2. Mocks revision

Question 1

Ligand definition, what do ligands differ in?

Answer 1

a neutral molecule (or anion) that contains a non-bonding pair of electrons that can form coordinate (dative) covalent bonds with metal ions and form complex ions
ligands differ in how many lone pairs they donate (one, two, six)

Question 2

Types of ligands and examples of different types

Answer 2

monodentate: H2O, F-, CL-, NH3, OH-, SCN-, CN-
bidentate: 1,2 diaminoethane (H2NCH2CH2NH3), ethanedioate (C2O4)2-
polydentate: EDTA (ethylenediaminetetraacetic acid)

Question 3

What is the coordination number and how does it determine the shape of a complex ion?

Answer 3

the number of lone pair bonded to the metal ion
complex ions with CN 2 have a linear shape, with CN 4 have either square planar or tetrahedral, and with CN 6 have an octahedral shape

Question 4

Why are some complex ions colorless and if they are not, what determines their color?

Answer 4

if compounds have no d-shell electrons or if they have a complete d shell
if they have incomplete d shell then the color is determined by:
1| The nature of the transition metal
2| The oxidation state of the transition metal
3| The identity of the ligand
4| The stereochemistry of the complex (shape)

Question 5

Why is it important that a ligand splits the d-orbitals?

Answer 5

because then electrons from lower energy orbitals of the same subshell can absorb E and be promoted to a higher level orbital and reflect the complementary color from that which was absorbed (that’s why we see colors)

Question 6

Spectrochemical series

Answer 6

how ligands are arranged according to their strength (ability to split orbitals – how far apart can they be split)
I− < Br− < S2− < Cl− < F− < OH− < H2O < SCN- < NH3 < CN− < CO

Question 7

Intramolecular bonds types

Answer 7

bonds between atoms
1| Ionic bonding
2| Metallic bonding
3| Covalent bonding

Question 8

Ionic bond

Answer 8

a chemical bond resulting from the transfer of electrons from a cation to an anion in an exothermic reaction – the energy released is called lattice energy – ionic bonding is the sum of all electrostatic reactions between oppositely charged ions

Question 9

Characteristics of ionically bonded compounds

Answer 9

1| Crystalline at room temp
2| High melting and boiling points
3| Conductors in molten or solution state (not in solid)
4| Polar compounds

Question 10

Metallic bonding, what does it strength depend on

Answer 10

electrostatic attraction between a lattice of positive metal ions and delocalized electrons
the number of delocalized electrons, and the charge and the ionic radius of metal ions.

Question 11

Physical properties of metals

Answer 11

1| High melting point (decreases as the size of cations increases)
2| Malleable (can be beaten into shape)
3| Ductilie (can be drawn into a wire)
4| Electrical conductors (delocalized electrons)

Question 12

Covalent bonding

Answer 12

chemical bonding resulting from the sharing of electrons between two bonding atoms (formed between two nonmetals) – can be single, double, or triple – electrons are not shared equally because of different electronegativities of different atoms

Question 13

How does the difference in electronegativity determine the bond type

Answer 13

if the difference is more than 1.8, the bond is ionic, if it’s less than 1.8 but more than 0, it’s polar covalent, and if it is equal to 0 then it is non-polar (even distribution of charge)

Question 14

Physical properties of covalent bonds

Answer 14

1| Definite and predictable shapes
2| Lower melting and boiling points
3| Generally insoluble in water
4| Nonconductors

Question 15

Coordinate (dative) bonding

Answer 15

the electrons in a shared electron pair came from the same atom, e.g. (ligands) CO, NH4+, H3O+, SO2, SO3.

Question 16

VSEPR (Valence Shell Electron Pair Repulsion) theory and electron domain

Answer 16

the most important factor in determining geometry is the relative repulsion between electron pairs: LP-LP>LP-BS>BS-BS
region of electron density (not necessarily the direction of one bond)

Question 17

Different possible molecule shapes

Answer 17

linear (2 ED 0 LP, 5 ED 3 LP, 6 ED, 4 LP)
trigonal planar (3 ED 0 LP)
angular/bent (3 ED 1 LP, 4 ED, 2 LP), tetrahedral (4 ED 0 LP)
trigonal pyramidal (4 ED 1 LP)
trigonal bipyramidal (5 ED 0 LP)
seesaw (5 ED 1 LP)
T-shaped (5 ED 2 LP, 6 ED 3 LP)
octahedral (6 ED 0 LP)
square pyramidal (6 ED 1 LP)
square planar (6 ED 2 LP)

Question 18

Molecular substances vs network solids

Answer 18

atoms held together by weak covalent bonds (I2, S8, fullerene), have low melting and boiling points – (giant structures) atoms held together by strong covalent bonds in a 3D lattice structure (graphite, diamond, graphene, SiO2), have high melting and boiling points, insulators

Question 19

Fulerrene, diamond, graphite, and graphene structure and properties

Answer 19

graphene is the basic structural element of other allotropes, a very thin C layer (good conductor)
fullerene and graphite have similar structures: stacked graphene sheets of linked hexagonal (and pentagonal) rings, graphene layers in graphite linked by weak VdW (lower boiling and melting point than diamond, conductor)
diamond has a tetrahedral, strong structure, high melting and boiling point, is an insulator

Question 20

Silicon dioxide

Answer 20

giant covalent structure, each Si bonded to 4 O and each O bonded to two Si, very high melting and boiling point and is an insulator