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Alevel Chemistry Edexcel > Topic 2 - Bonding and Structure > Flashcards

Topic 2 - Bonding and Structure Flashcards

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1
Q

What is ionic bonding?

A

the strong electrostatic attraction between oppositely charged ions
-metal atoms (become cations) give electrons to non-metal atoms (become anions)

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2
Q

What factors affect the strength of an ionic bond?

A
  • ionic radius

- charge

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3
Q

How does ionic radii affect the strength of an ionic bond?

A

as ionic radii increases, the strength of the bond decreases

smaller ions = greater attraction

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4
Q

How does charge affect the strength of an ionic bond?

A

as charge increases, the strength of the bond increases

higher charge = great attraction

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5
Q

How does an atom become a cation?

A

by loosing (giving away) electrons so that it becomes positively charged

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6
Q

How does an atom become an anion?

A

by gaining electrons so that it becomes negatively charged

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7
Q

What is the trend in ionic radii down a group and for a set of isoelectronic ions and why?

A

number of protons increases down the group/set of isoelectronic ions
meaning that the electrons get pulled in more closely
∴ ionic radii decreases

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8
Q

What is the evidence for the existence of ions?

A

the migration of ions
eg. using copper sulfate in a u-tube -blue Cu 2+ ions migrate towards cathode
using potassium manganate crystals -purple MnO4 - ions (manganate ions) migrate towards positive ions

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9
Q

What is covalent bonding?

A

the strong electrostatic attraction between two nuclei and the shared pair of electrons between them
-overlap of orbitals where there is a shared area of electron density

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10
Q

What is a sigma bond?

A

strongest type of covalent bond formed by the overlap of s/p orbitals or 2 p orbitals end-to-end

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11
Q

What is a pi bond?

A

weaker type of covalent bond formed by the overlap of p orbitals side-to-side
-only exist when a sigma bond is present too

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12
Q

What is the relationship of bond strength and bond length in covalent bonds?

A

the larger the bond (greater the distance between the two nuclei), the weaker the bond

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13
Q

What is a dative covalent bond?

A

a covalent bond where more bonding electrons come from one atom in the bond than the other

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14
Q

Name some examples of molecules containing a dative bond

A

Al2Cl6

ammonium ion NH4 +

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15
Q

What is the linear shape of molecules?

A

2 bonding pairs of electrons and 0 long pairs of electrons

  • bond angle 180°
    eg. CO2 BeCl2
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16
Q

What is the trigonal planar shape of molecules?

A

3 bonding pairs of electrons and 0 long pairs of electrons

  • bond angle 120°
    eg. BCl3
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17
Q

What is the tetrahedral shape of molecules?

A

4 bonding pairs of electrons and 0 long pairs of electrons

  • bond angle 109.5°
    eg. CH4
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18
Q

What is the V-shaped shape of molecules?

A

2 bonding pairs of electrons and 2 long pairs of electrons

  • bond angle 104.5°
    eg. H2O
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19
Q

What is the pyramidal shape of molecules?

A

3 bonding pairs of electrons and 1 long pairs of electrons

  • bond angle 107.5°
    eg. NH3
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20
Q

What is the trigonal bipyramidal shape of molecules?

A

5 bonding pairs of electrons and 0 long pairs of electrons

  • bond angle 120° and 90°
    eg. PCl5
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21
Q

What is the octahedral shape of molecules?

A

6 bonding pairs of electrons and 0 long pairs of electrons

  • bond angle 90°
    eg. SF6
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22
Q

What is the shape of a simple molecule or ion is determined by?

A

the repulsion between the electron pairs that surround a central atom

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23
Q

Name an example of a linear molecule

A

CO2 BeCl2

24
Q

Name an example of a trigonal planar molecule

A

BCl3

25
Q

Name an example of a tetrahedral molecule

A

CH4

26
Q

Name an example of a pyramidal molecule

A

NH3

27
Q

Name an example of a V-shaped molecule

A

H2O

28
Q

Name an example of a trigonal bipyramidal molecule

A

PCl5

29
Q

Name an example of an octahedral molecule

A

SF6

30
Q

What is electronegativity?

A

the ability of an atom to attract the bonding electrons in a covalent bond

31
Q

What is created when there is a significant difference in electronegativity?

A

a permanent dipole (separation of charges)

-bond is polar

32
Q

Why is a molecule (like carbon dioxide) not polar even though it has polar bonds?

A

the molecule is symmetrical (in all directions) so the dipoles cancel
-there is an even pull of electrons in opposite directions

33
Q

What are the four types of ionic/covalent bonding?

