Question

Using only the periodic table, arrange each set of atoms in (a) \(\mathrm{Cs}\), Se, Te; order of increasing radius: (b) \(\mathrm{S}, \mathrm{Si}, \mathrm{Sr} ;\) (c) P, Po, Pb.

Short answer

a) \(Se < Te < Cs\) b) \(Si < S < Sr\) c) \(P < Po < Pb\)

Step-by-step solution

Locate the Elements on the Periodic Table

Using the periodic table, find the positions of Cs (Cesium), Se (Selenium), and Te (Tellurium). Cs is in Group 1 and Period 6, Se is in Group 16 and Period 4, and Te is in Group 16 and Period 5.

Compare the Positions

Notice that Se and Te are in the same group but in different periods, so Te has a larger atomic radius than Se. Cs is in Group 1 and is in a period lower than Te, so it has the largest atomic radius among the three elements.

Arrange the Elements

Therefore, the order of increasing atomic radius is: Se, Te, Cs b) Arrange S, Si, and Sr in the order of increasing radius:

Locate the Elements on the Periodic Table

Using the periodic table, find the positions of S (Sulfur), Si (Silicon), and Sr (Strontium). S is in Group 16 and Period 3, Si is in Group 14 and Period 3, and Sr is in Group 2 and Period 5.

Compare the Positions

Sulfur and Silicon are in the same period but different groups. Since the atomic radius decreases across a period, S has a larger atomic radius than Si. Sr is in Group 2 and a period lower than Sulfur and Silicon, so Sr has the largest atomic radius among the three elements.

Arrange the Elements

Therefore, the order of increasing atomic radius is: Si, S, Sr c) Arrange P, Po, and Pb in the order of increasing radius:

Locate the Elements on the Periodic Table

Using the periodic table, find the positions of P (Phosphorus), Po (Polonium), and Pb (Lead). P is in Group 15 and Period 3, Po is in Group 16 and Period 6, and Pb is in Group 14 and Period 6.

Compare the Positions

Notice that Po and Pb are in the same period but different groups. Since the atomic radius decreases across a period, Po has a smaller atomic radius than Pb. P is in Group 15 in a period higher than Po and Pb, so it has the smallest atomic radius among the three elements.

Arrange the Elements

Therefore, the order of increasing atomic radius is: P, Po, Pb

Key concepts

Atomic Radius

The atomic radius refers to the distance from the nucleus of an atom to the outermost electron cloud. It gives insights into the size of the atom. When considering elements, the atomic radius can influence their chemical behavior, as larger atoms often have looser-held outer electrons. This makes them more reactive in some situations.

• The atomic radius typically increases as we move down a group in the periodic table.
• Conversely, as we move across a period from left to right, the atomic radius tends to decrease.

Understanding this trend is crucial for comparing atomic sizes among different elements.

Group Trends

In the periodic table, elements are arranged in vertical columns known as groups. The elements within the same group share similar valence electron configurations, leading to comparable chemical properties. A notable trend seen in groups is the increase of atomic radius as you move down the group. This is due to additional electron shells being added, which outweighs the increase in nuclear charge.

• For example, in Group 16, Selenium (Se) and Tellurium (Te) exhibit this trend, with Te being larger than Se.
• The increase in atomic size can also influence the reactivity of elements along a group.

Period Trends

The periodic table's horizontal rows are known as periods. As you move across a period from left to right, several notable trends regarding atomic properties occur, including the atomic radius. The atomic radius generally decreases across a period due to the increase in nuclear charge without a significant increase in shielding.

• This increase in protons pulls the electrons closer to the nucleus, reducing the size of the atom.
• In the same period, elements tend to become less metallic and more non-metallic as you move from left to right.

Such trends are witnessed in periods where elements like Sulfur and Silicon are on display. Sulfur is slightly larger than Silicon because it is to the left of Silicon within the same period.

Element Position

The position of an element in the periodic table can reveal much about its atomic properties and chemical behavior. This is determined by its group and period, which indicates the element's electron configuration. For instance, elements in higher periods have larger atomic radii because they have more energy levels or shells.

• Ce and Sr, as seen in different scenarios, have differing properties and sizes affected by their particular positions.
• Each element's position also helps predict reactivity and potential chemical reactions with other elements.

Such insights are fundamental when ordering elements like Cesium, Selenium, and Tellurium by atomic radius.

Cross-Period Comparison

Sometimes, it's necessary to compare atomic properties across different periods, and this is known as a cross-period comparison. This can be somewhat complex as it involves considering both group and period trends simultaneously.

• For instance, Phosphorus (P), located in a higher period, is compared with Polonium (Po) and Lead (Pb), which are in the same, albeit lower, period.
• The decrease in atomic radius across a period and the increase down a group together shape each element's size and properties.

Understanding these comparisons can help predict the behavior of elements under different conditions, offering valuable insights for discussing and exploring chemical reactions.