PeriodicityE.Q.: What information can be obtained from the periodic

table and how is it used?

Hypothesize (Face Partners)• How do valence electrons change as you go:

a) Across a period - (increases, decreases, stays the same)b) Down a group - (increases, decreases, stays the same)

• How does ionization energy change as you go: a) Across a period - (increases, decreases, stays the same)b) Down a group - (increases, decreases, stays the same)

• How does atomic radius change as you go: a) Across a period - (increases, decreases, stays the same)b) Down a group - (increases, decreases, stays the same)

Periodicity

• Atomic radius

• Ionization energy

• Electronegativity

• Metallic character

Atomic radius

• One half the distance between the nuclei of identical atoms that are bonded together.

• Atoms shrink as you advance across a period because added protons in the nucleus pull the added electrons more tightly in the absence of effective shielding.

• Atoms in the same column increase in size as you go down the family since electrons are being added on successively higher energy levels and are well shielded by the previous completed electron energy levels.

ATOMIC RADIUS

As you move from left to right across a period, more protons (atomic number increases) are present in the nuclei of atoms and they can pull-in the electrons closer to the nucleus thus shrinking the radius of the atom.

ATOMIC RADIUS

As you move from top to bottom down a column, atomic number increases but also the number of energy levels increases and it becomes much harder for the protons to pull-in the electrons in the outer energy levels (effective shielding). Thus atomic radius increases.

ATOMIC RADIUS DECREASES

AT

OM

IC R

AD

IUS

INC

RE

AS

ES

Atomic radius• Radius (or size):

– Decreases from left to right (across periods)– Increases from top to bottom (within a family)

ATOMIC RADIUS

In other words……..atomic radius increases in the direction of the arrow!

IONIZATION ENERGY• Ion: An atom of an element that has lost or

gained an electron/s and now has gained a positive or negative charge (no longer neutral).

• It takes energy to remove an electron.

Ionization Energy

• Amount of energy required to remove an electron from an atom.

• The outer-most electron becomes increasingly more difficult to remove as you advance across a period since shielding is very poor and the added protons continue to exert a stronger attraction.

• The outer-most electron is easier to remove as you move down a column since each time you are one energy level farther from the nucleus, benefiting from that much more shielding.

IONIZATION ENERGY INCREASES

ION

IZA

TIO

N E

NE

RG

Y D

EC

RE

AS

ES

Electronegativity• The ability of a bonded atom to attract the electrons

in that bond.• As you move across a period from left to right,

atoms are able to attract electrons since shielding is ineffective and protons in nuclei can attract electrons from other atoms of different elements. Electronegativity increases.

• As you move down a group, number of energy levels increases and it becomes more difficult for the nuclei to hold on to the outermost electrons. Electronegativity decreases.

ELECTRONEGATIVITY INCREASES

EL

EC

TR

ON

EG

AT

IVIT

Y D

EC

RE

AS

ES

Metallic characterMetallic properties are related to the freedom

of the outer electrons to move in a macroscopic sample and thus these properties are most pronounced at the left side of the table where shielding is at a maximum.

• This means that metallic properties will also increase as you move down a family since shielding improves.

Metallic character

Fr (Francium) is the most reactive metal.

F (Fluorine) is the most reactive non-metal.

The noble gases are very un-reactive.

Summary of Periodic Trends

Electronegativity and Ionization energy increase

Atomic radius metallic character increase

Summary of Periodic Trends

Conclusions• Valence electrons:

a) Across a period - (increases)b) Down a group - (stays the same)

• Ionization energy: a) Across a period - (increases)b) Down a group - (decreases)

• Atomic radius: a) Across a period - (decreases)b) Down a group - (increases)