The 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

1834 - 1907

In 1869 he published a table of the elements organized by increasing atomic mass.

Lothar Meyer

1830 - 1895

At the same time, he published his own table of the elements organized by increasing atomic mass.

Henry Moseley

1887 - 1915

In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number.*“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”

Periodic Table Geography

Periodic Table

• Columns called Families/Groups– Family # indicates # valence (outer shell)

electrons– Elements in same family have similar

properties• Rows called Periods

– Row # indicates # energy levels in atom

The horizontal rows of the periodic table are called PERIODS.

The vertical columns of the periodic table are called GROUPS, or FAMILIES.

The elements in any group of the periodic table have similar physical and chemical properties!

Metals/Nonmetals/Semiconductors

• Metals: excellent conductors of heat & electricity; have luster, are ductile/malleable

• Nonmetals: poor conductors of heat & electricity; are dull & brittle

• Semiconductors(Metalloids): elements that under certain conditions conduct heat & electricity

Families of Elements

• Family 1: Alkali Metals• Family 2: Alkaline Earth Metals• Families 3 to 12: Transition Metals• Family 13: Boron Family• Family 14: Carbon Family• Family 15: Nitrogen Family• Family 16: Oxygen Family• Family 17: Halogens• Family 18: Noble Gases• Three general groups: metals, nonmetals, &

semiconductors(metalloids)

Periodic Table

Periodic LawWhen elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

Alkali Metals

Alkaline Earth Metals

Transition Metals

Metals• Alkali metals (Family 1)

– Very reactive– Has 1 valence electron– When ionized has charge of 1+

• Alkaline Earth metals (Family 2)– Reactive– Has 2 valence electrons– When ionized has charge of 2+

• Transition metals (Families 3 to 12)– Somewhat reactive– Valence electron number varies– Ionized charge varies

InnerTransition Metals

These elements are also called the rare-earth

elements.

Halogens

Noble Gases

Nonmetals• Include H, some elements from families 13 to 16, all

elements from families 17 & 18. Zig-zag line divides metals from nonmetals.

• Inert gases are unreactive; contain 8 valence electrons• Halogens are very reactive; contain 7 valence

electrons; gain electrons becoming negatively charged

• Elements in other families gain electrons to become negatively charged

• These elements plentiful on Earth

Semiconductors(aka Metalloids)

• Located along the zig-zag line• Includes:

– Boron (B); Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Polonium (Po)

• Notice that Al is not considered a metalloid, it is considered a metal

• Conduct heat & electricity under certain conditions• B is hard & added to steel to increase hardness; Sb is

bluish-white and shin, Te is silvery-white & electrical conductivity increases with light exposure, Si important in solar cells & integrated circuits

Periodic Table Trends

#1. Atomic Size - Group trends• As we increase the

atomic number (or go down a group). . .

• each atom has another energy level,

• so the atoms get

bigger.

HLi

Na

K

Rb

#1. Atomic Size - Period Trends• Going from left to right across a period, the size

gets smaller.

• Electrons are in the same energy level.

• But, there is more nuclear charge.

• Outermost electrons are pulled closer.

Na Mg Al Si P S Cl Ar

#2. Trends in Ionization Energy

• Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom).

• Removing one electron makes a 1+ ion.

• The energy required to remove only the first electron is called the first ionization energy.

Ionization Energy

• The second ionization energy is the energy required to remove the second electron.– Always greater than first IE.

• The third IE is the energy required to remove a third electron.– Greater than 1st or 2nd IE.

#3. Trends in Electronegativity• Electronegativity is the tendency for an

atom to attract electrons to itself when it is chemically combined with another element.

• They share the electron, but how equally do they share it?

• An element with a big electronegativity means it pulls the electron towards itself strongly!

Electronegativity Group Trend• The further down a group, the

farther the electron is away from the nucleus, plus the more electrons an atom has.

• Thus, more willing to share.• Low electronegativity.

Electronegativity Period Trend• Metals are at the left of the table.

• They let their electrons go easily

• Thus, low electronegativity

• At the right end are the nonmetals.

• They want more electrons.

• Try to take them away from others

• High electronegativity.

The periodic table is the most important tool in the chemist’s

toolbox!