General Classifications

The broadest classification of elements in the periodic table is a representative element or not.

Representative Elements

The representative elements are the elements that tend to behave as expected on the basis of their electronic structure. These include the elements in groups 1, 2, and 13-17 or those in the s-block and p-block. The big takeaway here is that d orbitals and f orbitals get a bit funky and tend not to behave. So only atoms in s-blocks and p-blocks are said to be representative.

Following this metallic character is the next broadest. We can break this down into three general categories: definitely a metal, definitely not a metal, and kinda a metal kinda not, which we call metals, non-metals, and metalloids respectively.

Definitely A Metal

Metals in appearance are exactly what you expect them to be, shiny, malleable, and able to conduct electricity. These properties derive from a metal’s electronic structures which is characterized by the ability to easily lose electrons and readily form cations. If we frame this in terms of our periodic trends, metals are elements with low electronegativity, low electron affinity, and low ionization energy. So we will find them near the left-hand side and bottom of the periodic table.

Definitely Not A Metal

Non-metals are the exact opposite of metals in appearance and properties. They are brittle, dull, poor conductors of electricity, and liable to form anions. With high electronegativity, high electron affinities, and high ionization energies we find the non-metals in the top right of the periodic table.

Kinda A Metal Kinda Not

Metalloids rest in between metals and nonmetals and have intermediate properties. They are so-so conductors, tend to be neutral, and while they look like metals they act more like non-metals. They straddle the division between metal metals and non-metals in a stair step fashion.

Why This Matters

Understanding every property of a metal, non-metal, and metalloids is of pretty low importance on the MCAT. Instead, we can use this information when predicting what a molecule will do when bonding with others. For example, metals tend to give away electrons easily while nonmetals take electrons more easily.

When a nonmetal and a metal get together to form a bond the metals gives it electrons away to the nonmetal. This results in an ionic bond, where the electrons aren’t equally shared. In contrast, two nonmetals will form a bond where they share their electrons since neither wants to give them up, resulting in a covalent bond.

Additionally, we can use these classifications to predict whether or not a molecule will be a conductor or an insulator. For example, the copper core of a wire is made out of a metal which as we have already seen conducts electricity really well. Rubber on the other hand doesn’t. This occurs because rubber consists of large carbon chains. Since carbon is a metalloid and hydrogen is a non-metal rubber acts as an insulator.