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AS Chemistry Unit 1 + 2 > Unit 1.4 - Bonding > Flashcards

Unit 1.4 - Bonding Flashcards

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1
Q

Ionic bond

A

Electrostatic attractions between oppositely charged ions.

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2
Q

Which elements form electrovalent compounds?

A

Group 1 and 2 with group 6 and 7.

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3
Q

1) What influences the formation of an ionic compound for a cation?
2) What influences the formation of an ionic compound for an anion?

A

1) Ionisation energy

2) Electron affinity

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4
Q

State 3 conditions that favour ionic bonding.

A

Low ionisation energy to form cations, highly exothermic formation if anions and attainment of a noble gas electron configuration in the ion.

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5
Q

Why are ionic bonds strong?

A

Energy released by the oppositely charged ions coming together to form a crystal lattice held by electrostatic forces.

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6
Q

Describe the relationship between the charge and force of an ion.

A

Larger charges on the ions, the bigger the attractive forces and the energy released.

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7
Q

State the order of shells.

A

1s2 2s2 2p6 3s2 3p6 4s2 3d10

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8
Q

When do repulsive forces exist in ionic crystals?

A

Repulsions between ions of the same charge, between inner shells of electrons in ions and between positively charged nuclei.

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9
Q

Inter-atomic distance - ionic and covalent

A

Balance between attractive and repulsive forces determines how closely cations and anions approach each other.

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10
Q

1) Why do group 1 element form ions most readily?

2) Why does ionisation energy occur more readily down a group?

A

1) Lowest effective nuclear charge.

2) Increase electron shielding which results in a decrease of the effective nuclear charge.

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11
Q

Describe relationship between electron affinity and its effect on the nucleus.

A

Electron affinities (energy released) becomes more exothermic across a period because the incoming electron is attracted more strongly by the increasingly positive charge on the nucleus.

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12
Q

Describe relationship between electron affinity and stability.

A

More exothermic (negative) electron affinity, more stable the anion that is formed.

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13
Q

State the name of the bond when there is a sharing of:

1) 2 electrons
2) 4 electrons
3) 6 electrons

A

1) Single bond
2) Double bond
3) Triple bond

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14
Q

What is covalent bonding?

A

Sharing of a pair of electrons with opposite spins between 2 atoms.

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15
Q

When do repulsive forces exist in covalent molecules?

A

Repulsions between inner shells of electrons on each atom, between those shells and charge cloud of the bond and between the positive charges on the nuclei.

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16
Q

What is the force of attraction in covalent bonding?

A

Directional

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17
Q

Covalent bond

A

Attraction between the nuclei and the shared pair of electrons.

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18
Q

What is another name for a coordinate bond?

A

Dative covalent bond.

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19
Q

How are aluminium chloride dimers formed?

A

Molecules dimerise together and monomers are held together by coordinate bonding.

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20
Q

1) When are coordinate bonds formed?

2) What is used to represent a coordinate bond?

A

1) Compounds containing unshared pairs of electrons (lone pairs).
2) Arrow - drawn from donor of electron pair to the acceptor.

21
Q

Coordinate bond

A

Type of covalent bond, formed when one atom supplies the shared pair of electrons for the bond.

22
Q

Electronegativity

A

Ability of an atom to attract shared pair of electrons in a covalent bond towards itself when combined with different atoms in a compound.

23
Q

How does electronegativity vary:
1) Across a period?

2) Down a group?

A

1) Increases - atoms similar size, nuclear charge increases . Higher value, more attraction for bonding.
2) Decreases - atoms larger, more electron shielding.

24
Q

Name the 4 most electronegative elements.

A

Fluorine, oxygen, nitrogen and chlorine. - alkalis have high values.

25
Q

Polar covalent bond

A

Unequal distribution of bonding electron pair due to a difference in the electronegativity.

26
Q

Polarisation

A

Unequal sharing of electrons and said to be polar.

27
Q

Dipole

A

Separation of a charge in a molecule.

28
Q

1) What forms electronegativity?
2) Describe the relationship between polarity and electronegativity.
3) What type of molecule would you fins non-polar covalent bonding?

