounds are formed by a reaction between a metal and a non-metal. They are a result of the electrostatic attraction between a positive and negative ion.

Properties

  •  Form crystals with a cubic shape and straight edges due to structure of ionic lattice.
  • High melting and boiling points as ionic bonds are strong and need a lot of heat to break them
  • Dissolve in water. Water is a polar compound (slightly negative end & slightly positive end), and this means the positive ions are attracted the the slightly negative ends and the negative ions to the slightly positive therefore seperating the ionic lattice.
  • Do not conduct electricity when solid as the particles cannot move but do conduct when liquid as particles can move.
  • Brittle, not malleable or flexible. They snap or crumble when force is applied. (Like charges line up and repel and this means that layers break off and the lattice snaps).
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Covalent Bonding

A Covalent Bond - formed when a pair of electrons are shared between two non-metal atoms.

  •       Non-metal atoms usually need just one or two electrons to fill their outer-shells.
  •       When two non-metal atoms have incomplete outer-shells, they share electrons to become stable.

A covalent bond is the result of the electrostatic force of attraction between the positively charged nuclei and negatively charged shared electrons.

  •       Can be drawn using dot and cross diagrams.

(http://www.ducksters.com/science/chemistry/chemical_bonding_co2.gif)

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Covalent Compounds/Covalent Molecular Substances

Properties

  • Can exist as solid, liquid or gas at room temperature.
  • Low melting and boiling points. There are strong bonds betwen atoms but that forces that hold the molecules together (intermolecular forces) are not as strong as there are electrical distortions.
  •  Cannot conduct electricity in any state as electricity is the flow of charged particles and covalent molecules have no charge. All electrons are also involved in bonding.
  • Usually crumble easily as there are weak intermolecular forces.
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Giant Covalent Structures

In some substances, millions of atoms are joined together by covalent bonds. The bonds in these substances do not form molecules but large 3D lattices called Giant Covalent Substances. They have high melting and boiling points as all bonds are covalent and they are usually very hard.

Allotropes- different structural forms of the same element, i.e diamond and graphite are both allotropes of carbon. They both only contain carbon atoms but the atoms are bonded differently.

Diamond (Each carbon atom bonded to four others).

  • High melting and boiling point, covalent bonds require large amounts of energy to be broken.
  • Do not conduct electricity as electrons are involved in bonds.
  • The 3D Lattice structure makes it very strong.

Graphite (Each carbon atom bonded to three others).

  • High melting and boiling point, covalent bonds require large amounts of energy to be broken.
  • Does conduct electricity as each carbon atom has a delocalised electron which can move.
  • Soft and slippery as layers of atoms are held by weak forces, layers can slide.
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Metallic Substances

Metals are just giant structures of atoms. They have a Lattice structure and are formed in tightly packed layers.

They also have a 'sea of electrons' formed by the outer electrons of atoms. The electrons are delocalized and so are free to move. The metal atoms become positive ions and are then attracted to the sea of electrons. This is known as metallic bonding.

Properties

  • High melting and boiling points due to the strong attraction between the sea of electrons and the positively charged metal ions.
  • Metals are malleable and ductile. Layers of ions can slide over each other meaning that the metal does not shatter. The metallic bonds don't break as the delocalised electrons are free to move and they can move with the ions.
  • Conduct heat and electricity. As a metal is heated, electrons gain kinetic energy resulting in them moving faster and therefore transferring heat energy throughout the metal. As the electrons can move and transfer current, metals also conduct electricity.
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