Question

In each of the following sets of elements, indicate which element has the smallest atomic size. a. \(\mathrm{Ba}, \mathrm{Ca}, \mathrm{Ra}\) b. \(\mathrm{P}, \mathrm{Si}, \mathrm{Al}\) c. \(\mathrm{Rb}, \mathrm{Cs}, \mathrm{K}\)

Short answer

Smallest atomic sizes in each set: Set A: Ca Set B: P Set C: K

Step-by-step solution

As we go across a period (horizontal row) in the periodic table, atomic size decreases. This is because the number of protons increases, causing a higher effective nuclear charge which effectively "pulls" electrons closer to the nucleus. Conversely, atomic size generally increases as we go down a group (vertical column), since there are more occupied energy levels and increased shielding effect caused by the increased number of electron shells. With this understanding of periodic trends, let's analyze each set of elements: #Step 2: Determine atomic size for Set A: Ba, Ca, Ra#

Recall that atomic size increases as we go down a group. Ba, Ca, and Ra belong to Group 2 (alkaline earth metals) in the periodic table. Ba is below Ca, and Ra is below Ba. Thus, the atomic size will decrease as we move up from Ra to Ba to Ca. Therefore, Ca has the smallest atomic size in Set A. Smallest atomic size in Set A: Ca #Step 3: Determine atomic size for Set B: P, Si, Al#

As explained in Step 1, atomic size decreases as we go across a period. P, Si, and Al are in Period 3 of the periodic table, with Al belonging to Group 13, Si to Group 14, and P to Group 15. Therefore, the atomic size will decrease as we move from Al to Si to P. Consequently, P has the smallest atomic size in Set B. Smallest atomic size in Set B: P #Step 4: Determine atomic size for Set C: Rb, Cs, K#

In this set, all elements belong to Group 1 (alkali metals) in the periodic table. K is above Rb, and Rb is above Cs. As mentioned in Step 1, atomic size increases as we move down a group. Thus, the atomic size will decrease as we move up from Cs to Rb to K. Hence, K has the smallest atomic size in Set C. Smallest atomic size in Set C: K In conclusion, the elements with the smallest atomic size in each set are Ca (Set A), P (Set B), and K (Set C).

Key concepts

Periodic Trends

Periodic trends are patterns observed in the properties of elements across different periods (rows) and groups (columns) in the periodic table. These trends are mainly influenced by the atomic structure. For atomic size, the trend is simple:

• Across a period: As you move from left to right, the atomic size decreases. This happens because as you go across, more protons are added to the nucleus, increasing the positive charge and effectively pulling the electrons closer to the nucleus. This phenomenon is known as the effective nuclear charge.
• Down a group: As you move down, the atomic size increases. This is due to the addition of electron shells, which shield the outer electrons from the nuclear pull, allowing them to occupy a larger space.

By understanding these trends, you can predict and explain the behavior of elements, including their atomic size.

Atomic Radius

The atomic radius is a way of expressing how large an atom is. It is defined as the distance from the nucleus of an atom to the outermost electron shell. While the exact size of an atom can vary depending on the type of bond it forms with other atoms, the trend across periods and groups remains consistent.

• A smaller atomic radius indicates that electrons are held more tightly to the nucleus, due to higher effective nuclear charge.
• A larger atomic radius means there are more electron shells, and the outermost electrons are less tightly held due to increased shielding.

This concept is crucial for predicting chemical reactions and physical properties of elements.

Periodic Table

The periodic table is a systematic organization of elements in order of increasing atomic number. It is arranged in such a way that elements with similar properties fall into the same columns, known as groups. Each horizontal row is called a period.

• The table helps in understanding the periodic trends and properties of elements, including atomic size.
• Groups contain elements with similar properties due to their valence electron configuration, whereas periods show trends in properties like atomic size and electronegativity.

The periodic table is an essential tool for chemists, helping to predict the behavior of elements and their compounds.

Alkaline Earth Metals

Alkaline earth metals are found in Group 2 of the periodic table. They include elements like beryllium, magnesium, calcium, strontium, barium, and radium.

• These elements have two electrons in their outermost shell, making them quite reactive, though less so than the alkali metals in Group 1.
• Their atomic size increases down the group, as each subsequent element has an additional electron shell.

They are known for forming basic (alkaline) hydroxides and oxides and play critical roles in both industrial applications and biological systems.

Alkali Metals

Alkali metals belong to Group 1 of the periodic table and include elements like lithium, sodium, potassium, rubidium, cesium, and francium. These metals are known for their high reactivity.

• They have a single electron in their outermost shell, which they readily lose to form positive ions. This makes them very reactive, especially with water.
• Like the alkaline earth metals, the atomic size of alkali metals increases down the group due to the addition of electron shells.

Their reactivity and size make alkali metals important in various chemical processes and applications, such as batteries and mineral forms.