Transcript Periodic Table - Ralph C. Mahar

The first Periodic Table?
The order of filling sublevels as
seen on the periodic table.
Lanthanoids
Actinoids

Filled and half-filled sublevels are more
stable than partially filled sublevels.
E E EEE E EEE h h h h _
1s 2s
2p
3s 3p
3d

_
4s
Thus Cr takes an electron from 4s to put
one electron in each of its 3d orbitals and
Cu takes a 4s electron to fill each of its 3d
orbitals.
Electron configuration of ions


Ions gain or lose electrons to become more
stable.
The electron configuration for calcium is
1s2 2s2 2p6 3s2 3p6 4s2
The configuration for an ion of calcium would be
1s2 2s2 2p6 3s2 3p6
Ca2+
This is isoelectronic to (has the same electron
configuration as) an Argon atom.
Electron configuration
in excited state.
N 1s2 2s2 2p3
ground state
1s2 2s2 2p2 3s1
or 1s2 2s2 2p1 3p2
excited state
Reactivity

The most active metals are in the lower left
corner, and the most active nonmetals are in the
upper right corner.
Periodic Properties
Ex.: density
atomic radii
ionization energy
electronegativity
have a repeating pattern.
Atomic Radii


Increases down a group, since they have
increasing energy levels.
Decreases across a period due to
increasing nuclear charge (the force of
attraction between nucleus and electrons).
Atomic radii
What would this say about density trends?
Ionic radii
Metals lose electrons when they ionize, so
their ionic radii are smaller than their
atomic radii.
Nonmetals gain electrons, so are larger than
their atomic radii.
“Isoelectronic”- ions with the same number
of electrons. Ex. O2-, F- , Ne, Na+ Mg2+
Ionization energies






Energy needed to remove an electron from an
atom (kJ/mol)
Metals have low ionization energies.
Nonmetals have high ionization energies
(especially noble gases).
Going down a group, the ionization energy
decreases due to increased atomic radius and
the shielding effect.
Going across a period it increases due to
increasing nuclear charge.
Second ionization energy- the energy required
to remove a second electron from an atom.
Ionization energies of aluminum
(kJ/mol)
element
1st
2nd
3rd
4th
Al
577.5
1810
2750
11,580
1st e- is from the 3p sublevel.
2nd e- is one of the 3s pair.
3rd e- is the other 3s electron.
4th e- would be from a full 2p sublevel.
Looking at ionization energies can help us predict
oxidation numbers. Al usually has a 3+ oxidation number.
Electron affinity
The attraction of an atom for an electron (kJ/mol).
Same trend as ionization energy (metals- low,
nonmetals- high).
Electronegativity
The power of an atom in a molecule to attract
electrons to itself.
Electronegativity




is related to. . .
Ionization energy- measures how strongly
an atom holds onto its electrons
Electron affinity- measures how strongly
an atom attracts additional electrons
F has a high ionization energy and a very
negative electron affinity.