The History
of the
Modern
Periodic Table
During the nineteenth
century, chemists began to
categorize the elements
according to similarities in
their physical and chemical
properties. The end result
of these studies was our
modern periodic table.
Dmitri
Mendeleev
In 1869 he published a
table of the elements
organized by increasing
atomic mass.
1834 1907
• Mendeleev left blank
spaces in his table
• The existence of unknown
elements was predicted by
Mendeleev on the basis of
the properties of the blank
spaces.
• When the unknown
elements were discovered,
it was found that
Mendeleev had closely
predicted the properties of
the elements.
After the discovery of these
unknown elements between 1874
and 1885, and the fact that
Mendeleev’s predictions for Sc,
Ga, and Ge were amazingly close
to the actual values, his table
was generally accepted.
Periodic Law
When elements are arranged in
order of increasing atomic
number, there is a periodic
pattern in their physical and
chemical properties.
The periodic table is the most
important tool in the chemist’s
toolbox!
Trends on the
Periodic Table
Brainiac: Alkali Metals
Groups and Periods
 Groups or Families - a column of
elements on the periodic table.
 There are 18 groups on the table
 Period - a row of elements on the
periodic table.
 There are seven periods on the table
Groups and Periods
You need to know five family
names and locations
18
1
2
3-12
17
Properties of Families
Alkali metals (1)—The most reactive metal family,
must be stored under oil because they react
violently with water! They dissolve and create an
alkaline, or basic, solution, hence their name.
Alkaline earth metals (2)—These also are reactive
metals, but they don’t explode in water; pastes of
these are used in batteries.
Halogens (17)—Known as the “salt formers,” they
are used in modern lighting and always exist as
diatomic molecules in their elemental form.
Noble gases (18)—Known for their extremely low
reactivity, these were once thought to never react;
neon, one of the noble gases, is used to make
bright signs.
Periodic Table and Electron
Configurations
S
 Elements in the same group have the same outer shell
electron configuration so they have similar chemical
properties.
d
p
f
Metals, Nonmetals,
Metalloids
• There is a zig-zag
or staircase line
that divides the
table.
• Metals are on the
left of the line, in
blue.
• Nonmetals are on
the right of the
line, in orange.
Metals, Nonmetals,
Metalloids
• Elements that
border the stair
case, shown in
purple are the
metalloids or semimetals.
• There is one
important
exception.
• Aluminum is more
metallic than not.
Metals
• Metals are lustrous
(shiny), malleable,
ductile, and are
good conductors of
heat and
electricity.
• They are mostly
solids at room
temp.
• What is one
exception?
Nonmetals
• Nonmetals are the
opposite.
• They are dull,
brittle,
nonconductors
(insulators).
• Some are solid, but
many are gases,
and Bromine is a
liquid.
Metalloids
• Metalloids, aka semimetals are just that.
• They have
characteristics of both
metals and nonmetals.
• They are shiny but
brittle.
• And they are
semiconductors.
The Three Main Groups of
Elements on the Periodic Table
Metals
• luster (shine)
• good conductors of heat and electricity
• solid at room temperature
• most are malleable and ductile
Non-metals
•
•
•
•
Dull, not shiny
poor conductors of heat and electricity
neither malleable or ductile
many are gasses at room temperature
Semimetals or metalloids
• have some properties of metals and some of non-metals
Trends on the Periodic Table
Atomic Radius – the size (diameter)
of the atom
Decreases as you go across a period,
but increases as you go down a group.
Ionization energy – the energy
required to remove a valence
electron. (outer most electron)
Increases as you go across a period,
but decreases as you go down a group.
Trends
Decreasing Ionization Energy
Increasing ionization energy
Why the Trend in Atomic
Radius?
Across a period the radius decreases• As you go from left to right the protons in
the nucleus increase and the electrons
also increase which causes the atom to be
'sucked' together a little tighter.
Down a group radius increases • A new energy level of electrons is added
to the atom as you go down each row,
making each atom significantly larger.
Why the Trend in Ionization
Energy?
Increases as you go across a group
because the elements are getting smaller
and the electrons are closer to the nucleus
making it harder to remove an electron.
Decreases as you go down a column
because the electrons are further from the
nucleus and easier to remove. (lower
ionization energy)
Ionic size
• Metallic elements easily lose
electrons.
• Non-metals more readily gain
electrons.
How does losing or gaining an electron
effect the size of the atom (ion) ?
Positive ions
• Positive ions are always smaller that
the neutral atom. Loss of outer shell
electrons.
Negative Ions
• Negative ions are always larger than
the neutral atom. Gaining electrons.
Number of
protons
Charge = protons - electrons
Ion size trends in columns.
• Ion size increases
as you move down
a column for both
positive and
negative ions