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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 n value 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 [Ar]4s2
Loses 4s2 e-s becoming
Ca+2 and [Ar] Noble gas
Configuration. (Octet Rule)
Nonmetals Gain electrons
becoming negative.
Chlorine – Cl [Ne]3s23p5
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 n value 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
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
The energy required to remove an electron from an atom is ionization energy. (measured in kilojoules, kJ)
Ionization Energy
IONIZATION ENERGY
The larger the atom is, the easier its electrons are to remove.
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.
is a measure of the energy change when an electron is added to a neutral atom to form a negative ion
Electron Affinity
ELECTRON AFFINITYWhy do the Alkaline Earth Metals and Noble Gases not have measurable Electron Affinities?