Q23.26P - Chemistry: Molecular Nature Of Matter And Change

Question

The green patina of Cu-alloy roofs results from corrosion in the presence of ${\mathbf{O}}_{\mathbf{2}}\mathbf{,}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{,}{\mathbf{CO}}_{\mathbf{2}}$, and sulfur compounds. The other members of Group 1B(11) Ag and Au, do not form a patina. Corrosion of Cu and Ag in the presence of sulfur compounds leads to a black tarnish, but Au does not tarnish. This pattern is different from that in Group 1A(1), where ease of oxidation increases down the group. Explain these different group patterns.

Step-by-Step Solution

Answer

The smaller the radius, the stronger the attraction between the nucleus and the electrons. The similar sizes of the group 1B transition metals, and stronger attraction going down the group (given the increase in the number of protons and electrons in the atom) make the trend opposite the trend of group 1A metals.

Step 1: The definition of oxidation

Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Oxidation occurs when the oxidation state of a molecule, or atom.

Step 2: The different group patterns

In group 1A(1), main-group elements exhibit a different trend in ease of oxidation compared to group 1B(11) which includes transition metals. In group 1A, going down the group, it gets easier to oxidize the metal, while in group 1B, the trend does not apply, and the atoms, going down the group, get harder to oxidize.

 

This disparity in trends could be attributed to differences in atomic sizes among elements. In group 1A, the atomic size of the elements greatly increases going down, while elements of group 1B have barely any difference in their atomic sizes. The closer the electrons are, the smaller the atomic radius. The smaller the radius, the stronger the attraction between the nucleus and the electrons. The similar sizes of the transition metals and stronger attraction going down the group (given the increase in the number of protons and electrons in the atom) make the trend opposite the trend of group 1A metals.