The Periodic Table
Objectives
• Relate the organization of periodic table to the
arrangement of electrons within an atom
• Explain why some atoms gain or lose electrons to
form ions
• Determine how many protons, neutrons, and
electrons an atom has, given its symbol, atomic
number, & mass number
• You will be able to describe how the abundance of
isotopes affects an element’s average atomic
mass
History of the Periodic Table
• Russian chemist Dmitri Mendeleev is generally
credited as being the “father” of the periodic
table
• His work was based on earlier versions of
periodic tables by a number of scientists,
including:
A. E. Béguyer de Chancourtois
John A. R. Newlands.
Lothar Meyer
History of the Periodic Table cont.
• The modern periodic table is based on one
presented by Mendeleev in 1869
• He realized that certain properties repeat
periodically when the elements are arranged
horizontally in order of atomic weight
• He also placed chemically similar elements in
vertical columns, leaving empty spaces as needed
• From the empty spaces, Mendeleev deduced the
existence of unknown elements and predicted
some of their properties
• When Mendeleev published his first table,
scientists did not know about subatomic particles
The Modern Periodic Table
• Today, elements are arranged by atomic
number instead of by atomic weight
• The modern periodic table has 118 elements
• Only 114 have official names
• Many more than the 63 elements known to
scientists in Mendeleev’s time
Organization of the Periodic Table
• It groups similar elements together
• The organization makes it easier to predict
the properties of elements
• Elements are represented by their symbols
• Position in the table helps to determine
properties of elements
• The order of arrangement is based on the
number of protons an atom of that element
has in the nucleus
Periodic Law
• States that the repeating chemical
and physical properties of elements
change periodically with the atomic
numbers of the elements
Transuranium Elements
• Are elements past uranium on the periodic
table
• Have been difficult to study because they do
not exist in nature.
• They must be created in a laboratory, and
many exist for a very short period of time.
• One particularly troublesome element is
element 104
•
American scientists Albert Ghiorso and James
Harris created this elusive element at the
Lawrence Radiation Laboratory at the University
of California at Berkeley in 1969
Determining Electron Arrangement
• You can determine how an atom’s electrons are
arranged if you know where that element is located
in the table
• A group is a column of elements in the periodic table
• Elements in the same group have the same number
of valence electrons!
• Elements in the same group have similar properties
• Periods are the horizontal rows in the periodic table
• The number of protons & the number of electrons
increases as you move across a period left to
right
Electron Arrangement Examples
• Hydrogen & Helium are in the same
period
Energy Level Orbital # of Electrons
1
s
1
1
s
2
Electron Arrangement Examples
• Lithium & Carbon are in the same period
Energy Level
Orbital
Number of Electrons
1
s
2
2
s
1
Energy Level
Orbital
1
s
2
2
s
2
2
p
2
Number of Electrons
Electron Arrangement Table
You Try!---What about oxygen?
Energy Level
Orbital
# of Electrons
Atoms Form Ions
• Atoms that do not have filled outer orbitals
can experience ionization
• Ionization is the ability to gain or lose valence
electrons, resulting in charged atoms
• Ions are charged atoms and can be positive or
negative
• Cations are positive ions
• Anions are negative ions
Specific Examples
• Lithium loses 1 electron to form a 1+ charged
ion
• Lithium has 3 electrons
• 1 in the outer most orbital
Specific Examples
• Fluorine gains 1 electron to form a 1charged ion
• It has 7 electrons in its outer orbital
How Do the Structures of Atoms
Differ?
• Atomic number (Z) equals the number of
protons as well as the number of electrons
• Atoms are always neutral!
• Mass number (A) equals the total number
of subatomic particles in the nucleus
• The number of protons & neutrons
• It is also the “average atomic weight” of
an element
Isotopes
• Are atoms of the same element that differ
by the number of neutrons in the nucleus
• They DO NOT differ in atomic number
• They ONLY differ in mass number & their
physical properties
Calculating the # of Neutrons
Let’s Practice!
• K
• Au
• B
• Si
• U-235
K = 20
Au = 118
B = 6
Si = 14
U-235 = 143
The Mass of an Atom
• Is very small
• We usually work with atomic mass units
• Atomic mass unit (amu) is equal to onetwelfth of the mass of carbon-12 atom
• Average atomic mass is a weighted average
of the masses of all naturally occurring
isotopes of an element
• The more common the isotope the greater
the effect on the average
Mass of an Atoms
More Practice!
•
Calculate the # of protons, electrons, &
neutrons in the following isotopes
1.
Carbon-14
2.
Nitrogen-15
3.
Sulfur-35
4.
Calcium-45
5.
Iodine-131