Topic 2: Bonding and Structure

Question 1

What is an ionic bond?

Answer 1

An electrostatic force of attraction between oppositely charged ions

Question 2

What is a covalent bond?

Answer 2

An electrostatic force of attraction between two positive nuclei and the shared negative electrons between them

Question 3

What is a metallic bond?

Answer 3

An electrostatic force of attraction between the positive metal ions and the negatively-charged sea of delocalised electrons

Question 4

What is a lone pair?

(of electrons)

Answer 4

A pair of electrons not being used in covalent bonds

Question 5

What is a dative covalent bond?

Answer 5

A covalent bond where both electrons in the ‘shared’ pair come from one of the atoms (which come from the lone pair in the atom!)

Question 6

How are dative covalent bonds represented in the stick diagrams for covalent structures?

Answer 6

They are an arrow, from the atom from which the two electrons in the bond are from, to the other atom

Question 7

Draw the Al2Cl6 molecule

Answer 7

(Should have two Al atoms and six Cl atoms, where the two Al atoms are not bonded to each other, but have two Cl atoms in common, and two Cl atoms each. The dative bonds are between the shared Cl atoms and one each of the Al atoms.)

Question 8

Draw the NH4+ molecule

Answer 8

(Should have a central N atom, with three H atoms that are normal covalent bonds, and one H atom that is a dative covalent bond, where both electrons come from the N atom.)

Question 9

Write the order of strength of repulsion between different kinds of electron pair.

Answer 9

1. Lone pair - Lone pair
2. Lone pair - Bonding pair
3. Bonding pair - Bonding pair

Question 10

How much more do double bonds repel than single bonds

Answer 10

None - they repel the same

Question 11

How much more do lone pairs repel than a bonding pair

Answer 11

2.5 degrees more

Question 12

2 electron pairs: 2 bond pairs around a central atom

Answer 12

Name: Linear
Bond angles: 180

Question 13

3 electron pairs: 3 bond pairs around a central atom

Answer 13

Name: Trigonal Planar
Bond angles: 120

Question 14

3 electron pairs: 2 bond pairs and 1 lone pair around a central atom

Answer 14

Name: Bent
Bond angle: 119

Question 15

4 electron pairs: 4 bond pairs around a central atom

Answer 15

Name: Tetrahedral
Bond angles: 109.5

Question 16

4 electron pairs: 3 bond pairs and 1 lone pair around a central atom

Answer 16

Name: Trigonal pyramidal
Bond angles: 107

Question 17

4 electron pairs: 2 bond pairs and 2 lone pairs

Answer 17

Name: Angular
Bond angles: 104.5

Question 18

5 electron pairs: 5 bond pairs around a central atom

Answer 18

Name: Trigonal bipyramidal
Bond angles: 120 and 90

Question 19

5 electron pairs: 4 bond pairs and 1 lone pair around a central atom

Answer 19

Name: See-saw
Bond angles: 117.5 and 87.5

Question 20

5 electron pairs: 3 bond pairs and 2 lone pair around a central atom

Answer 20

Name: T-shaped
Bond angles: 87.5

Question 21

6 electron pairs: 6 bond pairs around a central atom

Answer 21

Name: Octahedral
Bond angles: 90

Question 22

6 electron pairs: 5 bond pairs and 1 lone pair around a central atom

Answer 22

Name: Square pyramidal
Bond angles: slightly less than 90

Question 23

6 electron pairs: 4 bond pairs and 2 lone pair around a central atom

Answer 23

Name: Square planar
Bond angles: 90 (lone pair are on opposite sides and effectively balance each other out)

Question 24

What is electronegativity?

Answer 24

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

Question 25

What are the most electronegative elements? | (Top 4)

Answer 25

Flourine, oxygen, chlorine and nitrogen

Question 26

Why are the most electronegative elements the most electronegative?

Answer 26

They have smaller atomic radius and higher nuclear charges

Question 27

What is the trend in electronegativity across groups and periods | (And why!?)

Answer 27

* Electronegativity increases across the period because the nuclear charge increases. * Electronegativity increases up the group because the atomic radius decreases.

Question 28

What makes a covalent bond polarised?

Answer 28

A difference in the electronegativity of the atoms

Question 29

What does it mean if a covalent bond is polar?

Answer 29

The electron density will be pulled towards the more electronegative atom, so each atom has a partial charge. The more electronegative atom will be 'slightly negative', while the other side is 'slightly positive' (denoted by delta- or delta+).

Question 30

What characteristics of the two atoms in a covalent bond are needed for the bond to be non-polar?

Answer 30

They need to have the same or similar electronegativities (e.g in diatomic molecules)

Question 31

What does dipole mean?

Answer 31

A difference in charge between the two atoms caused by a shift in the electron density in the bond.

Question 32

What does overall dipole mean?

Answer 32

When there is a permenant charge across the moleucle because the polar bonds aren't 'balanced'.

Question 33

What is a molecule called when the polar bonds in the molecule are uneven (so don't balance out)

Answer 33

The molecule will be a polar molecule, and will have an overall permenant dipole.

Question 34

How do you know if a molecule with polar bonds is a polar molecule or not?

Answer 34

Whether or not a molecule is polar or not depends on the symmetry of the molecule's shape, and whether the forces will 'balance' out (think like vectors!!!)