Chapter 8 Properties of Transition Elements

Question 1

The diagram shows under which conditions endothermic reactions are feasible

Answer 1

• stable ions with an incomplete d subshell
• They are all metals found in the d-block of the Periodic Table, between Groups 2 and 13
  
  • Sometimes they are referred to as transition metals

Question 2

Not all d-block elements are classed as transition elements:

Answer 2

scandium and zinc, for example, are not classed as transition elements, despite being in the d-block

Question 3

Scandium is not classed as a transition element because:

Answer 3

• It only forms one ion, Sc³⁺
• The Sc³⁺ion has no electrons in its 3d subshell; it has the electronic configuration of [Ar]

Question 4

Zinc is also not classed as a transition element because:

Answer 4

• It also forms only one ion, Zn²⁺
• The Zn²⁺ ion has a complete 3d subshell; it has the electronic configuration [Ar]3d¹⁰

Question 5

• The transition elements all have incomplete d subshells
• There are five orbitals in a d subshell. Some of these orbitals may have similar shapes but different orientations, whereas others may have completely different shapes

Answer 5

• The five orbitals are
  
  • 3d_yz
  • 3d_xz
  • 3d_xy
  • 3d_{x2 - y2}
  • 3d_z2
• Note that students are required to sketch the shapes of the 3d_xy and 3d_z2 orbitals only

Question 6

Shapes of the 3d orbitals

Answer 6

• The 3d_yz, 3d_xz, and 3d_xy orbitals are orbitals which lie in the y-z, x-z and x-y plane respectively
  
  • They all have four lobes that point between the two axes

Question 7

The 3d_{x2 - y2} orbital looks like the 3d_yz, 3d_xz, and 3d_xy orbitals, as it also consists of

Answer 7

• four lobes
• The difference is that these lobes point along the x and y axes and not between them

Question 8

The 3d_z2 orbital is different from the other orbitals, as there are two main lobes which form a

Answer 8

• dumbbell shape
• The two main lobes point along the z-axis and there is a “doughnut” ring around the centre

Question 9

Although the transition elements are metals, they have some properties unlike those of other metals on the periodic table, such as:

Answer 9

• Variable oxidation states
• Behave as catalysts
• Form complex ions
• Form coloured compounds

Question 10

Ions of transition metals

Answer 10

• Like other metals on the periodic table, the transition elements will lose electrons to form positively charged ions
• However, unlike other metals, transition elements can form more than one positive ion
  
  • They are said to have variable oxidation states

Question 11

Oxidation states of transition elements table

Answer 11

Question 12

Coloured complex

Answer 12

• Another characteristic property of transition elements is that their compounds are often coloured
  
  • For example, the colour of the [Cr(OH)₆]^3- complex (where oxidation state of Cr is +3) is dark green
  • Whereas the colour of the [Cr(NH₃)₆]³⁺ complex (oxidation state of Cr is still +3) is purple

Question 13

Transition elements as catalysts

Answer 13

• Since transition elements can have variable oxidation states, they make excellent catalysts
• During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction
  
  • For example, iron (Fe) is commonly used as a catalyst in the Haber Process, switching between the +2 and +3 oxidation states
• Substances can also be adsorbed onto their surface and activated in the process

Question 14

Complex ions

Answer 14

• Another property of transition elements caused by their ability to form variable oxidation states, is their ability to form complex ions
• A complex ion is a molecule or ion, consisting of a central metal atom or ion, with a number of molecules or ions surrounding it
• The molecules or ions surrounding the central metal atom or ion are called ligands
• Due to the different oxidation states of the central metal ions, a different number and wide variety of ligands can form bonds with the transition element