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Chemistry > Chapter 3 - Bonding > Flashcards

Chapter 3 - Bonding Flashcards

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1
Q

Describe the structure of ionic crystals

A

Ionic lattice structure with positive (cations) and negative (anions)

E.g. Each Na+ ions and Cl-

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2
Q

Describe the bonding present in ionic structures

A

Formed because of a transfer of e- from metal to the non-metal

Ionic bonds have STRONG ELECTROSTATIC attractions BETWEEN oppositely charged ions

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3
Q

What is the melting point of ionic structures?

A

High mp. because of the large number of strong electrostatic attraction between + and - charged ions, meaning the energy required to overcome these bonds is high

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4
Q

Do ionic structures conduct electricity?

A

Only when molten or in aq solution because the ions are free to move and carry charge

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5
Q

Are ionic substances soluble in water and why?

A

Yes

Because water is polar, the negative parts of the water are attracted to the positive metal ions and vice versa

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6
Q

The (smaller/larger) the ion and the (lower/higher) the charge on the ions the stronger the ionic bond

A

smaller

Higher

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7
Q

Positive ions are usually (larger/smaller) than the atoms from which they are formed

Negative ions are usually (larger/smaller)

A

Smaller

Larger

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8
Q

Give the formula for hydrogen carbonate, carbonate, ammonium, nitrate

A

(HCO3)- (CO3)2- (NH4)+ (NO3)-

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9
Q

Define a metallic bond

A

The electrostatic attraction between the sea of delocalised electrons and the positive metal ions in the lattice

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10
Q

Metals have (high/low) densities

A

High

Positive ions are packed tightly together

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11
Q

Why do metals conduct electricity?

A

In the sea of delocalised electrons the electrons are free to move, electric current flows because of the movement of electrons

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12
Q

Suggest why metals conduct heat

A

Because in the sea of delocalised e- the e- are close enough to transfer heat

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13
Q

Why are metals ductile and malleable?

A

Layered structure of the lattice, the layers can slide over one another without disrupting the bond

Top layer moves with the force applied to it

Strong attraction btwn sea of delocalised e- and positive metal ions holds the structure together

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14
Q

Most metals have (low/high) melting points

A

High
Relatively large regular structure with strong forces of attraction between the positive ions and delocalised electrons

This force of attraction has to be overcome which requires a lot of energy

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15
Q

What are the similarities and differences between simple molecular and macromolecular?

A

Both contain covalent bonds

Macromolecular are giant/larger

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16
Q

What are molecular covalent crystals? and give 2 examples

A

Solid molecular substances that form crystallin structures, don’t conduct electricity

e.g. iodine and ice due to the attractions

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17
Q

Name 3 properties of molecular covalent crystals

A

Low melting points
Brittle bc they don’t have strong bonds holding together like other crystalline substances
Don’t conduct electricity bc they have no charged free particles

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18
Q

Give 2 examples of macromolecular substances

A

Diamond

Graphite

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19
Q

What are allotropes?

A

Different forms of the same element in the same physical state (e.g. 2 allotropes of carbon are diamond and graphite

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20
Q

Describe the properties of diamond

A

has many strong cov bonds and rigid 3D structure

Very high melting point, bc of strong cov b which require a lot of energy to break

Each C atom is strongly bonded to four others in a tetrahedral arrangement

Bond angle 109.5

Don’t conduct heat or electricity as no charged particles that can move

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21
Q

Describe the main properties of graphite

A
  • Conducts electricity due to delocalised electrons between the layers which can move and carry charge
  • V high mp bc of its many strong covalent bonds which require a lot of energy to break
  • Flaky as the force of attraction between the layers of carbon are weak so can be broken easily allowing layers to slide over each other
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22
Q

Describe the structure of graphite

A

Layered structure with weak forces of attraction between the layers

Each C atoms is bonded to 3 others in hexagonal arrangement w bond angle 120

Each C atom have 4 unpaired electrons so can form 4 covalent bonds

In diamond the 4th electron is used to bond but in graphite the 4th is used as a free electron

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23
Q

What are the TYPES of crystalline substances?

