Periodic Trends Worksheet (Page 7 of 18) in pdf

Periodic Trends Worksheet Page 7

Honors Chemistry - Michalek

Unit 06 Periodic Trends

Unit 06 – Periodic Trends

NAME: ______________________

Discussion Sheet 6a – Atomic Radius and Ionic Radius

The relative size of an atom or ion can be determined based on its location in the periodic table. The radius of an atom is half the

distance between the nuclei of two like atoms. Therefore, radius is directly proportional to size.

Atomic size generally increases as you move down a group of the periodic table. As you descend, electrons are added to successively

higher principal energy levels and the nuclear charge increases. The outermost orbital is larger as you move downward. Atoms at the

bottom of the table are bigger than atoms at the top.

Atomic size generally decreases as you move from left to right across a period. As you go across a period, the principal energy level

remains the same. Each element has one more proton and one more electron than the preceding element. The electrons are added to

the same principal energy level. The effect of the increasing nuclear charge on the outermost electrons is to pull them closer to the

nucleus. Atoms on the left of a period are bigger than atoms on the right.

This trend is more pronounced as you move through a group (up or down) than through a period (right or left), because of the addition

of new orbitals as you move down the table. An up/down move in the periodic table is a much more important change in atomic

size than a left/right move.

The trend described above is also true for positive and negative ions. However, there is one fundamental difference caused by the

formation of the ions. Positive ions are formed when an atom loses electrons. Therefore, the relative nuclear charge of the ion is more

than that of a neutral atom. Positive ions are always smaller than neutral atoms. In a similar fashion, negative ions are formed

when an atom gains electrons. The relative hold of the nucleus is less in a negative ion than it is for a neutral atom. Therefore,

negative ions are always bigger than neutral atoms.

Periodic Trends Worksheet Page 7