Question

which of the following atom has the lowest ionization potential? (A) \({ }^{14}{ }_{7} \mathrm{~N}\) (B) \({ }^{40}{ }_{18} \mathrm{Ar}\) (C) \({ }^{133} 55 \mathrm{Cs}\) (D) \({ }^{16}{ }_{8} \mathrm{O}\)

Short answer

The atom with the lowest ionization potential is (C) \({ }^{133} 55 \mathrm{Cs}\) (Cesium), as it is farther down and to the left in the periodic table compared to the other options.

Step-by-step solution

Identify each atom's position on the periodic table

To analyze the ionization potential, first, we need to determine the position of each atom in the periodic table. The atomic number (number of protons) will help in identifying the element, and the period and group they belong to. (A) \({ }^{14}{ }_{7} \mathrm{~N}\) : Nitrogen, Period 2, Group 15 (5A) (B) \({ }^{40}{ }_{18} \mathrm{Ar}\) : Argon, Period 3, Group 18 (8A) (C) \({ }^{133} 55 \mathrm{Cs}\) : Cesium, Period 6, Group 1 (1A) (D) \({ }^{16}{ }_{8} \mathrm{O}\) : Oxygen, Period 2, Group 16 (6A)

Compare the atoms' ionization potentials based on their position in the periodic table

As mentioned before, ionization potential decreases down a group and increases across a period. We can now compare the atoms according to their position: - Nitrogen and Oxygen are in the same period (Period 2), but Oxygen has a higher ionization potential because it is farther to the right. - Argon is in a higher period (Period 3) than Nitrogen and Oxygen and is in Group 18, which is the farthest right group on the periodic table, thus having a very high ionization potential. - Cesium is in Period 6 and Group 1. It is farther down and to the left on the periodic table, indicating lower ionization potential compared to the other atoms.

Determine which atom has the lowest ionization potential

Based on the positions of each atom on the periodic table, we can conclude that Cesium (\({ }^{133} 55 \mathrm{Cs}\)) has the lowest ionization potential among the given options. Thus, the correct answer is (C) \({ }^{133} 55 \mathrm{Cs}\).

Key concepts

Periodic Table

The periodic table is an organized chart of all known elements. It is arranged by increasing atomic number, which represents the number of protons in an atom. This organization helps scientists and students understand the properties of elements easily.

The table has rows called periods and columns called groups. Each period indicates the energy level for the electrons in an atom's outer shell. Elements in the same group share similar chemical properties because they have the same number of valence electrons.

For instance, the elements listed in the question are placed in different periods and groups:

• Nitrogen is in Period 2, Group 15.
• Oxygen is in Period 2, Group 16.
• Argon is in Period 3, Group 18.
• Cesium is in Period 6, Group 1.

Their positions on the periodic table help us predict their chemical behavior, like ionization potential.

Atomic Number

Each element on the periodic table is uniquely identified by its atomic number. This number tells us how many protons are present in the nucleus of an atom of the element.

Protons are positively charged particles, and their number matches the number of electrons in a neutral atom, determining the element's identity and place on the periodic table.

In the context of the problem, the atomic numbers for the elements are:

• Nitrogen has an atomic number of 7.
• Oxygen has an atomic number of 8.
• Argon has an atomic number of 18.
• Cesium has an atomic number of 55.

Knowing the atomic number allows us to place these elements in their correct position on the periodic table, crucial for understanding their ionization potential.

Periodic Trends

Periodic trends are patterns that occur across periods and groups in the periodic table. These trends help predict important element properties such as electronegativity, atomic size, and ionization potential.

Ionization potential refers to the energy required to remove an electron from a neutral atom. The trend shows that ionization potential generally increases across a period, as atoms have more protons and a stronger attraction for electrons. It decreases down a group, as the electrons are further from the nucleus's pull.

For elements listed:

• Cesium has the lowest ionization potential because it is in a lower period (6) and a left-most group (1).
• Argon, being in Group 18, has high ionization potential but is in a higher period (3) compared to nitrogen and oxygen.
• Oxygen, with a higher atomic number than nitrogen, shows higher ionization energy among them because it is further to the right in the same period (2).

Understanding these trends is key to solving the exercise as it leads us to identify cesium as having the lowest ionization potential.

Elements

Elements are pure substances consisting of only one type of atom. They cannot be broken down into simpler substances through chemical reactions. Each element is represented by a unique symbol on the periodic table and has distinct chemical properties.

In the given exercise, nitrogen (N), oxygen (O), argon (Ar), and cesium (Cs) are elements. Each of these has its own properties and place in the periodic table:

• Nitrogen and oxygen are gases and non-metals found close together in Period 2.
• Argon is a noble gas, chemically inert, found in Group 18.
• Cesium is an alkali metal known for its reactivity, found far down in Group 1.

The elements' behaviors and reactivity are influenced by their position on the periodic table, which helps explain why cesium has the lowest ionization potential in the problem. This understanding aids students in predicting element behavior in chemical reactions.