SCH3U - Unit 4 - Inter/intramolecular forces and solubility in water

Properties of ionic compounds

• Solids

• Conductive in solution (electrolytes)

• Low mp/bp

• Hard & brittle

Properties of molecular compounds

• Can be in any state of matter

• Poor conductivity

• Low mp/bp

• Solids can be hard, brittle, powder, waxy, etc.

Intramolecular attraction

Ionic or covalent bonds

Intermolecular attraction

Forces between molecules

(London) dispersion forces (LDFs)

• Random fluctuation of electron location in an atom/molecule (polarization)

• All particles have LDFs

• Temporary force of attraction

• Strength of LDF depends on the molecule

Dipole-dipole forces

• Affects polar molecules with permanent dipoles

• Opposite ends attract each other

• Stronger force than LDF

Hydrogen bonding

• Strongest type of dipole-dipole interaction

• Only happens between highly electronegative atoms (N,O,F)

• Positive ends attract negative ends

Ionic compound

Metal+nonmetal

Molecular compound

Nonmetal+nonmetal

Factors of structure that determine properties

• Shape (Bent/tetrahedral/trigonal pyramidal, etc)

• Symmetry

• Charge distribution

Cohesion

(Water) molecules sticking together

Adhesion

Water sticks to container (ex. xylem, graduated cylinder)

Formation of meniscus

Water molecules are attracted to the sides, other water molecules cling together to create a chain on the surface

Covalent bond

Electrons shared between atoms

Hydrogen bonds

Hydrogen atoms shared between molecules

Dissolving process (simplified)

1. Break IMFs between solute molecules (depending on the type of molecule)

2. Solvent molecules need to break bonds

3. Solvent and solute molecules form new bonds