Question

According to general trends in the periodic table, predict which element in each of the following pairs has the larger atomic radius: (a) Li or Na (b) \(\mathrm{N}\) or \(\mathrm{P}\) (c) \(\mathrm{Mg}\) or \(\mathrm{Ca}\) (d) Ar or Kr

Short answer

Na, P, Ca, and Kr have the larger atomic radii in their respective pairs.

Step-by-step solution

Understanding Atomic Radius Trends

The atomic radius of an atom refers to the distance from the center of its nucleus to the outermost electron. In general, atomic radius increases as you move down a group (column) in the periodic table because additional electron shells are added. Conversely, atomic radius decreases as you move from left to right across a period (row) due to the increase in positive charge which pulls electrons closer to the nucleus.

Comparing Li and Na

Here, we compare lithium (Li) and sodium (Na). Both elements belong to Group 1, but sodium is below lithium in the periodic table. According to the trend in the periodic table, because Na is further down the group than Li, it has a larger atomic radius.

Comparing N and P

Nitrogen (N) and phosphorus (P) are elements in Group 15. Phosphorus is below nitrogen in the periodic table. Following the trend, since P is further down the group, it will have a larger atomic radius than N.

Comparing Mg and Ca

Magnesium (Mg) and calcium (Ca) are members of Group 2 with Ca below Mg. Consequently, according to periodic trend, Ca should have a larger atomic radius than Mg as it is further down the group.

Comparing Ar and Kr

Argon (Ar) and krypton (Kr) are noble gases located in Group 18. Krypton is positioned below argon. As expected by periodic trends, Kr will have a larger atomic radius than Ar because it is further down the group.

Key concepts

Periodic Table Trends

Periodic trends are patterns that can be observed within the periodic table. These trends help us understand how certain elemental properties change as we move across different parts of the table.

One of the key trends is about atomic radius. The atomic radius is essentially the size of an atom, from its nucleus to the outermost valence electron. Despite seeming abstract, this concept is incredibly practical! By knowing the trend of atomic radius, we can predict the size of an atom and understand how it behaves in chemical reactions.

• Moving down a group (vertical column), atomic radius increases. This happens because each row adds a new electron shell, making atoms larger as you descend further down the group.
• Conversely, moving across a period (horizontal row), atomic size decreases. This is due to an increase in the number of protons and electrons; however, since all additional electrons are added to the same shell, they are pulled closer by the stronger positive charge of the nucleus.

Understanding these trends is essential for chemistry students to predict how different elements will interact.

Group and Period Comparison

When comparing elements in the periodic table, knowing in which group or period an element is located can clarify expectations about its properties, including its atomic radius.

**Group Comparison**
Elements that are in the same group share similar chemical properties but differ in atomic radius. For instance, in Group 1, lithium (Li) and sodium (Na) are part of the same group, but Na will have a larger atomic radius than Li since it is further down the column. The additional electron shell makes Na bigger despite their similar reactivity.

**Period Comparison**
When comparing elements in the same period, such as nitrogen (N) and oxygen (O), they showcase smaller differences in size as you move right across the table. This indicates that although they lie on the same horizontal axis, an increase in positive nuclear charge makes atoms slightly smaller across the period. Hence, understanding these differences is key to predicting their electron arrangements and bonding characteristics.

Elemental Properties

Elemental properties such as atomic radius are crucial for understanding how elements bond and behave. These properties are largely dictated by where an element sits on the periodic table.

• Atomic Radius: Affects reactivity and bonding. Larger atoms may bond differently because their outermost electrons are further from the nucleus.
• Ionization Energy: This property, correlated with atomic size, is the energy required to remove an electron. It tends to be lower for elements with larger atomic radii because electrons are less tightly held.
• Electronegativity: Related to how strongly an atom can attract and hold onto electrons in a bond. Smaller atoms with more concentrated nuclear charge often have higher electronegativities.

Understanding these properties helps predict how an element reacts and what types of compounds it might form. It becomes easier to see why, for instance, noble gases such as argon (Ar) and krypton (Kr) are largely unreactive; their full electron shells make them quite content as they are!
In conclusion, the periodic table is more than just a chart; it's a tool that offers insights into the behavior of elements based on their atomic properties.