Question

Using only the periodic table, arrange each set of atoms in order from largest to smallest: $(\mathbf{a})\mathrm{K},$ Li, $\mathrm{Cs};(\mathbf{b})\mathrm{Pb},\mathrm{Sn},\mathrm{Si};(\mathbf{c})\mathrm{F},$ $\mathrm{O},\mathrm{N}.$

Short answer

Using the periodic table and atomic trends, the order of the elements from largest to smallest can be arranged as follows: (a) $\mathrm{Cs},\mathrm{K},\mathrm{Li}$ (b) $\mathrm{Pb},\mathrm{Sn},\mathrm{Si}$ (c) $\mathrm{N},\mathrm{O},\mathrm{F}$

Step-by-step solution

Identifying atomic trends relating to size

We must first understand that within the periodic table, atomic size increases as we move from right to left and from top to bottom. In other words, elements located towards the bottom and left side of the table are larger. This will help us arrange the elements according to their size.

Locating elements and analyzing their size

On the periodic table, K, Li, and Cs are alkali metals and found in Group 1. K (potassium) is in Period 4, Li (lithium) is in Period 2, and Cs (cesium) is in Period 6. As atomic size increases from top to bottom, we can determine that Cs is the largest element among the three and Li is the smallest.

Listing elements in order

Now that we have analyzed the size of these elements based on their position in the periodic table, we can arrange them in order from largest to smallest: Cs, K, Li. For set (b): $\mathrm{Pb}$, $\mathrm{Sn}$, $\mathrm{Si}$

Identifying atomic trends relating to size

As described earlier, atomic size increases from right to left and from top to bottom. This trend will help us arrange the elements of this set according to their size.

Locating elements and analyzing their size

In the periodic table, Pb (lead) is in Group 14 and Period 6, Sn (tin) is in Group 14 and Period 5, and Si (silicon) is in Group 14 and Period 3. Since atomic size increases from top to bottom, we can determine that Pb is the largest element among them and Si is the smallest.

Listing elements in order

With the sizes determined based on their position in the periodic table, we can arrange these elements in order from largest to smallest: Pb, Sn, Si. For set (c): $\mathrm{F}$, $\mathrm{O}$, $\mathrm{N}$

Identifying atomic trends relating to size

Again, we will follow the atomic size trend of increasing from right to left and from top to bottom in the periodic table.

Locating elements and analyzing their size

On the periodic table, F (fluorine) is in Group 17 and Period 2, O (oxygen) is in Group 16 and Period 2, and N (nitrogen) is in Group 15 and Period 2. As atomic size increases from right to left, we can determine that N is the largest element in the set, and F is the smallest.

Listing elements in order

Having analyzed the size of these elements based on their position in the periodic table, we can arrange them in order from largest to smallest: N, O, F.

Key concepts

Atomic Size

Atomic size, also known as atomic radius, refers to the size of an atom. It is measured as the distance from the nucleus to the outermost electron shell. Understanding atomic size is crucial for predicting the properties and behavior of elements in chemical reactions.

In the periodic table, there are clear trends that can help us estimate atomic size. As you move from top to bottom within a group (vertical columns), atomic size increases. This is because additional electron shells are added to the atom, making it larger. Conversely, as you travel from left to right across a period (horizontal rows), atomic size generally decreases. This is due to the increase in nuclear charge—the number of protons—which pulls the electron cloud closer to the nucleus, slightly reducing the atomic size.

Understanding these trends allows us to quickly arrange elements in order of size without needing specific numeric measurements.

Periodic Table Groups

The periodic table is organized into groups. These groups are the vertical columns and are numbered from 1 to 18. Elements within the same group often share similar properties and exhibit predictable trends in their chemical behavior.

For instance, Group 1 elements, known as alkali metals, such as lithium (Li), potassium (K), and cesium (Cs), are all highly reactive metals. As you move down a group, the atomic size increases. This means that cesium is larger than potassium, which is larger than lithium, due to the additional electron shells added at each successive element in the group.

Another example can be seen in Group 14, where elements like silicon (Si), tin (Sn), and lead (Pb) reside. The trend of increasing atomic size as you move down the group applies here too, making lead the largest among them. This predictable pattern of increasing size down a group helps in understanding the physical and chemical properties related to the size of the atoms.

Periodic Table Periods

Horizontal rows in the periodic table are called periods. Unlike groups, which have recurring property trends, periods show a gradual change in these properties. As you move across a period from left to right, elements change from metals to nonmetals.

During this movement across a period, one observes that atomic size generally decreases. This is because, with each step to the right, a proton and an electron are added, increasing the nuclear charge without adding new electron shells. This increased charge pulls the electrons closer to the nucleus, slightly reducing the size of the atom.

Among the elements nitrogen (N), oxygen (O), and fluorine (F) in Period 2, this trend is evident. Nitrogen is the largest amongst them, followed by oxygen, and fluorine is the smallest. Understanding how atomic size changes across periods is essential in predicting element behavior in various chemical contexts.