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Chemistry A Level > Bonding and Structure > Flashcards

Bonding and Structure Flashcards

1
Q

In the process of bonding…

A

… electrons move from a higher energy level to a lower energy level to form a more stable structure; achieved by a transfer or a sharing of electrons

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2
Q

How do sections of the periodic table hold their valence electrons?

A
  • metals hold their valence electrons weakly
  • non-metals have a strong pull on their valence electrons

Therefore, there is a tendency for metal atoms to transfer electrons to jon-metal atoms, forming an électropositive metal ion and ah electronegative non-metal ion in a stable octet structure

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3
Q

Electron density maps

A
  • found by deflecting X-rays off solids, causing X-day diffraction
  • show lines which represent areas of equal electron density
  • the cation can distort the electric field of the anion, turning the outer circles more square
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4
Q

Strength of the ionic bonding depends upon

A

Charge density

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5
Q

Charge density depends upon

A
  • charge of the ion

* radius of the ion

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6
Q

Ionic radius going down a group

A
  • ions have the same charge
  • atoms become larger; so too do ions
  • ionic radius increases
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7
Q

Isoélectronic ions

A
  • ions that have the same number of electrons

* ionic radius is determined by nuclear charge

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8
Q

Physical properties as evidence for ions

A
  • high melting and boiling points indicate strong electrostatic attraction between oppositely charged ions in ionic compounds
  • ability to conduct when aqueous or molten indicates the presence of mobile, charge-carrying particles
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9
Q

Electrolysis as evidence for ions - set up

A
  • shows ion migration
  • soak a rectangle of filter paper in water
  • place on a slide
  • connect électrodes and power pack
  • place à crystal of ionic material between electrodes o
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10
Q

Electrolysis as evidence for ions - potassium manganate (VII)

A
  • potassium ions are colourless
  • manganate(VII) ions are purple
  • purple colour shoes negative manganate(VII) ions migrate towards positive electrode
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11
Q

Electrolysis as evidence for ions - copper (II) chromate

A
  • copper (II) ions are blue
  • chromate (VI) ions are yellow
  • blue colour shows the positive copper(II) ions migrate towards the negative electrode
  • yellow colour shows negative chromate (VI) ions migrate towards positive electrode
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12
Q

Bonding pair

A
  • the pair of electrons which are shared between electron deficient atoms to form molecules
  • can form simple molecules, polymers or giant molecules
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13
Q

Covalent bonding

A
  • short covalent bond means electron pairs are closer to nucleus; stronger
  • higher bond energy
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14
Q

Bond energy

A
  • measure of how strong a bond is

* amount of energy given out as a bond forms/ amount of energy required to break a bond

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15
Q

Sigma bond

A
  • lies directly between two atoms
  • symmetrically on the axis, joining the two nuclei
  • overlap is end-on; large
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16
Q

Pi bond

A
  • forms when a double bond is present
  • forms alongside the atoms in two halves
  • overlap is parallèl; small
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17
Q

Expansion of the octet

A
  • the octet is not the only stable molecular structure
  • atoms in period 3 and greater can increase the number of single electrons (number of covalent bonds to can form) by splitting a lone electron pair
  • splitting an electron pair costs energy because an electron is being promoted to the d sub-shell (higher energy level)
  • elements in period 2 can never have an oxidation level higher than 2
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18
Q

Dative covalent bonding

A
  • aka co-ordinate bonding
  • electrostatic attraction between the protons in the nuclei and the shared pair of electrons between them, both of these electrons having come from one atom
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19
Q

Shapes of molecules

A
  • depends on electronic structure

* valence e-s girl bonds which determine molecular shape

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20
Q

Electrons take up positions to…

A

… minimise répulsion between them; electron pair repulsion theory

Lone pairs have a greater repulsion than bonding pairs
Pushes the binding pairs closer together

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21
Q

Linear

A
  • 180°
  • 2 bonding pairs
  • 0 lone pairs
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22
Q

Trigonal planar

A
  • 120°
  • 3 bonding pairs
  • 0 lone pairs
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23
Q

Tetrahedral

A
  • 109.5°
  • 4 bonding pairs
  • 0 lone pairs
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24
Q

Trigonal pyramidal

A
  • 107.5
  • 3 bonding pairs
  • 1 lone pair
25
Q

Trigonal bipyramidal

A
  • 90°, 120°
  • 5 bonding pairs
  • 0 lone pairs
  • caused by expansion of the octet
26
Q

Octahedral

A
  • 90°
  • 6 bonding pairs
  • 0 lone pairs
  • caused by expansion of the octet
27
Q

Bent

A
  • 104.5°
  • 2 bindings pairs
  • 2/1 lone pair(s)
28
Q

Electronegativity

A

The ability of an atom with a covalent bind mind to attract the bonding pair of electrons

29
Q

Perfect covalent bond

A
  • bonding electron region is shared equally by each atom
  • atoms have same electronegativity
  • e.g. O2, Br2, N2
30
Q

Distorted covalent bond

A
  • in most molecules, one atom has a greater electronegativity
  • distorts electron region; polarisation
  • depends on the difference in electronegativity
31
Q

Polarisation

A
  • causes the region surrounding the more electronegative atom to become partially negative; creates a polar bond
  • δ+ / δ-
32
Q

