Open Question
Explain why atomic radius decreases as you move to the right across a period for main-group elements but not for transition elements.
10. Periodic Properties of the Elements
Periodic Trend: Atomic Radius
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Which of the following statements correctly describes the trend in atomic radius across a period in the periodic table?
A
Atomic radius remains constant across a period.
B
Atomic radius increases from left to right across a period.
C
Atomic radius decreases from left to right across a period.
D
Atomic radius first decreases and then increases across a period.
Verified step by step guidance1
Understand the concept of atomic radius: Atomic radius is the distance from the nucleus of an atom to the outermost shell of electrons. It is a measure of the size of an atom.
Identify the trend in atomic radius across a period: As you move from left to right across a period in the periodic table, the atomic number increases, meaning more protons are added to the nucleus.
Consider the effect of increased nuclear charge: With more protons in the nucleus, the positive charge increases, which pulls the electrons closer to the nucleus, reducing the atomic radius.
Account for electron shielding: Although electrons are added as you move across a period, they are added to the same energy level, so the shielding effect does not significantly counteract the increased nuclear charge.
Conclude the trend: Due to the increased nuclear charge and relatively constant shielding, the atomic radius decreases from left to right across a period in the periodic table.
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