How do the physical properties of transition metals vary across the period?

Across the period, transition metals generally increase in density, melting point, and atomic size, but decrease in reactivity.

Transition metals are found in the middle of the periodic table, specifically in groups 3-12. As you move across the period from left to right, there are several noticeable trends in their physical properties. One of the most significant changes is the increase in density. This is due to the fact that the atomic mass of these elements generally increases, but the atomic radius does not increase at the same rate. As a result, the atoms are packed more closely together, leading to a higher density.

Another trend is the increase in melting and boiling points. This is because transition metals have more unpaired electrons available for metallic bonding, which makes these bonds stronger and requires more energy to break. Therefore, the melting and boiling points of transition metals tend to be higher than those of other elements.

The atomic size or radius of transition metals also generally increases across the period. This is due to the addition of more protons in the nucleus, which increases the positive charge and pulls the electrons closer, making the atom smaller. However, the addition of more electron shells counteracts this effect, resulting in an overall increase in atomic size.

In terms of reactivity, transition metals tend to be less reactive as you move across the period. This is because they have more electrons in their outer shell, which makes it harder for them to lose or gain electrons and therefore react with other elements. This is why elements like gold and platinum, which are found on the right side of the transition metals block, are less reactive and do not corrode easily.

In summary, as you move across the period of transition metals, you can expect to see an increase in density, melting point, and atomic size, but a decrease in reactivity. These trends are due to changes in atomic structure and electron configuration.