Question

Using only the periodic table, arrange each set of atoms in order from largest to smallest: \((\mathbf{a}) \mathrm{Ar},\) As, \(\mathrm{Kr} ;\) (b) \(\mathrm{Cd}, \mathrm{Rb}, \mathrm{Te} ;(\mathbf{c})\) \(\mathrm{C}, \mathrm{Cl}, \mathrm{Cu}\).

Short answer

Using the periodic trends in atomic size, we can order the sets of atoms as follows: (a) As > Ar > Kr, (b) Rb > Cd > Te, and (c) Cu > Cl > C.

Step-by-step solution

Locate the atoms on the periodic table

Locate each atom in the periodic table by finding its symbol and identifying its position in terms of the periods (rows) and groups (columns).

Compare the elements within the set

Use the periodic trends in atomic size to compare the elements' sizes within each set. If they are in the same period, compare their positions from left to right. If they are in the same group, compare their positions from top to bottom. (a) Ar, As, Kr:

Step 3(a): Arrange the atoms from largest to smallest

Ar is in period 3, As is in period 4, and Kr is in period 4. As and Kr are in the same period, with Kr being on the right side of As, therefore As is larger than Kr. Comparing Ar and As, we find that As is below Ar (in the same group), so As is larger. Thus, the order is As > Ar > Kr. (b) Cd, Rb, Te:

Step 3(b): Arrange the atoms from largest to smallest

Cd is in period 5, Rb is in period 5, and Te is in period 5. All three elements are in the same period. Comparing their positions from left to right: Rb is the farthest left, followed by Cd and then Te. Hence, the order is Rb > Cd > Te. (c) C, Cl, Cu:

Step 3(c): Arrange the atoms from largest to smallest

C is in period 2, Cl is in period 3, and Cu is in period 4. Cl and Cu are in the same period, with Cu being on the left side of Cl, therefore Cu is larger than Cl. Comparing Cl and C, we find that Cl is below C (in the same group), so Cl is larger. Thus, the order is Cu > Cl > C.

Key concepts

Periodic Table Trends

One of the most helpful tools in chemistry is the periodic table. It organizes elements in a meaningful way that reveals various periodic trends. One such trend involves the atomic size of elements, which can be observed across periods (rows) and down groups (columns). Here is how these trends generally work:

• As you move from left to right across a period, atomic size typically decreases. This happens because as you add more protons to the nucleus, the increased positive charge draws the electrons closer, reducing the atomic radius.
• Conversely, as you move down a group, atomic size generally increases. This is due to the addition of more electron shells, which places the outermost electrons further from the nucleus.

Understanding these trends is crucial for predicting how different atoms will interact and helps in arranging elements based on their atomic size.

Atomic Radius

Atomic radius is a key factor in determining the size of an atom. It is the distance from the center of the nucleus to the outermost shell of electrons. Here's what you need to know:

• The atomic radius decreases across a period from left to right. This shrinking is due to increased nuclear charge pulling electrons closer to the nucleus.
• The atomic radius increases down a group as more electron shells are added, making atoms larger despite the greater nuclear charge.

Different elements can be compared by their atomic radii values. For instance, within the same period, such as in the case of Cd, Rb, and Te, the order from left to right (decreasing radius) often reflects the order from largest to smallest. However, within the same group, the element lower down will have a larger atomic radius.

Element Comparison

When comparing elements based on atomic size, it's important to use their positions in the periodic table. This allows us to predict relative sizes using the trends discussed:

• For elements in the same period, like As and Kr, Kr is smaller because it is further right. However, in a different period, like Ar compared to As, As is larger because it is a period below.
• In period-based comparisons like Cd, Rb, and Te, moving left to right decreases size, so Rb is the largest, followed by Cd, then Te.
• For elements across different periods such as C, Cl, and Cu, the order of size considers both period location and group placement, giving Cu as the largest, then Cl, then C.

By understanding where each element sits in the periodic table, we can make informed judgments about these comparisons, predicting sizes with accuracy.