Effects of Bonding & Structure on Physical Properties
- Different types of?structure?and?bonding?have different effects on the?physical properties?of substances such as their?melting?and?boiling points,?electrical conductivity?and?solubility
Ionic bonding & giant ionic lattice structures
- Ionic compounds are?strong
- The?strong electrostatic forces?in ionic compounds keep the ions strongly together
- They are?brittle?as ionic crystals can split apart
- Ionic compounds have?high melting?and?boiling?points
- The strong electrostatic forces between the ions in the lattice act in all directions and keep them strongly together
- Melting and boiling points increase with charge density of the ions due to the greater?electrostatic attraction?of charges
- Mg2+O2-?has a higher melting point Na+Cl-
- Ionic compounds are?soluble?in water as they can form?ion - dipole bonds
- Ionic compounds only?conduct?electricity?when?molten?or in?solution
- When molten or in solution, the ions can freely move around and conduct electricity
- In the solid state they’re in a fixed position and unable to move around
Metallic bonding & giant metallic lattice structures
- Metallic compounds are?malleable
- When a force is applied, the metal layers can slide
- The?attractive forces?between the metal ions and electrons act in all directions
- So when the layers slide, the metallic bonds are re-formed
- The lattice is not broken and has changed shape
- Metallic compounds are?strong?and?hard
- Due to the strong attractive forces between the metal ions and delocalised electrons
- Metals have?high melting?and?boiling points
- Pure metals?are?insoluble?in water
- Metals can?conduct electricity?when in the?solid?or?liquid?state
- As both in the solid and liquid state there are?mobile electrons?which can freely move around and conduct electricity
Metals are malleable as the layers can slide over each and reform
Covalent bonding & simple covalent lattice structures
- Simple covalent lattices?have low?melting?and?boiling points
- These compounds have weak intermolecular forces between the molecules
- Only little energy is required to break the lattice
- Most compounds are insoluble with water
- Unless they are polar (such as HCl) or can form hydrogen bonds (such as NH3)
- They do not?conduct electricity?in the?solid?or?liquid?state as there are no charged particles
- Some simple covalent compounds to conduct electricity in solution such as HCl which forms H+?and Cl-?ions
Covalent bonding & giant covalent lattice structures
- Giant covalent lattices?have?melting?and?boiling points
- These compounds have a large number of?covalent bonds?linking the whole structure intermolecular forces between the molecules
- A lot of energy is required to break the lattice
- The compounds can be?hard?or?soft
- Graphite is?soft?as the forces between the carbon layers are weak
- Diamond and silicon(IV) oxide are?hard?as it is difficult to break their 3D network of strong covalent bonds
- Most compounds are insoluble with water
- Most compounds do not?conduct electricity?however some do
- Graphite has?delocalised?electrons between the carbon layers which can move along the layers when a voltage is applied
- Diamond and silicon(IV) oxide do not conduct electricity as all four outer electrons on every carbon atom is involved in a?covalent bond?so there are no free electrons available
Characteristics of different compound structure types table
Worked example: Bonding & structure
Answer
The correct answer is 4
The relatively high melting point, solubility in water and electrical conductivity when molten suggest that?X?is a?giant ionic structure.
The low melting point of?Y?suggests that little energy is needed to break the lattice which corresponds to a?simple molecular structure. This is further supported by the low electrical conductivity and its being almost insoluble in water.
Compound?Z?has a very high melting point which is characteristic of either metallic or giant molecular lattices, however since it conducts electricity, compound Z must be a?giant metallic lattice.
