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Periodic Trends in Atomic Size, Ionization Energy, and Electronegativity, Lecture notes of Chemistry

An in-depth analysis of periodic trends in atomic size, ionization energy, and electronegativity. It covers the factors influencing atomic size, the shielding effect, group trends, period trends, and exceptions. The document also explains the concepts of electron affinity, ionic size, and the configuration of ions.

What you will learn

  • What is the relationship between electron affinity and electronegativity?
  • How does the shielding effect influence atomic size and ionization energy?
  • Why do atoms get smaller as you go across a period but bigger as you go down a group?

Typology: Lecture notes

2021/2022

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GHS Honors Chem
Periodic Trends
OBJECTIVES:
Interpret group trends in atomic
radii, ionic radii, ionization energies,
and electronegativities.
Interpret period trends in atomic
radii, ionic radii, ionization energies,
and electronegativities.
GHS Honors Chem
Trends in Atomic Size
First problem: Where do you start
measuring from?
The electron cloud doesn’t have a
definite edge.
They get around this by measuring
more than 1 atom at a time.
GHS Honors Chem
Atomic Size
Atomic Radius = half the distance between
two nuclei of atoms
in the solid state (by X-ray diffraction)
or of a diatomic molecule.
}
Radius
GHS Honors Chem
Atomic Size
Influenced by three factors:
1. Energy Level
Higher energy level is further away.
2. Charge on nucleus
More positive charge pulls electrons in
closer.
3. Shielding effect
The inner electrons shield the outer
electrons from the nuclear
charge/attraction.
GHS Honors Chem
Shielding
The electron on the outermost
energy level has to look through all
the other energy levels to see the
nucleus.
Second electron has same
shielding, if it is in the same
period
Shielding Increases down a Group,
and is Constant across a Period.
Shielding Across a Period is
Constant, but the EFFECTIVE
NUCLEAR CHARGE INCREASES.
GHS Honors Chem
Group Trends in Atomic Size
As we go down a group...
each atom has another
energy level,
so the atoms get bigger.
Shielding increases as
well, so the nucleus has
less of a hold on e-
distance is longer.
The Increased size of
the Energy Levels down a
group outweighs the
increased nuclear charge
H
Li
Na
K
Rb
pf3
pf4
pf5

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GHS Honors Chem

Periodic Trends

OBJECTIVES:

� Interpret group trends in atomic

radii, ionic radii, ionization energies,

and electronegativities.

� Interpret period trends in atomic

radii, ionic radii, ionization energies,

and electronegativities.

GHS Honors Chem

Trends in Atomic Size

� First problem: Where do you start

measuring from?

� The electron cloud doesn’t have a

definite edge.

� They get around this by measuring more than 1 atom at a time.

GHS Honors Chem

Atomic Size

Atomic Radius = half the distance between

two nuclei of atoms

� in the solid state (by X-ray diffraction)

� or of a diatomic molecule.

Radius

GHS Honors Chem

Atomic Size

Influenced by three factors:

1. Energy Level

  • Higher energy level is further away.

2. Charge on nucleus

  • More positive charge pulls electrons in

closer.

3. Shielding effect

  • The inner electrons shield the outer

electrons from the nuclear

charge/attraction.

GHS Honors Chem

Shielding

� The electron on the outermost energy level has to look through all the other energy levels to see the nucleus.

� Second electron has same shielding, if it is in the same period

� Shielding Increases down a Group, and is Constant across a Period. � Shielding Across a Period is Constant, but the EFFECTIVE NUCLEAR CHARGE INCREASES.

GHS Honors Chem

Group Trends in Atomic Size

� As we go down a group... � each atom has another energy level, � so the atoms get bigger. � Shielding increases as well, so the nucleus has less of a hold on e -^ … distance is longer. � The Increased size of the Energy Levels down a group outweighs the increased nuclear charge

H Li

Na

K

Rb

GHS Honors Chem

Periodic Trends in Atomic Size

� As you go across a period, the radius

gets smaller.

