13.1 First-row d-block elements

Question 1

Electron configuration of Cr and Cu

Answer 1

Question 2

Trend of atomic radii in d-block

Answer 2

Radius decreases across period due to inrease in charge of nucleus

Question 3

Eelectron configurations in d block elements

Answer 3

Question 4

Why is the decrease in atomic radii relatively small across d block?

Answer 4

Because there is small increase in effective nuclear charge experienced by 4s electrons

Addition of proton (in nucleus) - small effect as another e in 3d is added

This similarity leads to ability to form alloys in d block: one atom can be replaced with another without large disruption of the structrue

Question 5

Common physical properties of d block elements

Answer 5

• high electrical and thermal conductivity
• high melting point
• malleable (easily beaten into shape)
• high tensile strength (can hold large loads without breaking)
• ductile (can easily drawn into wires)
• some ferromagnetic (Fe, Co, Ni)

Explained: strong metallic bonding, 3d and 4s electrons are close in E - involved in bonding - form delocalised sea of e - large number -> strong bonding

Question 6

Common chemical properties of d block elements

Answer 6

• form complexes with more than one ox number
• form variety of complex ions
• form coloured complexes
• act as catalysts

Question 7

Which metal in d block is not cinsidered a transition metal?

Answer 7

Zn

• does not form coloured complexes/solutions
• does not display common physical, chemical characteristics of transition metals
• only ⁺² ox state

Because: different e configuration - Zn⁺² ion has complete d sub-level while other transition metals don’t

Question 8

Why are ox numbers variable in transition metals?

Answer 8

Because of ionisation energies patterns

Question 9

Facts about transition metals

Answer 9

• all have ⁺² and ⁺³ ox numbers
• M⁺³ - stabel state from Sc to Cr
• M⁺² - stable state from Mn to Cu (increase nuclear charge makes it difficult to remove 3rd e)
• max ox state at Mn⁺⁷
• ox states above +3 show covalent character (large charge density)
• compounds with higher ox states - tend to be oxidising agents (ex: K₂Cr₂O₇)

Question 10

Define complex ion

Answer 10

COMPLEX ION: an ion formed when central atom is surrounded by ions/molecules which have a lone pair of e

Surrounding species - ligands - attached in coordinate bonds

Question 11

How transition metals form complex ions

Answer 11

Transition ions in solutions have high densities - attract water - coordinate bonds with +ive transition ions

Question 12

Define coordination number

Answer 12

COORDINATION NUMBER: the number of coordination bonds formed between the ligands and the central ion

Question 13

Common complex ions, ox state, shape

Answer 13

Question 14

Define polydentate ions

Answer 14

POLYDENTATE IONS: ions which have more than one lone pair of e available to form coordinate bond with a central transition metal ion

Example: EDTA^4- - can attach 6 transition ions - hexadentate ligand

Question 15

Define chelate

Answer 15

CHELATE: coordination/complex compound which consists of a central metal atom attached to a ligand to from cyclical/ring structure

Question 16

Why transition metals can be catalysts

Answer 16

E configuration - free orbitals to place electrons and speed the reaction

3d and 4s e form weak bonds with reactants - effective catalysts - provide surface to come together in correct orientation

Examples:

• Fe in Haber process
• Ni in conevrsion of alkenes to alkanes
• MnO₂ in decomposition of H₂O₂
• V₂O₅ in contact process

Question 17

Define heterogenous catalyst

Answer 17

HETEROGENOUS CTALYST: a catalyst which is in a different state from reactants

catalyst - solid, reactants - gaseous

Question 18

Define homogenous catalyst

Answer 18

HOMGENOUS CATALYST: catalyst in the same state fo matter as the reactants

Mix well with reactants - common in human body

Question 19

Why transition metals are homogenous catalysts

Answer 19

Because have mutiple ox states

Examples:

• Fe²⁺ in heme
• Co³⁺ in vitamin B₁₂

Question 20

How magnetic properties are created?

Answer 20

Each e has its own spin - cancelled out by pairing of another e - in transition metals not all e in shells paired - magnetic properties

Question 21

Define diamagnetism, paramagnetism, ferromagnetism

Answer 21

DIAMAGNETISM: property of all materials to produce a weak opposition to applied magnetic field

PARAMAGNETISM: property of substances which have an unpaired e - stronger than diamagnetism (produces magnetisation proportional to the applied field in the same direction)

FERROMAGNETISM: property to produce magnetisation sometimes of greater magnitude than the applied field (strongest effect of all)

Question 22

Ferromagnetic tranistion metals

Answer 22

Fe, Co, Ni - unpaired d e

Question 23

Transition metal complexes are paramagnetic

Answer 23

Show paramagnetic properties because of unpaired e - pulled into magnetic field

Paramgnetism increases with the number of unpaired e; max at Cr - decreases; Zinau - no unpaired e - only diamagnetic