Unit 1 Bonding and Structure

Question 1

What are three intermolecular forces?

Answer 1

London Dispersion forces, Permanent-Dipole-Permanent dipole and Hydrogen bonding.

Question 2

How is a covalent bond held together?

Answer 2

Two positive nuclei being held together by their common attraction for the shared pair of electrons.

Question 3

What is a pure covalent bond?

Answer 3

In a pure covalent bond, electrons are equally shared

Question 4

When do molecules have pure covalent bonding?

Answer 4

Atoms have the same electronegativity, for example diatomic elements

Question 5

What is another name for Pure covalent bond?

Answer 5

Non-polar

Question 6

What is a polar covalent bond?

Answer 6

Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons is different. So difference in electronegativity.

Question 7

When do molecules have polar covalent bonds?

Answer 7

Difference in electronegativity creates a permanent dipole as electrons are pulled closer to one atom

Question 8

What does the symbol delta (δ) signify?

Answer 8

Delta positive (δ+) and delta negative (δ-) notation can be used to indicate the partial charges on atoms

Question 9

What is electronegativity?

Answer 9

Electronegativity is a measure of the tendency of an atom to attract a binding pair of electrons

Question 10

What is an ionic bond?

Answer 10

Ionic bonds are the electrostatic attraction between positive and negative ions. Ionic compounds form lattice structures of oppositely charged ions.

Question 11

What determines the ionic character of a compound?

Answer 11

The difference in electronegativities between bonded atoms gives an indication of the ionic character.

Question 12

What is an isoeletric substance?

Answer 12

A substance where both ions have the same electron arrangement (nearest noble gas)

Question 13

What is the overall charge of an ionic compound?

Answer 13

Zero

Question 14

Do ionic compounds conduct electricity?

Answer 14

Only when molten or in solution, solid ionic compounds do not conduct electricity as the lattice holds the ions in place

Question 15

What is the most ionic compound?

Answer 15

The one with the largest electronegativity difference.

Question 16

What name is given to bonding:

a) inside molecules
b) between molecules

Answer 16

a) inside molecules (intramolecular bonds)
b) between molecules (intermolecular bonds).

Question 17

What are the two types of covalent molecular bonding? (Hint-Electronegativity)

Answer 17

Non-polar (pure) covalent and polar covalent.

Question 18

What are intermolecular forces?

Answer 18

The forces of attraction which hold molecules together

Question 19

What are the three main types of intermolecular forces?

Answer 19

• London dispersion forces (weakest)
• Permanent dipole - Permanent dipole attraction
• Hydrogen bonding (strongest)

Question 20

Discuss London Dispersion Forces

Answer 20

• Occur between atoms (noble gases) and molecules
• Only force between non polar molecules and monatomic elements
• Weakest intermolecular force

Question 21

Discuss PD-PD attraction

Answer 21

• Occur between polar molecules
• Stronger than LDF
• Some molecules can have an overall polarity because of a PD

Question 22

What causes a non-polar (pure) covalent bond to be formed?

Answer 22

Non-polar (pure) covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons are similar (electronegativity).

Question 23

Why are some individual covalent bonds polar, but the molecule is not polar?

Answer 23

If the molecule is symmetrical it will be non polar - the dipoles cancel each other out

Question 24

What is meant by the bonding continuum?

Answer 24

Pure covalent bonding and ionic bonding can be considered as being at opposite ends of a continuous range with polar covalent bonding lying between these two extremes.

Question 25

What affects the strength of London dispersion forces?

Answer 25

The strength of London dispersion forces depends on the size of the molecule or atom.

Larger atoms and molecules have more electrons. This leads to larger temporary dipoles being established.

Question 26

Explain carbon tetrachloride is non-polar despite containing polar bonds.

Answer 26

A substance that contains polar covalent bonds may not be overall polar due to symmetry cancelling out the dipoles. Carbon tetrachloride is a tetrahedral molecule, so the charges are pulled in equal and opposite directions so cancel out. So, the molecule is non-polar.

Question 27

Describe what is meant by permanent dipole interactions.

Answer 27

Molecules with a permanent dipole are polar.

Polar molecules display attractions between the oppositely charged dipoles of the molecules.

This type of intermolecular bond is stronger than London dispersion forces.

Question 28

What name is given to the strongest type of intermolecular bond?

Answer 28

Hydrogen Bonding

Question 29

What is needed for hydrogen bonding to occur between molecules?

Answer 29

Hydrogen bonding occurs when a hydrogen atom is covalently bonded to a highly electronegative small atom such as nitrogen, oxygen or fluorine.

As with permanent dipole to permanent dipole attractions, the oppositely charged ends of molecules attract.

Question 30

What are the weakest intermolecular forces and how do they arise?

Answer 30

London’s dispersion forces which exist between all atoms and molecules.

They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.

Question 31

How do the melting and boiling points of a polar substance compare to a non-polar substance with similar numbers of electrons?

Answer 31

The melting and boiling points of polar substances are higher than the melting and boiling points of non-polar substances with similar numbers of electrons.

Question 32

Describe the properties (melting and boiling points, conductivity) of covalent network compounds.

Answer 32

All covalent network structures have very high melting points and boiling points. They are all hard and do not conduct electricity. (except for graphite)

Question 33

Describe the properties (melting and boiling points, conductivity) of covalent molecular compounds.

Answer 33

They have low melting points and boiling points. They do not conduct electricity.

Question 34

Which molecule ethanol or ether would have the higher melting and boiling points and why?

Answer 34

Both ethanol and ether have the same molecular mass, however, their melting points and boiling points are different due to the ethanol containing hydrogen bonding.

Ether is a symmetrical molecule, so even though it contains polar bonds, the molecule itself is non-polar and the only intermolecular force present will be weak London dispersion forces.

Question 35

Describe the solubility of ionic compounds, polar molecules and non-polar molecules.

Answer 35

Ionic compounds and polar molecular compounds tend to be soluble in polar solvents such as water and insoluble in non-polar solvents. Non-polar molecular substances tend to be soluble in non-polar solvents and insoluble in polar solvents. The molecules must be ab
to have similar intermolecular forces.