Question

Arrange these elements in order of increasing atomic size: \(\mathrm{Ca}, \mathrm{Rb}, \mathrm{S}, \mathrm{Si}, \mathrm{Ge}, \mathrm{F}\)

Short answer

From smallest to largest: F, S, Si, Ge, Ca, Rb.

Step-by-step solution

Understand Atomic Size

Atomic size generally increases as one moves down a group in the periodic table, since there are more electron shells. As one moves from right to left across a period, atomic size also increases due to the decreasing pull of the nucleus on the electron cloud.

Locate Elements in the Periodic Table

Locate each element on the periodic table to determine their positions in terms of periods and groups. This will help in comparing their atomic sizes.

Compare Atomic Size Within the Same Group

For elements within the same group, such as Ca (calcium) and Rb (rubidium), compare their atomic size based on their period. Rb is below Ca, so Rb has a larger atomic size.

Compare Atomic Size Within the Same Period

For elements that are in the same period such as S (sulfur), Si (silicon), and Ge (germanium), the atomic size increases as you move left in the period. So the order from smallest to largest is Ge, Si, then S.

Combine Relative Sizes

Finally, combine the information from steps 3 and 4, and also compare the remaining elements. Rb is the largest because it is located the furthest down and to the left in the periodic table, while F (fluorine) is the smallest.

Key concepts

Periodic Table Trends

The periodic table is a systematic arrangement of the elements, ordered by their atomic number, electronic configuration, and recurring chemical properties. One of the most critical trends observed across the periodic table is the variation in atomic size, which is an element's radius.

The atomic size decreases as one moves from left to right within a period. This is due to the increase in the positive charge of the nucleus, which pulls the electrons closer, reducing the size. Conversely, as one goes down a group, the atomic size increases. This phenomenon happens because each successive element has an additional electron shell, increasing the distance between the outermost electrons and the nucleus.

To visualize these trends, imagine a staircase from the bottom left to the top right of the periodic table; atomic size decreases as you go up each step and increases as you step down.

Electron Shells

Electron shells are levels of orbits in which electrons reside around the nucleus. These shells are also referred to as energy levels, and they play a crucial role in determining the atomic size of an element. Each shell can only house a certain number of electrons, with outer shells accommodating more electrons than inner ones.

When a new shell is added, it increases the average distance of the electrons from the nucleus, which in turn increases the atomic size. This is why elements in the same group, with the same number of outer shell electrons, increase in size on descending the group: each element has more filled shells than the one above it. On the periodic table, the number of electron shells increases as you move from top to bottom, which is directly linked to the trend of increasing atomic size down a group.

Atomic Structure

Understanding atomic structure is vital for grasping concepts such as atomic size. The structure of an atom is composed of a central nucleus, made up of protons and neutrons, and an electron cloud, which consists of electrons found in various shells around the nucleus.

The balance between the attractive forces of the positively charged nucleus and the repulsive forces between electrons determines the physical size of the electron cloud and hence the atomic size. Elements with a higher nuclear charge (more protons in the nucleus) have stronger attractive forces on the electrons, resulting in smaller atomic radii. Comparatively, as the electron shells increase with each subsequent element in a group, the shielding effect causes the outermost electrons to feel less attraction to the nucleus, making the atomic size to be larger.