Topic 2 - Structure and Bonding Flashcards
What`s Ionic Bonding?
The electrostatic force of attraction between oppositely charged ions in a regular, ionic lattice.
What`s a covalent bond?
The electrostatic force of attraction between two oppositely charges nuclei and a shared pair of electrons.
What`s Metallic bonding?
The electrostatic force of attraction between cations and a sea of delocalized electrons.
What is a Dative Covalent bond?
A bond which contains a shared pair of electrons with both electrons supplied by one atom
Describe a Tetrahedral shape.
A molecule with 4 bonding pairs of electrons.
- No lone pairs
- Bond angle = 109.5
- e.g. CH4
Describe an Octahedral shape.
A molecule with 6 bonding pairs of electrons.
- No lone pairs
- Bond angle = 90
- e.g. SF6
Describe a Trigonal Planar shape.
A molecule with 3 bonding pairs of electrons.
- No lone pairs
- Bond angle = 120
- e.g. AlCl3
Describe a Linear Shape.
A molecule with 2 bonding pairs of electrons.
- No lone pairs
- Bond angle = 180
- e.g. CO2
Describe a Non-Linear Shape.
A molecule with 2 bonding pairs of electrons.
- 1 or more lone pairs
- Bond angle = 109.5 - 2.5 (per lp)
- e.g. SO2 - 107
Describe a Pyramidal shape.
A molecule with 3 bonding pairs of electrons.
- 1 lone pair
- Bond angle = 107
- e.g. NH3
Describe a Trigonal Bipyramidal shape.
A molecule with 5 bonding pairs of electrons.
- No lone pairs
- Bond angles 120 and 90
- e.g. PCl5
Define Electronegativity
The power of an atom to to attract the pair of electrons in a covalent bond.
What is the trend in electronegativity across a period?
Increases across a period.
- Nuclear charge increases
- Atomic radius decreases
- Shielding remains the same
-Bonding electrons are closer to attractive power of nucleus
What is the trend in electronegativity down a group ?
Decreases down a group.
- Atomic Radius increases
- Shielding increases
- Bonding electrons are further from attractive power of nucleus.
Properties of a polar molecule.
- Bonds between atoms of elements with different electronegativity values are polar.
- Polar molecules are asymmetric (contain a net dipole moment)
Van der Waal forces
IMFs that exist between all molecules.
- Electrons are always moving.
- Causing unequal distribution of electrons, resulting in temporary induced dipole.
- VDW forces are attractions between these induced dipoles
- The more electrons the greater the VDW forces
Permanent dipole-dipole forces
Attractive forces between the delta +ve on one molecule and the delta -ve on another molecule. Occurs in polar molecules.
Hydrogen Bonds
A strong intermolecular force between a delta +ve Hydrogen covalently bonded to O,F or N and a lone pair of electrons on the delta -ve O,F or N on a nearby molecule.
Physical properties of an Ionic Crystal
- Crystalline, hard, brittle - repulsion between ions if structure distorted
-High mpt. and High bpt. - Conducts when molten or aqueous
- Soluble in polar substances - contains +ve and -ve ions.
Physical properties of a Metallic crystal
- Hardness
- High mpt. (strong attraction between +ve ions and -ve electrons)
- Good electrical conductivity (delocalized electrons can move and carry charge)
Physical properties of a simple molecular crystal
- Low melting point (weak IMFs are broken)
- Non-conductor of electricity (no free electrons)
- Insoluble in water (they are non-polar so don`t interact with water)
- soft
Properties of Diamond
- High melting point ( strong covalent bonds)
- Very hard (Rigid 3 dimensional structure holding surface atoms in place)
- Doesn`t conduct (No free electrons)
Properties of Graphite
