shapes of molecules

Question 1

model answer for shapes of molecules

Answer 1

– electron pair regions repel one another as far apart as possible
– () electron pair regions around the central (name of atom) atom
– () bonding pairs- () lone pairs surrounding the central atom
– lone pairs repel more strongly than bonding pairs
– So () has a () shape
–with a bond angle of

Question 2

2 bond pairs, no lone pairs

Answer 2

• linear
• 180 degrees

Question 3

3 bonding pairs, no lone pairs

Answer 3

• trigonal planar
• 120 degrees

Question 4

3 bonding pairs one lone pair

Answer 4

• trigonal pyramidal
• 107 degrees

Question 5

4 bond pairs 0 lone pairs

Answer 5

• tetrahedral
• 109.5 degrees

Question 6

2 bond pairs 2 lone pairs

Answer 6

• bent/ non-linear
• 104.5 degrees

Question 7

6 bond pairs, 0 lone pairs

Answer 7

• octahedral
• 90 degrees

Question 8

5 bond pairs 0 lone pairs

Answer 8

• trigonal bipyramidal
• 120 and 90 degrees

Question 9

What is electronegativity?

Answer 9

A measure of attraction of a bonded atom for the pair of electrons in a covalent bond.

Question 10

Define polar

Answer 10

Bonding electrons that unevenly distributed between the atoms that make up the bond.

Question 11

Define polar covalent bond

Answer 11

A bond with a permanent dipole, having positive and negative partial charges on the bonded atom.

Question 12

Define dipole

Answer 12

Separation of electrical charge so that one atom of a polar covalent bond or one end of a polar molecule has a small positive charge and the other has a small negative charge.

Question 13

Define ionic bonding

Answer 13

Electrostatic attraction between negative and positive ions.

Question 14

Define covalent bonding.

Answer 14

Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 15

What are the melting and boiling points like for ionic compounds?

Answer 15

• High temperatures are needed to provide the large quantity of energy needed to overcome the strong electrostatic attraction between the ions. Therefore, most ionic compounds have high melting and boiling points.
• The higher the charge, the stronger attraction between ions, the higher the melting and boiling points.

Question 16

What is solubility like for ionic bonds?

Answer 16

• Many ionic compounds dissolve in polar solvents, such as water.
• Polar water molecules break down the lattice and surround each ion in solution.

Question 17

What’s the solubility like for ionic compounds with large charges?

Answer 17

• Ionic attraction may be too strong for water to be able to break down the lattice structure.
• The compound will not be very soluble.

Question 18

What are the two main processes for solubility?

Answer 18

• The ionic lattice must be broken down.
• Water molecules must attract and surround the ions.

Question 19

What does solubility depend on?

Answer 19

Ionic charge. As ionic charge increases, solubility decreases.

Question 20

what is electrical conductivity like for ionic compounds?

Answer 20

• In solid state, the ions are in a fixed position in the giant ionic lattice. There are no mobile charge carriers.
• When liquid or dissolved in water, the solid ionic lattice breaks down and the ions are free to move as mobile charge carriers.

Question 21

What is a dative covalent bond?

Answer 21

A dative covalent bond is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only.

Question 22

How is electronegativity measured?

Answer 22

• Pauling scale is used to compare electro negativity of atoms of different elements.
• Across and up the periodic table the electro negativity increases.
• Fluorine is the most electronegative atom.

Question 23

What is the electronegativity difference between the three bond types?

Answer 23

Covalent - 0
Polar covalent - 0-1.8
Ionic - Greater than 1.8

Question 24

When will a bond be non-polar?

Answer 24

• The bonded atoms are the same
• The bonded atoms have the same or similar electronegativity.

Question 25

what are the three types of intermolecular forces?

Answer 25

- London forces (induced dipole-dipole interactions) - Permanent dipole-dipole interactions - Hydrogen bonding

Question 26

How is a london force created?

Answer 26

- Electrons are constantly moving, which creates an uneven distribution of electrons, causing an instantaneous dipole. - This instantaneous dipole induces dipoles on other neighbouring molecules. - These dipoles attract each other.

Question 27

Why does neon have a higher boiling point than helium?

Answer 27

Neon has more electrons than helium, the more electrons there is, the stronger the london forces, therefore the more energy required to break the forces.

Question 28

What can result in a molecule having a permanent dipole?

Answer 28

Polar bonds within a molecule.

Question 29

What does molecules with permanent dipoles attract?

Answer 29

- Other molecules with permanent dipoles. - The “positive” end of one molecule attracts the “negative” end of another molecule and so on.

Question 30

What are examples of simple molecular substances?

Answer 30

- Neon, Hydrogen, Water and Carbon dioxide.

Question 31

In a simple molecular lattice, what are the molecules held in place by and what are the atoms within each molecule bonded by?

Answer 31

- The molecules are held in place by weak intermolecular forces. - The atoms within each molecule are bonded together strongly by covalent bonds.

Question 32

For simple molecular substances what are the melting and boiling points like and why?

Answer 32

- In a simple molecular lattice, the weak intermolecular forces can be broken by little energy so low melting and boiling points. - Only the weak intermolecular forces break, the covalent bonds are strong and do not break.

Question 33

What is solubility like for simple molecular substances?

Answer 33

- Non- polar molecular substances tend to be soluble in non-polar solvents. - Simple molecular substances tend to be insoluble in polar solvents.

Question 34

What is the electrical conductivity like for simple molecular substances?

Answer 34

- No mobile charged particles in simple molecular structures - Particles cant carry charge so simple molecular structures are non-conductors of electricity.

Question 35

What does a hydrogen bond contain?

Answer 35

- An electronegative atom with a lone pair of electrons e.g oxygen, nitrogen or fluorine. - A hydrogen atom attached to the electronegative atom.

Question 36

Why can ice float?

Answer 36

- Solid ice is less dense than liquid water and floats as hydrogen bonds hold water molecules apart in an open lattice structure. - The water molecules in ice are further apart than in water.

Question 37

Why has water got a relatively high melting and boiling point?

Answer 37

- Water contains hydrogen bonds. A large amount of energy is needed to break the hydrogen bonds in water, so water has much higher melting and boiling points than would be expected from just London forces.