Transcript Periodic Trends

PERIODIC TRENDS
What are they?
Properties we can predict from the
periodic table
Why are they?
A few reasons explain them
Why do we care?
• So we know what's gonna go BOOM!
Or what medicines will work
Or how to make an iPod work
Or how to make plastic
Or how to make perfume…
Or how to make food taste good
etc.etc.etc.
To figure out REACTIONS!
You will learn
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Why metals lose electrons
Why non-metals gain electrons
2 periodic trends dealing with size
3 periodic trend dealing with electrons
What causes the trends in groups
What causes the trends in periods
LAW OF OCTETS
Atoms tend to gain, lose, or share electrons to
acquire a full outer energy level of either 2 or 8
electrons.
Atoms want to have electron configurations like the
noble gases.
Atoms trying to acquire a full 1st energy level are full with 2
electrons in the s orbital. Atoms trying to acquire a full outer
energy level beyond the first, try for 8 electrons, the result of
full s and p orbitals)
VALENCE ELECTRONS
The electrons available to gained, lost, or shared in
the formation of chemical compounds.
They are often located in the incompletely filled
main energy levels.
They are in the s and p sublevels for the main group
elements.
Ionic charges
• If electrons are lost, a positive ion is formed.
– Metals
• If electrons are gained, a negative ion is
formed.
– Non-metals
Group
Val. El
Ionic Charge
1 2 13 14
15 16 17
1 2 3
4
5
6
7
1+, 2+, 3+, 4+ or-, 3-, 2-, 1-,
18
8
0
WHAT ELSE AFFECTS TRENDS?
Let’s use a magnet to illustrate the ideas.
A magnet will provide a model for the nucleus with
its positive charge, pulling on the electrons with
their negative charges.
Paper clips will represent electrons in energy levels.
How many paper clips can stick to a magnet,
end to end?
Why do they stick?
The magnet pulls on the clips.
What if you had a stronger magnet?
It would pull harder on them or the magnet
would pull them closer.
What does this have to do with
ATOMS and PERIODIC TRENDS?
The magnet represents the positive pull of the nucleus.
This is called the NUCLEAR CHARGE…the positive
charge of the nucleus, created by protons, pulling on
the negative electrons.
The more + protons there are, the stronger the
nuclear charge.
Note:
The NUCLEAR CHARGE is NOT THE SAME as the
charge on an ion that we talked about earlier. The
NUCLEAR CHARGE is the POSITIVE CHARGE OF THE
NUCLEUS FROM THE PROTONS.
What happened as you tried to add more?
It’s harder to get them to stick. It’s easier to pull them off.
Why?
They are farther from the magnet so they don’t feel the force
as strongly.
Paper clips correspond to electrons in successive energy
levels.
As ENERGY LEVELS are added, each one is
successively farther from nucleus, therefore
affected less by NUCLEAR CHARGE. Electrons
will be attracted less strongly.
Any other reason why the paper clips don’t stick as well?
They are shielded by other clips…anything between
magnet and clips reduces the effect of magnet
Electrons in lower energy levels create
SHIELDING. The presence of more electrons in
the inner energy levels between the nuclear
charge and valence electrons reduces the effect
of nuclear charge on the outer valence
electrons.
Trends that have to do with size:
ATOMIC RADIUS (AR)
<up and right
IONIC RADIUS (IR)
<up and right
These trends DECREASE as you move UP A GROUP and
OVER TO THE RIGHT THROUGH A PERIOD
ATOMIC RADIUS: The size of the atom.
One-half the distance between the nuclei of two
identical atoms that are bonded together.
IONIC RADIUS: The size of the ion.
Atomic radius
Trends that have to do with size:
ATOMIC RADIUS (AR)
<up and right
IONIC RADIUS (IR)
<up and right
Group effect:
Fewer energy levels as you go up…smaller
Less shielding…more effect from pull of + nucleus
Period effect:
More protons, greater nuclear charge as you go right
Trends that have to do with electrons:
IONIZATION ENERGY (IE)
>up and right
ELECTRON AFFINITY (EA)
>up and right
ELECTRONEGATIVITY (EN)
>up and right
These trends INCREASE as you move UP A GROUP and
OVER TO THE RIGHT THROUGH A PERIOD
IONIZATION ENERGY: The energy required to remove an
electron from an atom to form an ion
ELECTRON AFFINITY: The energy change when an
electron is acquired by a neutral atom.
ELECTRONEGATIVITY: A measure of the ability of an atom
to attract electrons from another atom in a compound.
Trends that have to do with electrons:
IONIZATION ENERGY (IE)
>up and right
ELECTRON AFFINITY (EA)
>up and right
ELECTRONEGATIVITY (EN)
>up and right
These trends INCREASE as you move UP A GROUP and
OVER TO THE RIGHT THROUGH A PERIOD
Group Effect:
Fewer energy levels, closer to nuclear charge as you go
up.
Less shielding, fewer inner electrons between valence
electrons and + pull of nucleus
Period Effect:
More protons, greater nuclear charge as you go right
Trends that have to do with size: <
ATOMIC RADIUS (AR)
<up and right
IONIC RADIUS (IR)
<up and right
These trends DECREASE as you move UP A GROUP and
OVER TO THE RIGHT THROUGH A PERIOD
Trends that have to do with electrons: >
IONIZATION ENERGY (IE)
>up and right
ELECTRON AFFINITY (EA)
>up and right
ELECTRONEGATIVITY (EN)
>up and right
These trends INCREASE as you move UP A GROUP and
OVER TO THE RIGHT THROUGH A PERIOD
Because of the Law of Octets…
CATIONS
t +charge
Metals
Lose electrons to
acquire noble gas
configuration.
ION IS SMALLER THAN
ATOM…WHY?
•Loss of outer energy
level.
•Unbalanced + charge
pulls electrons closer.
ANIONS
N -charge
Non-metals
Gain electrons to
acquire noble gas
configuration.
ION IS LARGER THAN
ATOM…WHY?
•Same outer energy level,
•but more electrons are
added to it.
•+ charge remains the
same, but more – charge.
•More electrons repel
each other more.
NON-METALLIC
CHARACTER
Best non-metal, gains e- most easily
upper right
F
METALLIC
CHARACTER
Best metal, loses e- most easily
lower left
Fr
SUMMARY
3 factors
# of protons (nuclear charge)
# of energy levels (size and distance from
nucleus)
# of inner electrons (shielding )
Trends that have to do with size: <
ATOMIC RADIUS (AR)
<up and right
IONIC RADIUS (IR)
<up and right
Trends that have to do with electrons: >
IONIZATION ENERGY (IE)
>up and right
ELECTRON AFFINITY (EA)
>up and right
ELECTRONEGATIVITY (EN)
>up and right
Metals lose electrons, and the + cations are
smaller than the neutral atoms.
Non-metals gain electrons, and the - anions
are bigger than neutral atoms.