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Chem 2 (2.2 Electrons, Bonding & Structure) > 2.2.2 Electronegativity + Bond Polarity > Flashcards

2.2.2 Electronegativity + Bond Polarity Flashcards

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1
Q

Why aren’t all covalent bonds symmetrical (rarely equally shared)

A

As atoms have different electronegativities

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2
Q

What’s electronegativity

A

The power of an atom to withdraw electron density toward itself from a covalent bond (pull electrons toward itself in a covalent bond)

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3
Q

How does EN increase on the periodic table

A

Going up a group

going right across a period

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4
Q

What part of the periodic table has the most electronegativity
What’s the element with most EN

A

Top right

F (4.0)

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5
Q

How does electronegativity increase

Why

A

From left -> right
As the nuclear charge increases, the shielding of outer electrons remains the same but the attraction of the bond pair to the nucleus increases

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6
Q

What are non-polar bonds

A

If 2 atoms at the end of a covalent bond have similar electronegativities (small difference), electrons mostly stay in the middle as there’s little electron density distortion

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7
Q

What’s a polar bond

A

A covalent bond where the electron pair distribution isn’t symmetrical

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8
Q

How’s a polar bond formed

A

If 1 atom in a covalent bond is more EN than the other, the more En atom draws the electron density towards itself and get partially negatively charged (d-).

The other atom becomes partially positively charged (d+) as it’s now short of electron density

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9
Q

What can a polar bond be shown as

What is this

A

A ‘bond dipole’
Combination of a + and an arrow

+ - d+
Arrow - d-

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10
Q

What charge does the more EN atom get in a polar bond

A

Partially negative charge (d-)

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11
Q

What 4 elements covalently bonded to another atom usually form a polar bond

A

N
O
F
Cl

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12
Q

What are dipole moments

A

Directions in which polar bonds move (overall polarity)

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13
Q

Why would CO2 and CCl4 not have dipole moments

A

As the bonding dipole effect acts with equal force in opposite directions, cancelling out

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14
Q

What leaves open the possibility of permanent dipole-dipole forces forming

A

If there’s a large difference in electronegativity of 2 atoms in a covalent bond , the bond will be polar and contain d- and d+ regions

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15
Q

What directions to dipole moments go in

A

d+ -> d-

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16
Q

What molecules do intermolecular forces of attraction only occur between

E.g

A

Simple covalently-bonded molecules

E.g ethanol

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17
Q

What happens to the IMFs when a substance melts/boils

What bonds can’t do this as they’re too strong

A

IMFs break

Covalent bonds are too strong

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18
Q

What are IMFs of attraction like compared to covalent bonds

A

Very weak

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19
Q

What must be refer the first 2 types of IMFs as instead of bonds and why
What are they

A

Must refer to them as interactions as they’re so weak

Induced dipole-dipole interactions (very,very weak)
Permanent dipole-dipole interactions (very weak)

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20
Q

What are the 3 types of IMFs in order of weakest to strongest

A

Induced dipole-dipole interactions
Permanent dipole-dipole interactions
Hydrogen bonding

