Covalent Dot & Cross Diagrams
Covalent compounds
- The atoms in covalent compounds will share their outer valence electrons to achieve a noble gas configuration
Dot-and-cross diagrams of covalent compounds in which the atoms share their valence electrons
Double covalent bonding
Oxygen, O2
Covalent bonding in oxygen
Carbon dioxide, CO2
Covalent bonding in carbon dioxide
Ethene, C2H4
Covalent bonding in ethene
Triple covalent bonding
Nitrogen, N2
Covalent bonding in nitrogen
Dative covalent bonding
- In simple covalent bonds, the two atoms involved share electrons
- Some molecules have a lone pair of electrons that can be donated to form a bond with an electron-deficient atom
- An electron-deficient atom is an atom that has an unfilled outer orbital
- So both electrons are from the same atom
- This type of bonding is called dative covalent bonding or coordinate bonding
- An example with a dative bond is in an ammonium ion
- The hydrogen ion, H+ is electron-deficient and has space for two electrons in its shell
- The nitrogen atom in ammonia has a lone pair of electrons which it can donate to the hydrogen ion to form a dative covalent bond
Ammonia (NH3) can donate a lone pair to an electron-deficient proton (H+) to form a charged ammonium ion (NH4+)
Aluminium chloride
- Aluminium chloride is also formed using dative covalent bonding
- At high temperatures aluminium chloride can exist as a monomer (AlCl3)
- The molecule is electron-deficient and needs two electrons to complete the aluminium atom’s outer shell
- At lower temperatures the two molecules of AlCl3 join together to form a dimer (Al2Cl6)
- The molecules combine because lone pairs of electrons on two of the chlorine atoms form two coordinate bonds with the aluminium atoms
Aluminium chloride is also formed with a dative covalent bond in which two of the chlorine atoms donate their lone pairs to each of the aluminium atoms to form a dimer
Examiner Tip
Covalent bonding takes place between nonmetal atoms.
Remember: Use the Periodic Table to decide how many electrons are in the outer shell of a nonmetal atom.