Bonding. Flashcards
Ionic bond definition.
Bond formed between positively charged ions and negatively charged ions (oppositely charged ions) due to the electrostatic forces of attraction between them. Holds together cations (positive) and anions (negative) in ionic compounds.
Ionic lattice structure.
Giant ionic lattice.
Number of ions determined by the size of the crystal.
Regular arrangement.
3 dimensional.
Attached by strong electrostatic attractions.
Properties of ionic compounds.
High melting and boiling pints.
Hard and brittle in nature.
Strong.
Good insulators.
Conduct when dissolved in water or molten.
Overall charge is 0.
Strength of compound depends on ionic charge (Bigger charge=greater attractive forces between each other=greater charge on ions involved=strong bond).
Soluble in water/polar solvents.
Explanation of high melting point/boiling point.
Large quantity of energy needed to overcome strong electrostatic attraction between ions. This means a high temperature is needed to provide this energy to break the strong ionic bonds.
Melting points are higher in lattices containing ions with greater ionic charges.
Covalent bond definition.
The strong electrostatic attraction between a shared pair of electrons and the
nuclei of the bonded atoms.
Dative covalent bond definition.
A shared pair of electrons in which the bonded pair has been provided by one of
the bonding atoms only; also called a coordinate bond.
Practice dot and cross.
Dative and single and double.
Metallic bond definition.
The electrostatic attraction between positive metal ions (cations)and delocalised electrons.
Average bond enthalpy.
The energy required to break one mole of a specified type of bond in a gaseous molecule.
Always endothermic.
Always have a positive enthalpy value.
Can be used to measure covalent bond strength.
Higher bond enthalpy value=more energy required to break bond=stronger bond.
Structure of metals.
-Each metal atom has donated its negative outer-shell electrons to a shared pool of electrons (delocalised throughout the whole structure).
- Positive ions remaining consist of the nucleus and the inner electron shells of the metal atoms.
- Cations are in a fixed position, maintaining structure and shape of the metal.
- Delocalised electrons are mobile and able to move throughout the structure. Only the electrons move.
Description of solid giant covalent lattices of Carbon (diamond, graphite and graphene) and silicon.
Networks of atoms bonded by strong covalent bonds.
Physical properties of giant metallic lattices and explanations.
High melting and boiling points:
Depends on the strength of the metallic bond, holding the atoms together.
Stronger bond=higher energies needed to overcome strong electrostatic attraction between cations and electrons.
Strong intermolecular forces between atoms.
Not soluble:
- As any interaction (between polar solvents and the charges in the lattice) would lead to a reaction, not just dissolving.
Can conduct in solid and liquid states:
-When voltage applied, deloc elecs are mobile (can move through structure) and can carry charge.
Physical properties of giant covalent lattices and explanations.
High melting and boiling points:
- Strong covalent bonds.
- High temps needed to provide large amounts of energy to break the bonds.
Insoluble in most solvents:
- Covalent bonds holding together atoms in the lattice are too strong to be broken by interactions with solvents.
Non-conductors:
- All four outer-shell electrons involved in cov bonding so none available.
Conductors in graphene and graphite:
- One electron free on outer shell so available for conducting.
Graphene, Graphite, Diamond, allotropes of carbon.
Trends across period 3 and 2 (melting points).
- Melting point increases from group 1-14.
- Sharp decreases in melting point from group 14 to 15.
- Melting points comparatively low from 15 to 18.
Explanation of the trends in terms of structure and bonding.
Sharp decreases- marks change from giant to simple molecular structures.
Diagonal divide between metal and non-metal elements starts to emerge.
Giant structures have strong forces to overcome= high melting points.
Simple molecular have weak forces to overcome= lower melting points.
Only have to break weak intermolecular forces not strong covalent bonds.
