Chem-To-Go Lesson 11Unit 3

ATOMIC RADIUS & IONIC RADIUS

TRENDS

Trend = a repeating pattern

Periodic Trend = a repeating pattern on the periodic table

ATOMIC RADIUS

Definition: ½ the distance between the nuclei of two identical touching atoms

ATOMIC RADIUSPeriod trend: [row pattern]; atomic radius DECREASES from left to right across a row Group trend: [column pattern]; atomic radius DECREASES from bottom to top of a column

WHY?•Radius decreases across a period because the nucleus is gaining more protons to become larger and more strongly positive. The electron cloud is drawn in by forces of attraction.

• Radius decreases up a group because there are fewer energy levels at the top of the periodic table.

PERIOD TREND

GR

OU

P T

REN

D

ATOMIC RADIUSMemory

Tool

SAMPLE MULTIPLE CHOICE:

1. Which of the following atoms will has the smallest radius?

a. Tin b. Strontium c. Selenium d. Arsenic

• Use a periodic table!• Find all of the elements.• Apply the trend.

ATOMIC RADIUSMemory

Tool

SAMPLE MULTIPLE CHOICE:

2. Which of the following atoms will has a larger radius than calcium?

a.Aluminum b. Copper c. Potassium d. None

• Use a periodic table!• Find all of the elements.• Apply the trend.

IONIC RADIUS

Definition: size of the ion; usually compared to the size of its neutral atom

CATION RADIUS

ANION RADIUS

IONIC RADIUS

Cations form by losing electrons. As electrons are

lost, the ion becomes smaller.

Anions form by gaining electrons. As electrons are

gained, the ion becomes larger.