Bonding & Polarity SCH3U/4C Ms Richardson

Ionic or Covalent? Recall that bonding between atoms can be divided into three types: Ionic Electrons are transferred Non-polar Covalent Electrons are shared equally Polar-covalent Electrons are shared unequally, creating a partial charge The type of bond can be determined by looking at the difference in electronegativities (∆ 𝐸 𝑁 ) between the two elements involved

Properties of Ionic Compounds The different types of bonds in molecules cause them to have very different properties: Very high melting points Often solid crystal lattice at room temperature Soluble in water, but not non-polar substances Conducts electricity when in liquid state (but not solid) Conducts electricity when in an aqueous solution (example: salt water)

Properties of Covalent Compounds The force of attraction due to shared electrons is less than that of transferred electrons. For this reason, covalent (molecular) compounds tend to differ in properties: Gas, liquid or solid at room temperature Low melting and boiling points Poor electrical conductivity (in all states) Soluble in nonpolar substances, but not water

Bonding & Polarity When electrons are shared unevenly between two atoms, a partial charge (dipole) is formed on one end of the molecule. This is known as a polar-covalent bond and can be identified by observing a ∆ 𝐸 𝑁 of 0.5-1.6

Molecules & Polarity Some molecules with polar bonds form non-polar molecules. This occurs due to their shape. When a molecule has opposing, but equal dipoles, the dipoles cancel each other, resulting in a non-polar molecule