Chapter 2 - Chemical bonding and structure (L)

Question 1

In metallic bonding, what 2 factors change the melting temperature?

Answer 1

• Size of cation

- Number of delocalised electrons per cation

Question 2

How does the size of the cation affect the melting temperature in metallic bonding?

Answer 2

The bigger the size, the lower the melting temperature- this is because there will be a larger distance between the delocalised electrons and nuclei of the cations

Question 3

How do the number of delocalised electrons per cation affect the melting temperature?

Answer 3

The larger the number of delocalised electrons per cation, the higher the melting temperature- this is because will be a stronger electrostatic attraction

Question 4

Why are metals ductile and malleable?

Answer 4

Because the electrons are free moving, and so move with the cation and prevent strong forces of repulsion occurring between cations in one layer and another layer

Question 5

What is metallic bonding?

Answer 5

The electrostatic attraction between the nuclei of metal cations and delocalised electrons

Question 6

In ionic bonding, what 2 factors change melting temperature?

Answer 6

• The stronger the ionic charge, the higher the melting temperature
• The smaller the ion, the higher the melting temperature

Question 7

Explain the brittleness of ionic compounds

Answer 7

When a stress is applied on an ionic compound, the layers of ions may slide over one another, causing ions of the same charge to be side by side and repel; this can cause the crystal to break apart

Question 8

Are ionic compounds soluble?

Answer 8

Yes. This is because polar water molecules are attracted to the positive and negative ions

Question 9

What is the relationship between bond length and bond strength in covalent bonds?

Answer 9

The shorter the bond length, the stronger the bond

Question 10

How does electronegativity change from left to right across a period?

Answer 10

Increases from left to right

Question 11

What is a polar covalent bond?

Answer 11

A covalent bond in which the bonding electrons are unequally distributed, causing one atom to be delta negative and one delta positive

Question 12

How does electronegativity change down a group?

Answer 12

Decreases down a group

Question 13

What is electronegativity?

Answer 13

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

Question 14

Shape of 2 bond pairs 0 lone pairs

Answer 14

Linear (e.g. CO2)

Question 15

Shape of 3 bond pairs 0 lone pairs

Answer 15

Trigonal planar (e.g. BCl3)

Question 16

Shape of 4 bond pairs 0 lone pairs

Answer 16

Tetrahedral (e.g. CH4)

Question 17

Shape of 5 bond pairs 0 lone pairs

Answer 17

Trigonal bipyramidal (e.g. PCl5)

Question 18

Shape of 6 bond pairs 0 lone pairs

Answer 18

Octahedral (e.g. SF6)

Question 19

Shape of 3 bond pairs 1 lone pair

Answer 19

Trigonal pyramidal (e.g. NH3)

Question 20

Shape of 2 bond pairs 2 lone pairs

Answer 20

V-shaped (e.g. H2O)

Question 21

What is the order of electron pair repulsion according to electron pair repulsion theory?

Answer 21

Lone pair-lone pair>lone pair-bond pair>bond pair-bond pair repulsion

Question 22

How do electron pairs arrange themselves around the central atom?

Answer 22

So repulsion is at a minimum

Question 23

What are the 3 types of intermolecular forces?

Answer 23

London forces, permanent dipoles and hydrogen bonds

Question 24

What causes an temporary dipole to be generated?

Answer 24

Electron density on either side of a molecule fluctuates over time- if at any instant the electron density become unsymmetrical, a dipole will be generated

Question 25

How are induced dipoles created?

Answer 25

When a temporary dipole (which has a delta postive and negative side) approaches another molecule, the molecule will become delta negative and positive. This is because the delta negative end of the temporary dipole will repel the electrons in the other molecule to the opposite side, or vise versa.

Question 26

What are London forces?

Answer 26

The attraction between the delta positive and negative sides of instantaneous and induced dipole

Question 27

What factor increases the strength of London forces?

Answer 27

The number of electrons in the molecule

Question 28

What are permanent dipoles?

Answer 28

Polar molecules

Question 29

How are induced dipoles aligned in London forces and what does this mean?

Answer 29

Induced dipoles are always aligned with the instantaneous dipole so that their interaction is favourable- this means their attraction is often stronger than permanent dipole interactions, which aren’t always aligned

Question 30

Why are hydrogen bonds often the strongest of intermolecular forces?

Answer 30

Due to their orbital overlap, which leads partial bond formation

Question 31

What elements does hydrogen bonding mainly occur between?

Answer 31

Hydrogen and oxygen, nitrogen or fluorine