2.2.2 Bonding and structure Flashcards
State the three main types of chemical bonds?
ionic, covalent, metallic
Define ionic bonding
Electrostatic attraction between oppositely charged ions
Define covalent bonding
Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Define metallic bonding
Electrostatic attraction between positive metal ions and delocalised electrons
Explain how the conductivity of an ionic compound changes in solid and liquid state
solid - non-conductive as ions are fixed in position
liquid - conductive as ions are mobile and can carry charge
Explain why ionic compounds have high melting and boiling points
Ionic compounds have a high melting and boiling point as the electrostatic attraction between oppositely charged ions is strong and requires a lot of energy to overcome.
Explain the solubility of ionic compounds
Ionic compounds are soluble in polar solvents.
The oppositely charged ions are attracted to the slightly charged atoms of the solvent.
What is a single covalent bond?
Atoms bonded by a single pair of shared electrons
Define multiple covalent bonding
Atoms share more than one pair of electrons - double or triple bond.
Define dative covalent bond
The electrons in the shared pair are supplied by one atom
What is a lone pair?
Electrons in the outer shell that are not involved in bonding
Define average bond enthalpy
A measurement of covalent bond strength
The average energy needed to break the bond
Describe the bonding in simple molecular lattice structure
Atoms within a molecule are held by strong covalent bonds, each molecule is attracted to each other by weak intermolecular forces.
Explain the low melting point of simple molecular structures
Weak intermolecular forces require little energy to overcome
Explain the conductivity of simple molecule structures
Non-conductive
No free charged particles in the structure
Explain the solubility of simple molecular structures
Soluble in non-polar solvents
State and explain the properties of giant covalent structures e.g. graphite, silicon dioxide, diamond
High melting and boiling points - strong covalent bonds require a lot of energy to overcome
Non conductive - no free charged particles in structure (except graphite)
Insoluble - strong covalent bonds require a lot of energy to overcome
Why is graphite conductive?
Each carbon atom in graphite form three covalent bonds with other carbon atoms
The delocalised electrons are free to move
Describe linear shape and angle
2 bonding pairs, 0 lone pairs
180 degree angle
Describe trigonal planar shape and angle
3 bonding pairs, 0 lone pairs
120 degree angle
Describe tetrahedral structure and bond angle
4 bonding pairs, 0 lone pairs
109.5 degree angle
Describe trigonal bi-pyramidal shape and bond angles
5 bonding pairs, 0 lone pairs
90 and 120 degree angles
Describe octahedral shape and angle
6 bonding pairs, 0 lone pairs
90 degree angle
describe pyramidal shape, bond angle and give an example
3 bonding angles, 1 lone pair
107 degree angle
NH3
Describe non linear shape, bond angle and give example
2 bonding pairs, two lone pairs
104.5 degree angle
H2O
By how many degrees does a lone pair reduce a bond angle?
2.5 degrees
Define electronegativity
The tendency for an atom to attract a shared pair of electrons in a covalent bond
Define polar bond and permanent dipole
Polar bond - covalently bonded atoms with different electro-negativities
Permanent dipole - slightly positive or negative charge of an atom in a polar bond
Polar molecules must have…
Polar bonds with dipoles that do not cancel out due to their direction - this is determined by molecular shape
Why is H2O polar but CO2 is not?
H2O has a non-linear molecular shape, and is asymmetrical, so there is an overall dipole.
CO2 has a linear shape, and is a symmetrical molecule, so there is no overall dipole.
Describe Van der Waals’ forces
An intermolecular force caused by attraction between dipoles
Broad term for dipole interactions and London forces.
Describe permanent dipole-dipole interactions
Intermolecular attraction between two polar molecules
Describe induced dipole-dipole interactions
Intermolecular attraction between a polar molecule and a non polar molecule with an induced dipole.
Describe London forces and how do they become greater?
Intermolecular attraction between instantaneous dipoles caused by random movements of electrons in a molecule.
London forces are greater in molecules with more electrons.
Describe hydrogen bonding
Strong intermolecular bond between H atom and a lone pair of electrons on O, N or F.
Forms an O-H, N-H or F-H bond.
Explain why ice is less dense than water?
Water molecules with hydrogen bonding arrange in an open lattice structure.
Molecules in ice are further apart than in liquid water.
Explain why water has a higher melting and boiling point than expected d
Hydrogen bonding is a relatively strong intermolecular force, so more energy is required to overcome this.
What must be always stated about electron bond pair in molecular shape questions?
- Electron pairs repel as much as possible
- Lone pairs repel more than electron bonding pairs
