Periodic Table and Valence electrons

Periodic Trends

Goal

•

Students know

how to use the

periodic table to identify

trends

in

ionization energy,

electronegativity

,

and the relative sizes of ions and

atoms.

Definition: Half of the distance
between nuclei in covalently bonded
diatomic molecule

❖Radius decreases across a period

❖ Increased effective nuclear charge
due to decreased shielding

❖Radius increases down a group

❖ Each row on the periodic table adds
a “shell” or energy level to the atom

Atomic Radius

Table of

Atomic

Radii

Period Trend:

Atomic Radius

❑ Tends to increase across a period

❑ As radius decreases across a period,
the electron you are removing is closer
to the nucleus and harder to remove

❑ Tends to decrease down a group

❑ Outer electrons are farther from the
nucleus and easier to remove

Ionization Energy

Definition: the energy required to remove an
electron from an atom

Periodic Trend:

Ionization Energy

Electronegativity

Definition: A measure of the ability of an
atom in a chemical compound to attract
electrons

o
Electronegativity tends to increase

across a period

o As radius decreases, electrons get
closer to the bonding atom’s nucleus

o
Electronegativity tends to decrease

down a group or remain the same

o As radius increases, electrons are
farther from the bonding atom’s
nucleus

Periodic Table of

Electronegativities

Periodic Trend:

Electronegativity

Summary

of

Periodic

Trends

Ionic Radii

Cations

❑
Positively charged ions formed when
an atom of a metal loses one or
more electrons

❑
Smaller than the corresponding
atom

Anions

❑
Negatively charged ions formed
when nonmetallic atoms gain one
or more electrons

❑
Larger than the corresponding
atom

Graphic courtesy Wikimedia Commons user Popnose

Valence

Electrons:

ELECTRONS

AVAILABLE

FOR

BONDING

Definition

Valence electrons

are electrons in

the outmost shell (energy level).

They are the electrons available

for bonding.

Group 1 (alkali metals) have 1
valence electron

Group 2 (alkaline earth metals)
have 2 valence electrons

Group 13 elements have 3
valence electrons

Group 14 elements have 4
valence electrons

Group 15 elements have 5
valence electrons

Group 16 elements have 6
valence electrons

Group 17 (halogens) have 7
valence electrons

Group 18 (Noble gases) have 8
valence electrons, except
helium, which has only 2

Transition metals (“d” block)
have 1 or 2 valence electrons

Lanthanides and actinides
(“f” block) have 1 or 2 valence
electrons

Dot Notations

An atom’s valence electrons can be represented
by Lewis dot notations.

1 valence e

-

X

2 valence

e

-

X

3 valence

e

-

X

4 valence

e

-

X

5 valence

e

-

X

6 valence

e

-

X

7 valence

e

-

X

8 valence

e

-

X

Dot Notations

–

Period 2

Lewis dot notations for the valence electrons of
the elements of Period 2.

lithium
Li

beryllium
Be

boron
B

carbon
C

nitrogen
N

oxygen
O

fluorine
F

neon
Ne