Periodic Properties
Atomic Size
 Atomic size: the radius of an atom (distance from
nucleus to electron cloud) is considered.
 Measured in angstroms (A) : 1 cm = 1x108 A
Atomic size increases
•Periodic Trend: Atomic size within a group increases
and decreases as atomic number increases.
Atomic size increases
Ionic Size
 Some elements tend to gain or lose electrons to form
ions.
 Metals lose electrons and form positive ions called
cations.
 Nonmetals gain electrons and form negative ions
called anions.
Fe2+
Iron has a 2+ charge
because it lost 2 electons.
Ionic Size
 Periodic Trend:
 Cations are smaller than original atom. Losing electrons
means the nucleus has a greater attraction for electrons
remaining.
 Anions are bigger than original atom. Gaining electrons
means the nucleus has less attraction for a greater
number of electrons.
Learning Check
 For each of the following sets of atoms and ions,
decide which is the smallest.
a. Na, Na+
b. Cl, Clc. Na+, Cld. H+, H, He. Fe2+, Fe3+
f. F-, Ne, Na+
Learning Check
 For each of the following sets of atoms and ions,
decide which is the smallest.
a. Na, Na+
b. Cl, Clc. Na+, Cld. H+, H, He. Fe2+, Fe3+
f. F-, Ne, Na+
Classwork
 Textbook p 255 #1,2
p 257 # 3,4
p 266 # 19
Ionization energy
 Energy required to remove an electron from an atom.
 Measured when element is in gaseous state.
 First ionization energy: energy required to remove
first electron from the highest occupied energy level.
 Measured in kJ/mol
 Some elements have second, third… ionization energy,
meaning they can lose more than one electron forming
positive ions.
Trends in ionization energy
Ionization energy increases
Ionization energy increases
Trends in ionization energy
Ionization energy increases within a period.
As the number of protons increases, the nuclear force
increases making harder to remove an electron.
Ionization energy decreases within a group.
As the size of the atom increases, nuclear force has a
smaller effect on electrons on highest energy level.
Ionization energy
increases
Ionization energy increases
Electronegativity
 Is the ability of an element to attract electrons when
the atom is in a compound.
 Noble gases are omitted because they don’t form many
compounds.
 Most electronegative element is Fluorine
 Least electronegative element is cesium
Trends in electronegativity
Electronegativity increases
Electronegativity increases