Families of Elements II: Transition & Rare Earth Elements – SS2 Chemistry Lesson Note (First Term)

Transition elements are the metals of the d-block, placed between groups II and III of the periodic table. Lanthanides (rare earth elements) and actinides are two further series of 15 elements each, placed in periods six and seven.

Behavioural objectives

1. State where transition elements are found in the periodic table and name the elements of the first transition series.
2. List the properties of transition elements and give an example of each.
3. Name the lanthanides (rare earth elements) and state their period and number.
4. Name the actinides and state their period.
5. Explain why elements with atomic numbers 93 to 103 are called artificial elements.

What are transition elements?

Transition elements are metals whose atoms fill the d-sublevel, found between groups II and III of the periodic table.

• Position: they lie between groups II and III of the periodic table.
• Block: they form the d-block, because their last electrons enter the d-sublevel.
• Nature: they are all metals, such as iron, copper and nickel.

What are the elements of the first transition series?

The first transition series has ten elements in period four, from scandium (21) to zinc (30).

What are the electron arrangements of some transition elements?

In transition elements, the 4s sublevel fills first and the 3d sublevel then fills up across the series.

• Scandium (21): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ 4s².
• Iron (26): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s².
• Chromium (24): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹, an exception to the usual order.
• Copper (29): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹, also an exception.

What are the properties of transition elements?

Transition elements are hard, strong metals with high melting points, variable oxidation states, coloured compounds and catalytic ability.

• High tensile strength: they resist being pulled apart, which is why iron is used for bridges and buildings.
• High melting and boiling points: most are solid at room temperature, for example iron and copper.
• Variable oxidation states: one element forms ions of different charges, as in Fe²⁺ and Fe³⁺.
• Coloured ions: their compounds are often coloured, as in blue Cu²⁺ and green Fe²⁺.
• Complex ions: they form ions in which a central metal ion is joined to other groups, such as the deep blue [Cu(NH₃)₄]²⁺.
• Paramagnetism: many of their compounds and ions are weakly attracted by a magnet.
• Catalytic ability: they speed up reactions without being used up.

How do transition metals differ from group I metals?

Group I metals (alkali metals) are soft, very reactive metals such as sodium and potassium, with one outer electron.

Transition metals are hard, dense metals such as iron and copper, and they are much less reactive.

What are examples of transition metals as catalysts?

A catalyst is a substance that speeds up a reaction without being used up, and many transition metals act as catalysts.

• Iron: catalyst in the Haber process for making ammonia.
• Vanadium(V) oxide: catalyst in the contact process for making sulphuric acid.
• Nickel: catalyst in turning vegetable oils into margarine (hydrogenation).
• Manganese(IV) oxide: catalyst in the decomposition of hydrogen peroxide.

What are the common uses of transition metals?

Transition metals are used for building, wiring, coating and plating.

• Iron: made into steel for roofing sheets, rails and vehicles.
• Copper: used for electrical wires because it conducts well.
• Zinc: coats iron sheets (galvanising) to stop rusting.
• Chromium: used for plating to give a shiny, rust-resistant surface.

What are lanthanides (rare earth elements)?

Lanthanides are the 15 elements from lanthanum to lutetium placed in period six, also called rare earth elements.

• Period: they are found in period six.
• Number: there are 15 of them.
• Range: the series begins with lanthanum (La, atomic number 57) and ends with lutetium (Lu, atomic number 71).
• Similarity: they resemble one another greatly in their properties.
• Position in the table: they are usually shown in a separate row below the main table.

What are the 15 lanthanides in order?

1. Lanthanum (La)
2. Cerium (Ce)
3. Praseodymium (Pr)
4. Neodymium (Nd)
5. Promethium (Pm)
6. Samarium (Sm)
7. Europium (Eu)
8. Gadolinium (Gd)
9. Terbium (Tb)
10. Dysprosium (Dy)
11. Holmium (Ho)
12. Erbium (Er)
13. Thulium (Tm)
14. Ytterbium (Yb)
15. Lutetium (Lu)

What are actinides?

Actinides are the 15 elements from actinium to lawrencium placed in period seven.

• Period: they are found in period seven.
• Number: there are 15 of them, like the lanthanides.
• Range: the series begins with actinium (Ac, atomic number 89) and ends with lawrencium (Lr, atomic number 103).
• Similarity: they are similar to one another and to the lanthanides.
• Radioactivity: all actinides are radioactive.
• Example: uranium (U, atomic number 92) is a well-known actinide, used as fuel in nuclear reactors.

What are the actinides in order?

1. Actinium (Ac)
2. Thorium (Th)
3. Protactinium (Pa)
4. Uranium (U)
5. Neptunium (Np)
6. Plutonium (Pu)
7. Americium (Am)
8. Curium (Cm)
9. Berkelium (Bk)
10. Californium (Cf)
11. Einsteinium (Es)
12. Fermium (Fm)
13. Mendelevium (Md)
14. Nobelium (No)
15. Lawrencium (Lr)

What are artificial elements?

Artificial elements are elements made by people in nuclear reactions, not taken from nature.

• Definition: artificial elements are elements made by people, not taken from nature.
• Atomic numbers: the elements from 93 to 103 are known as the artificial elements.
• Reason: they do not occur naturally in useful amounts. They are formed during nuclear reactions.
• Examples: neptunium (93), plutonium (94) and lawrencium (103).

How do the three families compare?

The first transition series, the lanthanides and the actinides differ in position, number and range.

Evaluation

1. Name the elements of the first transition series.
2. State four properties of transition elements.
3. In which period are the lanthanides found, and how many are there?
4. Which element begins the actinide series and which one ends it?
5. Why are the elements with atomic numbers 93 to 103 called artificial elements?

Assignment

1. Draw a table of the first transition series showing each element’s name, symbol and atomic number. Then give one use or one catalytic role of any three of the elements.