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PERIODIC PATTERNS
Unit 3 – Periodic Table
What patterns exist on the periodic table?
Lesson Essential Question:
METALLIC TREND
INCREASE
S
INC
REA
SE
S
ATOMIC RADIUS
Radius is the distance from the center of the nucleus to the “edge” of the electron cloud.
Atomic radii are usually measured in picometers (pm) or angstroms (Å). An angstrom is
1 x 10-10 m.
ATOMIC RADIUS
BROMINE = Br2
Since a cloud’s edge is difficult to define, scientists use define covalent radius, or half the distance between the nuclei of 2 bonded atoms.
2.86 Å1.43 Å 1.43 Å
ATOMIC RADII TRENDS
As you go down a family the number of energy levels increases making the radius larger.
DOWN A FAMILY OR GROUP WHY?
INC
REA
SES
ATOMIC RADII TRENDS
As you go across a period the number of protons increases, (nuclear charge) pulling the electrons in tighter making the radius smaller.
ACROSS A PERIOD WHY?DECREASES
IONS - remember
Metals Lose electrons
becoming positive.
Calcium (Ca)Loses 2 electrons
becomingCa+2 and [Ar] Noble
gas Configuration. (Octet Rule)
Nonmetals Gain electrons
becoming negative.
Chlorine (Cl)Gains one e-
becoming Cl-1 and [Ar] Noble gas configuration.
(Octet Rule)
IONS – How can I remember?
Metals Nonmetals
This is Ann ion - ANIONShe is unhappy and
negative.
This is Cat-ion - CATIONHe is a “plussy”
cat!
IONIC RADII TRENDS
As you go down a family the number of electron shells increases making the radius larger.
DOWN A FAMILY OR GROUP WHY?
INC
REA
SES
IONIC RADII TRENDS
For the metals the nuclear charge is greater than then number of electrons pulling them in tighter making the radius smaller.
At the nonmetals the radius gets larger because the ion has gained electrons.
ACROSS A PERIOD WHY?DECREASES then INCREASE
METALLIC ATOM AND ION COMPARISON
NONMETALLIC ATOM AND ION COMPARISON
Why do the Noble Gases not have an ionic Radius?
ATOM AND ION COMPARISON
Why does Hydrogen not have an ionic Radius?
As more electrons are added to atoms, the inner layers of electrons shield the outer electrons from the nucleus.The effective nuclear charge on those outer electrons is less, and so the outer electrons are less tightly held
Shielding Effect
Example of Shielding Effect
The energy required to remove an electron from an atom. (measured in kilojoules, kJ)
Ionization Energy
IONIZATION TREND
INC
REA
SE
S
Why?• Closer to
nucleus (more +) • Electrons
less likely to be removed• Requires
more energy to form ion• Less
shielding
IONIZATION ENERGY
The larger the atom is, the easier its electrons are to remove. (Why?)
Ionization energy and atomic radius are inversely proportional.
Ionization energy is always endothermic, that is energy is added to the atom to remove the electron.
IONIZATION TREND
INCREASES
NC
REA
SE
SWhy?• Elements in
alkali metals have 1 valence electron so what to remove that electron, they therefore take the least amount of energy to remove an electron
is a measure of the tendency of an atom to attract a bonding pair of electrons.
Electronegativity
Electronegativity
Why?•Closer to nucleus (more +) so electrons are more attracted
INC
REA
SE
S
http://www.thecatalyst.org/electabl.html
Electronegativity
Why?• Elements in
halogens only need 1 more electron to have a full valence shell so are MOST likely to attract electrons. As you move to left elements are more likely to LOSE electrons.
INCREASES
http://www.thecatalyst.org/electabl.html
In Summary….Electronegativity
Ele
ctro
negati
vit
y