Week 3 content

Question 1

There are two main types of chemical bonds:

Answer 1

1. Ionic bonds – result from the attractive force of oppositely charged ions
2. Covalent bonds – results from the equal sharing of valence
   electrons between two atoms.

Question 2

Lewis electron-dot symbol:

Answer 2

a notation in which the electrons in the
valence shell of an atom or ion are represented by dots placed
around the chemical symbol of the element.

Question 3

Boron Trifluoride: (Draw it)

Answer 3

The B atom has a share in only 6 pairs of
electrons (or 3 pairs). B atom is often electron
deficient because it can “hyperconjugate” to many
atoms.

Question 4

Molecular geometry:

Answer 4

the general shape of a molecule, as
determined by the relative positions of the atomic nuclei.

Question 5

VSEPR model predicts the…

Answer 5

… shapes of molecules and ions by
assuming that the valence-shell electron pairs are arranged about
each atom so that electron pairs are kept as far away from one
another as possible, thus minimizing electron-pair repulsions.

Question 6

A higher number of lone
pairs leads to…

Answer 6

… a higher
repulsion, and thus a
smaller angle

Question 7

e “density maps”
of a sulphur lone pair (lp) vs. a
sulphur-fluorine bonding pair
(bp). (draw?)

Answer 7

It is obvious that the lone pair
have a larger spatial domain than
the bonding pair, and thus will contort the geometry of a molecule by
decreasing the angle between bonding pairs:

Question 8

Multiple Bonds are…

Answer 8

…slightly more repulsive than single bonds, but not as repulsive
as lone pairs

lp-lp > lp-bp > bp-bp

Question 9

similar molecules - same terminal atoms - different central atom, the electronegativity of the central atom…

Answer 9

distorts the structure.

decreases in electronegativity as we go down the
group

Question 10

central atom less electronegative…

Answer 10

…, the bonding electron
domains get smaller. The bond angle decreases with decreasing
electronegativity

effect of decreasing the repulsion between bonding pairs,
- repulsive effect of lone pairs unchanged - bond
angle decreases as the lone pairs push the bonding pairs closer
together.

Question 11

more electronegative terminal atoms cause

Answer 11

bonding
pair to have a smaller domain than less electronegative terminal
atoms. Thus, the bond angle increases with decreasing
electronegativity.

Question 12

Hybridization on an atoms are known as…

Answer 12

hybridized orbitals: orbitals which
maintain characteristics of both of its “parent” orbitals.

Question 13

Hybridization of e orbitals on two (or more) different atoms, these are
called…

Answer 13

molecular orbitals.

• This is what forms a bond…when an orbital on one atom comes to
  occupy a portion of the same region of space as an orbital on the
  other atom. The orbitals are said to overlap. The greater the orbital
  overlap, the stronger the bond.

Question 14

Polar Bonds:

Answer 14

A polar bond is characterized by separation of electrical
charge. Polar molecules, therefore, have nonzero dipole moments.

Question 15

Since opposite charges attract, an ion eill be attracted to a…

Answer 15

a polar molecule.

• This attraction is on the order of 40 – 600 kJ/mol and is
  comparable to lattice stabilization.
• About 10 - 25% the strength of covalent bonds

Question 16

Some ionic solids are soluble in water because:

Answer 16

• There is an increase in entropy
• There is a compensation of enthalpy
• Lattice stabilization energy is compensated by ion-dipole
  interactions

Question 17

Attraction between ions and dipole depends on:

Answer 17

• Ion charge, magnitude of dipole and ion-dipole distance.
• Measured by H for Mn+ + H2O → [M(H2O)x]n+

Question 18

Dipole-Dipole Forces:

Answer 18

• Depending on orientation can be attractive or repulsive.
• Such forces bind molecules having permanent dipoles to one another.

Question 19

μ=?

Answer 19

= Q·R
(units of debyes D (3.336x10-30 C·m)):

where Q is the charge (δ-) and R is the bond length

Question 21

Van der Waals or
London Dispersion
Forces:

Answer 21

Features:

• Small differences in
  electronegativity
• Very small dipole moments
• Essentially non-polar bonds

Ex: Just C and H
present, i.e. CH4

Question 22

Dipole-dipole:

Answer 22

Features:
* Larger difference in
electronegativity causes the
bonds to be more polar

Ex:
C-O, C-X, C-N, e.g.
CH3Cl

Question 23

Hydrogen bonding:

Answer 23

Features:

• Very large difference in
  electronegativity which is
  achieved by having a
  hydrogen attached to
  something other than
  carbon
• Two unshared electrons
  must be attached to the
  heteroatom
• Very strong intermolecular
  attractions
  *important dipole-dipole interaction
  *account for high bp

Question 24

H bonds in H2O:

Answer 24

Abnormally high specific heat capacity of water (4.184 g/Kmol).

This is the reason water is used to put out fires, it is the reason
lakes/oceans control climate, and is the reason thunderstorms release
huge amount of energy.

Question 25

Induced Dipole:

Answer 25

• Materials without a dipole moment can have one temporarily
  induced by having electron density brought close by…
• These interactions can be very weak: (0.05 – 40 kJ/mol)

Question 26

Polarizability:

Answer 26

degree and ease of distortion of electron cloud (related to
size and number of electrons)