Typical transition elements

The elements below have properties that are typical of transition elements:

chromium, Cr
manganese, Mn
iron, Fe
cobalt, Co
nickel, Ni
copper, Cu

The table shows the melting point and density of some transition elements, compared to three metals in the that are not transition elements.

Metal	Position	Melting point	Density
Sodium	Group 1	98°C	0.97 g/cm³
Magnesium	Group 2	650°C	1.74 g/cm³
Aluminium	Group 3	660°C	2.70 g/cm³
Chromium	Transition elements	1890°C	7.19 g/cm³
Manganese	Transition elements	1240°C	7.20 g/cm³
Iron	Transition elements	1538°C	7.87 g/cm³
Cobalt	Transition elements	1492°C	8.90 g/cm³
Nickel	Transition elements	1453°C	8.90 g/cm³
Copper	Transition elements	1083°C	8.92 g/cm³

Metal	Sodium
Position	Group 1
Melting point	98°C
Density	0.97 g/cm³

Metal	Magnesium
Position	Group 2
Melting point	650°C
Density	1.74 g/cm³

Metal	Aluminium
Position	Group 3
Melting point	660°C
Density	2.70 g/cm³

Metal	Chromium
Position	Transition elements
Melting point	1890°C
Density	7.19 g/cm³

Metal	Manganese
Position	Transition elements
Melting point	1240°C
Density	7.20 g/cm³

Metal	Iron
Position	Transition elements
Melting point	1538°C
Density	7.87 g/cm³

Metal	Cobalt
Position	Transition elements
Melting point	1492°C
Density	8.90 g/cm³

Metal	Nickel
Position	Transition elements
Melting point	1453°C
Density	8.90 g/cm³

Metal	Copper
Position	Transition elements
Melting point	1083°C
Density	8.92 g/cm³

Worked example

Compare the properties of sodium and chromium. How does the data show that chromium is a typical transition element, and sodium is a typical group 1 metal?

Chromium has a much higher than sodium. The of chromium is also greater than sodium. Most transition elements have high melting points and densities, so chromium is a typical transition element. The group 1 elements have low melting points and densities, so sodium is a typical group 1 element.

Question

Predict the differences in the hardness and strength of nickel and potassium. Give a reason for your prediction.