CHEM BONDING Flashcards
Describe the giant metallic structure and its properties
Metal cations held in fixed positions in an orderly arrangement surrounded by sea of delocalised electrons.
They have high mp/bp due to their strong electrostatic FOA between cations and delocalised electrons.
Good electrical conductivity due to delocalised electrons acting as mobile charge carriers
Malleable and ductile as mobility of delocalised electrons allows layers of cations to slide over each other without shattering lattice structure.
Describe giant ionic structure and its properties
They are ions in fixed position held in an orderly arrangement by strong electrostatic FOA
They have high mp/bp due to the amt of E needed to overcome strong electrostatic FOA between opp charged ions
In molten and aq state they have mobile charge carriers
They are hard due to lattice structure being held by strong FOA
They are brittle as a slight displacement brings ions of like charges together, resulting in strong repulsion that shatters the lattice structure
Describe structure and properties of simple molecular structure
They are held together by weak intermolecular FOA
Low mp/bp because little amt of energy is required overcome weak (id-id or pd-pd) interactions
Very soft
Describe diamond and its properties
Each C atom is bonded to 4 other C atoms in a repeated tetrahedral arrangement giving rise to extensive network of C bonds.
high mp/bp to overcome strong extensive C bonds throughout the entire structure
poor electrical conductor
describe structure of graphite and its properties
Each C covalently bonded to 3 other C atoms forming extensive network of planar hexagonal rings where the last valence electron is delocalised into layers, giving rise to continuous electron cloud.
High mp/bp to overcome extensive C bonds throughout the whole structure
Is an electrical conductor in direction parallel to layers because the delocalised electron acts as a mobile charge carrier but bad in direction perpendicular as electrons cannot jump across layers
Flaky and slippery because adjacent layers are held by weak id-id attractions that can slide over each other easily
what affects metallic bonds
charge density q+/r which affects attraction between cations and delocalised elections and number of delocalised electrons which affects the extent of interactions
what affects the strength of ionic bonds?
lattice energy which is (q+ x q-)/(r+ + r-)
What affects the strength of covalent bonds?
1.Bond length - bigger the size of atoms, more diffuse the orbitals which makes the extent of overlap less effective so the bond is weaker
2.Multiplicity of bond - greater number of shared electron pairs means stronger electrostatic FOA between the 2 partial charges
3.Polarity of bond - polar > non-polar because of the additional energy required to overcome electrostatic FOA between partial charges
4.Proximity of lp of electrons - closer means excessive repulsion
Why do some ionic bonds have C character? what is the degree dependent on?
This is because the cation has the tendency to attract the outer electrons of anions which results in the polarization of the anions electron cloud. Dependent on polarising power of the cation proportional to charge density, as well as the polarisability of anions where larger is more polarisable
Why do covalent bonds have ionic C? what affects?
Shared pair of electrons are pulled towards more electronegative atom which results in it gaining a partial negative charge while the other atoms gains a partial positive charge. Greater electronegativity diff means greater character.
Factors affecting id-id interactions
- Number of electrons/ electron cloud size - the greater the … , the greater the ease of electron cloud polarization which results in stronger id-id interactions
- Degree of branching - branched molecules have smaller SA for molecular interaction, leading to lower extent of id-id interactions
What affects pd-pd interactions
Overall dipole moment - the larger, the stronger the pd-pd interactions
What are H bonds? What affects the strength of H bonds?
H bonds are electrostatic FOA between a highly electron deficient H atom covalently bonded to a small highly electronegative atom (FON) and lp of small highly electronegative atom on another molecule.
- Extent of H bonds is affected by no of lp available and number of highly e- deficient H
- Strength is dependent of dipole moment, larger dipole moment means stronger H bonds
Why does 2-nitrophenol have a lower bp than 4-nitrophenol despite having the same molecular formula?
This is because the close proximity of the phenol and nitro groups allows for the formation of intramolecular H bonds which means there are fewer sites available for the formation of intermolecular H bonds.
Describe how H2O is like in the liquid state
Molecules interact in clusters forming H bonds with 2 other neighbouring H2O molecules. H bonds constantly break and reform so they can move and slide pass each other easily
