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Periodic Trends

Atomic radius, ionization energy, electronegativity, ionic radius
by

Maria Heininger

on 19 January 2016

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Transcript of Periodic Trends

Ionic Radius
Ionization Energy
Electronegativity
Atomic Radius
What is Ionization Energy?
How can we tell if an atom wants more electrons?
Remember that ALL elements want to be
like noble gases.

Therefore, they want to have 8 valance
electrons.

Which types of elements will GAIN electrons
to be like a noble gas?
Periodic
Table
Trends

Electronegativity is a measure of an atom's attraction for another atom's electrons.
What is Electronegativity?
Since Fluorine is the most electronegative element, which element is the least electronegative?
Electronegativity combines the trends for atomic radius and ionization energy...
Ionization energy and atomic radius are inversely proportional.






The larger the atom is, the easier its electrons are to remove.
What is the horizontal trend for atomic radius?
Quick Practice
Quick Practice
As we go across a row, the atomic radius gets SMALLER.

So the amount of ionization energy needed to remove the electron gets...
What is the horizontal trend for ionization energy?
Ionization Energy
The goal of most atoms (except H and He) is to have 8 valance electrons.

We call this an
octet
.

As we saw previously, this is accomplished by an atom either gaining or losing valance electrons.

Atoms that have lost or gained electrons are called
ions.
The Octet Rule
The Periodic Law

When arranged by increasing atomic number,
the chemical elements
display a repeating pattern
of chemical and physical properties.
Periodic trends are patterns that are present in the periodic table.

They show different properties of elements, and how these characteristics increase or decrease as you move across a row or down a column of the periodic table.
Periodic Trends
4 Main Periodic Trends
- Atomic Radius
- Ionization Energy
- Electronegativity
- Ionic Radius
What is Atomic Radius?
Atomic radius is the distance from the nucleus to the valance electrons (outermost energy level).
valance electrons
What is the trend for atomic radius as we go down a group?
Vertical Trend
As we go down a family, we add a new energy level to the atom.

Therefore smaller atoms will be on top and larger atoms will be on the bottom.
Which has a SMALLER atomic radius?
Ca
Be
Which one has a LARGER atomic radius?
O
S
Imagine that we are having a tug of war

electrons v. protons
(children) (adults)
So what does this mean in terms of atomic radius?
In terms of atoms...
We add 1 proton to the nucleus of the atom

And we are adding 1 electron to the
SAME
energy level.
What happens to the atom as we move from

Lithium - Beryllium - Boron - Carbon

What is being added?
As we move across a row, we are still in the same energy level.

However...
Lithium
The 5 adults will pull the rope closer to the nucleus than 3 or 4 adults will!
As we add 1 kid (electron) we also add 1 adult (proton).
3 kids v. 3 adults
Kids (e-) are pulling outwards.

Adults (p+) are pulling in towards nucleus.
In which scenario will the adults pull the rope the farthest?

3 kids v 3 adults

4 kids v 4 adults

5 kids v 5 adults?
So, basically, as long as there are an even number of kids and adults playing tug of war, the kids will never win :(
Horizontal Trend for Atomic Radius
The more protons, the closer they will pull the electrons in towards the nucleus.
Can we come up with a horizontal trend?
As we go across a row, the atomic radius will get
SMALLER
Which has a LARGER radius?
Mg
Si
Which has a SMALLER radius?
Ga
As
What does the overall trend for atomic radius look like?
Predict:
Which element will have the largest radius?

Which one will be the smallest?
Ionization is the energy required to
remove an electron
from an atom. (measured in kilojoules, kJ)
The amount of energy required to remove an electron depends on
SHIELDING
.

Shielding is when the core (inner) electrons block the protons from pulling on the valance (outer) electrons.

As we saw with atomic radius, the proton are stronger and can pull electrons towards the nucleus.
Electrons in lower energy levels are CLOSER to the protons so the protons have a LARGE amount of control over them.
(Harder to remove e- = A LOT of energy required)





Electrons in higher energy levels are FARTHER away from the protons so the protons have LESS control over them.
(Easier to remove e- = A LITTLE energy required)
Let's have a few student volunteers...
What is the vertical trend for ionization energy?
As we go down a group, the atomic radius gets BIGGER.


