Structure Bonding and Equilibria Flashcards
What is covalent bonding
The formal sharing of electrons between two atoms, typically found in elements with high electronegativity or when the atoms have a small difference in electronegativity
What is ionic bonding
electrons being formally transferred from one atom to another to form a charged ionic compound, in compounds where constituent elements have a large electronegative difference
What is metallic bonding
elements with low electronegativity, electrons are delocalised
What is hydrogen bonding
electrostatic interaction, non-covalent interaction
In the van Arkel-Ketelaar Triangle, what values relate to what bonding
-where x is electronegativity
-delta x>2 - ionic bonding
-0.5<delta x<2 - polar covalent bonding
-delta x<0.5 - covalent bonding
What are the trends in ionisation energy across period 1
-number protons inc so nuc charge inc
-electrons are in the same area of space so theres no shielding. effective nuclear charge increases (Zeff), attractive between nucleus and electrons increase so IE increases
-dip at B-2p not penetrate 2s too well-Zeff is lower
-dip at O- 2e- in same p orbital so repulsion
what are the IE trends down group 1
-decreases
-principle quantum number increases, e- spend more time away from nucleus, less attraction
- not even trend (d orbital full small increase in Zeff) due to e- not efficiently shielding the add H+
what is the trend in electron gain enthalpy across period 1
same argument for for 1st IE of O but in reverse
what are the lattice enlthalpy trends down group 1
-decreases as ion size increases
-the greater the charge on the ion the greater the lattice enthalpy
-only compare salts with the same structure
How do you work out the number of valence electrons
number of e- in shell
+1 per bond
+1 if neg charge -1 if pos charge
How do you work out the geometry of an atom
-Draw lewis structure
-decide on atom
-count e-s
-use number of e- bairs, bonding pairs and lone pairs to determine geometry
What factors impact molecular geometry
-Lone pairs
-Electronegative groups
-Multiple bonds
How do lone pairs effect geometry
lone pairs occupy more space,
angle between bonding pairs compressed
lp;bp repulsion greater than bp;bp
How do electronegative groups effect the geometry
pulls the bps closer
angle H-C-H increases
how do multiple bonds effect the geometry
occupy more space than single bonds
the four electrons occupy more space so the bond angle is greater
whats special about trigonal bipyramidal
two distinct environments-2 axial and 3 equatorial
e-e 120, e-a 90, a-a 180
what are the limitations of vsepr
doesnt take into account stereochemically inactive lone pairs (bottom of periodic table lps occupy spherical s orbitals)
Cant use for radicals
What is the assumption in valence bond theory
bonds are located between pairs of atoms
what is hybridisation
sp3-hybrid orbitals
What does it look like?
what happens when there is more s character in a given bond
the bond is shorter due to the the s electrons being held closer to the nucleus
for resonance what needs to happen
the groups need to be conjugated, +M and -M on neighbouring atoms
what resonance form is favoured
the negative charge on the most electronegative atom
what is thermodynamics
how far a reaction will proceed, based on energies between starting and end material
what is kinetics
how fast a reaction will proceed, governed by activation energy
what is the bronsted lowry definition of of acids and bases
an acid is a substance which is a proton donor, a base is a substance that accepts a proton
what is the lewis definition of acids and bases
an acid is a substance which is an electron pair acceptor and a base is a substance which is an electron pair donor
What is the conjugate base (bronsted)
the species formed from the acid after the proton loss
What is the conjugate acid (bronsted)
the species formed from the base after it has accepted a proton
what is the equation for pKa
-log10ka
What controls acidity (4)
- strength of the H-A bond
- Electronegativity of A
- Stabilisation of A- compared to HA, resonance
- the solvent
how does the stability of the conjugate base increase
as the charge per oxygyen atom decreases
the negative charge is spread over a greater number of electronegative atoms
what does a low pka mean
the stronger the acid and the better its ability to donate a pair of electrons or proton, it measures how completely an acid dissociates in an aqueous solutions
the more stable the conjugate base
acidity increases
the stronger the base..
the weaker the conjugate acid, therfore a lower ka and a higher pka
ka =
conc of products/conc of acid
kc =
conc of products^n/conc of reactants^n
how do yuo differentiate very strong acids
appear to be same strength due to being completel dissociated (water good proton acceptor)
solvent levelling
use a solvent that is more difficult to protonate than water for example ehtanoic acid
how dop you differnetiate between strong bases
same as acid with water
use a solvent like liquid ammonia
what is amphiprotic
capable of donating and accepting a proton
what is amphoretic
it is both an acid and a base
what is kw
for water self ionising
kc=conc of products^n/conc of reactant^n
kw=conc of products
pH=
-log10[H3O+]
the pH of water varies with temp
when a reaction is endothermic
equilibrium moves to the right
for a weak acid
[H3O+]=[A-]
degree of dissociation
=[H3O+]/[HA].100
Buffer
resist change in pH
made from weak acids and their conjugate bases or from weak bases and their conjugate acids eg Ch3COOH+CH3COONa or
NH3+NH4Cl
buffer capacity
depends on conc of salt and acid used
Henderson Hasselbach equation
pH=pka+log10[A-]/[HA]
ph of buffer will be close to pka of acid so can be tuned by cahanging A/HA
Titration curve strong acid-base
equivalence point at pH 7
titration curve weak acid-strong base
equivalence point>7