� Electrons are in same energy level.

� More nuclear charge.

� Shielding is constant … not an issue.

� Outermost electrons are closer.

Na Mg Al Si P S Cl Ar GHS Honors Chem

Atomic Radius

Overall

GHS Honors Chem

Trends in Ionization Energy

� The amount of energy required to

completely remove an electron from a gaseous atom.

� Removing one electron makes a 1+

ion.

� The energy required to remove the

first electron is called the first ionization energy.

GHS Honors Chem

Ionization Energy

� The second IE is the energy required to remove the second electron.

� Always greater than first IE.

� The third IE is the energy required to remove a third electron.

� Greater than 1st or 2nd IE.

GHS Honors Chem

Symbol First Second Third

H

He Li Be B C N O F Ne

Ionization Energy Table

Where are the Group Effects?

1A 2A 3A

GHS Honors Chem

H

He

Li

Be

B

C

N

O

F

Ne

Symbol First Second Third

Can we See the Effect of

Nuclear Charge in this Table?

GHS Honors Chem

Trends in Electron Affinity

� It’s easiest to add an electron to

Group 7A.

� It gets them to a full energy level, or

completes the OCTET.

� Increase from left to right: atoms

become smaller, with greater nuclear

charge.

� Decrease as we go down a group.

GHS Honors Chem

Electron Affinity in the Periodic Table

GHS Honors Chem

Trends in Ionic Size

� Cations form by losing electrons.

� Cations are smaller that the atom they come from.

� Metals form cations.

� Cations of representative elements have noble gas configuration.

GHS Honors Chem

� Anions form by gaining electrons.

� Anions are bigger that the atom they come from.

� Nonmetals form anions.

� Anions of representative elements

have noble gas configuration.

Trends in Ionic Size

GHS Honors Chem

Revisiting Configuration of Ions

� Ions always have noble gas

configuration.

� Na is: 1s^2 2s^2 2p 6 3s^1

� Forms a 1+ ion: 1s^2 2s^2 2p 6

� Same configuration as Neon.

� Metals form ions with the

configuration of the noble gas before them - they lose electrons.

GHS Honors Chem

� Non-metals form ions by gaining

electrons to achieve noble gas configuration.

� They end up with the configuration of the noble gas after them.

Revisiting Configuration of Ions

GHS Honors Chem

Group Trends

� Going down a Group,

you are adding energy

levels

� Ions get bigger as you

go down.

Li 1+ Na1+ K1+

Rb 1+

Cs1+

GHS Honors Chem

Periodic Trends

� Across the period, nuclear charge increases so they get smaller.

� Energy level changes between anions and cations.

Li 1+

Be2+

B3+

C 4+

N 3- O2-^ F 1-

GHS Honors Chem

Size of Isoelectronic ions

� Iso- means the same

� Iso electronic ions have the same #

of electrons

� Al 3+^ Mg2+^ Na 1+^ Ne F 1-^ O 2-^ and N 3-^ all

have 10 electrons

� all have the configuration:

1s^2 2s^2 2p 6

GHS Honors Chem

Size of Isoelectronic ions

� Positive ions that have more protons

would be smaller.

� Increase in size from most positive to

most negative

Al 3+

Mg 2+

Na1+^

Ne F^

1- O

2- N^

GHS Honors Chem

Electronegativity

� The tendency for an atom to attract

electrons to itself when it is chemically

combined with another element.

� How fair is the sharing?

� Big electronegativity means it pulls the

electron towards it.

� Atoms with large negative electron

affinity have larger electronegativity.

GHS Honors Chem

Electronegativity Group Trend

� The further down a group, the farther

the electron is away, and the more

electrons an atom has.

� Pull/Attraction of the positive nucleus is

lessened due to increased distance and

Shielding.

� Electronegativity decreases.

� More willing to share.