Bonding and structure overview

• Non-metallic elements


  Exist as simple covalently bonded molecules. In the solid state, they form a simple covalent lattice structure held together by weak intermolecular forces therefore have a low melting and boiling point.
• Non-metals carbon, boron and silicon

  Have different lattice structures to simple covalent lattice structures. They're held together by strong covalent bonds and form giant covalent structures which consists of billions of atoms.
• Giant covalent lattice


  Three-dimensional structure of atoms held in place by strong covalent bonds that extend throughout the solid structure. When a solid melts it's the strong covalent bonds that must be broken, requiring a large amount of energy.
• Properties of giant covalent lattices

  All covalent structures are solid at RTP with very high melting points. Covalent bonds are strong and provide a stable structure, so a lot of energy is needed to break them.

  Giant covalent structures do not conduct electricity in any state because atoms are neutral so cannot conduct electricity.

  Giant covalent structures do not dissolve in any solvent. There are no new attractions possible between the atoms and solvent molecules.
• Diamond


  Every carbon atom in the lattice is at the centre of a tetrahedral of covalent bonds to four other carbon atoms. Covalent bonds extend throughout the giant structure.
• Physical properties of diamond

  High melting point due to strong bonds throughout the structure.

  Hard due to strong bonds throughout the structure.

  Low conductivity due to no charged particles being free to move.

  Insoluble due to not being able to form new attraction with any solvent molecules.
• Graphite


  Every carbon atom forms three strong covalent bonds to three other carbon atoms within a layer of carbon hexagons. The fourth outer shell electron of each carbon is delocalised across each surface of hexagons. The separate layers of carbon atoms are held together by weak intermolecular London forces.
• Physical properties of graphite

  Has an anomalous giant covalent lattice structure and so some of it's properties are anomalous. Has a typical melting point through strong covalent bonds within the carbon hexagon layers but:

  Soft due to weak forces between layers allowing them to slide. Making a good lubricant and is used in graphite pencils.

  High conductivity due to delocalised electrons across the layers so electrons are free to move when voltage is applied.
• Graphene


  A single layer of graphite that has the same conductivity as copper and is the thinnest and strongest material ever made. Every carbon atom forms three strong covalent bonds to three other carbon atoms within a single layer of carbon hexagons. The fourth outer shell electron of each carbon is delocalised across the surface of hexagon layer.
• Properties of graphene


  Has a high melting point due to strong bonds throughout the structure.

  Extremely strong due to strong bonds throughout the structure.

  Conducts electricity due to delocalised electrons across carbon layers.

  Insoluble due to not being able to form new attraction with any solvent molecules.
• Silicon


  Has the same network of atoms as diamond structure of carbon but Silicon replaces carbon atoms. Every atom in the lattice is at the centre of a tetrahedral of covalent bonds to four other atoms. Covalent bonds extend between Silicon atoms throughout the whole giant structure.
• Silicon properties


  High melting point due to strong bonds throughout the structure.

  Does not conduct electricity due to no charge carriers being free to move.

  Insoluble in solvents due to no new attractions with solvent possible.
• Silicon dioxide (SiO2)


  Extremely high melting point, found in sand.
• Periodic trends in melting points

  Metals generally possess a high melting point.

  Most non-metals possess low melting points.

  The non-metal carbon possesses the highest melting point of all the elements. The semi-metal boron also possesses a high melting point. The decrease in melting point shows a change from giant to simple molecular structures. The divide between metals and non metals can be shown.
• Metallic bonding


  Attraction between positive metal ions and delocalised electrons. The positive metal ion (cation) consists of the nucleus and the inner shell electrons on the atom. Cations are in a fixed position and maintain the structure and shape of the metal. Only delocalised electrons can move.
• Properties of metals


  High melting points and boiling points

  Conduct electricity

  Insoluble in solvents

  All metals except for mercury are solid at RTP.
• High melting points and boiling points in metals

  Depending on the strength of the metallic bonds, metallic bonds are strong and extend throughout the structure so a lot of energy is needed to break the bonds and overcome the strong electrostatic attractions between cations and electrons. The strength of metallic bonding increasing across a period with increasing nuclear charge.
• Examples of comparing melting points

  Al3+ has a higher melting points than Mg2+ because there are more delocalised electrons in the nucleus, greater pull between electrons and the nucleus. Requiring more energy to break the bonds.
• Conductivity in metals


  Metals conduct electricity in the solid and liquid states. Delocalised electrons are free to move through the giant metallic lattice when a voltage is applied.
• Solubility of metals


  Insoluble in solvents. It's expected that they would have some interaction between polar solvents and metallic charges as with ionic compounds, any interaction would lead to a reaction rather than dissolving. E.g. Sodium with water. Metal atoms are unable to form new attractions with solvent molecules.
• Delocalised electrons


  Outer shell electrons that are shared between more than two atoms and are free to move. Any charged particle that is free to move is able to conduct electricity. Ions that are free to move can conduct electricity just as well as delocalised electrons.
• Rules for drawing metallic bonding

  Must draw 9 positive metal ions and the sea of electrons. The nuclear charge of the cation must equal the number of delocalised electrons it releases. E.g. Magnesium, Mg2+ ions have 2 delocalised electrons per ion.
• Lattice structure


  Particles (atoms, ions, cations or molecules) in a solid are arranged in a regular network that repeats in three-dimensions.
• Giant lattice


  Has strong bonds that extend throughout the whole structure. These may be ionic bonds, covalent bonds or metallic bonds.
• Simple lattice


  Has weak forces that extend throughout the whole structure. These weak intermolecular forces may be permanent dipole dipole, induced dipole dipole (London forces) or hydrogen bonds.
• Giant metallic lattice


  Lattice type: Giant metallic

  Particles: Positive ions and delocalised electrons

  Nature of attraction: Between positive ions (cations) and delocalised electrons.

  Amount of energy required to break the attraction: High since metallic bonds are strong

  Melting and boiling point: High

  Conduct electricity when solid and liquid as electrons are free to move.
• Giant ionic lattice


  Lattice type: Giant ionic

  Particles: Oppositely charged ions

  Nature of attraction: Electrostatic attraction between positive and negative ions

  Amount of energy required to break the attraction: High since ionic bonds are strong

  Melting and boiling point: High

  Does not conduct electricity as a solid as ions are in a fixed position and aren't free to move.

  Do conduct electricity when dissolved in water/molten as ions are free to move.
• Giant covalent lattice


  Lattice type: Giant covalent

  Particles: Atoms

  Nature of attraction: Covalent shared pairs of electrons

  Amount of energy required to break the attraction: High since covalent bonds are strong.

  Melting and boiling point: High

  Do not conduct electricity in any state as the atoms are neutral. Graphite and graphene are exceptions because the carbon atoms only form 3 bonds and there are delocalised electrons across layers.
• Simple molecular lattice


  Lattice type: Simple molecule

  Particles: Simple molecules

  Nature of attraction: Intermolecular forces between molecules.

  Amount of energy required to break the attraction: Low since intermolecular forces are weak

  Melting and boiling point: Low

  Do not conduct electricity in any state as the molecules are neutral. Pure water does not conduct, it is the presence of ions in 'normal' water that allows to conduct slightly.