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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
Q

What molecules do permanent dipole-dipole interactions act between

E.g

A

Molecules with permanent dipoles (dipole moments)

E.g HCl, H2O

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26
Q

What are permanent dipole-dipole interactions like compared to IDDI
A covalent bond

A

Stronger than IDDI

Very weak compared to a covalent bond

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27
Q

When’s does hydrogen bonding occur

A

When hydrogen is directly bonded to a very EN atom

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28
Q

3 atoms hydrogen bonding occurs between

A

N
O
F

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29
Q

What must there be on the N, O or F for hydrogen bonding to occur

A

A lone pair

30
Q

What’s hydrogen bonding formed from

A

The lone pair of electrons on 1 molecule to a H on an adjacent molecule

31
Q

What’s the strongest IMF

A

Hydrogen bonding

32
Q

What happens in water when it boils

A

The O-H covalent bonds don’t break, the hydrogen bonds between water molecules do

33
Q

What does water turn to when it’s boiled and hydrogen bonds are broken

A

Stream

34
Q

3 factors that affect electronegativity

A

Nuclear charge (no. of protons)
Shielding
Atomic radius

35
Q

How does nuclear charge affect EN

A

More protons -> stronger attraction of electrons to positive nuclei

36
Q

How does shielding affect EN

A

More shells -> weaker attraction

37
Q

How does atomic radius affect EN

A

Smaller atomic radius (closer bonding pair to nucleus) -> stronger attraction

38
Q

Why does En decrease down a group (2)

A

More shielding so less positive attraction from nuclei can be felt
Atom gets bigger

39
Q

Why does EN increase across a period (3)

A

Nuclear charge increases (protons)
Atom gets smaller
Stronger attraction between bonding pair and nucleus

40
Q

What does hydrogen bonding affect

A

Boiling points

41
Q

What molecules are easier to boil

A

Non-polar molecules that don’t contain N, O or F

42
Q

What’s the boiling point like for a molecules with hydrogen bonding

A

High

43
Q

What’s water MP + BP like and why (2)

A

High due to:
It’s size + Mr
The hydrogen bonds that need more energy to break

44
Q

What formations are molecules in ice arranged in

A

Tetrahedral formations

45
Q

When do hydrogen bonds become fixed in water

A

Not when waters a liquid only when it cools to ice

46
Q

Why does ice float on water

A

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
Q

What are hydrogen bonds responsible for in biology

A

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
Q

What are the 2 types of covalent structures

A 
Simple (molecular) lattice structures
Giant covalent (macromolecular) lattice structures
49
Q

Common example of a simple (molecular) lattice structure

A

Iodine - I2

50
Q

How strong are simple (molecular) lattice structures

A

Soft and easy to break

51
Q

What’s the melting and boiling point of simple (molecular) lattice structures like

A

Low melting point and boiling point

Sublimed easily with barely any heat (solid->gas)

52
Q

Do simple (molecular) lattice structures conduct electricity? Why

A

No

There aren’t any charged particles to carry current

53
Q

What are the forces and bonds like in simple (molecular) lattice structures

A 
Long IDDI (London forces)
Short covalent bonds
54
Q

3 examples of giant covalent (macromolecular) lattice structures

A

Diamond
Graphite
Silicon dioxide (sand)

55
Q

What’s the structure of diamond like (3)

A

3D
Each carbon bonds to 4 others
Each carbon has a tetrahedral structure

56
Q

What’s the strength and melting point like of diamond? Why?

A

Hard

High MP as many strong covalent bonds must be broken to separate atoms (macromolecular)

57
Q

Does diamond conduct electricity? Why?

A

Doesn’t conduct electricity as particles are fixed and don’t have a charge

58
Q

What’s the structure of graphite like (2)

A

Has layers of carbon atoms

Each C covalently bonded to 3 others

59
Q

What is between the layers of graphite?

What does this allow them to do

A

Weak London forces

Allow them to side over each other and behave as lubricant

60
Q

Does graphite conduct electricity

Why

A

Yes

As it has delocalised electrons between layers

61
Q

What’s the strength + melting point like of graphite

Why

A

High MP due to strong covalent bonds (macromolecular)

Soft due to weak IDDI

62
Q

What’s graphene and its structure

A

A single layer of graphite

Hexagonally arranged carbon atoms linked by strong covalent bonds

63
Q

What 2 things does graphene conduct

What’s its thickness and strength like

A

Conducts electricity + copper

Thinnest + strongest material ever made

64
Q

What structure is silicon dioxide (sand) similar to

What’s the exception

A

Similar to diamond structure

Except oxygen atoms are covalently bonded between silicon atoms

65
Q

What properties is silicon dioxide similar to

A

Diamond

66
Q

What structure won’t dissolve in water and will conduct at all states

A

Metallic

67
Q

What happens to particles in a solid when heating it

A

They vibrate more about a fixed position, causing temperatures to rise
Slightly expand as particles move apart

68
Q

What does heat break when turning a solid to a liquid

So what’s the temperature like at melting point

A

Heat breaks forces between particles

Temperature is constant at melting point

69
Q

Why does temperature rise more when heating a liquid

Why does expansion occur again

A

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
Q

When a liquid is turning to a gas what does the heat do

What’s temperature like at boiling point

A

Breaks all intermolecular forces between particles

So temperature is constant at boiling point

71
Q

Why does temperature rise further when heating a gas

A

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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