Problem 31 - General Chemistry: Principles and Modern Applications

Question

Compare the elements \(\mathrm{Al}, \mathrm{Si}, \mathrm{S},\) and \(\mathrm{Cl}.\) (a) Place the elements in order of increasing ionization energy. (b) Place the elements in order of increasing electron affinity.

Step-by-Step Solution

Answer

For increasing ionization energy, the order of the elements is Al, Si, S, Cl. For increasing electron affinity, the order is identical: Al, Si, S, Cl.

Step 1: Understand the position of each element on the periodic table

Find the position of the given elements - Al, Si, S, and Cl - on the periodic table. Al is in group 13 and period 3. Si is in group 14 and period 3. S is in group 16 and period 3. Cl is in group 17 and period 3.

Step 2: Order the elements based on ionization energy

Recall that ionization energy increases going from left to right across a period on the periodic table. So, the elements, in increasing order of ionization energy are: Al < Si < S < Cl.

Step 3: Order the elements based on electron affinity

Electron affinity increases across a period from left to right. Following this rule, the elements in increasing order of electron affinity are: Al < Si < S < Cl.

Key Concepts

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. It is an important periodic trend that helps us understand how elements interact with each other and form bonds. As you move from left to right across a period on the periodic table, ionization energy generally increases. This is because the atomic number increases, meaning there are more protons in the nucleus. Each additional proton increases the positive charge, which attracts the electrons more strongly and requires more energy to remove one.

• Higher ionization energy means it's harder to remove an electron.
• As electrons are removed, they are held more tightly by the nucleus.

When comparing elements like Al, Si, S, and Cl, you will find that Aluminum (Al) has the lowest ionization energy, followed by Silicon (Si), then Sulfur (S), and Chlorine (Cl) with the highest. Chlorine's higher ionization energy reflects its stronger nuclear pull on its valence electrons.

Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom to form a negative ion. Like ionization energy, electron affinity also illustrates periodic trends. As you move from left to right across a period, electron affinity becomes more negative, which means that the atom releases more energy when it gains an electron. Atoms with higher electron affinities tend to gain electrons more easily, forming negative ions.

• Higher electron affinity means greater energy release upon gaining an electron.
• Atoms on the right side of the periodic table usually have higher electron affinities.

Looking at elements Al, Si, S, and Cl, we see that Aluminum (Al) has the lowest electron affinity, followed by Silicon (Si) and then Sulfur (S). Chlorine (Cl) has the highest electron affinity, as it most readily gains an electron to achieve a full outer electron shell.

Periodic Table

The periodic table is a tabular display of chemical elements, organized based on their atomic number, electron configuration, and recurring chemical properties. The table is structured in such a way that it reflects periodic trends such as ionization energy and electron affinity.

• Columns are called groups, and rows are called periods.
• Elements in the same group typically have similar properties.
• Across each period, certain properties increase or decrease in a predictable manner.

Understanding the layout of the periodic table isn't just about memorizing where elements are; it's about understanding why elements behave the way they do. From left to right across a period, the atomic radius decreases, ionization energy increases, and electron affinity usually becomes more negative. These trends help us predict how elements will react chemically. For Al, Si, S, and Cl, noticing their positions can give you insights into their reactivity and bonding characteristics, governed by their ionization energies and electron affinities.