Problem 117 - 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. \(\mathrm{F}, \mathrm{Cl}, \mathrm{Br}, \mathrm{I}\) b. \(\mathrm{Li}, \mathrm{Be}, \mathrm{Na}, \mathrm{Mg}\) c. \(\mathrm{N}, \mathrm{O}, \mathrm{F}, \mathrm{Ne}\)

Step-by-Step Solution

Answer

Question: Arrange the following groups of elements in order of increasing ionization energy. a) F, Cl, Br, I b) Li, Be, Na, Mg c) N, O, F, Ne Answer: a) I < Br < Cl < F b) Li < Na < Be < Mg c) N < O < F < Ne

Step 1: Group a: F, Cl, Br, I

These elements belong to the same group (Group 7, Halogens), so we can use the trend of ionization energy decreasing down a group: F > Cl > Br > I. Therefore, the order of increasing ionization energy will be: I < Br < Cl < F.

Step 2: Group b: Li, Be, Na, Mg

These elements are from different periods (Rows 2 and 3) and belong to the same groups (Group 1 and 2 respectively). As ionization energy generally increases from left to right across a period, we know that the ionization energy of Li < Be and Na < Mg. Ionization energy generally decreases down a group, so the ionization energy of Li < Na and Be < Mg. Therefore, the order of increasing ionization energy will be: Li < Na < Be < Mg.

Step 3: Group c: N, O, F, Ne

These elements belong to the same period (Row 2) of the periodic table – Period 2. As ionization energy generally increases from left to right across a period, we can arrange them in order of increasing ionization energy as: N < O < F < Ne.

Key Concepts

Periodic Trends

Periodic trends are patterns observed in the periodic table that describe various properties of elements, such as ionization energy. Ionization energy refers to the energy required to remove an electron from an atom or ion. Understanding periodic trends helps predict how elements behave in different chemical contexts.
These trends arise due to changes in atomic structure, such as the number of electron shells and the effective nuclear charge.

• Across a period (left to right): Ionization energy tends to increase because atoms have more protons, leading to a stronger attraction between the nucleus and electrons.
• Down a group (top to bottom): Ionization energy tends to decrease. Electrons are further from the nucleus and feel less pull due to additional inner electron shells acting as a shield.

Recognizing these trends allows students to predict properties like reactivity and stability across different families of elements.

Halogens

Halogens consist of elements in Group 7 of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). These elements are highly reactive nonmetals and are known for forming salts when combined with metals.
Their reactivity is partly due to their high electronegativity and tendency to gain electrons. In terms of ionization energy, which is the focus of this exercise:

• Halogens show decreasing ionization energy as you move down the group. This is because as atomic size increases, the outer electrons are farther from the nucleus, making them easier to remove.
• Consequently, fluorine has the highest ionization energy among this group, followed by chlorine, bromine, and iodine.

These properties explain why halogens are often found in compounds, as they readily react with other elements to achieve a more stable electronic configuration.

Periodic Table Groups

Periodic table groups refer to the columns in the periodic table, where elements share similar valence electron configurations and display similar chemical properties. Each group has its own name and characteristic traits.

• For example, Group 1 elements are known as the alkali metals, which are highly reactive and have a single valence electron.
• Group 2 elements, called alkaline earth metals, have two valence electrons, making them slightly less reactive than their Group 1 neighbors.
• Halogens, in Group 7, are very reactive, largely due to their desire to gain an electron to complete their outer shell.

Understanding these groups is essential in predicting how elements react and bond with each other. Elements within the same group tend to have similar reactions and often form analogous compounds. This knowledge is fundamental for students when organizing elements and predicting chemical behavior during their studies.