Textbook Question
Little is known about the chemistry of astatine (At) from direct observation, but reasonable predictions can be made.
(a) Is astatine likely to be a gas, a liquid, or a solid?
Ch.22 - The Main Group Elements
Chapter 22, Problem 145
Why does chemical reactivity decrease from top to bottom in group 7A?
Verified step by step guidance1
Step 1: Understand that Group 7A elements are known as halogens, which include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements are highly reactive nonmetals.
Step 2: Recognize that chemical reactivity in halogens is largely determined by their ability to gain an electron to achieve a stable noble gas electron configuration. This is because they have seven valence electrons and need one more to complete their outer shell.
Step 3: Consider the atomic structure of halogens. As you move down the group from fluorine to astatine, the atomic radius increases because additional electron shells are added.
Step 4: Realize that with an increase in atomic radius, the outermost electrons are further from the nucleus. This results in a weaker attraction between the nucleus and the valence electrons, making it harder for the atom to attract additional electrons.
Step 5: Conclude that the decrease in effective nuclear charge and the increase in atomic size as you move down the group lead to a decrease in the ability of the halogens to attract electrons, thus decreasing their chemical reactivity.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Group 7A Elements (Halogens)
Group 7A, also known as the halogens, includes elements like fluorine, chlorine, bromine, iodine, and astatine. These elements are known for their high reactivity due to their tendency to gain one electron to achieve a stable octet configuration. The reactivity of halogens is influenced by their electronegativity and the ability to attract electrons.
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Atomic Size and Shielding Effect
As you move down Group 7A, the atomic size increases due to the addition of electron shells. This increase in size leads to a greater distance between the nucleus and the outermost electrons, which reduces the effective nuclear charge experienced by these electrons. Additionally, the shielding effect from inner electrons further diminishes the nucleus's ability to attract additional electrons, thus decreasing reactivity.
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Electronegativity Trends
Electronegativity is a measure of an atom's ability to attract and hold onto electrons. In Group 7A, electronegativity decreases as you move down the group. This decrease means that larger atoms are less effective at attracting electrons, which contributes to the overall decrease in reactivity of halogens from top to bottom, as their ability to gain an electron diminishes.
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