Page 78 - Chemistry eBook
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Atomic Radius
ATOMIC RADIUS: The size of the atom
( Reffy: pp. 10-11)
• As we go down a group on the Periodic
Table, the atomic radius increases
because there are more energy levels. • As we go across a period on the Periodic
Table, the atomic radius decreases. Why? The number of protons and
electrons increases, but the number of shells stays the same. The forces of attraction between the protons and electrons are so strong, they pull the atom together.
This is a common Regents question.
“Hey, that makes sense. An element with one energy shell will be smaller than an element with three energy shells.”
Opposites attract. The positive protons and negative electrons are strongly attracted. So they don’t stay spread apart, they come close together for a tight hug!
78 © UNIT 3: PERIODIC TABLE OF ELEMENTS
