Problem 13 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The first ionization energy (in \(\mathrm{kJ} / \mathrm{mol}\) ) of \(\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}\) and \(\mathrm{Si}\) respectively, are: (a) \(496,737,577,786\) (b) \(496,577,737,786\) (c) \(786,737,577,496\) (d) \(496,577,786,737\)

Step-by-Step Solution

Answer

Option (b) \(496, 577, 737, 786\) is the correct order of increasing ionization energy for Na, Mg, Al, and Si.

Step 1: Understanding Ionization Energy

Ionization energy is the energy required to remove the outermost electron from a neutral atom in its gaseous state. Generally, ionization energy increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table.

Step 2: Locate Elements in the Periodic Table

The elements given are \(\text{Na (Sodium)}, \text{Mg (Magnesium)}, \text{Al (Aluminum)},\) and \(\text{Si (Silicon)}\). All of them belong to the same period (Period 3) of the periodic table. The order from left to right is: \(\text{Na}, \text{Mg}, \text{Al}, \text{Si}\).

Step 3: Determine General Ionization Energy Trend

Within a given period, ionization energy increases across the period from left to right. Thus we expect the order of increasing ionization energy to be: \(\text{Na} < \text{Mg} < \text{Al} < \text{Si}\).

Step 4: Match Data with Trends

According to the trend, the increasing order should be \(496, 577, 737,\) and \(786\). Comparing this to the given options: (a) \(496, 737, 577, 786\) (b) \(496, 577, 737, 786\) (c) \(786, 737, 577, 496\) (d) \(496, 577, 786, 737\), option (b) matches the expected trend.

Key Concepts

Periodic Table Trends

Understanding the periodic table trends is essential for predicting various properties of elements, one of which is ionization energy. Ionization energy generally increases as we move across a period from left to right. This is because elements on the right side of the periodic table have more protons, leading to a greater effective nuclear charge. This increase in positive charge means that electrons are held more tightly, which requires more energy to remove one.
On the other hand, ionization energy tends to decrease as we move down a group. As you go down a group, the outermost electron is further from the nucleus due to added energy levels or shells. This increased distance reduces the nuclear attraction compared to elements higher in the group, causing less energy to be needed to remove an electron.
These trends are vital for predicting how an element will react, its bonding tendencies, and its general chemical behavior.

Periodic Table Groups

Groups in the periodic table are columns that share similar chemical properties. Each group contains elements that have the same number of electrons in their outermost shell, also known as valence electrons. This similarity in electron configuration means that elements in the same group typically show similar reactivity and other chemical behaviors.
For example, Group 1 contains alkali metals like sodium (\(\text{Na}\)) which are very reactive, especially with water, due to their single valence electron. Groups can help predict the behavior of elements; elements within the same group often form similar compounds.
It's also crucial to note that as you move down a group, the elements increase in atomic size, which influences properties such as ionization energy, because the outer electrons are held less tightly by the nucleus.

Periodic Table Periods

Periods are rows on the periodic table and represent elements organized by increasing atomic number. As you move across a period from left to right, the characteristics of elements often change significantly. One major trend is the increasing ionization energy. This occurs because as protons are added to the nucleus, electrons are held more tightly.
The periodic table is structured such that each period corresponds to the filling of a different electron shell. For instance, in Period 3, where elements like sodium (\(\text{Na}\)), magnesium (\(\text{Mg}\)), aluminum (\(\text{Al}\)), and silicon (\(\text{Si}\)) are located, electrons are added to the third shell. This electron addition results in various changes in atomic properties across the period.
Understanding periods can help one predict how elements react with one another and how their properties change systematically across the table.