IQ4 - Bonding

Ionic Compounds

Contain oppositely charged ions held together by electrostatic attraction, arranged in 3D lattices. Examples include: Sodium Chloride

Ionic Compounds (physical properties)

Hard and brittle, non-conductors of electricity in solid state, good conductors in molten or aqueous solution, have high melting and boiling points

Why are Ionic Compounds Brittle?

Results from the layer of ions needing to be forced to slide past another layer. The orderly arrangement of ions is disturbed. The crystal then cracks, as the ionic arrangement is moved and ions of similar charge move closer, thus repulsing.

Why are ionic compounds good conductors in liquid state but not solid state?

Because of fixed positions in solid states and ions have free movement in liquid states

Covalent Network Structures

Three-dimensional network of strong covalent bonds that hold the lattice together. Examples include, Silicon Dioxide and Silicon Carbide.

Covalent network structure (properties)

Very high melting and boiling points, non-conductors of electricity (in all states), extremely hard and brittle, chemically inert (don’t react), insoluble in water and other solvents

Why are Covalent network substances extremely hard?

They have stronger electrostatic attraction

Covalent Molecular Structure

Formed by the sharing of a valence shell electrons to allow the formation of full outer shells of electrons. Electron sharing generates electrostatic attraction. It has a very strong intramolecular bond between two atoms bonded. However, as weak forces of attraction between molecules.

How does boiling seperate molecules from another in covalent bonds?

The intermolecular force is broken when heating. However, it does affect the covlanet bonds (intramolecular bonds). This also accounts for why it has low boiling and melting points.

Why do covalent molecular bonds have low boiling and melting points?

Because they have weak forces of attraction (intermolecular bonds)

Give examples of covalent molecular bonds

Water (H2O), Ammonia (NH3),

Bond Polarity

is the unequal share of electrons in covalent bonds. This results in one atom being slightly more positively or negatively charged. More electronegativity = more negatively charged. Less electronegativity = more positively charged

Spectrum of Bonds

Covalent and ionic bonds exist on a spectrum from less polar to more polar, to an ionic bond. (Polar < 0, Non-Polar = 0, Ionic Bond > 1.7)

Non-Polar Bond

= electronegativity values

Polar Covalent Bond

unequal electronegativity values

Ionic Bond (on spectrum)

great difference in electronegativity values (positive ions being more attracted)

Types of Forces between Molecules

Dipole-Dipole, Hydrogen Bonding, Dispersion Forces

Dipole-Dipole

are attractive electrostatic forces between polar molecules (forces are weaker than hydrogen bonding)

Hydrogen bonding

a type of intermolecular force that involves a partially positive hydrogen atom bonded to an O, N or F atom in one molecule

Dispersion forces

are weak attractive forces between molecular substances that result from an uneven electron distribution around the nucleus and between neighbouring atoms (weakest force)

Allotropy

the ability for an element to adopt two or more physical forms. For example Carbon can adopt the form of diamond, graphene and graphite.

Metallic Bonding

positive ions arranged in a 3D lattice, with freely moving electrons that are delocalised.

Properties of Metallic Bonding

Relatively high densities, good conductors of heat and electricity, malleable, ductile, high melting points.