A
  • pure covalent
  • polar covalent
  • ionic with covalent character
  • pure ionic
34
Q

Describe a pure covalent bond

A

no difference in electronegativity at all so no permanent dipole
eg. O2, Cl2, etc (diatomic molecules with two of the same atoms)

35
Q

Describe a polar covalent bond

A

some difference in electronegativity, giving a dipole

eg. O-H, N-H, etc

36
Q

Describe a pure ionic bond

A

zero overlapping of orbitals (sharing of electrons)

  • 2 opposite ions are completely separate entities
    eg. CsF
37
Q

Describe an ionic bond with covalent character

A

where the anion’s electron cloud is distorted by the cation’s polarising power (due to its high charge density -high charge and small radius)

  • the higher the charge density of the cation (and larger the anion), the more the anion’s electron cloud can be distorted, giving rise to covalent character
    eg. CaBr2, BeI3, MgBr2, etc
38
Q

What are the three types of intermolecular forces?

A 
London forces (weakest)
Permanent dipole interactions
Hydrogen bonds (strongest)
39
Q

How is a London force created?

A

(instantaneous induced-dipole induced-dipole interactions)

  • bonding electrons are constantly moving randomly so a small temporary dipole could be created
  • this induces a temporary dipole in a neighbouring molecule (which can induce another, etc)
  • dipoles are weak and constantly changing ∴ are very weak
40
Q

What affects the strength of London forces?

A

-number of electrons
-size of molecules
(electrons can move over a larger area -temporary dipole is bigger and stronger)
-shape of molecules
(longer, thinner molecules make stronger London forces -electron movement can occur over larger SA and the molecules can lie closer together)

41
Q

How is a permanent dipole interaction created?

A

if a molecule contains atoms where there is a significant difference in electronegativity, there will be a permanent dipole
-there is an attraction between the 𝛿+ end of one molecule and the 𝛿- end of another

42
Q

How is hydrogen bonding created?

A

forms between a N, O or F atom and a H atom (which is itself bonded to a N, O or F atom)
-creates a very significant dipole which creates attraction between the molecules

43
Q

How do the strengths of permanent dipole interactions and London forces compare?

A
  • PD is generally stronger
  • unless the molecule is particularly big -in larger molecules, movement of electrons within the whole molecules creates London forces that are stronger than the permanent dipole at one end of the molecule
44
Q

Why is ice less dense than liquid water?

A
  • when water molecules hydrogen bond together, it forms a lattice-like structure
  • there are gaps/empty spaces
  • making it less dense (and therefore is able to float on water)
45
Q

Why does water have a relatively high melting temperature and boiling temperature?

A

water molecules can hydrogen bond with eachother which requires a lot of energy to overcome

46
Q

Why do the boiling points of alkanes increase as chain length increases?

A
  • stronger London forces which require more energy to break

- the molecules are larger and there are more electrons meaning that there induced dipoles are stronger

47
Q

What effect does branching in the carbon chain in alkanes have on their boiling temperatures?

A
  • decreasing boiling point
  • have a smaller surface area
  • weaker London forces
48
Q

Why do alcohols have higher boiling points than an alkane with the same carbon length?

A
  • alkanes can only form London forces
  • alcohols form London forces and hydrogen bonds (because of their OH)
  • hydrogen bonds are stronger than London forces so require more energy to break
49
Q

What happens when an ionic lattice dissolves in water?

A
  • energy is required to break ionic lattice (endothermic process)
  • H20 molecules are interacting with eachother by hydrogen bonds
  • oppositely charged ions become surrounded by water molecules and an ion-dipole interaction is formed
  • this interaction between 𝛿- in water and positive ion releases energy (exothermic process)
  • this is known as hydration energy
50
Q

Why is a short-chained alcohol soluble in water but a long-chained alcohol is not?

A
  • short-chained alcohol can hydrogen bond with water molecules (due to their OH group)
  • longer chains are hydrophobic and disrupt potential hydrogen bonds
51
Q

What is metallic bonding?

A

the strong electrostatic attraction between metal ions and the delocalised electrons

52
Q

Describe giant covalent lattices

A
  • strong covalent bonds
  • high mp
  • doesn’t conduct electricity (except graphite which has delocalised electrons that can carry charge)
    eg. diamond, silicon oxide, graphite
53
Q

Describe giant ionic lattices

A
  • ionic bonds
  • ions are surrounded by oppositely charged ions in all directions
  • strong electrostatic attractions
  • high mp
  • conducts when molten/aqueous (ions can carry the charge) but not as solid
    eg. NaCl, MgO
54
Q

Describe giant metallic lattices

A
  • strong metallic bonding
  • a lattice of positive ions surrounded by a sea of delocalised electrons
  • conducts (due to delocalised electrons which can carry charge)
  • high mp
55
Q

Describe simple molecules

A
  • covalent bonds
  • weak intermolecular forces (London, PD, H bonds)
  • low mp/bp
  • don’t conduct
    eg. I2, H2O, etc.

Alevel Chemistry Edexcel (19 decks)

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