Question

Choose the element with the larger atoms from each pair. (a) \(\mathrm{Al}\) or \(\mathrm{In}\) (b) Si or \(\mathrm{N}\) (c) \(\mathrm{P}\) or \(\mathrm{Pb}\) (d) \(\mathrm{C}\) or \(\mathrm{F}\)

Short answer

The elements with the larger atoms for each pair are: (a) In, (b) Si, (c) Pb, (d) C.

Step-by-step solution

Analyze Elements in Periodic Table

To determine which element has larger atoms, look at their positions in the Periodic Table. Atoms tend to increase in size down a group because they have more electron shells. Across a period, atomic size decreases due to the increase in nuclear charge pulling electrons closer.

Compare Elements in Pair (a)

Compare Al and In, which are in the same group (13). In is below Al, meaning it has more electron shells, and thus larger atoms.

Compare Elements in Pair (b)

Compare Si and N. Si is to the right and below N in the Periodic Table, which typically indicates larger size. However, they are in the same period, so the increase in size from left to right is not applicable. Since Si is below N in the same group, Si has larger atoms.

Compare Elements in Pair (c)

Compare P and Pb. Pb is below P in the same group (15), so Pb has more electron shells and therefore larger atoms.

Compare Elements in Pair (d)

Compare C and F. They are in the same period, but since atomic size decreases across a period, C on the left side has larger atoms than F on the right.

Key concepts

Atomic Radius Comparison

Understanding the relative size of atoms is essential in chemistry, as it influences how elements interact with each other. When comparing the atomic radius between two elements, the position of the elements on the periodic table provides a reliable clue. Atoms increase in size as you move down a group in the periodic table. This is because additional electron shells are being added, which are further away from the nucleus, adding to the overall size of the atom.

However, as you move across a period from left to right, the atoms tend to become smaller. This occurs due to an increase in the number of protons in the nucleus, enhancing its charge and pulling electrons closer to the center. As a result, even though electron shells are added as you go down the groups, the increasing nuclear charge across a period can counteract the effect of additional shells, resulting in smaller atomic radii.

Group and Period Trends

The periodic table is neatly organized to display trends in atomic properties, including the atomic size. Groups are the columns of the periodic table and provide insight into the number of electron shells an element has. Elements in the same group typically have the same number of valence electrons, which can also affect their radius. As you move down a group, every step introduces a new electron shell, increasing the distance between the outermost electrons and the nucleus, leading to a larger atomic radius.

On the other hand, periods are the rows stretching from left to right across the periodic table. Across a period, each element has the same number of electron shells, but they possess more protons in their nucleus, causing greater attraction to the electrons and thus, a smaller atomic radius. These trends simplify the comparison of atomic radii and provide a systematic way to understand and predict the relative sizes of different elements.

Electron Shells

The concept of electron shells is fundamental to understanding atomic size. Electron shells are regions around the nucleus where electrons are statistically likely to be found. Each shell can hold a different maximum number of electrons: the first shell can hold up to 2, the second up to 8, and this increases with each subsequent shell following a specific pattern defined by quantum mechanics.

When an atom has more electron shells, it consequently means there's a larger radius since the outermost electrons are further away from the nucleus. However, it is crucial to understand that not all electron shells contribute equally to the atom's size. The farther from the nucleus an electron shell is, the less influence the nucleus has on the outermost electrons, due to increased electron-electron repulsion within the atom. This is why elements with more electron shells typically have a larger atomic size, a key point to remember when comparing atomic radii.