Describe the characteristic properties of the transition elements and contrast them with Group I metals, and explain the unreactivity and uses of the noble gases in terms of full outer shells

What this dot point is asking

SEAB wants you to describe the characteristic properties of the transition elements (the block of metals in the middle of the table) and contrast them with the Group I metals, and to explain why the noble gases (Group 0) are so unreactive and how this leads to their uses. Together these complete the survey of the Periodic Table started with the main groups.

The answer

The transition elements

The transition elements are the block of metals in the centre of the Periodic Table (such as iron, copper, zinc, nickel and chromium). They share a set of characteristic properties:

• High density and high melting points (unlike the soft, low-density Group I metals).
• They are hard, strong and tough, useful as structural metals.
• They form coloured compounds (for example copper(II) compounds are blue, iron(II) green, iron(III) brown).
• They show variable valency (oxidation states): the same metal can form more than one ion, such as iron(II), $\text{Fe}^{2+}$, and iron(III), $\text{Fe}^{3+}$.
• They and their compounds often act as catalysts (for example iron in the manufacture of ammonia).

Contrasting transition metals with Group I metals

The contrast with the alkali metals is a favourite exam question:

• Density: transition metals are dense; Group I metals are so light that some float on water.
• Melting point: transition metals melt at high temperatures; Group I metals melt at low temperatures.
• Reactivity: transition metals are much less reactive (iron reacts only slowly with water); Group I metals react vigorously.
• Coloured compounds: transition metal compounds are coloured; Group I compounds are white or colourless.
• Valency: transition metals show variable valency; Group I metals form only $+1$ ions.
• Catalysis: transition metals are common catalysts; Group I metals are not.

The noble gases

The noble gases (helium, neon, argon and the rest of Group 0) are very unreactive gases. The reason is their electronic structure: they have a full outer shell of electrons (helium has $2$, the others have $8$). With a complete, stable outer shell, they have no tendency to gain, lose or share electrons, so they do not readily form bonds or react.

Uses of the noble gases

Their unreactivity and other physical properties give them useful applications:

• Helium is much less dense than air and non-flammable, so it is used in balloons and airships.
• Argon is inert, so it fills light bulbs (it does not react with the hot filament) and provides an inert atmosphere in welding.
• Neon is used in glowing signs because it gives a bright light when a current is passed through it.

Examples in context

Example 1. Iron as an industrial catalyst. Iron is used to speed up the manufacture of ammonia from nitrogen and hydrogen. Its ability to act as a catalyst, a typical transition-metal property, lowers the cost of a hugely important industrial process, illustrating why transition metals matter beyond construction.

Example 2. Argon protecting a weld. During welding, argon is blown over the hot metal to keep oxygen away, because argon's full outer shell makes it inert and unable to react with the metal. The same inertness that defines Group 0 chemistry is put to practical use.

Try this

Q1. State two physical properties typical of transition metals. [2 marks]

• Cue. High density and high melting point (also hard and strong).

Q2. Explain why the noble gases are unreactive. [2 marks]

• Cue. They have a full outer shell of electrons, so they have no tendency to gain, lose or share electrons, and therefore do not readily react.

Q3. Give one chemical property of transition metals that Group I metals do not show. [1 mark]

• Cue. They form coloured compounds (or show variable valency, or act as catalysts).