Problem 118 - Chemistry: An Atoms-Focused Approach

Question

Without referring to Figure \(3.37,\) arrange the following groups of elements in order of increasing first ionization energy. a. \(\mathrm{Mg}, \mathrm{Ca}, \mathrm{Sr}, \mathrm{Ba}\) b. \(\mathrm{He}, \mathrm{Ne}, \mathrm{Ar}, \mathrm{Kr}\) c. \(\mathrm{P}, \mathrm{S}, \mathrm{Cl}, \mathrm{Ar}\)

Step-by-Step Solution

Answer

Question: Arrange the following groups of elements in order of increasing first ionization energy: a) Mg, Ca, Sr, Ba b) He, Ne, Ar, Kr c) P, S, Cl, Ar Answer: a) Ba < Sr < Ca < Mg b) Kr < Ar < Ne < He c) P < S < Cl < Ar

Step 1: Group a: \(\mathrm{Mg}, \mathrm{Ca}, \mathrm{Sr}, \mathrm{Ba}\)

These elements belong to the same group (Group 2, alkaline earth metals) in the periodic table, so we apply the trend of ionization energy decreasing down a group. The order of increasing first ionization energy is: Ba < Sr < Ca < Mg.

Step 2: Group b: \(\mathrm{He}, \mathrm{Ne}, \mathrm{Ar}, \mathrm{Kr}\)

These elements belong to the same group (Group 18, noble gases) in the periodic table, so we apply the trend of ionization energy decreasing down a group. The order of increasing first ionization energy is: Kr < Ar < Ne < He.

Step 3: Group c: \(\mathrm{P}, \mathrm{S}, \mathrm{Cl}, \mathrm{Ar}\)

These elements belong to the same period (Period 3) in the periodic table, so we apply the trend of ionization energy increasing from left to right along a period. The order of increasing first ionization energy is: P < S < Cl < Ar.

Key Concepts

Periodic Table Trends

The periodic table is a powerful chart that displays the elements in a systematic way, reflecting their properties. A key trend shown is the change in ionization energy, which is the energy required to remove an electron from an atom. There are two main trends to remember when discussing ionization energy:

• Moving from left to right across a period, ionization energy tends to increase. This is because electrons are added to the same energy level while protons are added to the nucleus, increasing the nucleus' pull on electrons.
• Moving down a group, ionization energy tends to decrease. As we move down a group, additional electron shells are added, making the outer electrons further from the nucleus and easier to remove.

These trends help predict and explain the behavior of elements in chemical reactions, playing a significant role in their reactivity and bonding characteristics.
Understanding periodic trends allows for a deeper comprehension of the periodic table and the forces that govern element behavior.

Alkaline Earth Metals

Alkaline earth metals, located in Group 2 of the periodic table, are made up of elements like magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). These elements are known for being highly reactive, though less so than their alkali metal neighbors in Group 1.
One of the prominent characteristics of alkaline earth metals is their ionization energy.

• As you move down Group 2 from Mg to Ba, the first ionization energy decreases.
• This is due to the additional electron shells which increase the distance between the nucleus and the outermost electrons, thus reducing the effective nuclear charge felt by those electrons.

This trend explains why barium is more reactive compared to magnesium: it requires less energy to lose its outer electron, an essential step in many chemical reactions.

Noble Gases

Noble gases form Group 18 in the periodic table and include helium (He), neon (Ne), argon (Ar), and krypton (Kr). These elements are best known for their lack of reactivity, which stems from their full valence electron shell. In terms of ionization energy:

• Noble gases have some of the highest ionization energies in the periodic table.
• Their ionization energy decreases when moving down the group from helium to krypton.
• This decrease occurs because outer electrons are further from the nucleus in larger atoms, making them easier to remove despite the completed electron shell.

This property of high ionization energy keeps noble gases stable and unlikely to form chemical bonds under normal conditions.

Periodic Trends

Periodic trends not only include changes in ionization energy but also other properties like atomic radius, electronegativity, and electron affinity. These trends are consistent because the periodic table is arranged based on atomic number, which influences electron configurations. Here are some important periodic trends: - Atomic Radius: Generally increases down a group as electron shells add, but decreases across a period due to increased nuclear charge pulling electrons closer. - Electronegativity: Tends to increase across a period as the desire for electrons strengthens while decreasing down a group. These trends assist chemists in predicting element behavior, understanding reactivity, and designing new compounds. The periodic table, with its patterns and regularities, allows us to make sense of the diverse array of chemical elements and their interactions.