Periodic Trends: Atomic Radius and Ionization Energy
Periodic Trends!
Periodic Law
When elements are
arranged
in order of
increasing atomic
number
,
there is a periodic
pattern
in their
physical
and
chemical
properties.
There are many trends in the
periodic table, but you must
know the reasoning behind
3
of
them
Atomic Radius:
Gives us an idea of the
size of an
atom
The trend:
A.R.
increases
as you move
down
a group
A.R.
decreases
as you move
across
a period from left to right
Why?
As atomic # increases, the number of
protons
and
electrons
increases
To accommodate the electrons, there must be more
energy levels.
This is why A.R.
increases
as you move down a group.
As you go across a period, an atom is
not
gaining
energy levels
The atom is still gaining
protons
and
electrons
, though, so the atom
becomes more and more dense
This causes the electrons to be
drawn closer
to the
positive
nucleus.
This is why A.R.
decreases
as you move across a period.
Ionization Energy
The
energy
required to remove an
electron from the
valence
shell of an
atom
The trend:
I.E.
decreases
as you go
down a group
I.E.
increases
as you go
across a
period
from left to right
Draw the arrows for the trend on the
periodic table sheet!
Why?
As you go down a group, the atomic radius
increases
This means that the valence electrons in a l
arge
atom are
further
away
from the nucleus, than the valence electrons in a
small
atom
If the
valence
electrons are far away from the
positive nucleus
, it
will take
less energy
to remove them. Large atoms tend to be lower
down in a group.
This is why I.E.
decreases
as you go down a group.
As you go across a period, atomic radius
decreases
This means the electrons will be held closer and closer to the
positive nucleus
as you go across the period
This means that atoms of elements to the
right
of the periodic table
will have
valence
electrons that are
harder
to remove.
This is why I.E.
increases
as you go across a period.
Electronegativity
the tendency of an atom to
attract
electrons
to itself
when it is
chemically
combined with other elements
The trend:
E.N.
decreases
as you go
down a
group
E.N.
increases
as you go
across a
period
left to right
Draw the arrows for the trend on the
periodic table sheet!
Why?
As you go down a group, the atomic radius
increases
This means that in elements lower down in the group,
the additional electrons will not feel a
strong attraction
to the nucleus, which is already surrounded by
electrons.
This is why E.N.
decreases
as you go down a group.
As you go across a period, the atomic radius
decreases
This means that in elements further to the
right
,
additional electrons will feel a
stronger
attraction to the
nucleus than in elements further to the left.
This is why E.N.
increases
as you go across a period.
The Periodic Table displays a systematic organization of elements based on their increasing atomic number, leading to periodic patterns in their physical and chemical properties. Key trends like Atomic Radius and Ionization Energy provide insights into the size of atoms and the energy required to remove electrons. The Atomic Radius increases down a group and decreases across a period due to changes in energy levels and electron density. Conversely, Ionization Energy decreases down a group and increases across a period as valence electrons are held closer to the nucleus. Understanding these trends enhances our comprehension of elemental behavior and properties.
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Presentation Transcript
Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.
There are many trends in the periodic table, but you must know the reasoning behind 3 of them
Atomic Radius: Gives us an idea of the size of an atom The trend: A.R. increases as you move down a group A.R. decreases as you move across a period from left to right
Why? As atomic # increases, the number of protons and electrons increases To accommodate the electrons, there must be more energy levels. This is why A.R. increases as you move down a group. As you go across a period, an atom is not gaining energy levels The atom is still gaining protons and electrons, though, so the atom becomes more and more dense This causes the electrons to be drawn closer to the positive nucleus. This is why A.R. decreases as you move across a period.
Ionization Energy The energy required to remove an electron from the valence shell of an atom The trend: I.E. decreases as you go down a group I.E. increases as you go across a period from left to right
Draw the arrows for the trend on the periodic table sheet!
Why? As you go down a group, the atomic radius increases This means that the valence electrons in a large atom are further away from the nucleus, than the valence electrons in a small atom If the valence electrons are far away from the positive nucleus, it will take less energy to remove them. Large atoms tend to be lower down in a group. This is why I.E. decreases as you go down a group. As you go across a period, atomic radius decreases This means the electrons will be held closer and closer to the positive nucleus as you go across the period This means that atoms of elements to the right of the periodic table will have valence electrons that are harder to remove. This is why I.E. increases as you go across a period.
Electronegativity the tendency of an atom to attract electrons to itself when it is chemically combined with other elements The trend: E.N. decreases as you go down a group E.N. increases as you go across a period left to right
Draw the arrows for the trend on the periodic table sheet!
Why? As you go down a group, the atomic radius increases This means that in elements lower down in the group, the additional electrons will not feel a strong attraction to the nucleus, which is already surrounded by electrons. This is why E.N. decreases as you go down a group. As you go across a period, the atomic radius decreases This means that in elements further to the right, additional electrons will feel a stronger attraction to the nucleus than in elements further to the left. This is why E.N. increases as you go across a period.
