1.4 Bonding

• Covalent bond: attraction of the nucleus to the shared pair of electrons.
• Electronegativity decreases down a group.
• The stronger the forces between the molecules, the more energy needed to break them, so the higher the melting and boiling points of a substance.
• Inter-forces between molecules.
• The type of bond that forms is dependent on the difference in electronegativity between the atoms.
• Ionic bonding: Occurs when there's a large difference in electronegativity (greater than 2.0), for example, NaCl has a difference in electronegativity of 2.1.
• Intermolecular forces are stronger when the molecules have a larger surface area - greater surface area for forces to occur.
• Intermolecular forces are stronger when the molecules are larger (larger Mr) because there are more electrons in the molecules and therefore a stronger intermolecular force and more energy is needed to break them.
• The forces between molecules govern the physical properties of compounds including: melting point, boiling point, and solubility of a compound.
• The difference in electronegativity between polar covalent bonds is less than 2.0, more than 0.5, for example, H-Cl = 1.4.
• Pure covalent bonds are non-polar molecules that form temporary dipoles, and van der waal's forces occur between molecules.
• Lone pairs - Electron pairs that are not involved in bonding (they are more negative than bonding pairs as they are only under the influence of one nucleus)
• Pauling scale measures electronegativity on a scale from 0 to 4, 4 being the most electronegative.
• External force moves rows, like charges repel so crystal shatters
• A coordinate covalent bond is a shared pair of electrons where both electrons come from one atom only
• If an atom is electron deficient, it doesn't have a full outer shell of electrons (e.g
• Ionic bond: Strong electrostatic forces of attraction between oppositely charged ions