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Periodic Trends (simplified)

Atomic radius, ionization energy, electronegativity, ionic radius
by

Maria Heininger

on 21 January 2016

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Transcript of Periodic Trends (simplified)

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 ionization energy gets
BIGGER
.


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.
A trend is a repeating pattern.

There are many different trends on the Periodic Table.

We can see how certain characteristics change 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
With each row, we ADD a new energy level to the atom.

Smaller atoms will be at the 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 AND 1 electron
to the
SAME
energy level.
What is different about
each element?

Think of what is being added as we move from

Lithium -> Beryllium -> Boron


What do atoms that are in the same row have in common?
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 adults will always win because they
are stronger & bigger!
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.
The amount of energy required to remove an electron depends on
SHIELDING
.

Inner electrons block the protons from "seeing" the valance electrons.


Electrons close to nucleus (less shielding) means the protons have a lot of control over them.
(Hard to steal = LOTS of energy needed)





Electron far from nucleus (more shielding) means the protons have less control over them.
(Easy to steal = LITTLE energy needed)
Let's have a few student volunteers...
What is the vertical trend for ionization energy?
As we go down a group, the ionization energy gets
SMALLER!



WHY????

As we go down a column, the atomic radius will get BIGGER.
More shielding
(lots of inner electrons).

Protons can't see the valance e- making them easy to steal.
Less shielding
(not many inner electrons).

Protons CAN see the valance e- making them hard to steal.
Quick Practice
Which element has a LOWER ionization energy?
Which element has a HIGHER ionization energy?
Al
B
F
Cl
Quick Practice
WHY???
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.

Metals at the bottom are so big that they want another element take away eletrons.

Nonmetals at the bottom have the reach over all their energy levels making it harder to steal an electron
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 atoms become nonmetals and have more valance electrons.

They are closer having the same # of electrons as a noble gas.



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-
They all have the same
number of energy levels.

That would make us think
that they should be the
same size BUT that's
not true!
As we go across a row, the electronegativity will
INCREASE
.
WHY???
Full transcript