structure, bonding and equilibria - SEMESTER 1

What is the octet rule?

Where compounds aim to don’t an electron configuration of a noble gas.

How is the octet rule proven wrong?

Ionic and covalent bonding proves this wrong

How do electrons have a frequency of light?

• the electron becomes excited and jumps to a higher energy level

• The electron emits energy and returns to ground state

• The energy emitted is light and the frequency is given by the energy change

How is the energy of an atom described?

Quantized

Strengths of Bohr model?

Does a good job at predicting the energies of the emission of light spectrum.

Weakness’ of the Bohr model?

• doesn’t explain why the electron doesn’t fall into the nucleus

• Doesn’t explain why atoms are quantized

• Doesn’t explain why only certain energy levels are available

What are wavefunctions another term for?

Orbitals

What does a wavefunction show about orbitals?

Shows orbitals can be described by 3 quantum numbers and that atoms are quantised.

What are the three quantum numbers of wavefunction?

N - principal number

L - second quantum numbers (gives the shape of the orbital)

Ml - magnetic quantum number (can be positive or negative)

What does the radial value tell you about the mathmatical orbit of an electron?

How the electron distribution changes with the distance from the nucleus

What does the angular value of the mathematical orbit of an electron tell you?

How the orbital changes with angle from the nucleus

On a graph, what is the radial distribution function and where is it found?

The most probable distance to find an electron in the orbital, found as the highest point on the graph.

What is the node?

Where the wavefunction is 0

What does the angular part tell us?

The shape of the orbital

What are the two possible phases of an electron?

Positive or negative

What happens to the phase of an electron as you pass through the nucleus?

It stays the same

How does ionisation energy change across a period and why?

Increases,

• proton number increases

• Nuclear charge increases

• Attraction increases

• Sheilding stays the same

How does ionisation change going down a group and why?

Decreases

• principal quantum number increases (number of shells)

• Electrons further from nucleus

• Attraction decreases

Explain the trend in ionisation energies from potassium to rubidium.

• 10 extra protons, so nuclear charge increases

• Electron shielding stays the same

• Electrons become harder to remove

• Ionisation slightly increases.

Is a 2nd ionisation higher or lower than 1st ionisation number?

Higher, harder to remove a second electron from a cation

Explain the trend in lattice enthalpy as ion size increasers, and why?

decreases

• ions are further away from each other

• Weaker attraction

What makes noble gases unreactive?

electron gain enthalpy is so high it is unfavourable to remove

Which is more stable, a half full shell or a full shell and why?

A half full shell

• electrons stay in the same spin as far apart as possible

• Reduces repulsion

Define bond dissociation energy.

The energy required to break bonds between carbons in a compound in a gas state.

How does bond dissociation energy change from single to double to triple bonds?

• get shorter

• Increase in bond dissociation energy

How does bond dissociation energy change as atom get larger and why?

Decreases

• Principal quantum number increases

• Orbitals increase in size and spread out

• Can’t overlap efficiently

• Bond gets weaker

How does electronegativity effect bond length and why?

as electronegativity increases, bond length decreases

• Increases in ionic character

• Orbitals get smaller

• Therefore overlap more efficiently

How does nitrogen disobey trends in bond lengths?

Nitrogen has a lone pair of electrons, causes repulsion therefore weakening the C-N bond.

How is a covalent bond formed?

A molecule forms by sharing two electrons

What is meant by an equilibrium bond length?

Where the amount of attractive interactions outweigh the repulsive interactions

What does the Lewis model state about the octet rule?

• an atom can never have more than 8 electrons in its outer shell

• A compound can form with fewer than 8 electrons in its outer shell

How can it be calculated wether a species obeys or disobeys the octet rule?

1) group number

2) add/remove 1 e- for each bond

3) add/remove 1 e- for charges

If the result is 8, it obeys the octet rule.

State the order of electron repulsion from least to most in bonding

Bp-bp, bp-lp, lp-lp

How can VEP and shape of a compound be calculated?

1) group number

2) add num of bonding pairs

3) remove/add 1 for charges

4) divide by 2 → gives you VEP

5) VEP- bp = lp → gives you shape

How does a larger electronegativity effect bond angle and why?

As electronegativity increases, bond angle decreases.

• electron pairs are pulled towards the electronegative atom

• Gives a smaller bond angle

How do double bonds effect bond angles and why?

• greater electron density therefore the electrons occupy more space

• Causes a grater angle

What bond angle are axial bonds?

90

What bond angle are equatorial bonds?

120

What is the favourable shape for 4bp 1lp?

Trigonal bipyramid

What is the most favourable shape for 3bp 2lp?

T-shape

What is the favourable shape for 4bp 2lp?

Square planar

State some limitations of VSEPR

• cannot be used for free radicals- don’t have lone pairs

• Does wk for transition metals or f-block element compounds

What is the valance bond theory?

The idea that a bond is placed between 2 atoms

What is hybridization?

The combining of s and p orbitals to make sp3-hybrid orbitals

Feature of sp3-hybrid orbitals

Have one small and one bigger orbital both of equal energy

What are the two bonding combinations of sp3-hybrid orbitals and how are they different?

• constructive interference: both electrons in the same phase, places electron density between the nuclei.

• Anti-bonding combination: when the phases are different so the amplitude is 0 and the electron density is not placed between the nuclei.

What is a pi bond?

Formed by an overlap of unhybridised p-orbitals

What is resonance?

Where there are 2 forms of a structure that do not have an independent existence but are not in equilibrium.