Download Ch 5: Periodiciy 2

The Periodic Table




Elements are arranged in a way that
shows a repeating, or periodic, pattern.
Dmitri Mendeleev created the first periodic
table of the elements in 1869.
He ordered the ~70 known elements by
their atomic masses and their chemical
properties.
He found that some elements could not be
put into groups with similar properties and
at the same time stay in order.
Mullis
1
Modern Periodic Table

Later, Henry Moseley carried on the
work.



Moseley put the elements in order of
increasing atomic NUMBER.
He found that the position of the
element corresponded to its properties.
The modern periodic table shows the
position of the element is related to :


Atomic number AND
Arrangement of electrons in its energy
levels
Mullis
2
Electron Shells



7 periods (rows)
In general, each period represents an
energy level, or an electron shell
Move down P. table:

Principal quantum number (n) increases.
Recall that in describing the highest energy
electron of Cl, we found that electron in this
orbital: 3p5
n = 3 here.
(Configuration is 1s22s22p63s23p5.)


Atomic radius increases if same group
Metallic character increases if same group.
Mullis
3
Atomic Sizes using Periodic Table

As we move down a group, atoms
become larger.


Larger n = more shells = larger radius
As we move across a period, atoms
become smaller.


More protons = more effective nuclear
charge, Zeff
More positive charge increases the
attraction of nucleus to the electrons in the
outermost shell, so the electrons are pulled
in more “tightly,” resulting in smaller radius
Mullis
4
Ionization energy
Ionization energy of an ion or atom is the
minimum energy required to remove an
electron from the ground state of the isolated
gaseous atom or ion.
 The first ionization energy, I1 is the energy
required to remove one electron from an atom.
Na(g)  Na+(g) + e The 2nd ionization energy, I2, is the energy
required to remove an electron from an ion.
Na+(g)  Na2+(g) + e Larger ionization energy, harder to remove
electron.
Mullis

5
Periodic Trends in Ionization Energy


Highest = Fluorine
Ionization energy decreases down a
group.


Easier to remove electrons that are
farther from the nucleus.
Ionization energy increases across a
period.


Zeff increases, so it’s harder to remove
an electron.
Exceptions: Removing the 1st and 4th p
electrons
Mullis
6
Electron Affinity


Electron affinity is the energy change
when a gaseous atom gains an
electron to form a gaseous ion.
Electron affinity: Cl(g) + e-  Cl-(g)
Gain

Ionization energy: Cl(g)  Cl+(g) + eLose
Mullis
7
Isoelectronic species


Definition: Has exactly the same number
and configuration of electrons
Examples: Ne, Na+, O2



Ne = 10 eNa = 11 e- / Na+ = 11-1 = 10 eO = 8 e- / O2- = 8 + 2 = 10 e-
Even though these have the same number
of electrons, they retain all their protons.
Therefore the sodium ion (Na+) has the
highest effective nuclear charge with 11
protons attracting its 10 electrons.
Mullis
8
Ion size


The oxide ion is isoelectronic (has
exactly the same number and
configuration of electrons) with
neon, and yet O2– is bigger than Ne.
Why?
In any isoelectronic series the
species with the highest nuclear
charge will have the smallest radius.
Mullis
9
Metals



Metallic character increases down a group and
from left to right across a period.
Metals are found to the left of the zig-zag line
on the periodic table.
Metal properties:





Lustrous (shiny)
Malleable (can be shaped)
Ductile (can be pulled into wire)
Conduct electricity
Metals form cations (positive ions)


This means they lose 1-4 electrons
Therefore, they are usually found in IONIC
compounds
Mullis
10
Metal reactivity


Which of the alkali metals would
you expect to react most violently
with water? Li, Na, K, Rb
Of these four, rubidium has the
lowest ionization energy, making it
the most reactive. Rubidium reacts
explosively with water.
Mullis
11
Nonmetals



Lower melting points than metals
Diatomic molecules are nonmetals.
The seven (7) diatomic molecules are:
Br2 I2

N2
Cl2
H2
O2
F2
Two or more nonmetals form molecular
compounds with COVALENT bonds.
Mullis
12
Trends
See your book for full explanation.
Closer to F = more
ELECTRONEGATIVITY
 ELECTRON AFFINITY
 IONIZATION ENERGY

Closer to Cs = more



METALLIC CHARACTER
ATOMIC RADIUS
REACTIVITY
Mullis
13