Covalent Bonding

• Covalent bonds - sharing electrons
• When non-metal atoms bond together, they share electrons to make covalent bonds
• The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong
• Atoms only share electrons in their outer shells (highest energy levels)
• Each single covalent bond provides one extra shared electron for each atom
• Each atom involved generally makes enough covalent bonds to fill up its outer shell. Having a full outer shell gives them the electronic structure of a noble gas, which is very stable
• Covalent bonding happens in compounds of non-metals and non-metals
• You can use dot and cross diagrams to show the bonding in covalent bonds. Electrons drawn in the overlap between the outer orbits of two atoms are shared between those atoms

  
• Dot and cross diagrams are useful for showing which atoms the electrons in a covalent bond come from, but they don't show the relative sizes of the atoms, or how the atoms are arranged in space

  
• In dot and cross diagrams, drawing the orbitals isn't necessary
• The displayed formula for ammonia (NH3) shows the covalent bonds as single lines between atoms. This is a great way of showing how atoms are connected in large molecules

  
• Displayed formulas don't show the 3D structure of the molecule, or which atoms the electrons in the covalent bond have come from
• The 3D model of ammonia shows the atoms, the covalent bonds and their arrangement in space next to each other. But 3D models can quickly get confusing for large molecules where there are lots of atoms to include. They don't show where the electrons in the bonds have come from

  
• You can find the molecular formula of a simple molecular compound from any diagram by counting up how many atoms of each element there are
• A molecular formula shows you how many atoms of each element are in a molecule