Topic 13: Periodic Table HL

Question 1

What are lanthanoids?

Answer 1

Lanthanoids are elements from Z=57 to Z=71

Question 2

What are actinoids?

Answer 2

Actinoids are elements from Z=89 to Z=103

Question 3

Which elements of group 12 are not considered to be transition elements according to IUPAC and why not?

Answer 3

Zn, Cd, Hg, and Cn, because all four elements have full d-sublevels containing ten d-electrons

Question 4

What is a transition element?

Answer 4

A transition element is an element that has an atom with an incomplete d-sublevel or that gives rise to cations with an incomplete d-sublevel. These refer to elements in the 3-11 groups.

Question 5

In the first row of the transition metals there are two exceptions in terms of the electron configuration. Name those elements and write down their condensed configuration. Explain why that is.

Answer 5

Cr and Cu.
Cr : [Ar]3d5.4s1
Cu : [Ar]3d10.4s1
-extra stability of the half-filled and fully-filled d-sublevel
-increasing nuclear charge on the energies of the 4s and 3D levels and interactions between electrons that occupy the same orbital.

Question 6

What is a paring energy?

Answer 6

An orbital is assumed to have one energy level, but when two electrons occupy an orbital there is electrostatic repulsion (both are negatively charged), called pairing energy. As nuclear charge increases, there is a greater attraction of the electrons: d orbitals are not shielded from the nucleus to the same extent as s orbitals.

Question 7

Describe the characteristics of the transition elements.

Answer 7

There is a gradual increase in the first IE across the period, but the rate of increase is much lower compared to the main-group elements. This is because the electrons enter an inner-shell orbital, whereas for main-group elements, the electrons enter the valence shell orbital. Inner-shell orbital has a greater shielding effect than valence electrons.

They have variable oxidative states.

Compounds and their ions are often coloured.

Form complexes with ligands.

Often used as catalysts.

Magnetic properties depend on their oxidation states and coordination number.

Question 8

List the Type A elements and describe their characteristics.

Answer 8

Sc, Ti and V

• stable high oxidation states, eg. v is +5 in VO3^-
• unstable low oxidation states

Question 9

List the Type B elements and describe their characteristics.

Answer 9

Cr and Mn

• stable high oxidation states, eg. Mn is +7 in MnO4^-
• stable low oxidation states, eg. Mn is +2

Question 10

List the Type C elements and describe their characteristics.

Answer 10

Fe, Co, Ni, Cu and Zn

• unstable high oxidation states
• stable low oxidation states

Question 11

Which form of manganese is often used in a chemical lab? Describe its appearance.

Answer 11

Potassium permanganate (also called potassium manganite (VII))

Used in redox titrations and is characterised by a deep burgundy colour. In citing, manganese with an oxidation state +7 is reduced to manganese +2, which is almost colourless.

Question 12

What colour is chromium at high and low oxidation states?

Answer 12

Chromium at its highest oxidation state, +6, forms orange and yellow compounds, which can be reduced to green complexes with chromium in a +3 oxidation state

Question 13

Describe the oxidation process of primary alcohols.

Answer 13

It’s a two-step process. First the alcohol is oxidised into an aldehyde and then further oxidised into corresponding carboxylic acid.
Can be oxidised by strong oxidising agents, such as potassium dichromate (VI) in sulphuric acid to form ethanoic acid.

Question 14

Describe the oxidation process of secondary alcohols.

Answer 14

Secondary alcohols can be oxidised by eg. Potassium dichromate (VI) in sulphuric acid to form a corresponding ketone.

Question 15

Breathalyzer test

Answer 15

Based on the redox reaction involving potassium dichromate(VI), where in the presence of alcohol, the yellow/orange crystals change to green signifying the formation of Cr^(2+) species.

Question 16

List three ways to detect blood alcohol concentration (BAC).

Answer 16

1) Semiconductor oxide-based sensor - new, low cost, low power consumption but needs to calibrated often otherwise can result in systematic errors.
2) Fuel-cell sensors - ethanol is oxidised to carboxylic acid and then into CO2 and H2O. This chemical energy is converted into electrical energy, where the electric potential is used to determine the concentration of ethanol.
3) intoximeter - based on IR spectroscopy.

Question 17

Coordinate bonding

Answer 17

The pair of electrons comes from the same atom, unlike typical covalent bonding where the shared pair consists of electrons that originate from both atoms, A and B.

Question 18

Chromophore

Answer 18

A group of atoms responsible for the absorption of electromagnetic radiation.

Question 19

Ligand

Answer 19

An atom, molecule, or ion that contains a lone pair of electrons (non-bonding pair) that coordinates, through coordinate bonding, to a central transition metal ion to form a complex.

Question 20

Transition metal complex

Answer 20

Compounds that contain transition elements and in which the central metal ion, M^(n+), is bonded, via coordinate bonding, to a ligand.

Aka coordination compounds.

Question 21

List four examples of species with coordinate bonding.

Answer 21

1) Hydronium cation, [H3O]^+
2) carbon monoxide
3) ammonium cation, [NH4]^+
4) a transition metal complex, for example [Ni(NH3)6]^(2+)

Question 22

Pauling’s eletroneutrality principle.

Answer 22

Approximate method of estimating how charge is distributed in a molecule or complex ion.

Question 23

Monodentate ligand

Answer 23

Are able to form only one coordinate bond with a metal ion.

Contains a single donor atom and have one lone pair contributing to the coordinate bond in a complex.

e.g. water, ammonia, halides

Question 24

Polydentate ligand

Answer 24

Can form two or more coordinate bonds with metal ion.

