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Chemistry > 3.Bonding > Flashcards

3.Bonding Flashcards

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1
Q

What is ionic bonding

A

The electrostatic forces between oppositely charged ions in a giant lattice

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2
Q

Name properties of ionically bonded compounds

A
  • solid at room temperature
  • high melting point as they are giant structures as electrostatic forces extends throughout the compound
  • conduct when molten or dissolved
  • brittle
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3
Q

What is a covalent bond

A

A shared pair of electrons

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4
Q

How does sharing electrons hold atoms together

A

Atoms within a covalent bond are held together by the electrostatic attraction between the nuclei and shared electrons

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5
Q

What are properties of covalently bonded molecules

A
  • low melting point due to weak intermolecular forces

- don’t conduct electricity

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6
Q

What is dative covalent bonding

A

Covalent bonding in which both electrons come from one atom in the bond.

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7
Q

Which are stronger covalent or dative

A

Neither, they are the same strength

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8
Q

What is metallic bonding

A

The electrostatic attraction between lattice of positive ions and a sea of delocalised electrons

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9
Q

What does metallic bonding’s strength depend on

A
  • charge of the ion, greater the positive charge, greater the number of delocalised electrons, stronger the electrostatic attraction
  • size if the ion, the smaller the ion the closer the delocalised electrons are to the positive nucleus
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10
Q

What kind of structure is metal

A

Giant lattice structure

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11
Q

Describe properties of metals

A
  • can conduct electricity due to delocalised electrons
  • good conductors of heat due to sea of electrons
  • malleable and ductile
  • high melting points as they are giant structures
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12
Q

Define electronegativity

A

The power of an atom to attract the electron density in a covalent bond towards itself

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13
Q

What does electronegativity rely on

A
  • nuclear charge
  • the distance between the nucleus and the outer shell electrons
  • the shielding
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14
Q

Describe the trend in electronegativity up a group

A
  • electronegativity increases

- there is less shielding by electrons in inner shells

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15
Q

Describe the trend in electronegativity across a period

A
  • electronegativity increases

- nuclear attraction increases for the same amount of shielding

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16
Q

What is polarity

A

Unequal sharing of electrons between atoms that are bonded covalently

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17
Q

When atoms in a covalent bond have a large difference in electronegativity the bond is said to be

A

Polar

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18
Q

Name the 3 intermolecular forces in order of strength

A
  • van der Waals
  • Dipole-dipole
  • Hydrogen bonding
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19
Q

What is a dipole-dipole force

A

An intermolecular force that results from the attraction between molecules with permanent dipoles

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20
Q

What is a dipole moment

A

Sums up the effect of the polarity of all the bonds in the molecule

21
Q

What are van der Waals forces

A

An intermolecular force of attraction between instantaneous dipole and induced dipole and acts between all molecules

22
Q

How are instantaneous dipoles caused

A

The dipole is caused by the changing position of an electron cloud

23
Q

Why are van der Waals sometimes called instantaneous dipole-induced dipole forces

A

As the electron distribution of the original atom changes it will induce new dipoles in the atoms around it

24
Q

What causes a larger van der Waal force

A

The number of electrons present so atoms or molecules with large atomic or molecular masses produce stronger van der Waals

25
Q

Using the idea of van der Waal forces explain why the boiling point of noble gases increase down the group

A
  • as you go down the group the atomic numbers of the noble gases increase
  • this is because there are more electrons present
  • this causes larger instantaneous dipoles
  • larger van der Waal forces
26
Q

Using the idea of van der Waal forces explain why the boiling points of hydrocarbons increase with chain length

A
  • as hydrocarbons increase in chain length
  • larger surface area so more points of contact with adjacent molecules
  • this means more van der Waals forces are instantaneously formed
27
Q

What is hydrogen bonding

A

An intermolecular force in which a H d+ atom interacts with a more electronegative atom with a d- charge

28
Q

When do hydrogen bonds form

A
  • a hydrogen atom that is bonded to a very electronegative atom. This produces a strong partial charge
  • a very electronegative atom with a lone pair of electrons. These will be attracted to the partially charged H atom.
29
Q

What are the only atoms that are electronegative enough to form hydrogen bonds

A
  • O
  • N
  • F
30
Q

Why is water denser than ice

A
  • in water molecules can move around
  • in ice molecules can no longer move around, the hydrogen bonds hold a fixed position
  • this results in a 3D structure
  • to fit into this structure molecules are slightly less packed
  • this means ice is less dense
31
Q

Using the idea of intermolecular forces describe how ironing works

A
  • iron provides heat to break hydrogen bonds
  • pressure forces molecules to be flat
  • when you remove iron hydrogen bonds reform and hold the molecules in the new positions
32
Q

What is electron pair repulsion theory

A
  • explains the shape of molecules
  • each pair of electron around an atom will repel all other electrons
  • the pairs of electrons will therefore take up positions as far apart as possible to minimise repulsion
33
Q

Shape of molecule: two pairs of electrons

A

Linear. 180°

34
Q

Shape of molecule: three pairs of electrons

A

Trigonal planar. 120°

35
Q

Shape of molecule: four pairs of electrons

A

Tetrahedron. 109.5°

36
Q

Shape of molecule: five pairs of electrons

A

Trigonal bipyramid. 90° (same plane) 120° on different.

37
Q

Shape of molecule: six pairs of electrons

A

Octahedral. 90°

38
Q

What is the effect of a lone pair of electrons.

A

Reduces the bond angle by 2.5°

39
Q

Why is the bond angle reduced by lone pairs

A
  • lone pairs are only attracted by one nucleus
  • therefore are pulled closer to the nucleus and other electrons
  • electron repulsion theory, paired electrons are repelled further reducing angle by 2.5
40
Q

What is the order of electron pair repulsion strength.

A

bp-bp< bp lp< lp lp

41
Q

What is enthalpy change of melting/vaporisation

A

Energy required to weaken the forces holding a element in a solid (liquid) state resulting in a liquid (gas)

42
Q

What are crystals

A

Solids with a regular arrangement of particles held together by forces (covalent, ionic or metallic or weaker IMF)

43
Q

Name the 4 basic types of crystals

A
  • ionic
  • metallic
  • molecular
  • macromolecular
44
Q

Which two types of compounds exist as crystals

A

Ionic and metallic (lattices)

45
Q

Molecular crystals

A
  • held together by IMF

- low melting points as IMFs are weak

46
Q

Name 3 macromolecular crystals

A
  • diamond
  • graphite
  • buckminsterfullerene
47
Q

Diamond

A
  • each electron in carbon atoms outer shell is bonded with another carbon atom
  • bond angles of 109.5
  • forms a giant 3D lattice of covalent bonds
  • very hard
  • very high melting
  • does not conduct electricity
48
Q

Graphite

A
  • each carbon forms 3 covalent bonds
  • bond angle 120
  • 1 delocalised electron for each carbon free to move within graphene layer
  • layers of graphene held by weak van der Waals
  • soft (weak IMF)
  • high melting (strong covalent bonds in giant structure)
  • conducts electricity along layers (delocalised electron)

Chemistry (27 decks)

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