chem bonding: covalent bonds Flashcards
what are covalent bonds?
electrostatic forces of attraction between positively charged nuclei and negatively charged shared electons
what is a bond pair?
electrons involved in the formation of a covalent bond
what is a lone pair?
electrons not involved in the formation of the covalent bond
what is a dative covalent bond?
a special type of covalent bond in which only one of the bonded atoms contributes both of the shared pair of electrons
conditions for dative covalent bonding to occur
- one atom/molecule has a lone pair of electrons
2. the other atom/molecules has a vacant valance orbital
what is bond length?
the optimum bonding distance
what kind of overlap is in a sigma bond?
head-on overlap
what kind of overlap is in a pi bond?
sideways overlap
what bonds are in single, double and triple bonds?
single: sigma
double: sigma + pi
triple: sigma + 2 pi
exceptions to the octet rule
- nitrogen can have either 7 or 8 valence electrons
- compounds of B and AlCl3 have less than 8 electrons in their valence shells
- elements in period 3 and beyond can have more than 8 electrons in their valence shell
factors affecting strength of covalent bonds
- bond order
- bond length
- bond polarity
how does bond order affect strength of covalent bonds
triple bond > double bond > single bond
in multiple bonds more sets of orbitals overlap and electrostatic forces of attraction between bonded electrons and nuclei of atoms is stronger, causing stronger covalent bonds
how does bond length affect strength of covalent bonds?
shorter bond length = stronger covalent bonds
the npx orbital of 1 is smaller and less diffused than relative to the (n+1)px orbital of 2. the effective overlap is greater in H–1 than in H–2, resulting in higher bond energy and a stronger covalent bond
how does bond polarity affect strength of covalent bond?
higher bond polarity = higher bond strength
in addition to existing covalent bonds, the 2 partial charges lead to increase in electrostatic attraction and hence greater bond strength
how does strength of repulsion affect bond angle?
lp-lp repulsion > lp-bp repulsion > bp-bp repulsion
lp of electrons tend to push away the neighbouring bond pairs and force them closer together, causing bond angle to fall
how does electronegativity affect bond angle?
the more electronegative the central atom, the greater the repulsion between bond pairs.
the more electronegative atom pulls bonded electron pairs closer to itself, forcing bond pairs closer to each other and with more repulsion, bond angle increases
factors contributing to covalent character in ionic bond
- high charge on cation
- small size of cation
- large size of anion
why would an ionic bond possess covalent character?
when the cation polarises the anion and the electron cloud of the anion is distorted by the cation
why would a covalent bond possess ionic character?
when two atoms have different electronegativities and the more electronegative atom has a greater share of the bonding electrons which cause a shift in electron density towards the more electronegative atom