Two or more donor atoms

Aka chelate ligand

Question 25

EDTA

Answer 25

• A polydentate ligand that can form up to six coordinate bonds
• oxidation state: -4

Question 26

Name six uses of EDTA

Answer 26

1) removes heavy metals in e.g. treatment of lead poisoning. Na2[Ca(EDTA)] is adminitered to a patient and lead can displace calcium to form the anionic complex Pb[(EDTA)]^(2-), which can be passed by the kidneys
2) chelation therapy, used in heart by-pass surgery.
3) water softening
4) food preservation
5) restorative sculpture
6) cosmetics

Question 27

Why VSEPR cannot be used to deduce the geometry of transition metal complexes?

Answer 27

Because of the incomplete d-sublevels of the transition metal ions.

The structures of complexes can determined by X-ray crystallography, which show all bond angles and bond distances present in the structure.

Question 28

Bond angles of octahedral stereochemistry

Answer 28

90 and 180

coordination number: 6

Question 29

Bond angles of tetrahedral stereochemistry

Answer 29

109.5

coordination number: 4

Question 30

Bond angles of square planar stereochemistry

Answer 30

90 and 180

coordination number: 4

Question 31

What is the catalyst in the Haber process?

Answer 31

Fe(s)

Question 32

What is the catalyst in the decomposition of hydrogen peroxide?

Answer 32

MnO2(s)

Question 33

What is the catalyst in the hydrogenation of alkenes?

Answer 33

Ni(s)
Pd(s)
Pt(s)

Question 34

What is the catalyst in the hydrogenation of oils?

Answer 34

Ni(s)

Question 35

List two main disadvantages of hydrogenation of oils.

Answer 35

1) mono- and polyunsaturate fats are healthier for the heart than saturated fats
2) trans fatty acids can be formed in partial hydrogenation, which metabolize with difficulty and thus may accumulate in the fatty tissues f the body. They increase the level of LDL cholesterol.

Question 36

Nitrogen dioxide

Answer 36

Secondary pollutant that is primarily responsible for the brown colour of photochemical smog.

Toxic and can result in respiratory problems.

Question 37

What is the function of catalytic converters in cars?

Answer 37

Reduce NO(g) and and NO2(g) to N2(g), while oxidising CO(g) and unburned hydrocarbons to CO2(g) and H20(g)

Question 38

List three factors that affect the magnetic properties of transition metals and their complexes.

Answer 38

1) oxidation state of the metal
2) coordination number
3) geometry of the complex

Question 39

What are paramagnetic materials?

Answer 39

Contain unpaired electrons that behave like tiny magnets and are attracted by an external magnetic field.

Question 40

What are dimagnetic materials?

Answer 40

Do not contain unpaired electrons and therefore are repelled by external magnetic fields.

Question 41

Describe the d orbitals in a complex ion.

Answer 41

In an isolated atom, d orbitals have the same energy but in a complex ion, they split into two sublevels.
The electronic transitions between these sublevels leads to absorption and emission of photons of visible light, which are responsible for the colour of the complex.
The ligands are considered as point charges that surround the metal cation, M^(n+).

Question 42

Crystal field theory

Answer 42

CFT is based on an electrostatic model.

But it cannot explain the order of ligands in the spectrochemical series.

Question 43

According to CFT, what happens when the electrostatic

field created by the ligand point charges is isotropic?

Answer 43

The energies of the d orbitals will remain degenerate but will increase in energy uniformly.

Question 44

According to CFT, what happens when the electrostatic

field created by the ligand point charges is octahedral?

Answer 44

The d orbitals will split into two sets of degenerate energy, the t2g set and the eg set.
Three of the orbitals (the t2g set - dxy, dyz and dxz) will decrease in energy (that is, they
are stabilized) and two of the orbitals (the eg set) will increase in energy
(that is, they are destabilized).

Question 45

Why the t2g set orbitals are stabilised?

Answer 45

These three orbitals (dxy, dyz and dxz) have their lobes of electron density lying at 45° to the Cartesian axes.

Question 46

Crystal field splitting energy

Answer 46

The energy separation between the two split degenerate sets of orbitals, defined as Δo

Question 47

Pairing energy, P

Answer 47

Additional energy needed to pair the electron with another electron in an already filled orbital.
First three dn electrons occupy the t2g set of degenerate orbitals in an octahedral crystal field, after d3, the fourth electron has a choice, it can either occupy destabilized eg level or the stabilized tg2 level, but it would require additional energy - the pairing energy.

Question 48

List four factor that affect the crystal field splitting energy, Δo.

Answer 48

1) identity of the metal ion - influences the extent of the crystal field splitting. Δo increases descending a group with the metal in the same oxidation state
2) oxidation state of the metal ion - Δo increases as the oxidation state increases for a given metal
3) nature of the ligands - for M^(2+), ligands to the right of NO2^- are strong-field ligands; M^(3+), ligands to the right of H2O are strong-field ligands
4) geometry of the complex ion.

Question 49

Which configuration do weak-field ligands adopt?

Answer 49

Spin-free, ie both t2g and eg

Question 50

Which configuration do strong-field ligands adopt?

Answer 50

Spin-paired, ie. t2g

Question 51

Explain the colour of transition metal complexes.

Answer 51

The colour of transition metal ions is associated with partially filled d orbitals.

White light consists of all the colours of the visible spectrum. Transition metal complexes absorb some of these colours, allowing other colours to be transmitted.

If the d orbitals are partially filled, d-to-d electronic
transitions can occur, ie. an electron can jum from the lower energy t2g to the higher energy eg set of orbitals.

The colour will depend on the same factors that affect Δo.

Question 52

Denticity

Answer 52

The number of donor groups in a single ligand that bind to a central atom in a coordination complex