So the amount of ionization energy needed to remove the electron gets...
SMALLER!!!!
(easier to remove the electrons)
As we go down a column, the atomic radius will get LARGER.
As we go
down a column
, the ionization energy will get
SMALLER
.
LARGER!!!!
(more protons = stronger pull = harder to remove the electrons)
As we go
across a row
, the ionization energy will get
LARGER
.
Quick Practice
Which element has a LOWER ionization energy?
Which element has a HIGHER ionization energy?
Al
B
F
Cl
Quick Practice
Which element has a LOWER ionization energy?
Sr
N
Which element has a HIGHER ionization energy?
Sn
Xe
T
R
E
N
D
S
Periodic
So far we have learned about the distance of electrons from the nucleus and the energy required to remove each electron.

Electronegativity measures of how badly an atom is trying to take an electron...

...You can think of it as "kidnapping" an electron from another atom.
The Nonmetals!!!!
Nonmetals want to GAIN more electrons
to be like a noble gas.
Nonmetals are STRONG and SMALL!
Since nonmetals have more protons then metals in the same row, they are smaller but stronger.

This combined with their desire to gain electrons gives them a HIGH ELECTRONEGATIVITY.
The smaller the atom, the greater the electronegativity.





Which element will be the most electronegative?
Fluorine!!!
Why wouldn't it be Helium?
Helium already has the "perfect" number of electrons because it is a noble gas.
It has no interest in taking another atom's electrons.
Therefore, we can say that ALL Noble Gases will have an electronegativity of ZERO.
What about metals?

Do they want to lose or gain electrons to be like a noble gas?
Metals want to LOSE electrons.

They want another atom to come along and take their valance electrons!

Therefore, we can say that metals will have a LOW ELECTRONEGATIVITY.
In summary:
Nonmetals are electron takers and have high electronegativities.

Metals are electron givers and have low electronegativities.

Noble Gases do not want to take or give up electrons and have ZERO electronegativity.
What is the vertical trend for electronegativity?


Remember that smaller = stronger
As we go down a family the electronegativity will DECREASE.

The atoms at the bottom of the family are so big and have so many electrons that they want another element to come along and take one away.
Time for Quick Practice!
Which has a LARGER
electronegativity?
K
Li
Which has a SMALLER
electronegativity?
P
N
What is the horizontal trend for electronegativity?
As we go across a row, the atomic radius gets smaller and the atoms become nonmetals.

Therefore,

as we go across a row, the electronegativity will INCREASE.
Quick
Practice
Which has the LARGER electronegativity?
Al
Cl
Which has the SMALLER electronegativity?
K
Se
Fluorine:
Low (small) radius
High Ionization Energy
High Electronegativity

Francium:
High (large) Radius
Low Ionization Energy
Low Electronegativity
The
most reactive metals
are the
largest
since they are the
best electron givers.


The
most reactive nonmetals
are the
smallest
ones, the best electron takers.
The End
Types of Ions
When an atom GAINS electrons, it now has
more electrons than protons
.

It has a
NEGATIVE
CHARGE.

Negatively charged ions are called
ANIONS
.
ANION = A Negative ION
When an atom

LOSES

electrons, it now has more protons than electrons.

It has a

POSITIVE CHARGE
.

POSITIVELY charged ions are called

CATIONS
.
Just remember that...




CAT
ions are
PAWS
itive
Metals or Nonmetals?
Which are going to become anions?

cations?
Metals = cations
( + charge)


Nonmetals = anions
( - charge)
Ionic Radius
What happens to the radius
when an electron is either
gained or lost?
Let's think back to the tug-of-war between electrons and protons...


That means volunteer time!
Cations
will have a
SMALLER
radius than the original atom.

Since we LOSE electrons, there are
more protons
. The protons are able to
pull even harder towards the nucleus
.
ANIONS
will have a
LARGER
radius than the original atom.

Since we GAIN electrons, there are
more electrons
. The electrons are able to
pull a little further away from the nucleus.
Quick Practice
Which has a LARGER ionic radius?
Ca
Mg
2+
2+
Which has a SMALLER ionic radius?
O
F
2-
1-
Full transcript