Transcript Periodic Properties of the Elements

Periodic Properties of the
Elements
CHM 108
SUROVIEC
SPRING 2014
I. Development of the Periodic Table
 The modern periodic table is credited to Dmitri
Mendeleev
 Table is based on the periodic law
II. Electron Configuration
 Quantum Mechanical Theory describes the behavior
of electrons in atoms.
A. Electron Spin and the Pauli Exclusion Principle
 Electron configurations
can also be represented
in an orbital diagram
 In an orbital diagram the
direction of the arrow
shows the electron spin
Orbital diagram
number of electrons
in the orbital or subshell
1s1
principal quantum
number n
angular momentum
quantum number l
Orbital diagram
H
1s1
B. Multi-electron atoms
 In H and He the energy
of the orbital depends
only on principle
quantum number
 For atoms with more
than 2 electrons, the
energy depends on l & n
Example
 Lithium
 What are the possible
quantum numbers for
the last (outermost)
electron in Cl?
 Magnesium
C. Electron configuration of multi-electron atoms
 Now that we know the
energy of orbitals we can
build ground state
electron configuration
for other elements.
 We use Hund’s rule of
filling degenerate
orbitals to fill them
singly with up spin first
Hund’s Rule
III. Electron Configuration, Valence Electrons and the
Periodic Table
 The highest principle number
increases by 1 going down a
row
 As you move across a row the
number of electrons increases
by 1 in the outer most energy
level.
IV. QM Model Explains Ions
 A all atoms in a column
will have the same
number of valence
electrons
V. Periodic Variations of Physical Properties
 The chemical and physical properties of elements are
a periodic function of atomic number


Recall that the number of electrons is equal to the atomic
number of an element
Properties to be considered
Atomic Radius (and Ionic Radius)
 Effective Nuclear Charge
 Ionization Energy
 Electron Affinity

A. Atomic Radius
 Atomic radius is the
average bonding radii
between 2 nonbonding
atoms
Atomic Radius Trend
B. Effective Nuclear Charge
 Zeff is the “positive
charge” felt by an
electron.
B. Effective Nuclear Charge
Na
Mg
Al
Si
Z
(atomic
number)
Core
Electrons
Zeff
Radius (pm)
11
10
1
186
VI. Ionic Radius
 Radius of cations/anions
 Effects physical and
chemical properties of an
ionic compound
VI. Ionic Radius
A. Ionization Energy
 Minimum energy
required to remove an
electron from a gaseous
atom
B. Electron Affinity
 Measure of how easily an
atom will accept an
electron
C. Electronegativity
 An atom’s ability to
attract electrons to itself
in a chemical bond.