A

Metals
Ionic Compounds
Simple molecular
Macromolecular

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24
Q

Define electronegativity

A

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

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25
What are the factors affecting electronegativity?
1. Atomic radius 2. Atomic number 3. Shielding
26
What are the trends in electronegativity
Increases across a period - Atomic radius decreases across a period, giving progressively stronger attraction between the positive nucleus and the two e- in the cov bond -Nuclear charge increases across a period, increasing attraction for the electrons Decreases down a group - Atomic radius increases down a group, giving progressively weaker attraction btwn positive nucleus and cov bond electrons - Shielding increases down a group
27
The greater the electronegativity difference the (more/less) polar the bond
More
28
A large difference in electronegativity means...
An ionic bond
29
A smaller difference means ...
polar covalent bond (e.g. HCl)
30
No difference or a very small difference in electronegativity means....
Non-polar covalent bond (e.g. H2)
31
Put these in order of the greatest to weakest force: | lp-lp repulsion, bp-bp repulsion, lp-bp repulsion
lp-lp repulsion lp-bp repulsion bp-bp repulsion
32
What are intermolecular forces?
Attractive forces between covalent molecules
33
What are the 3 types of intermolecular forces and put them in order from weakest to strongest
Van der Waal Permanent dp dp Hydrogen bonds
34
How can a molecule be non-polar but contain polar bonds?
The polarity of its bonds may cancel out (.e.g CO2)
35
How do induced dipole dipole (vdwf) arise?
1. The movement of electrons in the shells unbalances the distribution of the charge in the electron shells 2. The uneven distribution of e- forms a temporary dipole in one molecule 3. The temporary dipole induces a dipole in the neighbouring molecule which then induces further molecules 4. The induced dipole dipole attract each other forming weak intermolecular forces 5. Delta + end of dipole in one molecule will attract the Delta - end
36
The greater/smaller the Mr of an atom or molecule the greater the stronger the van der Waal forces there are
Greater, bc greater number of electrons and therefore the stronger the vwfs between the atoms/molecules
37
Why do large non-polar molecules have a lot of van der Waals?
Because e.g. polymers have a high Mr but also a large surface area which means they have a lot of points of contact for the van der Waal forces to form
38
Do straight chain or branched have more van der Waal forces?
Straight | Molecules can be packed closely so more SA for van der Waals to form
39
All molecules have .... between the molecules | All polar molecules have ....
van der Waals | Permanent dipole dipole
40
Why do all polar molecules have permanent dipole dipole forces?
Bc of the attraction between the delta - end of the permanent dipole of one molecule and the neg end attract
41
When can hydrogen bonding occur?
When a H atom is directly attached via a covalent bond to an N, O or F atom A particular type of permanent dipole dipole bond
42
Why do the boiling points of the group 6 hydride increase?
``` Down group atomic radius increases Size of molecule increases More electrons More vdwf between molecules More energy needed ```
43
Why is the boiling point of water much higher than all the other group 6 hydrides? (2 marks)
- Because water is polar molecule - Has van der Waal forces and can hydrogen bond as there are H bonds between the water molecules - Hydrogen bonds are strong
44
Explain the following order of boiling points H2O -> HF -> NH3
- Fluorine is more e/n than nitrogen, the H-F bonds are more polar than N-H due to partial charges of the H and F, a hydrogen bond - Increased partial positive charge therefore lp on F is more strongly attracted to the H - Hydrogen bond between the H-F molecule is stronger than NH3
45
The boiling point of HF and NH3 are also much higher than all the group 7 and group 5 hydrides. Why do CH4 not follow the pattern?
- Because H-F and N-H3 are polar molecules and have van der Waal forces as well as hydrogen bonding - In the fluorine the lp are strongly attracted to the H, the hydrogen bonding is the strongest form of intermolecular forces therefore requires a lot of energy to break - CH4 is not polar and cannot hydrogen bond, has van der Waal forces, which are the weakest bonds therefore don't require a lot of energy to break
46
Name the steps in drawing the shape of molecule
w
47
Name of 2 bp 0lp
Linear (e.g. BeCl2) 180
48
3 bp and 0lp
Trigonal planar | -120
49
What is bent?
``` 2bp and 1lp -118 Or 2bp and 2lp -104.5 ```
50
What is 4bp and 0lp
Tetrahedral | 109.5
51
What is 3bp and 1lp
Trigonal pyramidal | 107
52
What is trigonal bipyramidal?
5bp and 0lp | -90 and 120
53
What is trigonal pyramidal/see-saw
4bp and 1 lp | -89 and 119
54
What is 3bp and 2lp
Trigonal planar | -120 0r 89 (T-shape)
55
What is octahedral?
6 bp and 0lp | -90
56
What is 5bp and 1lp
Square pyramid | -89
57
What is 4bp and 2lp
Square planar | -90
58
Draw and name the shape of NH4+
Tetrahedral
59
Draw and name the shape of XeF4
Square planar
60
Draw and name the shape of SF4
Trigonal bipyramidal
61
Why does ice have a lower density than water?
Because when water freezes the hydrogen bonds are more in a open 3D structure, molecules are further apart from each other
62
Why is ethanol soluble in water?
Because the water can form hydrogen bonds with ethanol molecules
63
Why does ethanol have a higher bp than expected
Because of hydrogen bonds between hydrogen molecules, whereas only forces of attraction between propane molecules are van der Waals
64
Which groups of elements are non-polar?
Halogens and Noble gases
65
What is a coordinate bond?
Bond that contains shared pair of electrons with both electrons supplied by one atom
66
Give an example of a molecule with a coordinate bond
Ammonium ion NH4+ When NH3 reacts with BF3 BF4- formed from BF3 and F-
67
When can dative bonding take place?
When an atom which has a lone pair of electrons bonds to another atom which has an empty orbital
68
Explain how the strongest type of intermolecular force arises between two molecules of ammonia (3 marks) (H=2.1 N=3.0)
- Large electronegativity difference, 0.9 (have to calc difference) - Forms a N delta - and H+ - Lone pair on N attracts the H+
69
In terms of electron pairs explain why the bond angles in NH4+ are all 109
- 4 bonding electron pairs - Repel equally - Repel as far apart as possible - Tetrahedral
70
Explain why the O-H bond in methanol molecule is polar
- Oxygen is more electronegative than hydrogen | - Causes higher electron density round oxygen atoms

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