OBJECTIVES:
1.
2.
Students will
understand the
Shielding Effect.
Students will explain
the Atomic Radius
Trend found on the
Periodic Table.

The attraction of
the valence
electrons to the
protons in the
nucleus. The
further away
they are from the
protons, the less
the attraction.
What is the
Shielding Effect?
As you move down a group- electrons
are placed on higher energy levels- more
shielded from the protons.
As you move across a period – electrons
are added to the same energy level- less
shielded from the protons.
How Does it Work?
Due to the Shielding Effect
– three trends have been
observed and explained:
1. Atomic Radius
2. Ionization Energy
3. Electronegativity

What are Periodic
Trends?

Trends are properties in
that increase or decrease
in a period or group for
a specific property.

No transition metals, too
many exceptions.
What are Periodic Trends?
Which Way?
Half the distance between
two nuclei of the same
atom (basically the size of
the atom).

Trend #1 Atomic Radius

Examples:
Put in increasing order
(smallest to largest):
K, Kr, Ge

Cs,, Na, K


What does it look like?
BELLWORK 11/09/15
Which of these alkali metals has the largest
atomic radius? Cs, Fr, Li, or Na?
OBJECTIVES:
Students will analyze the
trends for ionization
energy and
electronegativity.

Let’s Review How to
Identify Trends
We define trends based on how the
properties change relative to:
A. Groups
B. Periods
How do we Read the
Arrows?
INCREASE
I
N
C
R
E
A
S
E
I
N
C
R
E
A
S
E
INCREASE
Trend #2 Ionization Energy

The amount of energy required to
remove an electron from an atom.
The strength that an atom holds onto its
electrons.
 More shielding = less ionization energy
 Less Shielding = more ionization energy
(electrons held tight)

How does it work?

Examples:
Put in increasing order
(smallest to largest):
K, Kr, Ge

Cs, Na, K


Trend #3 Electronegativity
The ability for an atom to attract an electron (usually
from another atom).
 Noble gases left out of this trend, they don’t attract any
electrons.

More shielding= Less electronegativity
 Less Shielding = more electronegativity

Hey you! Get over
here!!
How it works:

Examples:
Put in increasing order
(smallest to largest):
K, Kr, Ge

Cs, Na, K


BELLWORK 11/10/15
Periodic trends vary as we move across
the periodic table. In general, as you move
across a row in the periodic table

A)
B)
C)
D)

ionic size increases
atomic radius decreases
nuclear charge decreases
ionization energy decreases
PRACTICE #1
Rank the following elements by
increasing (smallest to largest)atomic
radius: C, Al, O, K
PRACTICE #2
Rank the following elements by
increasing electronegativity (lowest to
highest ) : S, O, Ne, and Al
Classwork / Homework

Periodic Trend Worksheet
Answer Key