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Catalyst – pick up a periodic table before
starting class
1. Compare the number of protons in elements going from left to right
across the period 4 and group 18:
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
Choose two elements to compare
What are their atomic numbers?
2. Compare the atomic mass in elements going from left to right across
period 4 and group 18:
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
Choose two elements to compare
What are their atomic mass numbers?
Look at your periodic table to identify patterns.
3. The atomic number of elements in the periodic table
(increases/decreases) as you move from right to left across a period and
(increases/decreases) as you move from top to bottom down a group.
4. The atomic mass of elements in the periodic table (increases/decreases)
as you move from right to left across a period and (increases/decreases) as
you move from top to bottom down a group.
Homework
 Complete the study guide!
 STUDY! STUDY! STUDY! You can even use
your periodic table study guide to help you!
 What will be on tomorrow’s quiz?
Groups, periods
 Metals, metalloids, and non-metals
 Trends in the Periodic Table

How are you going to see it on the TCAP and on
your assessment?
 You should be able to recognize the trends in the
periodic table without seeing the atomic numbers
and atomic masses
 This means you need to be able to recognize what
happens as you move from left to right across a
period in the periodic table and as you move from
top to bottom down a group on the periodic table
 As you compare elements from left to right across
the periodic table, you will notice a trend or regular
change in a number of properties. The same thing
happens if you go up and down on the periodic table
and compare the properties of the elements.
 You need to know the trend for:
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# of protons
# of electrons
# of neutrons
Atomic number
Atomic mass
 Make sure you recognize if the trend is increasing or
decreasing as you move across a period (row)
 Make sure you recognize if the trend is increasing or
decreasing as you move down a group (column)
Atomic Number
 The periodic table is organized in order of increasing
atomic number! Therefore, atomic number will
increase as you move from left to right across a
period and as you move from top to bottom down a
group.
 We also know that the atomic number is exactly
equal to the number of protons so the trend for
protons will be the same
 In a neutral atom, the number of protons equals the
number of electrons, so the trend for electrons will
be the same as well
TREND IN ATOMIC NUMBER
Increases
Increase
TREND IN # of PROTONS
Increases
Increase
TREND IN # OF ELECTRONS
Increases
Increase
Trend in Atomic Mass
 Atomic mass is equal to the number of protons plus
the number of neutrons in the atom of an element
 We can think of atomic mass of how heavy a
substance is
 Since the number of protons is increasing across and
down the periodic table, the atomic mass increases
the same as atomic number
 Therefore, elements get heavier as you move from
left to right across a period and as you move from top
to bottom down a group
TREND IN ATOMIC MASS
Increases
Increase
Trend in Neutrons
 # of neutrons = atomic mass – atomic #
 As a result of the atomic mass and atomic number
increases, the number of neutrons will generally
increase as well as you move across a period from left
to right and as you move down a group
TREND IN # OF NEUTRONS
Increases
Increase
☐ Draw the trends we went over in class (show how these increase/decrease from right to left
across a period and increase/decrease from top to bottom down a group):
☐Atomic number
☐# of protons
☐# of electrons
☐Atomic mass number
☐# of neutrons
☐ Create a key to help you calculate “atomic math”
☐ How do you calculate the # of protons?
☐ How do you calculate the # of electrons?
☐ How do you calculate the # of neutrons?
☐ Write a minimum of one complete sentence including an explanation explaining each of the
trends. (Ex: The number of protons increases in the elements of the periodic table as you move
from left to right across a period and top to bottom as you move down a group because the
atomic number increases and the atomic number represent the number of protons in the atom
of an element.
☐Atomic number
☐# of protons
☐# of electrons
☐Atomic mass number
☐# of neutrons
Brain Teaser
 Solve the puzzle- what element is this?
Find the number of electrons for this
element
Find the atomic number for this element