Atomic Radius:
 Atomic Radius: Distance from the center of an atom to the outermost electron.
 Measured in Angstroms (Å)
 1 x 1010 Å = 1 meter (m)
 1 meter (m) = 1 x 1012 picometers (pm)
 Group Trend for Atomic Radius (Top to Bottom):
 Hydrogen:
+
)
1p
0n
1e Lithium:
3 p+
4n
 Sodium:
)
)
2e-
1e-
)
)
)
2e-
8e-
1e-
)
)
)
)
2e-
8e-
8e-
1e-
11 p+
12 n
 Potassium:
19 p+
20 n
 As you go down a group or family (top to bottom) on the periodic table, atomic
radius increases because you are adding energy levels.
 Periodic Trend for Atomic Radius (Left to Right):
 Lithium: 3 p+
4n
 Boron:
 Nitrogen:
5 p+
6n
7 p+
7n
)
)
2e-
1e-
)
)
2e-
3e-
)
)
2e-
5e-
 Fluorine:
9 p+
10 n
)
)
2e-
7e-
 As you go across a period (left to right) on the periodic table, atomic radius
decreases, because there are more protons present, which attracts the electrons
closer to the nucleus.
 Example:
Place the following elements in order of increasing atomic radius:
Bromine (Br), Chlorine (Cl), Iodine (I), Fluorine (F)
Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I)
 Example:
Place the following elements in order of increasing atomic radius:
Aluminum (Al), Sodium (Na), Phosphorus (P), Chlorine (Cl), Magnesium (Mg)
Chlorine (Cl), Phosphorus (P), Aluminum (Al), Magnesium (Mg), Sodium (Na)
 Example:
Place the following elements in order of increasing atomic radius:
Carbon (C), Tin (Sn), Fluorine (F), Rubidium (Rb), Silicon (Si), Germanium (Ge)
Fluorine (F), Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), Rubidium (Rb)
 Example:
Place the following elements in order of increasing atomic radius:
Arsenic (As), Francium (Fr), Bromine (Br), Fluorine (F), Potassium (K),
Calcium (Ca), Germanium (Ge)
Fluorine (F), Bromine (Br), Arsenic (As), Germanium (Ge), Calcium (Ca),
Potassium (K), Francium (Fr)