VESPR - and related points

Question 1

What electron geometries would have axial vs equatorial?

Answer 1

Only trigonal bipyramidal because all positions are equivalent

Question 2

Why is an axial position more crowded than neighboring equatorial atoms?

Answer 2

According to the VESPR theory of molecular geometry, an axial position is more crowded because an axial atom has three neighboring equatorial atoms (on the same central atom) at a 90° bond angle, whereas an equatorial atom has only two neighboring axial atoms at a 90° bond angle

Question 3

Why is the axial bond energies weaker than equatorial bond energies?

Answer 3

Axial bonds are more crowded because the axial position is more crowded so same charge is distributed amongst more atoms = weaker bond

equatorial bonds are less crowded because the equatorial position is less crowded so same charge is distributed amongst less atoms = stronger bond

Question 4

In the trigonal bipyramidal arrangement, why does a lone pair occupy an equatorial position rather than an axial position?

Answer 4

In the trigonal bipyramidal structure, a lone Pair occupies an equatorial position rather than axial position because the equatorial position has two neighboring Pairs at 90 degrees and two more at 120 degrees while the axial position has 3 neighboring Pairs at 90 degrees and one at 120 degrees thus the repulsion is smaller in case of equatorial position

Question 5

Why do lone pairs of electrons first occupy axial positions before occupying equatorial positions for species with octahedral geometry?

Answer 5

The main reason is repulsion with the electron pairs. Compare SF6 & SF42− as an example. To get from SF6 to SF42−, we need to replace two fluorines with lone pairs. The first replacement is arbitrary; in an octahedral geometry, all the positions are equivalent. Once we have replaced that first fluorine however, the bond positions are no longer equivalent. We will have four equatorial bonds (90 degree separation from the lone pair) and one axial bond (180 degree separation from the lone pair). Lone pairs are very repulsive, especially with respect to other lone pairs, so we want the next lone pair to be as separated as possible from the first. The axial bond is further from the lone pair then any of the equatorial bonds, so it makes sense for the lone pair to go there.

Question 6

Why do lone pairs prefer equatorial positions?

Answer 6

Lone pair repulsion is greater than bond pair repulsion. Therefore, to attain stability, the lone pairs should be kept at a position farthest from each other, so they occupy the equatorial positions.

Question 7

What is axial and equatorial

Answer 7

These are bonds to non ring atoms

axial - 90 degrees to ring plane
equatorial -

Question 8

What is the difference between shape and geometry?

Answer 8

Geometry of a molecule is the arrangement of lone pair + bond pair around the central atom and corresponds to the coordination number of the molecule while shape is the molecule structure excluding the lone pair on the central atom.Nov 15, 2018

Question 9

Why do lone pairs repel more than bond pairs?

Answer 9

Lone pairs have the greatest repelling effect because they are closer to the nucleus of the central atom compared to the bonding pairs, therefore they repel other lone pairs greater compared to bonding pairs.

Question 10

What does VSEPR stand for

Answer 10

valence shell electron pair repulsion

Question 11

Why do lone pairs take up more space than bonds?

Answer 11

The lone pairs are localized around the central atom. The lone pairs occupy more space because there is greater repulsion with each other.

Question 12

Do lone pairs increase or decrease bond angles?

Answer 12

Lone pair repulsion: Bond angle is affected by the presence of lone pair of electrons at the central atom. A lone pair of electrons at the central atom always tries to repel the shared pair (bonded pair) of electrons. Due to this, the bonds are displaced slightly inside resulting in a decrease of bond angle.

Question 13

What happens to the bond angles as the number of lone pairs increases?

Answer 13

It can be noted that the bond angle decreases with increase in the number of lone pairs on the central atom.

Question 14

What happens to the bond angle when you add or remove electron pairs?

Answer 14

Bond angle is affected by the presence or addition of lone pair of electrons at the central atom. Due to this, the bonds are displaced slightly inside resulting in a decrease of bond angle,and when you remove an electron domain the bond angle increases.

Question 15

Why are bond angles changed when you add another bond?

Answer 15

As more electron density remains on the central atom, electron repulsion between the bonded pairs increases and bond angles increase.

Question 16

Why is forming a bond exothermic? Why is breaking a bond endothermic?

Answer 16

Bond forming is exothermic because it releases energy?

Bond breaking is endothermic because it requires energy

Question 17

Is is easier or harder to remove an atom if it has a lower ionization energy?

Answer 17

We expend less energy so it is easier!!!

Ionization energies typically INCREASE across a Period (looking at the Table from left to right), but DECREASE down a Group.

Question 18

Why does it get easier to remove an electron from an atom as you go down a group in the periodic table?

Answer 18

Because outer electron are further away from the nucleus as you go down a group, they feel less pull from the nucleus, so they are easier to remove. Electronegativity is the ability of an atom to attract electron in a chemical bond.