Covalent Bonding Flashcards
What is a ‘pure’ sybstance?
Uniform composition
Cannot be separated into simpler substances by physical means
Define hetero/homogeneous mixtures
Hetero - components can be seen
Homogenous - uniform composition
Element anion suffix
-ide
Eg. H- = hydride
S2- = sulfide
What is an oxoanion?
Oxygen bonded (1 or more double bonds) to a central atom of a polyatomic ion
Eg. CO3^2-
End in -ate
Carbonate
Relative energy of bonded atoms vs non-bonding
Bonded have LOWER energy
Due to stronger attractive forces between -ve and +ve particles
Define covalent bond
Electron pairs between bonded atoms attracted to both NUCLEI (positive particles, NOT CATIONS) of bonded atoms
Is ionic bond formation exo or endo?
EXO
Driven by ions coming together (lattice formation)
Bond dipole moment units of measurement
Debye
Describe the morse curve
Energy vs distance between two atoms
Starts high, falls below x-axis, increases and tends to 0
At the minimum point, atoms approach each other and lose potential energy, electron pair bond formed
Why do C, O, N form multiple bonds but larger atoms do not?
Multiple bonds require overlap of particular e- clouds
Better overlap, stronger bond when atoms are SMALL
Lewis diagrams order of atoms general rule
The more electronegative atom is usually outer
Eg. N2O has N-N-O
Formal charge rules
Sum of formal charges = overall charge
- Assign an atom bonding + 1/2 nonbonding e-
- LESS than #valence e- = POSITIVE charge (more positive than isolated atom)
MORE = NEG
Why use formal charges to assess plausability
Relative plausability of lewis structures.
Separating charge requires energy, hence LOWER formal charges is a better representation of the species
Define resonance form
Energetically equivalent (same # bonding and nonbonding e-) structures differ only in e- position
What is the hybrid structure?
Has -ve charge delocalised, equivalent bonds
like all resonance forms combined
Of LOWER energy (less reactive) dud to delocalisation
VSEPR define
e- pair domains about an atom occupies regions in space which are AS FAR APART as possible to minimise repulsion
four electron areas possible shapes
all occupied = tetrahedral
3 occupied = trigonal pyramid
2 occupied = bent 109.5
5 electron areas possible shapes and angles
all occupied = trigonal bipyramidal
4 occupied = see saw
3 occupied = t-shaped
90 and 120 degree angles
6 electron areas possible shapes and angles
all occupied = octahedral
5 occupied = square pyramidal
4 = square planar
regular bond angles apply ONLY IF…
all e- domains are equivalent.
non-bonding e- pair domains occupy MORE space.
What property does bond strength affect?
the reactivity (energy required to break bond)
trend in the strength of bond in relation to atom size
bonds between SMALLER atoms are SHORTER and STRONGER
strength of multiple bonds in relation to single
multiple = SHORTER and STRONGER than single.
define covalent bond in terms of orbitals
merging / overlap of orbitals and pairing of electron spins
sigma bond
SINGLE BOND.
two e- in an orbital with cylindrical symmetry about the bond axis.
e- density concentrated between the nuclei of the bonding atoms. (bonding e- are localised)
eg. singly occupied pz orbital and s or another pz
(pz is taken as the orientation along bond axis)
pi bond
DOUBLE bond
formed by overlap of orbitals in a side-by-side fashion, lobes either side of the internuclear axis.
e- density concentrated above and below the plane of the nuclei of bonding atoms.
eg. two singly occupied px or py orbitals
triple bond (in terms of pi and sigma)
1 sigma, 2 pi bonds
what is a hybrid orbital?
blended valence orbital, so they are energetically equivalent
linear combination (addition)
number of hybrid orbitals =
number of atomic orbitals combined.
eg. 1s + 3p makes 4 identical sp3 hybrid orbitals
hybrid and shape - how do decide what hybrid set to use
#hybrid orbitals required at a particular atom = #sigma bonds + # non-bonding e- pairs
how do hybrid orbitals form sigma bonds?
can overlap with hybrid OR s-orbitals on adjacent atoms.
overall e- density at an atom =
sum of e- densities of the occupied orbitals.
atom w/ hybridised orbitals has the same overall e- density as unhybridised orbitals.
what are temporary dipoles
Van der Waals forces
e- cloud in adjacent uncharged particles induces temporary dipoles when particles are close (liquid)
present in condensed phase of EVERY molecule
larger e- cloud = polarised to greater extent = stronger attractive forces (hence Tb increases as size increases)
permanent dipoles
exist in a polar molecule with partial charge, when there is an electronegative element (O, N, halogen) present.
hydrogen bonding
when H bonded to O, N or F, a very strong dipole is formed, making H very strongly (partially) positive.
stronger than temporary/permanent dipoles, apt 1/10 the strength of a covalent bond