A

1) Relative attraction of the nuclei for the bonding of electrons in a covalent bond.
2) Bigger difference in electronegativity, more polar the bond.
3) Diatomic elements.

29
Q

What would a large difference in electronegativity lead to in ionic bonds?

A

Formation of a pure ionic bond and spherical ions.

30
Q

What would the electron density cloud look like when atoms are the same?

A

Electron density cloud would be symmetrical.

31
Q

Generally, when is ionic bonding favoured over covalent bonding? (3)

A

1) Atom from which the ion is derived is large for a cation and small for an anion - ionisation energy decreases, electron gain harder.
2) Formal charge on ion is small - more difficult no. electrons involved increase.
3) Electronic structure of ion corresponds to closed shell structure, especially noble gas configuration - stable which resistant to removal or addition of electrons.

32
Q

Intramolecular bonds

A

Bonds between atoms within a molecule. They’re strong C-Cl.

33
Q

Intermolecular forces

A

Forces of attraction between molecules (dipole-dipole). Easily broken to let molecules move independently so have low melting point and are usually gas/liquid at room temperature.

34
Q

1) What influences physical properties?

2) What influences chemical properties?

A

1) Forces between molecules.

2) Forces within molecules.

35
Q

What are dipole-dipole interactions?

A

Polar - any partial positive charge will be next to a negative partial charge.

36
Q

What are induced dipole-dipole reactions?

A

Non polar molecules - electrons in continual motion therefore electron cloud will not be symmetrical at any given point. Resulting in a temporary dipole.

37
Q

Describe the relationship between the size of a molecule and induced dipole attraction.

A

As size increases, number of electrons increases, causing induced dipole-induced dipole attraction to be stronger.

38
Q

Using induced dipole-induced dipole knowledge, explain why the elements at top of group 7 are gaseous.

A

As you go down group 7 the electron cloud gets larger, Van Der Wall’s forces get stronger, causing boiling points to increase.

39
Q

What increases Van Der Wall’s forces?

A

Increase in relative molecular mass.

40
Q

Why do branched hydrocarbons have lower boiling points than unbranched hydrocarbons?

A

Unbranched have more points of contact so more Van Der Wall’s forces.

41
Q

1) What is hydrogen bonding?

2) Is it stronger than Van Der Wall’s forces?

A

1) Attraction between the exposed proton of the hydrogen atom and the lone pair of electrons on the electronegative element of a neighbouring molecule.
2) Yes

42
Q

What is required for hydrogen bonding?

A

Hydrogen atom attached to a highly electronegative atom (N,O,F), unshared pair of electrons on the electronegative atom.

43
Q

Order the bonds from strongest to weakest.

A

Covalent bonds > hydrogen bonds > Van Der Wall’s forces

44
Q

Why do bonds get as far away from each other as possible?

A

Electron pairs have negative charge so they repel and spread out.

45
Q

VSEPR

A

Valence Shell Electron Pair Repulsion Theory.

46
Q

State the 3 main points of VESPR theory.

A

1) Between each valence electron pair is a force of repulsion which forces orbitals as far apart as possible.
2) Since lone pairs are closer to the nucleus than bonding pairs they will exercise a greater force of repulsion.
3) A multiple bond can be considered as equivalent to one pair of electrons.

47
Q

State the order of repulsion.

A

lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

48
Q

State the bond angle, example and bond/lone pairs in the following:

1) Linear
2) Trigonal Planar
3) Tetrahedral
4) Tetrahedral bent

A

1) 180°, 2bp
2) 120°, 3bp - BF3
3) 109.5°, 4bp - CH4, NH4 +
4) 104.5°, 2Lp, 2bp - H2O

49
Q

State the bond angle, example and bond/lone pairs in the following:

1) Pyramidal
2) Trigonal bipyramidal
3) Octahedral

A

1) 106.7°, 1Lp, 3bp - NH3
2) 120°, 90°, 5bp - PCl5
3) 90°, 6bp - SF6

AS Chemistry Unit 1 + 2 (6 decks)

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