Unit 1.4 - Bonding

Question 1

Ionic bond

Answer 1

Electrostatic attractions between oppositely charged ions.

Question 2

Which elements form electrovalent compounds?

Answer 2

Group 1 and 2 with group 6 and 7.

Question 3

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

Answer 3

1) Ionisation energy

2) Electron affinity

Question 4

State 3 conditions that favour ionic bonding.

Answer 4

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

Question 5

Why are ionic bonds strong?

Answer 5

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

Question 6

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

Answer 6

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

Question 7

State the order of shells.

Answer 7

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

Question 8

When do repulsive forces exist in ionic crystals?

Answer 8

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

Question 9

Inter-atomic distance - ionic and covalent

Answer 9

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

Question 10

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

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

Answer 10

1) Lowest effective nuclear charge.

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

Question 11

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

Answer 11

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.

Question 12

Describe relationship between electron affinity and stability.

Answer 12

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

Question 13

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

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

Answer 13

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

Question 14

What is covalent bonding?

Answer 14

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

Question 15

When do repulsive forces exist in covalent molecules?

Answer 15

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.

Question 16

What is the force of attraction in covalent bonding?

Answer 16

Directional

Question 17

Covalent bond

Answer 17

Attraction between the nuclei and the shared pair of electrons.

Question 18

What is another name for a coordinate bond?

Answer 18

Dative covalent bond.

Question 19

How are aluminium chloride dimers formed?

Answer 19

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

Question 20

1) When are coordinate bonds formed?

2) What is used to represent a coordinate bond?

Answer 20

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

Question 21

Coordinate bond

Answer 21

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

Question 22

Electronegativity

Answer 22

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

Question 23

How does electronegativity vary:
1) Across a period?

2) Down a group?

Answer 23

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

Question 24

Name the 4 most electronegative elements.

Answer 24

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

Question 25

Polar covalent bond

Answer 25

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

Question 26

Polarisation

Answer 26

Unequal sharing of electrons and said to be polar.

Question 27

Dipole

Answer 27

Separation of a charge in a molecule.

Question 28

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

Answer 28

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.

Question 29

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

Answer 29

Formation of a pure ionic bond and spherical ions.

Question 30

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

Answer 30

Electron density cloud would be symmetrical.

Question 31

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

Answer 31

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.

Question 32

Intramolecular bonds

Answer 32

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

Question 33

Intermolecular forces

Answer 33

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.

Question 34

1) What influences physical properties? | 2) What influences chemical properties?

Answer 34

1) Forces between molecules. | 2) Forces within molecules.

Question 35

What are dipole-dipole interactions?

Answer 35

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

Question 36

What are induced dipole-dipole reactions?

Answer 36

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

Question 37

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

Answer 37

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

Question 38

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

Answer 38

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

Question 39

What increases Van Der Wall's forces?

Answer 39

Increase in relative molecular mass.

Question 40

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

Answer 40

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

Question 41

1) What is hydrogen bonding? | 2) Is it stronger than Van Der Wall's forces?

Answer 41

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

Question 42

What is required for hydrogen bonding?

Answer 42

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

Question 43

Order the bonds from strongest to weakest.

Answer 43

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

Question 44

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

Answer 44

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

Question 45

VSEPR

Answer 45

Valence Shell Electron Pair Repulsion Theory.

Question 46

State the 3 main points of VESPR theory.

Answer 46

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.

Question 47

State the order of repulsion.

Answer 47

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

Question 48

State the bond angle, example and bond/lone pairs in the following: 1) Linear 2) Trigonal Planar 3) Tetrahedral 4) Tetrahedral bent

Answer 48

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

Question 49

State the bond angle, example and bond/lone pairs in the following: 1) Pyramidal 2) Trigonal bipyramidal 3) Octahedral

Answer 49

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