Question

Arrange the following elements in order of increasing size: Al, B, C, K, and Na. (Try doing it without looking at Figure \(7.6,\) then check yourself by looking up the necessary atomic radii.)

Short answer

The elements in increasing size order are: C, B, Al, Na, K.

Step-by-step solution

Identify the Elements

List the elements given in the exercise: Aluminum (Al), Boron (B), Carbon (C), Potassium (K), and Sodium (Na).

Recall Periodic Table Trends

Recall that atomic size increases as you move down a group and decreases as you move from left to right across a period in the periodic table.

Locate the Elements on the Periodic Table

Locate each element on the periodic table: Al is in Group 13, Period 3; B is in Group 13, Period 2; C is in Group 14, Period 2; K is in Group 1, Period 4; Na is in Group 1, Period 3.

Apply Periodic Trends

Based on the periodic trends, K, being lower in its group, is expected to be larger than Na, which in turn is expected to be larger than Al. B and C, being in Period 2, will be smaller than the elements in Periods 3 and 4, with B slightly larger than C due to its position going from left to right.

Arrange Elements by Increasing Size

Given the periodic trends, arrange the elements from smallest to largest: C, B, Al, Na, K.

Key concepts

Atomic Size

Atomic size, also known as atomic radius, is an important concept that helps us understand an element's physical properties. The atomic size is essentially the distance between the center of an atom's nucleus and its outermost electron shell. This distance can vary based on several factors and is not always straightforward to predict.

• Factors affecting atomic size include the number of electron shells and the effective nuclear charge, which is the net positive charge experienced by an electron in a multi-electron atom.
• The more electron shells an atom has, the larger its size because these shells stack like layers around the nucleus.
• However, as we move across a period in the periodic table from left to right, the protons increase, leading to a higher effective nuclear charge that pulls the electrons closer, reducing the atomic size.

Periodic Trends

The periodic table isn't just a tool for identifying where elements live; it reveals important trends that help us understand chemical behavior. Periodic trends, such as atomic size, ionization energy, and electronegativity, follow predictable patterns on the periodic table. These trends are mostly influenced by the arrangement of electrons.

• As you move down a group, atomic size increases because each successive element has an additional electron shell.
• Conversely, as you move from left to right across a period, atomic size decreases due to the increase in positive charge within the nucleus, pulling the electron cloud closer.
• Understanding these trends can help make predictions about an element's behavior without relying strictly on memorization.

Group and Period

The periodic table is organized into groups and periods, which play a critical role in determining the properties of elements. Each group is a column of the periodic table, and elements within the same group usually have similar properties. A period is a horizontal row, and elements within the same period have the same number of atomic orbitals.

• Elements in the same group have the same number of electrons in their outer shell, responsible for similar chemical properties.
• However, moving down a group, there is an additional electron shell, increasing the atomic size despite similar chemical behaviors.
• In a given period, moving left to right, atomic size decreases, but the elements differ more widely in chemical behavior.

Element Arrangement

Element arrangement on the periodic table is not random; it is based on atomic number and reflects the elements' repeating chemical properties. This arrangement allows us to predict and compare atomic size, among other traits, even if the elements are part of different groups or periods.

• When comparing elements like Al, B, C, K, and Na, knowledge of the periodic trends is crucial for arranging them by characteristics like size.
• Atomic size increases with the number of electron shells and can decrease with an increase in nuclear charge across a period.
• This makes understanding the periodic table not just about memorization but about mastering a consistent pattern that nature follows, leading to clearer insights into elemental behavior and interactions.