Atomic Radius – distance from nucleus of an atom to the outermost electron. Measured in picometers

Atomic Radius Trend• Group Trend – As you go down a

column, atomic radius increases

• Periodic Trend – As you go across a period (L to R), atomic radius decreases

Atomic radius vs. atomic number (Period)Atomic radius vs. atomic number (Period)

Ca

K

H He

Li

BBe

C N O FNe

NaMg

Al Si P S ClAr

0

50

100

150

200

250

0 2 4 6 8 10 12 14 16 18 20

Element

Atom

ic R

adiu

s (p

m)

Ionic RadiusIonic radius, rion, is the radius of an atom's ion.

Ionic Radius in a Period• Ionic Radius tends to decrease in size across

the Periodic Table

Ionic Radius in a Group• Ionic Radius tends to increase down a Group

Summary Diagram

• Which of the following is the smallest in size? 

• 1) N3- • 2) O2-

• 3) F-

• 4) Na+

Question 1

Question 2

The correct order of radii is: •a) N < Be < B•b) F- < O2- < N3-

•c) Na < Li < K•d) Fe3+ < Fe2+ < Fe4+

Question 3

The correct order of ionic radii is: •a) Ti4+ < Mn7+

•b) 37Cl- < 35Cl-

•c) K+ > Cl-

•d) P3+ > P5+

Ionization Energy

• The ionization energy (IE) is qualitatively defined as the amount of energy required to remove the most loosely bound electron of an isolated gaseous atom to form a cation.

IE in a PeriodIonization generally increases across a period.

IE in a Group

IE generally goes down in a Group

Summary Diagram

Questions

Electronegativity• Electronegativity is a measure of the

tendency of an atom to attract a bonding pair of electrons.

EN in Period tends to increase

EN in a Group tends to decrease

Summary Diagram

Questions

1. Which of the pairs are more Electronegative:

B or CMg or CaK or Sc

Nuclear Charge• The effective nuclear charge is the net

positive charge experienced by valence electrons.

Shielding Effect• Shielding effect can

be defined as a reduction in the effective nuclear charge on the electron cloud

• is due to inner electrons shielding valence electrons from the nucleus

Nuclear Charge within Group and Period

Questions

• Which elements have a higher nuclear charge?– Cr, Ni– Rb, Sr– Si, Ge

Shielding in a Group or Period

Questions

• Which elements experience a larger shielding affect?– Ti, V– Mg, Al– Cl, Br