The Periodic Table
Development of Periodic
Table
Dmitri
Mendeleev
grouped
elements by
similar
properties.
Mendeleev’s Table
1869
Development of Periodic
Table
Mendeleev predicted the discovery of
germanium (which he called eka-silicon) as an
element with an atomic weight between that
of zinc and arsenic, but with chemical
properties similar to those of silicon.
Metals, Non-metals and
Metalloids
Development of Periodic
Table
• Elements are
arranged in
vertical columns
called GROUPS
and horizontal
rows called
PERIODS.
Periodic Table
• Elements in the same group
have similar properties because
they have the same number of
electrons in their outermost
shell.
• These electrons are called
VALENCE ELECTRONS.
Significance of Groups
• Group 1 elements all have one
electron in their outer shell
• Group 2 elements all have two
electrons in their outer shell
• These electrons give elements
in the same group similar
properties.
Significance of Periods
• The elements in the first period
all have one shell.
• The elements in period 2 all
have 2 shells.
• The elements in period 3 all
have 3 shells
• And so on
Hydrogen Group
• This element does not match the
properties of any other group, so it
stands alone. It is place above group 1,
but it is not part of that group.
• It is very a reactive, colorless, odorless
gas at room temperature.
Group 1 – Alkali Metals
• Alkali metals are extremely reactive and
are never found in nature in their pure
form. They are silver colored and shiny.
Their density is extremely low so that
they are soft enough to be cut with a
knife. (1 outer level electron)
Group 2 – Alkaline Earth Metals
• Alkaline-earth Metals – Slightly less reactive
than alkali metals. They are silver colored
and harder and denser than alkali metals. (2
outer level electrons)
– Less reactive than group 1, but are also too
reactive to be found in nature as free elements.
Groups 3 – 12 – Transition Metals
• Transition Metals have a moderate range
of reactivity and a wide range of
properties. In general, they are shiny and
good conductors of heat and electricity.
They also have higher densities and
melting points than groups 1 & 2. (1 or 2
outer level electrons)
Lanthanide and Actinides
• The elements in each of these two periods
share many properties. The lanthanides are
shiny and reactive. The actinides are all
radioactive and are therefore unstable.
Elements above 92 do not exist in nature
but have been manufactured in the lab.
Lanthanide and Actinides
• Periodic table with lanthanide and actinides in
their “natural” position.
Group 17 - Halogens
• Halogens are all nonmetals. Very
reactive and poor conductors of heat and
electricity.
Group 18 – Noble Gases
• Noble Gases are unreactive nonmetals.
All are colorless, odorless gases at room
temperature. All found in earth’s
atmosphere in small amounts. (8 outer
level electrons)
• The outer electron shell is full making
them unreactive.
Groups 13 - 16
• Group 13: Boron Group –Reactive. (3 outer
level electrons)
• Group 14: Carbon Group –Varied reactivity.
(4 outer level electrons)
• Group 15: Nitrogen Group –metal. Varied
reactivity. (5 outer level electrons)
• Group 16: Oxygen Group – Reactive group.
(6 outer level electrons)
Valence Electrons
• Valence Electrons are the electrons in the
outermost shell.
–
–
–
–
–
–
–
–
Group 1 (1A) – 1 valence electron
Group 2 (2A) – 2 valence electrons
Group 13 (3A) – 3 valence electrons
Group 14 (4A) – 4 valence electrons
Group 15 (5A) – 5 valence electrons
Group 16 (6A) – 6 valence electrons
Group 17 (7A) – 7 valence electrons
Group 18 (8A) – 8 valence electrons.
Valence Electrons
• For groups 3 – 12 (transition metals) as
well as the lanthanide and actinide series
the number of valence electrons can not
be easily determined from the periodic
table.
Sizes of Atoms
The bonding atomic
radius is defined as
one-half of the
distance between
covalently bonded
nuclei.
Sizes of Atoms
Bonding atomic
radius tends to…
…decrease from left to
right across a row.
…increase from top to
bottom of a column
due to increasing value
of n
Ions
• An ion is an atom or group of bonded
atoms that has a positive or negative
charge
• A positive ion is a cation.
• A negative ion is an anion.
Sizes of Ions
• Ionic size depends
upon:
– Nuclear charge.
– Number of
electrons.
– Orbitals in which
electrons reside.
Sizes of Ions
• Cations are
smaller than their
parent atoms.
– The outermost
electron is
removed and
repulsions are
reduced.
Sizes of Ions
• Anions are larger
than their parent
atoms.
– Electrons are
added and
repulsions are
increased.
Sizes of Ions
• Ions increase in size
as you go down a
column.
– Due to increasing
value of n.
Ionization Energy
• Amount of energy required to remove
an electron from the ground state of
an atom or ion.
– First ionization energy is that energy
required to remove first electron.
– Second ionization energy is that energy
required to remove second electron, etc.
Trends in First Ionization
Energies
• As one goes down a
column, less energy is
required to remove
the first electron.
Electronegativity:
• The ability of atoms
in a molecule to
attract electrons to
itself.
• On the periodic chart,
electronegativity
increases as you go…
– …from left to right
across a row.
– …from the bottom to
the top of a column.