Why do metals have high densities?

Metals have high densities because their atoms are closely packed together in a regular lattice structure.

In more detail, the high density of metals is a result of their atomic structure and bonding. Metals are made up of a sea of delocalised electrons surrounding a closely packed, regular arrangement of positive ions, known as a metallic lattice. This structure is extremely compact, with very little space between the atoms, leading to a high mass per unit volume, which is the definition of density.

The metallic bonding that holds these atoms together is also very strong. This is due to the attraction between the positively charged metal ions and the negatively charged delocalised electrons. This strong bonding further contributes to the high density, as it pulls the atoms even closer together.

Furthermore, the atomic radii of metal atoms are generally small, especially for transition metals. This means that more atoms can fit into a given volume, increasing the density. For example, gold and platinum, which are transition metals, are among the densest elements because they have a large number of heavy atoms packed into a small volume.

In addition, the packing efficiency, or the fraction of volume in a crystal structure that is actually occupied by atoms, is high for metals. This is due to their regular, closely packed lattice structure. The high packing efficiency further contributes to the high density of metals.

In summary, the high density of metals is a result of their compact atomic structure, strong metallic bonding, small atomic radii, and high packing efficiency.