Problem 153 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following atoms has the highest first Ionization energy? (a) \(\mathrm{Na}\) (b) \(\mathrm{K}\) (c) \(\mathrm{Sc}\) (d) \(\mathrm{Rb}\)

Step-by-Step Solution

Answer

Scandium ( m Sc m) has the highest first ionization energy.

Step 1: Understand Ionization Energy

Ionization energy is the amount of energy required to remove the outermost electron from an atom in the gas phase. Generally, ionization energy increases across a period from left to right in the periodic table and decreases down a group.

Step 2: Identify Position in Periodic Table

Locate the given elements on the periodic table: -  m Na m  (Sodium) is in Group 1, Period 3. -  m K m  (Potassium) is in Group 1, Period 4. -  m Sc m  (Scandium) is in Group 3, Period 4. -  m Rb m  (Rubidium) is in Group 1, Period 5.

Step 3: Analyze Trends Across Periods and Groups

According to periodic trends, ionization energy increases across a period and decreases down a group. Therefore, Scandium  m ( m Sc), which is to the right in period 4 compared to Potassium  m ( m K) and is not as far down a group like Rubidium  m ( m Rb), should have a higher ionization energy.

Step 4: Answer Based on Trends

Given the periodic trends, Scandium ( m Sc m) is expected to have the highest first ionization energy because it is in period 4, further to the right than K or Na, and higher up in the column than Rb.

Key Concepts

Periodic Table Trends

Understanding periodic table trends helps us predict how different elements behave. One of the key trends is the variation in ionization energy across the periods and groups. As you move from left to right across a period, the ionization energy generally increases. This is because additional protons in the nucleus create a stronger attraction, making it harder to remove an electron.

Conversely, as you move down a group, ionization energy decreases. The outer electrons are further from the nucleus and more shielded by inner electron shells. This makes it easier to remove an electron, since the effective nuclear charge experienced by the outer electrons is reduced.

The combination of these movements helps in predicting element properties based on their position in the periodic table.

First Ionization Energy

First ionization energy refers to the energy required to remove the first outermost electron from a neutral atom. This energy is a measure of how tightly an electron is bound to an atom.

Elements with a high first ionization energy hold their electrons tightly. They tend to be more resistant to losing an electron and forming positive ions. What's fascinating is that this energy is influenced heavily by electronic structure.

• The first ionization energy is usually higher in small atoms, where the electron is nearer to the positively charged nucleus.
• Larger atoms with electrons in higher orbitals generally exhibit lower ionization energies.

These factors help in understanding the chemical reactivity and bonding behavior of elements.

Periodic Groups

A periodic group is a vertical column in the periodic table, and it brings together elements with similar chemical properties. Trends within these groups are quite distinct. For instance, all elements in a group typically have the same number of valence electrons, influencing their chemical behavior.

Across a given period, elements move from highly reactive metals to less reactive nonmetals. In groups, elements share chemical features like halogens being highly reactive nonmetals.
One interesting behavior in groups is their ionization energy trends. Those within the same group will tend to have lowering ionization energy as you move down due to increasing atomic size and electron shielding.

Atomic Structure

Atomic structure is the arrangement of electrons around the nucleus of an atom, determined by the number of protons, neutrons, and electrons. This structure defines an element's chemical and physical characteristics.

In any atom, electrons are arranged in energy levels or shells around the nucleus. The first levels are filled first, due to their lower energy state.

• Each energy level can hold a specific number of electrons: 2 on the first, 8 on the second, and so on.
• The outermost electrons, called valence electrons, are crucial for chemical bonding and reactivity.

The distribution of electrons helps explain why elements are more reactive or stable, influencing their position in the periodic table and their ionization energy.