Module 2.2.2 - Bonding and Structure definitions

Question 1

What is an ionic bond?

Answer 1

The electrostatic attraction between oppositely charged (positively and negatively) ions

Question 2

What is the octet rule?

Answer 2

The tendency to acquire a noble gas electron configuration (8 electrons in its outer shell)

Question 3

What is covalent bonding?

Answer 3

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 4

What are lone pairs (of electrons)?

Answer 4

Pairs of electrons in the outer shell of an atom not involved in covalent bonding

Question 5

What is a single covalent bond?

Answer 5

The sharing of one pair of electrons between two atoms

Question 6

What are multiple (double/triple) covalent bonds?

Answer 6

A double/triple covalent bond is the sharing of two/three pairs of electrons between two atoms

Question 7

What is dative covalent (coordinate) bonding?

Answer 7

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms, where only one of the atoms supplies both of the electrons shared

Question 8

What is metallic bonding?

Answer 8

The **strong electrostatic attraction ** of a lattice of cations (positive metal ions) to a ‘sea’ of delocalised electrons.

Question 9

What does the giant ionic lattice result from?

Answer 9

The regular arrangement of oppositely charged ions strongly attracted in all directions

Question 10

What do substances need in order to conduct electricity?

Answer 10

Mobile charge carrier such as delocalised electrons or mobile ions

Question 11

What does ‘mobile’ mean

Answer 11

Free to move

Question 12

What is average bond enthalpy?

Answer 12

Average bond enthalpy can be used as a measurement of covalent bond strength

Question 13

What is the basis of electron pair repulsion theory?

Answer 13

• Electron pairs repel each other to get as far away as possible
• Lone pairs repel more strongly than bonding pairs
• Shape is determined by the number and type of electron pairs (bond pairs / lone pairs) around the central atom

Question 14

What does a normal line in a 3D shape represent?

Answer 14

Shows a bond in the plane of paper

Question 15

What does a bold wedge in a 3D shape represent?

Answer 15

Bond comes out from the plane of the paper towards you

Question 16

What does a dashed line/dotted wedge in a 3D shape represent?

Answer 16

Bond going out from the plane of the paper away from you

Question 17

What is a linear molecule?

Answer 17

• 2 bonded pairs, 0 lone pairs
• bond angle 180°

Question 18

What is a trigonal planar molecule?

Answer 18

• 3 bonded pairs, 0 lone pairs
• bond angle of 120°

Question 19

What is a tetrahedral molecule?

Answer 19

• 4 bonded pairs, 0 lone pairs
• bond angle of 109.5°

Question 20

What is a octahedral molecule?

Answer 20

• 6 bonded pairs, 0 lone pairs
• bond angle of 90°

Question 21

What is a pyramidal molecule?

Answer 21

• 3 bonded pairs, 1 lone pair
• bond angle of 107° (109.5°-2.5°)

Question 22

What are the non-linear molecules?

Answer 22

• 2 bonded pairs, 1 lone pair
• bond angle of 117.5° (120°- 2.5°)
  OR
• 2 bonded pairs, 2 lone pairs
• bond angle of 104.5° (109.5°- 5°)

Question 23

What is electronegativity?

Answer 23

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

Question 24

What are non-polar bonds?

Answer 24

The difference in electronegativity is 0, bonded electrons are equally distributed

Question 25

When do non-polar bonds occur?

Answer 25

Where the bonding atoms are the same such as H-H and Cl-Cl

Question 26

What are polar covalent bonds?

Answer 26

Where there is a **medium to small difference in electronegativity** between the bonded atoms

Question 27

What happens between the bonded atoms in a polar covalent bond?

Answer 27

There is a permanent dipole across the bond due to the small difference in charge across the bond

Question 28

What happens to the shared electrons in a polar covalent bond?

Answer 28

Bonding electrons are attracted closer to the **more electronegative atom** , electron cloud is more dense

Question 29

What is the general trend for electronegativity in the periodic table?

Answer 29

Electronegativity increases towards the top right of the periodic table (halogens, excluding most noble gases)

Question 30

The **greater the difference in electronegativity** between the bonded atoms…

Answer 30

the **greater** the permanent dipole and the **more polar** the covalent bond.

Question 31

What do polar covalent bonds have in terms of charges?

Answer 31

Slight/Partial charges, represented with a dipole

Question 32

Why do carbon and hydrogen **not form** a polar covalent bond?

Answer 32

There is a very small difference in electronegativity between C and H

Question 33

Why are symmetrical molecules non-polar?

