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A-level Chemistry > Structure and Bonding > Flashcards

Structure and Bonding Flashcards

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1
Q

when does ionic bonding occur

A

when a outer shell electrons from a metal atom transfer to fill the outer shell of a non-metal atom

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2
Q

how does an ionic compound form

A 
The metal (magnesium) loses (2) electrons and become cations
The nonmetal (chlorine) each gain one electron and become anions so they all have full outer shell
The positive ions are attracted to the negative ions and have an electrostatic attraction between them
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3
Q

describe the bonding in an ionic compound

A

strong electrostatic attractions between the oppositely charged ions which extend across a giant lattice

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4
Q

coordination number

A

how many negative ions each positive ion is bonded to

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5
Q

factors affecting strength of ionic bonds

A

charge on the ions

size of ions (increase in radius decreases charge density so weaker attraction)

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6
Q

properties of ionic compounds

A 
high melting point
non conductive when solid
conductive when aq/molten
brittle
soluble in water
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7
Q

describe the structure of ionic compounds

A

giant lattice which extends in all directions

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8
Q

why do ionic compounds have a high melting point

A

millions of strong electrostatic attractions between the oppositely charged ions in the giant lattice which require a lot of energy to break

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9
Q

why do ionic compounds not conduct when solid

A

ions are fixed in a giant lattice so the ions are not free to move to their oppositely charged electrode

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10
Q

why do ionic compounds conduct when aq/molten form

A

ions are free to move to their oppositely charged electrode and carry a charge

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11
Q

why are ionic compounds brittle

A

a sharp blow displaces ions so the ions with like charges come in contact with each other causing the structure to shatter

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12
Q

why are ionic compounds soluble in water

A

ions break apart from the giant lattice as water is a polar molecules so can overcome the electrostatic attractions between the oppositely charged ions

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13
Q

how does covalent bonding occur

A

non-metal ions share electrons

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14
Q

examples of molecules with covalent bonding

A

simple molecules

macromolecules

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15
Q

what is dative bonding

A

when the shared pair of electrons come from the same atom
one species must have a lone pair of electrons
other species must have a vacant orbital to accept the lone pair

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16
Q

properties of simple molecules

A

low melting point
non-conductive
weak
insoluble in water

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17
Q

why do simple molecules have a low melting point

A

weak intermolecular forces between the molecules require little energy to break

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18
Q

are there any exceptions to simple molecules having low melting points

A

water has a high melting point for its Mr

has hydrogen bonds between the molecules which are the strongest type of intermolecular force

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19
Q

why are simple molecules non-conductive

A

no free ions or delocalised electrons that could carry a charge

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20
Q

why are simple molecules weak

A

weak intermolecular forces between the molecules require little force to break them apart

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21
Q

why are simple molecules insoluble in water

A

non-polar molecule so no interactions with water

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22
Q

why is ice more dense than water

A

hydrogen bonds hold h2o molecules far apart when solid

broken hydrogen bonds means that the molecules can be closer together

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23
Q

properties of diamond

A

high melting point
hard
non-conductive
insoluble

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24
Q

shape of diamond and bond angle

A

tetrahedral 109.5

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25
Q

why does diamond have a high melting point and is hard

A

millions of strong covalent bonds between the millions of carbon atoms in the rigid macromolecular structure which requires a lot of energy to break

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26
Q

why is diamond non-conductive

A

each carbon atom is bonded to 4 carbon atoms by strong covalent bonds so there are no delocalised electrons that can flow throughout the structure

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27
Q

why is diamond insoluble

A

strong covalent bonds do not break apart as the macromolecular structure is non-polar so the atoms are not attracted to the polar molecule

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28
Q

what are the properties of graphite

A

high melting point
conductive
soft
insoluble

29
Q

shape of graphite and bond angle

A

trigonal planar 120

30
Q

why does graphite have a high melting point

A

millions of strong covalent bonds between the millions of carbon atoms in the macromolecular structure which requires a lot of energy to break

31
Q

why is graphite conductive

A

each carbon atom is covalently bonded to 3 other carbon atoms so has delocalised electrons that can carry a charge throughout the structure

32
Q

why is graphite soft

A

has a macromolecular structure consisting of layers with weak intermolecular forces between them so can easily slide over one another

