Problem 77 - Chemistry Central Science

Question

Compare the elements fluorine and chlorine with respect to the following properties: (a) electron configuration, (b) most common ionic charge, (c) first ionization energy, (d) reactivity toward water, (e) electron affinity, (f) atomic radius. Account for the differences between the two elements.

Step-by-Step Solution

Answer

Fluorine and chlorine have similar properties, as they both are halogens. Their electron configurations are \(1s^2 2s^2 2p^5\) for fluorine and \(1s^2 2s^2 2p^6 3s^2 3p^5\) for chlorine. They both have a most common ionic charge of -1, with fluorine having a higher first ionization energy (1690 kJ/mol) than chlorine (1250 kJ/mol). Fluorine reacts more violently with water due to its higher electronegativity. Chlorine has a higher electron affinity (349 kJ/mol) than fluorine (328 kJ/mol) because of its larger atomic radius (99 pm for chlorine and 64 pm for fluorine). The differences between the two elements can be attributed to their atomic structures and the number of electron shells.

Step 1: Electron Configuration

First, let's understand the electron configuration for each element. The electron configuration helps to understand various aspects of the element, such as its reactivity and chemical behavior. Fluorine has an atomic number of 9, and Chlorine has an atomic number of 17. Their electron configurations are: - Fluorine: \(1s^2 2s^2 2p^5\) - Chlorine: \(1s^2 2s^2 2p^6 3s^2 3p^5\)

Step 2: Most Common Ionic Charge

The most common ionic charge of an element refers to the charge it acquires after it loses or gains electrons in its outermost shell, in order to achieve a stable configuration. Both fluorine and chlorine are halogens, with only one electron short of achieving a stable noble gas configuration. Thus, they tend to gain one electron to achieve a full outer electron shell, resulting in a negative one charge: - Fluorine: -1 - Chlorine: -1

Step 3: First Ionization Energy

The first ionization energy is the amount of energy required to remove one electron from a neutral atom to form a positive ion. Fluorine and chlorine have the following first ionization energies: - Fluorine: 1690 kJ/mol - Chlorine: 1250 kJ/mol Fluorine has a higher first ionization energy than chlorine.

Step 4: Reactivity Toward Water

Reactivity toward water is determined by the ability of an element to react with water molecules. Both fluorine and chlorine react readily with water, but fluorine is more reactive: - Fluorine: reacts violently with water, producing hydrogen fluoride (HF) and ozone (O3) - Chlorine: reacts with water to produce hydrogen chloride (HCl) and hypochlorous acid (HOCl)

Step 5: Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom to achieve a more stable configuration. Fluorine and chlorine have the following electron affinities: - Fluorine: 328 kJ/mol - Chlorine: 349 kJ/mol Chlorine has a higher electron affinity than fluorine.

Step 6: Atomic Radius

Atomic radius refers to the distance between the nucleus of an atom and its outermost electron shell. Fluorine and chlorine have the following atomic radii: - Fluorine: 64 pm - Chlorine: 99 pm Chlorine has a larger atomic radius than fluorine.

Step 7: Account for Differences

Differences between fluorine and chlorine can be explained by their atomic structures: - The electron configuration shows that fluorine has one fewer energy level than chlorine. This results in a smaller atomic radius for fluorine because there are fewer electron shells. - The higher first ionization energy of fluorine is due to its smaller atomic radius, which results in its electrons being more tightly bound to the nucleus. - Fluorine's greater reactivity with water is because it's more electronegative than chlorine, which means it attracts electrons more strongly and more easily forms chemical bonds. - The higher electron affinity of chlorine is due to its larger atomic radius, which means that the nucleus has a weaker hold on its outermost electrons, making it easier to gain an additional electron in the outer shell.