post-transition metals
Summary
Post-transition metals (poor metals) are the p-block metals right of the transition metals, such as Al, Ga, In, Sn, Tl, Pb and Bi. They are generally softer and lower-melting than transition metals, and the heavier ones often form ions with oxidation states two below the group maximum (Sn²⁺, Pb²⁺, Tl⁺).
Detail
Meaning: Post-transition metals lie in the p-block, just left of the metalloid staircase: Al, Ga, In, Sn, Tl, Pb and Bi (some lists add Po). They show metallic behavior: they conduct, are malleable and form cations. Compared with most transition metals they are softer and lower-melting (Ga melts just above room temperature). Their d subshells are empty or completely filled in their usual ions, so they lack the many colored, variable-charge compounds typical of transition metals, though some still have more than one common charge.
The heavier members show the inert pair effect: the ns² electrons are held tightly and are not always lost, so Tl⁺, Sn²⁺ and Pb²⁺ appear alongside Tl³⁺, Sn⁴⁺ and Pb⁴⁺.
On the MCAT: Expect questions that ask you to place an element on the periodic table, predict ion charge, or rank metallic character, which increases down a group and decreases left to right. Al₂O₃ is a standard amphoteric oxide. Pb²⁺ salts often appear in solubility and Ksp problems.
Common confusion: Post-transition metals are not transition metals (d-block) and not metalloids (B, Si, Ge, As, Sb, Te). They are p-block metals. Sn and Pb are metals even though carbon and silicon in the same group are not.
Sources
- Chemistry: The Central Science
- Chemistry (Zumdahl)
- General Chemistry (Ebbing and Gammon)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.