33
Q

why is graphite insoluble

A

attraction to the polar water molecules is weaker than the strong covalent bonds between the carbon atoms so they don’t break apart
can not form hydrogen bonds with water

34
Q

how does metallic bonding occur

A

outer shell electrons are donated to the ‘sea’ of delocalised electrons

35
Q

what is a metallic bond

A

strong electrostatic attractions between the positive ions and delocalised electrons to form a giant metallic lattice

36
Q

factors affecting strength of metallic bond

A

charge on ion
number of delocalised electrons per positive ion
size of ion

37
Q

properties of metallic structures

A 
high melting point
conductive
strong
malleable, ductile
insoluble
38
Q

why do metals have a high melting point

A

millions of strong electrostatic attractions between the positive ions and delocalised electrons require a lot of energy to break

39
Q

why are metals conductive

A

there are delocalised electrons which are able to freely move throughout the structure and carry a charge

40
Q

why are metals strong

A

strong electrostatic attractions extend across the structure

41
Q

why are metals malleable and ductile

A

positive ions in metals can easily slide over one another as they are arranged in regular, closely packed parallel layers

42
Q

how can metals become harder

A

add another metal element to form an alloy

different sized ions distort the layers

43
Q

why are metals insoluble

A

requires a lot of energy to break the electrostatic forces between the positive ions and delocalised electrons

44
Q

electronegativity definition

A

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

45
Q

factors affecting electronegativity

A

nuclear charge
atomic radius
shielding

46
Q

how does nuclear charge affect electronegativity

A

higher nuclear charge from more protons

stronger attraction between the nucleus and the bonding pair of electrons

47
Q

how does the atomic radius affect electronegativity

A

shared pair of electrons are closer to the nucleus so stronger attraction

48
Q

how does shielding affect electronegativity

A

less shells of electrons between the nucleus and the shared electrons decreases repulsion
stronger attraction

49
Q

electronegativity trend down a group

A

decreases down a group
atomic radius increasing
more shielding

50
Q

electronegativity trend across a period

A

increases across a period
atomic radius decreases
nuclear charge increases
same shielding

51
Q

what is a polar covalent bond

A

between elements of different electronegativities
shared electrons are unevenly distributed towards the element with the higher electronegativity
elements have partial charges

52
Q

what does charge separation create

A

permanent dipole-dipole attractions between the polar molecules

53
Q

why do some molecules have polar bonds but is not a polar molecule

A

bond polarities cancel each other out if the molecule is symmetrical

54
Q

types of intermolecular force

A

induced dipole-dipole (van der waals)
permanent dipole-dipole attraction
hydrogen bond

55
Q

what are intermolecular forces between and what do they affect

A

simple molecules

melting points

56
Q

what are van der waals forces between

A

between any molecule

57
Q

why are there van der waals

A

caused by temporary uneven electron distribution from constant movement of electrons
δ+ of one molecule is attracted to δ- of another

58
Q

how can van der waals forces be stronger

A

bigger molecules have stronger van der waals due to more electrons

59
Q

why are molecules with van der waals forces insoluble

A

non-polar so no interactions

can not form hydrogen bonds with water molecules

60
Q

what are permanent dipole-dipole attractions between

A

polar molecules

61
Q

why are there permanent dipole-dipole attractions

A

δ+ of one molecule is attracted to δ- of another

high electron density at the atom with the greatest electronegativity

62
Q

why are there hydrogen bonds

A

exposed nucleus of δ+H of one molecule is attacted to a lone pair of electrons of δ-F,O,N of another molecule
must have a large difference in electronegativity so the bond is very polar

63
Q

what are hydrogen bonds between

A

δ+H of one molecule and δ-F,O,N of another

64
Q

why are molecules with hydrogen bonds soluble

A

able to form hydrogen bonds with water molecules

65
Q

order of boiling points of CH4, NH3 and H2O

warum

A

H2O > HF > NH3
H2O has equal numbers of lone pairs as δ+H so can all hydrogen bond
N is not as electronegative as F or O so hydrogen bonds are not as strong

66
Q

strength of intermolecular forces

A

hydrogen bond > permanent dipole-dipole attraction > van der waals forces

67
Q

ionic equation to become a cation

A

X –> X^n+ + ne-

68
Q

ionic equation to become an anion

A

X + ne- –> X^n-

A-level Chemistry (17 decks)

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