Intermediate bonding

A

• when a covalent molecule has a polar bond, it gains ionic character

33
Q

Electronegativity values…

A

give an approximation of the predominant bonding type in a binary compound; type of bonding is a continuum

34
Q

Polarity

A
  • the presence of a polar bond may or may not lead to the formation of a polar molecule; it depends on the location of the charge centres
  • if there is no separation of charge (they are in the same place), the molecule is not polar
35
Q

Deflecting jets are used to…

A

… test of a molecule is polar

36
Q

Cyclohexane as a deflecting jet

A

Does not deflect the jet from the burette nozzle because it is not polar, so it does not interact with the charged polythene

37
Q

Propanone or ethanol as a deflecting jet

A

Because oxygen is electronegative, there is a dipole, causes δ+ carbon to be attracted to he negative polythene rod, deflecting the jet towards the rod

38
Q

Dipole

A

The separation of charge that exists in a polar molecule

39
Q

Dipole-dipole attractions

A

In polar materials, the positive charge in one molecule is attracted to the negative charge in another

40
Q

London forces

A
  • aka Van der Waals’, dispersion, idids
  • v. weak, become larger in larger molecules
  • increase as molecular mass increases due to greater chance of electron imbalance
  • present in all molecules
  • arise from electron imbalance due to the constant movement of e-s in atoms and molecules
  • the region to the atom or molecule at an instant where there is more electrons develops δ-
  • thus causes repulsion to electrons in the adjacent atom or molecule; inducing a dipole
41
Q

Noble gases

A

As molecular mass increases, so does boiling point, because the string London forces means molecules are harder to separate

42
Q

Hydrogen bonding

A
  • strongest
  • occurs when hydrogen is directly bonded to N, O or F
  • occurs because hydrogen shares its only electron in covalent bonding; high electronegativity draws the electron pair away, exposing hydrogen proton
  • lone pairs in N, O and F are attracted to this proton
  • 180° to minimise repulsion to electron pairs in hydrogen and covalent bonds
43
Q

Boiling points of alkanes

A
  • increase with molecular mass due to increased idids
  • inductive effect of idids increases with proximity; the closer the molecules can get, the stronger the force
  • branching decreases induction by decreasing possible contact area, lowering BO
44
Q

Water’s hydrogen bonding

A
  • can form 2 hydrogen bonds per molecule; melting and boiling points are high relative to molecular mass
  • during freezing, hydrogen bonds pull water molecules into fixed positions in a comparatively open lattice; ice is less dense than water -> it floats
  • entropy is low
  • Ice slows down the freezing process via insulation
45
Q

Solubility

A

A solvent will dissolve a substance that contains similar intermolecular forces

46
Q

Ionic compound solubility

A
  • water molecules are highly polar, and are therefore attracted to the ions
  • Oδ- in water is attracted to cations, Hδ+ is attracted to anions
  • hydration of ions
  • due to the vibration of water molecules, they shake the ions free from the lattice as they bind
  • some do not dissolve because the electrostatic attraction between the ions is too great for the water molecules to overcome
47
Q

Hydration of ions

A

Water molecules linking to ions

48
Q

Organic compound solubility

A
  • alcohols can form hydrogen bonds -> soluble
  • organic compounds that cannot form hydrogen bonds with water are insoluble
  • no interaction between hydrogen bonds within water have too strong an attraction
49
Q

Dissolving

A

Molecules of dissolving substance to intersperse themselves between solvent molecules

50
Q

Non-aqueous solvents

A
  • non-polar solvents dissolve non-polar materials

* allows easily interaction and therefore solubility

51
Q

Delocalised electrons region

A

Visualise as a cloud

52
Q

Malleability, ductility

A

Absence of fixed bonds allows ions to move; layers slide

53
Q

Factors affecting strength of metallic bonding

A

1) more valence electrons = stronger bonding

2) smaller metal ion = stronger bonding

54
Q

Why does having more valence electrons increase the strength of metallic bonding?

A
  • higher charge on the cations
  • higher charge density
  • higher charge in the electron field
  • electrostatic attraction increases
55
Q

Why does having a smaller metal ion increase the strength of metallic bonding?

A
  • charge density of cation increases

* electrostatic attraction increases

56
Q

More valence electrons =

A

Better conductivity

57
Q

Diamond

A
  • each C is connected to 4 other Cs
  • tetrahedral units
  • strong covalent bonds; high MP, BP and SP
  • hardest natural substance; drills
  • non-conductor (all e-s are taken up)
58
Q

Graphite

A
  • each C is connected to 3 other Cs (3 of 4e-s taken up)
  • remaining electron is delocalised; conductor
  • bond angles are 120°; hexagonal arrangement that joins in a plane to form a sheet
  • later structure is held together by idids
  • covalent bonds give high MP, BP and SP
  • malleable, solid lubricant
  • can be used in electrolysis; inert conductor
59
Q

Graphène

A
  • 200x stronger than steel
  • one atom thick (single hexagonal layer) -> 2D
  • most conductive material
  • stretchable, transparent, impermeable, flexible, strong
  • used for lightweight aircraft material, touch-screens

Chemistry A Level (12 decks)

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