Module 2: bonding and structure

Question 1

Define Ionic bond

Answer 1

Strong electrostatic forces of attraction between oppositely charged ions.

Question 2

Name the properties of ionic compounds

Answer 2

• High m.p and b.p
• Giant ionic lattice
• Strong electrostatic attractions which require a lot of energy to overcome
• The higher the charge - the stronger the bond
• Smaller ionic radius - the stronger the bond
• Soluble

Question 3

Define covalent bond

Answer 3

Shared pair of electrons between atoms

Question 4

What is a dative covalent bond?

Answer 4

Some compound e.g NH3 have a lone pair of electrons. Some ions have a vacant orbital e.g H+. This causes a bond to occur between the vacant orbital and the shared pair of electrons.

Question 5

How do you calculate the molecular structure of a molecule?

Answer 5

1. Identify group number of central atom
2. Add one for each extra atom
3. Divide total by 2 - gives number of electron pairs
4. Draw out correct shape

Question 6

Linear

Answer 6

• 2 pairs of electrons
• 2 bonding pairs
• 180 degrees

Question 7

Trigonal planar

Answer 7

• 3 pairs of electrons
• 3 bonding pairs
• 120 degrees

Question 8

Tetrahedral

Answer 8

• 4 pairs of electrons
• 4 bonding pairs
• 109.5 degrees

Question 9

Trigonal pyramid

Answer 9

• 4 pairs of electrons
• 3 bonding pairs
• 1 lone pair
• 107 degrees

Question 10

Trigonal Bipyramidal

Answer 10

• 5 pairs of electrons
• 5 bonding pairs
• 120 degrees and 90 degrees

Question 11

Non linear

Answer 11

• 4 pairs of electrons
• 2 bonding pairs
• 2 lone pairs

Question 12

Octahedral

Answer 12

• 6 pairs of electrons
• 6 bonding pairs

Question 13

Define electronegativity

Answer 13

The ability of an atom to attract a pair of electrons in a covalent bond

Question 14

What does electronegativity depend on?

Answer 14

• The nuclear charge (number of protons) of the atom (the higher the greater)
• The atomic radius of the atom (the smaller the greater)
• The number of principle energy levels the atom has (the fewer the greater)

Question 15

What atom is given the delta negative charge symbol?

Answer 15

• ## The element with a higher electronegativity

Question 16

What’s a polar bond?

Answer 16

A covalent bond where there is an unequal share of the electrons due to the differing electronegativities of the atoms involved.

Question 17

How can you work out if a molecule is polar or non polar?

Answer 17

• Add on any partial charges on polar bonds
• Look to see if there is an even or uneven distribution of the electron density in the molecule.

Question 18

What are common polar molecules?

Answer 18

• H2O
• NH3, PH3
• CH2, F2, CH3BR
• HCl, HF
• Alcohols, carboxylic acids

Question 19

What are common non-polar molecules?

Answer 19

• Br2, Cl2, O2, N2, H2, I2
• CO2 (linear, 2 dipoles cancel)
• CH4, CF4: tetrahedral

Question 20

Is CHCl3 or CCl4 non-polar?

Answer 20

CCl4 - symmetrical: dipoles cancel

Question 21

What do intermolecular forces apply to?

Answer 21

• Simple molecular structures

Question 22

Name the three types of intermolecular forces from weakest to strongest

Answer 22

1. Induced dipole-dipole
   2.Permanent dipole-dipole
2. Hydrogen bonding

Question 23

What do all molecules have?

Answer 23

Induced dipole-dipole forces

Question 24

What applies to polar molecules?

Answer 24

Permanent dipole-dipole forces

Question 25

What does hydrogen bond to?

Answer 25

Nitrogen, oxygen and fluorine

Question 26

What is an induced dipole-dipole bond?

Answer 26

- A temporary dipole induces a dipole in another molecule - There is an attraction between the delta positive on one molecule and the delta negative on an adjacent molecule. This is called the induced dipole dipole intermolecular force. - All simple molecules have induce dipole dipole intermolecular forces but some simple molecules have other intermolecular forces.

Question 27

What affects the strength of induced dipole-dipole forces?

Answer 27

- Size/Mr of the molecule (bigger molecule, more IDD forces between molecules) - Surface area contact (more SA contact, more IDD forces between molecules)

Question 28

How do you explain a permanent dipole-dipole bond?

Answer 28

- There is a polar bond due to the difference in elctronegativities. -There is an attraction between the delta positive on one molecule and the delta negative on the adjacent one.

Question 29

Why do hydrogen bonds only apply to oxygen, nitrogen and fluorine?

Answer 29

There's a large difference in electronegativity as they all have high electronegativities.

Question 30

What are features of a hydrogen bond diagram?

Answer 30

1. Partial charges on all atoms 2. All lone pairs clearly shown 3. Hydrogen bond shown clearly between the lone pair and the delta positive H on the other molecule. 4. Has to be 180 degrees around the hydrogen

Question 31

Why is ice less dense than liquid water?

Answer 31

- Fewer particles of water per unit volume in the solid state than the liquid state - In ice the water molecules are further apart than in liquid water. - This means there are more gaps/ spaces between the molecules

Question 32

Why does water have a relatively high boiling point?

Answer 32

- It's due to the presence of hydrogen bonds which are much stronger than the IDD's in the other hydrides.

Question 33

What are physical properties of Simple molecular structures?

Answer 33

1. Low melting and boiling points due to weak intermolecular forces which require very little energy to overcome. Actual m.p is determined on strength of EMFs 2. They will not conduct electricity in the solid state or in the molten state as there are no charged particles free to move. (no mobile charge carriers) 3. Non polar molecules do not generally dissolve in water - If the simple molecules can form hydrogen bonds they become more soluble.

Question 34

What are exceptions of ionic bonds?

Answer 34

BeCl2 and AlCl3

Question 35

What covalent molecules are happy with less than 8 e-?

Answer 35

BF3 and AlCl3

Question 36

What covalent molecules are happy with more than 8 e-?

Answer 36

SF6, PCl5