Answer 33

The dipoles cancel out between each polar bond, hence no net dipole across the molecule

Question 34

When are asymmetrical molecules polar?

Answer 34

When they contain one or more polar bonds

Question 35

How can you tell is a molecule is asymmetric?

Answer 35

- has lone pairs - surrounding atoms are not all the same

Question 36

Why are asymmetrical molecules polar?

Answer 36

The dipoles do not cancel out

Question 37

What are intermolecular forces?

Answer 37

Attractive forces **between** molecules which are much **weaker** than ionic or covalent bonds

Question 38

What structures have intermolecular forces?

Answer 38

Covalent structures

Question 39

What are induced dipole-dipole interactions?

Answer 39

**Very weak** intermolecular forces between molecules

Question 40

What are other names for induced dipole-dipole interactions?

Answer 40

- London forces - Dispersion forces

Question 41

Where do induced dipole-dipole interactions exist?

Answer 41

Between **all molecules**, whether polar or non-polar

Question 42

How do induced dipole-dipole arise between molecules?

Answer 42

- At any moment there may be an **uneven distribution of electrons** in a molecule, due to electron movement/change in electron density - This causes a **temporary dipole/instantaneous dipole** to occur - The instantaneous/temporary dipole in one molecule causes an **induced dipole in a neighbouring molecule** - The slightly positive charge of a dipole in one molecule **attracts** the slightly negative charge of a dipole in a neighbouring molecule, producing a **induced dipole-dipole attraction**

Question 43

What are permanent dipole-dipole interactions?

Answer 43

**Weak attractive forces** between **polar molecules**

Question 44

How do permanent dipole-dipole interactions occur?

Answer 44

- A molecule has bonds that are **permanently polar** as one atom is more electronegative than the other and is **asymmetrical** so the dipoles do not cancel each other out - the **slightly positive dipole** of one molecule **attracts** the **slightly negative dipole** of a **neighbouring molecule** to produce the **permanent dipole-dipole force of attraction** between the molecules

Question 45

What can both permanent dipole-dipole interactions and induced dipole-dipole interactions be referred as?

Answer 45

Van der Waals forces

Question 46

What are hydrogen bonds?

Answer 46

**A strong dipole-dipole attraction** between molecules containing O-H, N-H or F-H bonds, the strongest type of intermolecular force of attraction

Question 47

What does the hydrogen bond exist between?

Answer 47

- The slightly positive charge on the hydrogen in one molecule - a lone pair on a highly electronegative atom (O, N, F) on another molecule

Question 48

How do you draw a hydrogen bond? [3 marks]

Answer 48

- labelled atoms (with dipoles) - lone pairs of electrons - dotted line (hydrogen bond)

Question 49

Why does water have anomalous properties of water?

Answer 49

Due to the **hydrogen bonds** between water molecules

Question 50

Why is ice (solid H2O) less dense than liquid water?

Answer 50

- In the solid, H2O molecules are held further apart by the hydrogen bonds - This gives the ice an **open lattice structure** - The H2O molecules are fixed in their positions in the 3D ice crystal lattice by hydrogen bonds

Question 51

Why does water have relatively high melting and boiling points?

Answer 51

- Water has higher than expected melting and boiling points - Hydrogen bonds are relatively strong, therefore stronger than other intermolecular forces - **more energy is needed to break the hydrogen bonds**

Question 52

What does melting and boiling points depend on?

Answer 52

The **structure** and the **strength of the bonds**, which need to be overcome and broken

Question 53

When does a substance have a high melting/boiling point?

Answer 53

The bonds broken are **strong**

Question 54

What is the structure of substances with a high melting/boiling point?

Answer 54

Giant

Question 55

When does a substance have a low melting or boiling point?

Answer 55

When the bonds broken are **weak**

Question 56

What is the structure of substances with a low melting/boiling point?

Answer 56

Simple

Question 57

When is there a sharp decrease in melting and boiling points across a period?

Answer 57

Between group 4 and 5

Question 58

What does the decrease show across the period?

Answer 58

The change from giant structures to simple structures

Question 59

What are the bonds that need to be broken in substances with a high melting or boiling point?

Answer 59

Strong bonds between the particles/atoms

Question 60

What are the bonds that need to be broken in substances with a low melting or boiling point?

Answer 60

Weak **intermolecular** forces between **molecules**

Question 61

What happens to the melting or boiling point across a period from group 1 to group 4?

Answer 61

Increase gradually

Question 62

What are relative to the melting or boiling points across a period from group 5 to group 8?

Answer 62

They are comparatively low