Main points on bonding

METALLIC BONDING

  • All metals are elements.

  • Metals delocalise the outermost electrons to get a full outermost shell.

  • The delocalised electrons form a cloud surrounding the positive metal ions.

  • The delocalised electrons can move throughout the structure and conduct electricity.

  • When metals lose electrons, they become positive ions.

  • There are strong electrostatic forces of attraction between the positive metal ions and the cloud of delocalised negative electrons.

  • The electrostatic forces act in all directions to make a giant 3D metallic lattice.

  • The positive metal ions are all the same size and form regular layers.

  • When a force is applied to a metal, the layers can slide, and cause the metal to bend. Metals are malleable.

  • When a force is applied to both ends of a metal the layers will slide, and the metal can be drawn into wires. Metals are ductile

COVALENT BONDING

  • Covalent bonding occurs between non-metal elements only.

  • Atoms share electrons to obtain a noble gas electronic configuration.

  • The minimum number of electrons required to obtain a full outermost shell is the number of electrons shared.

  • Each atom must share the same number of electrons.

  • The structure produced is called a molecule.

  • Dot-and-cross diagrams can be drawn for H2, Cl2, H2O, CH4, NH3 and HCl molecules.

  • Covalent molecules have low melting and boiling points. Many are liquids and gases at room temperature.

  • Covalent molecules do not conduct electricity.

IONIC BONDING

  • Cations, in ionic bonding, are formed when metal atoms lose electrons to become positively charged ions.

  • Anions, in ionic bonding, are formed when non-metal atoms gain electrons to become negatively charge ions.

  • Metal atoms from Group I lose one electron to make single positively charged ions.

  • Non-metals ions from Group VII gain one electron to make single negatively charged ions.

  • The formation of ions can be shown using dot and cross diagrams.

  • Cations and anions are attracted to each other with strong electrostatic forces.

  • Ionic compounds have high melting and boiling points.

  • Ionic compounds are poor conductors when solid.

  • Ionic compounds are good electrical conductors when aqueous or molten