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21
Q

What are IDDI

A

The d- region of 1 atom weakly attracting the d+ region of another

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22
Q

What IMF is present in all atoms + molecules all the time

A

IDDI

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23
Q

What atom has the strongest IDDI

Why

A

Larger atom

As will have more electrons

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24
Q

What IMFs are only temporary

A

IDDI

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25
What molecules do permanent dipole-dipole interactions act between E.g
Molecules with permanent dipoles (dipole moments) E.g HCl, H2O
26
What are permanent dipole-dipole interactions like compared to IDDI A covalent bond
Stronger than IDDI | Very weak compared to a covalent bond
27
When’s does hydrogen bonding occur
When hydrogen is directly bonded to a very EN atom
28
3 atoms hydrogen bonding occurs between
N O F
29
What must there be on the N, O or F for hydrogen bonding to occur
A lone pair
30
What’s hydrogen bonding formed from
The lone pair of electrons on 1 molecule to a H on an adjacent molecule
31
What’s the strongest IMF
Hydrogen bonding
32
What happens in water when it boils
The O-H covalent bonds don’t break, the hydrogen bonds between water molecules do
33
What does water turn to when it’s boiled and hydrogen bonds are broken
Stream
34
3 factors that affect electronegativity
Nuclear charge (no. of protons) Shielding Atomic radius
35
How does nuclear charge affect EN
More protons -> stronger attraction of electrons to positive nuclei
36
How does shielding affect EN
More shells -> weaker attraction
37
How does atomic radius affect EN
Smaller atomic radius (closer bonding pair to nucleus) -> stronger attraction
38
Why does En decrease down a group (2)
More shielding so less positive attraction from nuclei can be felt Atom gets bigger
39
Why does EN increase across a period (3)
Nuclear charge increases (protons) Atom gets smaller Stronger attraction between bonding pair and nucleus
40
What does hydrogen bonding affect
Boiling points
41
What molecules are easier to boil
Non-polar molecules that don’t contain N, O or F
42
What’s the boiling point like for a molecules with hydrogen bonding
High
43
What’s water MP + BP like and why (2)
High due to: It’s size + Mr The hydrogen bonds that need more energy to break
44
What formations are molecules in ice arranged in
Tetrahedral formations
45
When do hydrogen bonds become fixed in water
Not when waters a liquid only when it cools to ice
46
Why does ice float on water
As it’s less dense than liquid water due to having long hydrogen bonds that cause water molecules in the ice lattice to pack further apart
47
What are hydrogen bonds responsible for in biology
For holding the 2 helices in DNA Strong - hold 2 strands together between replications Weak - to break 1 by 1 to allow it to unwind for copying during transcription
48
What are the 2 types of covalent structures
``` Simple (molecular) lattice structures Giant covalent (macromolecular) lattice structures ```
49
Common example of a simple (molecular) lattice structure
Iodine - I2
50
How strong are simple (molecular) lattice structures
Soft and easy to break
51
What’s the melting and boiling point of simple (molecular) lattice structures like
Low melting point and boiling point | Sublimed easily with barely any heat (solid->gas)
52
Do simple (molecular) lattice structures conduct electricity? Why
No | There aren’t any charged particles to carry current
53
What are the forces and bonds like in simple (molecular) lattice structures
``` Long IDDI (London forces) Short covalent bonds ```
54
3 examples of giant covalent (macromolecular) lattice structures
Diamond Graphite Silicon dioxide (sand)
55
What’s the structure of diamond like (3)
3D Each carbon bonds to 4 others Each carbon has a tetrahedral structure
56
What’s the strength and melting point like of diamond? Why?
Hard | High MP as many strong covalent bonds must be broken to separate atoms (macromolecular)
57
Does diamond conduct electricity? Why?
Doesn’t conduct electricity as particles are fixed and don’t have a charge
58
What’s the structure of graphite like (2)
Has layers of carbon atoms | Each C covalently bonded to 3 others
59
What is between the layers of graphite? | What does this allow them to do
Weak London forces | Allow them to side over each other and behave as lubricant
60
Does graphite conduct electricity | Why
Yes | As it has delocalised electrons between layers
61
What’s the strength + melting point like of graphite | Why
High MP due to strong covalent bonds (macromolecular) | Soft due to weak IDDI
62
What’s graphene and its structure
A single layer of graphite | Hexagonally arranged carbon atoms linked by strong covalent bonds
63
What 2 things does graphene conduct | What’s its thickness and strength like
Conducts electricity + copper | Thinnest + strongest material ever made
64
What structure is silicon dioxide (sand) similar to | What’s the exception
Similar to diamond structure | Except oxygen atoms are covalently bonded between silicon atoms
65
What properties is silicon dioxide similar to
Diamond
66
What structure won’t dissolve in water and will conduct at all states
Metallic
67
What happens to particles in a solid when heating it
They vibrate more about a fixed position, causing temperatures to rise Slightly expand as particles move apart
68
What does heat break when turning a solid to a liquid | So what’s the temperature like at melting point
Heat breaks forces between particles | Temperature is constant at melting point
69
Why does temperature rise more when heating a liquid | Why does expansion occur again
At heat supplied gives liquid particles more kinetic energy to move faster causing rise in temperature Expansion occurs as particles move apart slightly more
70
When a liquid is turning to a gas what does the heat do | What’s temperature like at boiling point
Breaks all intermolecular forces between particles | So temperature is constant at boiling point
71
Why does temperature rise further when heating a gas
As heat supplied is used to increase speed (kinetic) energy of gas particles Expanding gas rapidly as particles again move apart

Chem 2 (2.2 Electrons, Bonding & Structure) (4 decks)

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