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A-level Chemistry > Structure and Bonding > Flashcards

Structure and Bonding Flashcards

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
why does diamond have a high melting point and is hard
millions of strong covalent bonds between the millions of carbon atoms in the rigid macromolecular structure which requires a lot of energy to break
26
why is diamond non-conductive
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
27
why is diamond insoluble
strong covalent bonds do not break apart as the macromolecular structure is non-polar so the atoms are not attracted to the polar molecule
28
what are the properties of graphite
high melting point conductive soft insoluble
29
shape of graphite and bond angle
trigonal planar 120
30
why does graphite have a high melting point
millions of strong covalent bonds between the millions of carbon atoms in the macromolecular structure which requires a lot of energy to break
31
why is graphite conductive
each carbon atom is covalently bonded to 3 other carbon atoms so has delocalised electrons that can carry a charge throughout the structure
32
why is graphite soft
has a macromolecular structure consisting of layers with weak intermolecular forces between them so can easily slide over one another
33
why is graphite insoluble
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
how does metallic bonding occur
outer shell electrons are donated to the 'sea' of delocalised electrons
35
what is a metallic bond
strong electrostatic attractions between the positive ions and delocalised electrons to form a giant metallic lattice
36
factors affecting strength of metallic bond
charge on ion number of delocalised electrons per positive ion size of ion
37
properties of metallic structures
``` high melting point conductive strong malleable, ductile insoluble ```
38
why do metals have a high melting point
millions of strong electrostatic attractions between the positive ions and delocalised electrons require a lot of energy to break
39
why are metals conductive
there are delocalised electrons which are able to freely move throughout the structure and carry a charge
40
why are metals strong
strong electrostatic attractions extend across the structure
41
why are metals malleable and ductile
positive ions in metals can easily slide over one another as they are arranged in regular, closely packed parallel layers
42
how can metals become harder
add another metal element to form an alloy | different sized ions distort the layers
43
why are metals insoluble
requires a lot of energy to break the electrostatic forces between the positive ions and delocalised electrons
44
electronegativity definition
the power of an atom to attract a pair of electrons in a covalent bond
45
factors affecting electronegativity
nuclear charge atomic radius shielding
46
how does nuclear charge affect electronegativity
higher nuclear charge from more protons | stronger attraction between the nucleus and the bonding pair of electrons
47
how does the atomic radius affect electronegativity
shared pair of electrons are closer to the nucleus so stronger attraction
48
how does shielding affect electronegativity
less shells of electrons between the nucleus and the shared electrons decreases repulsion stronger attraction
49
electronegativity trend down a group
decreases down a group atomic radius increasing more shielding
50
electronegativity trend across a period
increases across a period atomic radius decreases nuclear charge increases same shielding
51
what is a polar covalent bond
between elements of different electronegativities shared electrons are unevenly distributed towards the element with the higher electronegativity elements have partial charges
52
what does charge separation create
permanent dipole-dipole attractions between the polar molecules
53
why do some molecules have polar bonds but is not a polar molecule
bond polarities cancel each other out if the molecule is symmetrical
54
types of intermolecular force
induced dipole-dipole (van der waals) permanent dipole-dipole attraction hydrogen bond
55
what are intermolecular forces between and what do they affect
simple molecules | melting points
56
what are van der waals forces between
between any molecule
57
why are there van der waals
caused by temporary uneven electron distribution from constant movement of electrons δ+ of one molecule is attracted to δ- of another
58
how can van der waals forces be stronger
bigger molecules have stronger van der waals due to more electrons
59
why are molecules with van der waals forces insoluble
non-polar so no interactions | can not form hydrogen bonds with water molecules
60
what are permanent dipole-dipole attractions between
polar molecules
61
why are there permanent dipole-dipole attractions
δ+ of one molecule is attracted to δ- of another | high electron density at the atom with the greatest electronegativity
62
why are there hydrogen bonds
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
what are hydrogen bonds between
δ+H of one molecule and δ-F,O,N of another
64
why are molecules with hydrogen bonds soluble
able to form hydrogen bonds with water molecules
65
order of boiling points of CH4, NH3 and H2O | warum
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
strength of intermolecular forces
hydrogen bond > permanent dipole-dipole attraction > van der waals forces
67
ionic equation to become a cation
X --> X^n+ + ne-
68
ionic equation to become an anion
X + ne- --> X^n-

A-level Chemistry (17 decks)

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