FoC : Structure, Bonding And Equalibria Flashcards
Covalent bonding
The formal sharing of electrons between two atoms. In heteroatomic molecules this is due to differences in electronegativity
Ionic bonding
The formal transfer of an electron from one atom to another
Metallic bonding
Low electronegativity elements, electrons are delocalised in a sea of electrons
Hydrogen bonding
Electrostatic interaction between a (H bonding to an electronegative atom )and an electronegative atom
Hydrogen bonding is an example of what type of interaction
Non covalent or electrostatic
Electrostatic
Positive charge is attracted to negative charge
Pauling definition of electronegativity
Ability of an atom to attract and electron to itself
Whose definition of electronegativity is based upon physical data
Allen
What are electrons with low electronegativity sometimes called?
Electropositive (meaning only very very weak electronegativity)
What is the van Arkel-Ketelaar triangle
Triangle that allows us to predict the dominant bonding in a compound using electronegativity and the different in electronegativity between the bonded atoms
If the reaction is exothermic what does that mean about the strength of the bond in the product
Stronger then the starting material
Thermodynamically favoured
If the charge in enthalpy is positive what does this mean about the thermodynamic favourability
It’s not
Trends in ionisation energy
Generally increases as protons increases
Shielding same
Therefore greater nuclear charge (Zeff)
What is the effect of d orbitals on ionisation energy
D orbitals being filled has a small increase in Zeff.
The 10 electrons don’t effectively shield the 10 added protons
Zeff is higher
Why is further IE’s higher then first IE
It’s harder to remove and electron from a cation
The attraction to the electron to positively charged ion is greater
Trends in electron gain enthalpy
Normally exothermic
Typically decreases with more protons
Sufficient attraction between the nucleus and new electron
Overcome electron pair repulsion
Exception at N
Electron pair repulsion means more energy required to gain an electron
Trends in lattice enthalpy
Lattice enthalpy decreases as ion size increases
Greater charge = greater lattice enthalpy
When formed from charges greater then +1 greater lattice enthalpy
Why don’t noble gases form ions
The IE is so high
as the nuclear charge is at maximum
Energy can’t be recouped forming bonds
Isn’t thermodynamically favourable
General strength of covalent bonds as opposed to ionic and h bonding
Weaker then ionic
Stronger then H
What is the shape of the p and s orbitals
P = dumbbell
S = spherical
Difference between multipul bonds and single bonds
Multiple bonds are shorter and stronger
Covalent bond dissociation energy trends
Generally bonds to large atoms are weak and longer
Orbitals increase in size and more diffuse
Can’t overlap as efficiently
Bonds to electronegative elements are shorter
Elec neg have smaller orbitals
E- more strongly attrac to nuc
So more overlap of orbitals
What are the limitations of VSEPR
•In some compounds (such as [TeBr6]2-) predicts inaccurately
As lp is stereochemically inactive
As lp occupies s orbital
•can’t use for radicals
•can’t use for transition metals
•can’t use for F block elements
what does the valence bond theory assume
bonds are located between pairs of atoms
what does hybridisation suggest will happen to 2s and 2p orbitals
combine to form 4 new sp3 hybrid orbitals so all bonds are identical and each contain an electron
what does hybridisation suggest about the formation of bonds
bond is formed through the overlap sp3 orbitals and the 1s orbital. overlap causes a 2 electron covalent bond
why do double bonded compunds not have sp3 bonding on the double bond
they wouldnt align with the geometry of the molecule
what hybridisation do double bonds have
sp2 created through the overlap of 2 p orbitals and 1 s orbital , 1 p orbital is not hybridised
c-c sigma bond formed from 2 sp2 overlap and pi bond formed from unhybridised p orbital overlap
when are sp orbitals found
in triple bonds the overlap of1 s and 1 pz orbital
how are all the bonds formed in a triple bond
2 pi bonds formed at 90 degrees from one another from the 2px overlap and 2py overlap (unhybridised) ans sp hybrisation 180 degrees from one another
bronstedlowry definition of acid & base
acid : proton donar
base: proton acceptor
lewis definition of acid & base
acid: electron pair acceptor
base: electron pair donar
how to calculate Ka
[A-][H3O+]/ [HA]
if the acid is stronger what does this mean in terms of conjugate acid, equalibrium and Ka
conjugate acid increases
equalibrium shifts further right
Ka increases
pKa calculation
pKa = -log10 Ka
what factors control acidity
strength of HA (acid)
electronegativity of A
stabilisation of A- (conjugate base)
the solvent
whats a polybasic acid
may lose more then one proton
how to calculate Kb
[BH+][OH-]/[B]
what is solvent leveling
strongest acids appear to have the same strength when fully dissociated because water is a good proton acceptor
what can water do that other molecules cannot
self ionise
how to calculate the degree of dissociation
( [H3O+]/[HA] ) x 100
how to calculate kw
[H3O+][OH-]
how to calculate the pH of buffer solutions
pH = pKa + log10[A-]/[HA]
