Question

Arrange each set of elements in order of increasing ionization energy. a. \(\mathrm{O}, \mathrm{N}, \mathrm{C}\) b. \(\mathrm{S}, \mathrm{P}, \mathrm{Cl}\) c. As, \(\mathrm{P}, \mathrm{N}\) d. \(\mathrm{Al}, \mathrm{Si}, \mathrm{P}\)

Short answer

a. \text{C}, \text{N}, \text{O}; b. \text{P}, \text{S}, \text{Cl}; c. \text{As}, \text{P}, \text{N}; d. \text{Al}, \text{Si}, \text{P}.

Step-by-step solution

Understand Ionization Energy

Ionization energy is the energy required to remove an electron from an atom. It generally increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table.

Analyze Elements in Group (a)

Arrange the elements \( \text{O}, \text{N}, \text{C} \) across Period 2. As we move from left to right, the ionization energy increases. Thus, the order is \( \text{C}, \text{N}, \text{O} \).

Analyze Elements in Group (b)

Arrange the elements \( \text{S}, \text{P}, \text{Cl} \) across Period 3. Moving left to right, ionization energy increases. Hence, the order is \( \text{P}, \text{S}, \text{Cl} \).

Analyze Elements in Group (c)

Arrange the elements \( \text{As}, \text{P}, \text{N} \) in Group 15. As we move up the group, ionization energy increases due to decreasing atomic size. Therefore, the order is \( \text{As}, \text{P}, \text{N} \).

Analyze Elements in Group (d)

Arrange the elements \( \text{Al}, \text{Si}, \text{P} \) across Period 3. Ionization energy increases as we move from left to right. Thus, the order is \( \text{Al}, \text{Si}, \text{P} \).

Key concepts

Periodic Table

The periodic table is a tabular arrangement of chemical elements. Elements are organized based on their atomic number, electron configurations, and recurring chemical properties. Each row in the table is called a period, and each column is called a group.
In general, moving from left to right across a period, atomic numbers increase and elements display a gradual change in properties. Moving down a group, elements have similar chemical properties because they have the same number of electrons in their outermost shell.
A fundamental trend in the periodic table related to our problem is how ionization energy changes as you move across periods and down groups.

Atomic Structure

The structure of an atom consists of a nucleus, containing protons and neutrons, and electrons that orbit around the nucleus. The arrangement of these electrons in shells or energy levels determines an element’s chemical properties and reactivity.
As you move across a period in the periodic table, the number of protons in the nucleus increases. This increased positive charge pulls the electrons closer, resulting in a smaller atomic radius. This smaller radius means electrons are held more tightly, which in turn increases ionization energy.
When you move down a group, additional electron shells are added, increasing the distance between the nucleus and the outermost electrons. This leads to a larger atomic radius and makes it easier to remove an electron, thus lowering the ionization energy.

Ionization Energy

Ionization energy is the amount of energy required to remove the outermost electron from an isolated atom in its gaseous state. It's a crucial property that reflects the strength with which an electron is held by an atom.
The trend in ionization energy across the periodic table is as follows: it generally increases from left to right across a period. This is because atoms are smaller and have a greater effective nuclear charge, making electrons more difficult to remove.
Conversely, ionization energy decreases as you move down a group. This is because atoms are larger, and the outermost electron is farther from the nucleus and experiences more shielding from inner shell electrons, making it easier to remove.

Chemical Properties

The chemical properties of an element are primarily determined by its electron configuration and position in the periodic table. Elements in the same group typically display similar chemical behavior because they have the same number of valence electrons.
For example, elements in Group 1 (alkali metals) are highly reactive and tend to lose one electron to form positive ions. In contrast, elements in Group 17 (halogens) tend to gain one electron to form negative ions.
Understanding the trends and patterns in the periodic table, including ionization energy, can help predict how an element will react chemically. For instance, knowing that ionization energy decreases down a group explains why elements lower in a group like alkali metals are more reactive compared to their counterparts higher up in the group.