Organization of the Periodic Table
Demetry Mendeleev organized the elements
in the first periodic table by order of mass in
1870.



Found repetition in
properties of elements
Widely accepted
because it was able to
predict the existence
and properties of
undiscovered elements
Problem: elements were
being placed in groups
of elements with
differing properties
In 1913 Henry Mosley, an English Chemist,
reorganized the Periodic Table based on the
number of protons.



Clear periodic patterns
Mendeleev’s problems of
properties are solved
Periodic law – there is a
periodic repetition of
chemical and physical
properties of the
elements when they are
arranged by increasing
atomic number
The Modern Periodic Table
Elements are placed on the Periodic Table
based on the number of protons in their
nucleus
Families
Each element in a particular family
contains the same number of outer shell
electrons, or valence electrons.
Families
Each family is numbered 1 through 8,
followed by the letter A or B.
 The families designated with an A (1A-8A)
are called representative elements
because they possess a wide range of
chemical and physical properties.
 Families designated with a B are referred
to as transition elements.

Periods
Other major divisions in the Periodic
Table include the metals, nonmetals,
and metalloids
Metals
Characteristics of Metals








Shiny and smooth
Solid at room temperature
Good conductors of heat and electricity
Ductile and malleable
Most group A and all group B elements are
metals
Group 1A elements (except H) are alkali metals
Group 2A elements are alkaline earth metals;
both are chemically reactive, alkali the more
reactive
Elements from group B (lanthanide series) are
used as phosphors, substances that emit light
when struck by e-
Nonmetals
Characteristics of Nonmetals







Upper right side of periodic table
Gases or brittle
Dull-looking solids
Poor conductors of heat and electricity
Br – only nonmetal that is a liquid at room temp.
Halogens – 7A, highly nonreactive
Noble gases – 8A, extremely nonreactive
Metalloids
Characteristics of Metalloids
Physical and chemical properties of both
metals and nonmetals
 Silicon and Germanium are two of the
most important metalloids, they are used
in computer chips and solar cells

Silicon – used in computer chips and solar
cells
Atomic Radius
Atomic radius



How closely an atom
lies to a neighboring
atom
Trends within periods =
decrease due to
outermost e- being
pulled toward nucleus
Trends within groups =
increase due to
shielding and increased
energy levels
Atomic Radius
Ionic Radius
Ionic radius



Ion=atom that has a + or –
charge due to the gain or
loss of eLose e-/ + charge / smaller
atom - electrostatic repulsion
decreases & valence eleaves unfilled orbital
Gain e-/ - charge / larger
atom – electrostatic
repulsion increases &
causes increase distance
between outer e- causing
larger radius
Ionic radii
Trends within periods = size of the + ion
decreases, then beginning in group 5A or
6A the larger – ion decreases
 Trends within groups = ion size increases
due to the ion’s outer e- being in higher
energy levels

Ionization energy is the energy
required to remove an electron
from a gaseous state atom
Ionization Energies
Ionization energy
1st, 2nd , 3rd etc.
 How strong atom’s nucleus holds onto the
valence e Large ionization energy, less likely to form
+ ions
 Low ionization energy, atom loses outer eeasily and easily forms + ions

Ionization Energy Trends
Trends within periods = increase due to
increase in nuclear charge producing an
increased hold on valence e Trends within groups = decrease due to
valence e- being farther from the nucleus
requiring less energy to remove them

Octet Rule




Atoms tend to gain, lose, or share e- in order to
acquire a full set of eight valence eException : 1st period completely filled with 2 eElements on the right side of the periodic table
tend to gain e- and tend to form – ions
Elements on the left side of the periodic table
tend to lose e- and form + ions

Electronegativity is
how much atoms pull
electrons away from
another atom
Electronegativity Values
Electronegativity Trends
Trends within periods = increase
 Trends within groups = decreases
 Lowest electronegativities are found at the
lower left side of the periodic table
 Highest electronegativities are found at the
upper right side of the periodic table
