Question

Arrange the following atoms in order of increasing atomic radius: \(\mathrm{Na}, \mathrm{Al}, \mathrm{P}, \mathrm{Cl}, \mathrm{Mg}\).

Short answer

Increase order: Cl, P, Al, Mg, Na.

Step-by-step solution

Understand Atomic Radius

Atomic radius is a measure of the size of an atom, typically the distance from the nucleus to the outermost electron shell. As you move from left to right across a period in the periodic table, the atomic radius decreases due to increased positive charge in the nucleus which attracts electrons more strongly.

Locate Elements on the Periodic Table

Identify the position of each element (\(\mathrm{Na, Al, P, Cl, Mg}\)) on the periodic table. They are all in the third period:\[\begin{align*}&\text{Na: Group 1 (Alkali metals)} \&\text{Mg: Group 2 (Alkaline earth metals)} \&\text{Al: Group 13} \&\text{P: Group 15} \&\text{Cl: Group 17 (Halogens)}\end{align*}\]

Analyze Atomic Radii Trend Across Period

Moving across the periodic table from left to right, the atomic number increases, leading to a decrease in atomic radius. This means that the order of increasing atomic radius from left to right in the period is \(\mathrm{Cl} \lt \mathrm{P} \lt \mathrm{Al} \lt \mathrm{Mg} \lt \mathrm{Na}\).

Arrange Elements by Increasing Atomic Radius

Based on the periodic trend explained in Step 2 and Step 3, arrange the elements according to increasing atomic radii: \(\mathrm{Cl} \lt \mathrm{P} \lt \mathrm{Al} \lt \mathrm{Mg} \lt \mathrm{Na}\).

Key concepts

Periodic table

The periodic table is an organized chart of chemical elements, structured in increasing atomic number. Each element is represented by its chemical symbol. The layout of the table is strategic, not random. It's organized into rows called periods and columns known as groups or families. Each period corresponds to the number of electron shells an atom has.

• Elements in the same group often exhibit similar chemical behavior because they have the same number of electrons in their outer shell.
• For example, sodium (\(\text{Na}\)) is in Group 1, so it shares characteristics with other alkali metals.
• The periodic table helps us understand the relationships between various elements, their reactivities, and properties.

Periodic trends

When we examine the periodic table, we notice certain patterns or trends in the properties of elements as we move across periods or down groups. These periodic trends help predict how an element will behave. One such significant trend is the atomic radius, which generally decreases as we move from left to right across a period.

• This decrease occurs because electrons are added to the same energy level while the nucleus simultaneously gains more protons, increasing nuclear charge.
• The stronger attraction between the nucleus and electrons pulls the electron shell closer, resulting in a smaller atomic radius.
• Conversely, as we move down a group, the atomic radius tends to increase due to additional electron shells being added to the atoms, outweighing the increase in nuclear charge.

Atomic size

The term "atomic size" refers to the volume of an atom, which encompasses the nucleus and the electron cloud around it. It is measured by the atomic radius, which directly affects its chemical and physical properties. Two atoms' sizes can be compared using the periodic table trends mentioned earlier.

• Atomic size decreases across a period, with every added electron occupying the same principal energy level but feeling a greater pull from an increasing number of protons.
• As electrons crowd closer to the nucleus, the atomic size reduces.
• In contrast, moving down a group, atomic size increases as each successive element has an additional electron shell compared to the previous element.
• This addition of shells outweighs the increased nuclear charge, causing the electron cloud to expand.

Electron shell

An electron shell is a group of atomic orbitals surrounding an atom's nucleus, where electrons reside. Each shell can hold a specific number of electrons and is organized by increasing energy levels.

• The first shell nearest the nucleus can hold up to 2 electrons, the second can hold up to 8, and so on.
• When electrons fill a shell, they move to the next higher energy level.
• The arrangement of electrons in these shells and their subshells determines an element's chemical properties.
• Understanding electron shells is important for explaining periodic trends, as elements in the same period have electrons filling the same outer shell, affecting their size and reactivity.

The electron configuration not only defines the electron shell structure but also influences properties such as atomic size and reactivity, tying back to various periodic trends observed across the table.