Why do atoms bond together?
The Octet Rule
- Under normal conditions, the only elements which can exist as single atoms (mono-atomically) are the Noble Gases (Group 0)
- The atoms of all other elements are bonded together.
- The Noble Gases get their name from their unreactivity - all electrons are paired and the bonding shells are full.
- This arrangement of electrons is very stable and is often known as an 'octet'.
- Other elements exist bonded together, as diatomic molecules, such as O2 and N2, or as compounds such as NaCl or CO2.
- In these molecules, electrons have been shared or transferred to create a Noble Gas structure in each atom - this is called the Octet Rule.
Types of Bonding
- Chemical bonds are classified into three main types: ionic, covalent and metallic.
- Ionic bonding occurs between a metal and a non-metal, e.g. NaCl or MgO
- Covalent bonding occurs between non-metals, e.g. H2O or CO2
- Metallic bonding occurs between metals, e.g. iron and zinc, or alloys such as bronze (copper and tin)
- Always determine the type of bonding before drawing a dot-and-cross diagram, predicting how a compound reacts or predicting the properties of a compound.
- An ionic bond is formed when electrons are transferred from a metal atom to a non-metal atom, forming oppositely-charged ions.
- An ionic bond is the electrostatic attraction between oppositely charged ions.
- Example: Sodium Chloride (NaCl) - Sodium chloride is formed by the transfer of one electron from a sodium atom to a chlorine atom, forming negative chloride (Cl-) ions and positive sodium (Na+) ions.
- Example: Magnesium Chloride (MgCl2) - A magnesium atom has two electrons in its outer shell; one is transferred to each of two chlorine atoms to form chloride ions and positive magnesium (Mg2+) ions.
Giant Ionic Lattices
- Ionic bonds are not just between two ions; each ion can attract oppositely charged ions in all directions.
- This results in a giant lattice structure which consists of hundreds of thousands of ions - an arrangement true to all ionic compounds.
Ionic Charges and the Periodic Table
- An ionic charge can be predicted from an element's…