Atomic Structure & the Periodic
Table
Basic Definitions
• Atom – smallest unit of an element that
retains the properties of that element
• Atoms are made up of several
subatomic particles called protons,
neutrons, and electrons
Protons, Neutrons, & Electrons
• Protons – have a +1 charge and are
found in the nucleus of the atom
• Neutrons – have no charge and are also
found in the nucleus of an atom
• Electrons – have a -1 charge and are
found on the outside of the nucleus
• Nucleus – made up of protons and
neutrons, has an overall + charge
Atomic Structure
Atomic Numbers
• The atomic number of an element is the
number of protons in the nucleus of an atom
of that element.
• It is the number of protons that determines
the identity of an element, as well as many of
its chemical and physical properties.
• The number of protons for an element
CANNOT be changed.
Atomic Numbers
• Because atoms have no overall electrical
charge, the number of protons must equal the
number of electrons.
• Therefore, the atomic number of an element
also tells the number of electrons in a neutral
atom of that element.
• The number of electrons can be changed
when determining the charge of an ion.
Masses
• The mass of a neutron is almost the same as
the mass of a proton.
• The sum of the protons and neutrons in the
nucleus is the mass number of that particular
atom.
• Isotopes of an element have different mass
numbers because they have different
numbers of neutrons, but they all have the
same atomic number (number of protons &
electrons)
Isotopes
• When writing isotopes, the atomic number (or
number of protons) will appear at the bottom left of
the formula
• The mass number (number of protons plus neutrons
will appear at the top left of the formula.
• The element symbol will appear to the right of the
numbers
• The different number of neutrons has NO bearing on
chemical reactivity
12
12
6 C
6
Writing the Names of Isotopes
• When writing the name of an isotope,
you will write the name of the element
– the mass number
• For example 126 C would be named:
• Carbon - 12
Try the following
Name
Symbol
# Protons
# Neutrons
1
2
# Electrons
Mass #
25
55
Carbon – 11
197
Au
79
Oxygen - 15
Try the following
Name
Symbol
# Protons
# Neutrons
# Electrons
Mass #
Carbon – 11
11
6
5
6
11
79
118
79
197
1
2
1
3
C
6
Gold - 197
Hydrogen –
3
197
Au
79
3
H
1
Manganese 55
55
Mn
25
25
30
25
55
Oxygen - 15
15
8
7
8
15
O
8
Try this one
Name
Iodine -1 - 130
Symbol
# Protons
# Neutrons
# Electrons
Mass #
Try this one
Name
Symbol
# Protons
# Neutrons
# Electrons
Mass #
Iodine -1 - 130
130
53
77
54
130
I -1
53
Atomic Mass
• Atomic mass –the
weighted average mass
of all the naturally
occurring isotopes of
that element.
• The number is usually
located at the bottom of
the periodic table and
has decimal places
Calculating Atomic Mass
Calculating Atomic Mass
• Copper exists as a mixture of two
isotopes.
• The lighter isotope (Cu-63), with 29
protons and 34 neutrons, makes up
69.17% of copper atoms.
• The heavier isotope (Cu-65), with 29
protons and 36 neutrons, constitutes the
remaining 30.83% of copper atoms.
Calculating Atomic Mass
• First, calculate the contribution of each
isotope to the average atomic mass,
being sure to convert each percent to a
fractional abundance.
Calculating Atomic Mass
• The average atomic mass of the
element is the sum of the mass
contributions of each isotope.
Try this one…
Calculate the atomic mass of germanium.
72.59 amu
You can tell many things from an
isotope formula
• Hydrogen has three naturally occurring
isotopes in nature: Hydrogen – 1,
Hydrogen – 2, and Hydrogen – 3.
– Which is the most abundant in nature?
• Hydrogen – 1
– Which is the heaviest?
• Hydrogen - 3
Periodic Table
• Periodic Table – arrangement of
elements in order of increasing atomic
number with elements having similar
properties in vertical columns
– Groups – vertical columns
– Periods – horizontal rows
Group Names
Group
1A
2A
6A
7A
8A
Name
Alkali Metals
Alkaline Earth Metals
Chalcogens
Halogens
Noble Gases
Groups
• The group tell you the number of
valence electrons that the element has
• Valence electrons are electrons in the
outermost shell of the atom
• All group 1A elements have 1 valence
electron. Likewise, all group 8A
elements have 8 valence electrons.
Characteristics
• Elements in the same group exhibit
similar chemical characteristics due to
the fact that they all have the same
number of valence electrons.
• The most stable number of valence
electrons is 8
• This is called an octet
Charges
• Every element wants 8 valence electrons to become
stable. They will gain or lose valence electrons to
form an octet
• For example…Group 1A elements have 1 valence
electron. They can either gain 7 electrons to have an
octet or lose 1.
• What is easier?
Lose 1
• If an element loses 1 electron (1 negative charge)
what charge will the resulting ion have?
+1
Charges
• Let’s go to group 7A. This group has 7
valence electrons
• It can either loose 7 or gain 1
• What is the easiest?
Gain 1
• What will be the resulting charge if the
element gain 1 electron (1 negative charge)?
-1
Physical States and Classes of
the Elements
• The majority of the elements are metals.
They occupy the entire left side and
center of the periodic table.
• Nonmetals occupy the upper-right-hand
corner.
• Metalloids are located along the
boundary between metals and
nonmetals.
Metals
• Metals are elements
that have luster,
conduct heat and
electricity, and usually
bend without
breaking.
• With the exception of
tin, lead, and bismuth,
metals have one, two,
or three valence
electrons.
Metal Video Clip
Metals
• All metals except mercury are solids at
room temperature; in fact, most have
extremely high melting points.
• The periodic table shows that most of
the metals (coded blue) are not main
group elements.
Transition Metals
• The elements in Groups
3 through 12 of the
periodic table are called
the transition elements.
• All transition elements
are metals.
• Many transition metals
can have more than one
charge
Various oxidation
States Video Clip
Inner Transition Metals
• In the periodic table, two series of elements,
atomic numbers 58-71 and 90-103, are
placed below the main body of the table.
• These elements are separated from the main
table because putting them in their proper
position would make the table very wide.
• The elements in these two series are known
as the inner transition elements.
Inner Transition Metals
• The first series of inner transition
elements is called the lanthanides
because they follow element number
57, lanthanum.
• The second series of inner transition
elements, the actinides, have atomic
numbers ranging from 90 (thorium, Th)
to 103 (lawrencium, Lr).
Non Metals
• Although the majority of the elements in
the periodic table are metals, many
nonmetals are abundant in nature
• The nonmetals oxygen and nitrogen
make up 99 percent of Earth’s
atmosphere.
Non Metals
• Most nonmetals don’t conduct electricity,
are much poorer conductors of heat than
metals, and are brittle when solid.
• Many are gases at room temperature;
those that are solids lack the luster of
metals.
• Their melting points tend to be lower than
those of metals.
Properties of Metals and
Nonmetals
Metalloids
• Metalloids have some chemical and
physical properties of metals and other
properties of nonmetals.
• In the periodic table, the metalloids lie
along the border between metals and
nonmetals.