Chem bonding I

Covalent bond

Electrostatic energy between shared pair of electrons and positively-charged nuclei

Dative covalent bond

Shared pair of electrons provided by only 1 of the bonding atoms

In neutral molecules, the central atom is ___ electronegative and has ___ unpaired electrons

less, more

In polyatomic cations, electrons are lost from the ___ electronegative atom

lessmore

In polyatomic anions, the electron is gained by the ___ electronegative atom

more

If the central atom has less than 8 electrons, it is ___ ___

electron deficient

If the central atom has unpaired electrons, it is a ___

radical

If the central atom has more than 8 electrons, it can ___ its octet

expand

Only atoms from period ___ onwards can expand its octet

3

Why is it that PCl5 exists and not NCl5?

Period 3 elements like P have vacant, low lying orbitals (eg. 3d orbitals) available for expansion of octet. Hence, PCl5 can be formed.

However, elements in Period 2, like N, do not have vacant, low lying orbitals for the expansion of octet. Hence, Period 2 elements can only acommodate a maximum of 8 valence electrons. NCl5 does not exist.

Arrange lp-bp, lp-lp, bp-bp in order of decreasing strength

lp-lp, lp-bp, bp-bp

What constitutes 1 region of electron density?

• each lone pair/ lone electron

• each single bond/ dative bond

• each double bond/ triple bond

As the difference in electronegativity increases, the dipole moment ___, and the polarity of the bond ___.

Increases, increases

Instantaneous dipole-induced dipole (id-id) interactions are the only type of intermolecular force between ___ molecules

non-polar

Factors affecting strength of id-id

1. Number of electrons/ electron cloud size

2. Surface area for molecular interaction

Id-id interactions are present between ___ particles

all

How does electron cloud size affect strength of id-id?

As the number of electrons increase, the electron cloud size increases. Larger electron clouds are more easily polarized than smaller ones, resulting in greater ease of formation of id-id. Hence, the strength of id-id increases

Why does the boiling point of halogens increase down the group?

Halogens are non-polar, so the attraction between their molecules is due to id-id interactions. The number of electrons of the halogens increase down the group. Therefore, size and ease of polarizability of electron clouds also increase down the group. Since more energy is needed to break stronger intermolecular interactions, the boiling points of halogens decrease down the group.

As branching increases, the surface area of the molecule ___ and the strength of id-id ___

decreases, decreases

How do id-id interactions arise?

• electrons are constantly moving in any particle. At any given moment, the electron density of a particle can be asymmetrical, resulting in an instantaneous dipole

• this dipole can induce a dipole in a neighbouring particle, which causes an attraction between them

• the id-id interactions are short-lived because the electrons keep moving and the dipoles vanish and reform

• the overall attraction tends to be weak

Straight-chained hydrocarbons have ___ surface area for intermolecular interactions, so id-id is ___ in straight-chained hydrocarbons

greater, stronger

Permanent dipole- permanent dipole (pd-pd) interactions are found in ___ molecules.

Polar

What gives rise to pd-pd interactions?

The electrostatic attraction between the delta + end of one molecule and the delta - end of the other molecule

For molecules with similar number of electrons, decrease in dipole moment results in increase in pd-pd strength. T/F?

F

Increase in dipole moment results in increase of pd-pd strength.

Hydrogen bonding is a type of ___ interaction

pd-pd

What are the 2 essential criteria for hydrogen bonding?

1. A hydrogen atom covalently bonding to F, O or N

2. A lone pair of electrons on a F, O or N atom in a neighing molecule bearing a delta - which can attract the delta + on the H atom.

Compounds can have all 3 intermolecular interactions at once. T/F?

T

Arrange pd-pd, id-id and H bonding in order of increasing strength (assuming number of electrons between the diff molcs are similar)

id-id, pd-pd, H bonding