In 1869, Russia's Dmitri Mendeleev and Germany's Lothar Meyer... Meyer Mendeleev

published nearly identical classification tables for the 63 elements known at the time... Meyer Mendeleev

based on recurring chemical and physical properties when elements were arranged... Meyer Mendeleev

in order of increasing atomic weight. Meyer Mendeleev

Although their observations were identical, Mendeleev is given the credit because he predicted the existence of undiscovered elements and left spaces for them.

Mendeleev's table, published in the journal Annalen der Chemie in 1871.

Mendeleev is known as the Father of the Periodic Table. And almost no one outside of Germany knows about Meyer.

In 1913, Henry Moseley developed the concept of atomic numbers.

Moseley correctly said that the atomic number was equal to the number of protons in the nucleus...

AND the number of electrons in the atom.

When Moseley arranged atoms by their increasing atomic number, the few problems with Mendeleev's table disappeared.

In 1945, Glenn Seaborg proposed pulling the lanthanide and actinide series out of the main body of elements on the table.

Seaborg

Elements on today's periodic table are arranged by increasing atomic number...

the lanthanide and actinide series are separated from the main body... f block

AND the d block elements...

separate the main body elements. s block p block

Every element is represented by a single square. Each square contains three things:

1. The chemical symbol for the element. If there are two letters, the first is ALWAYS a capital letter, and the second is ALWAYS a small letter.

1. The chemical symbol for the element. Solid The symbols on some tables indicate the physical state at room temperature. LiquidGas

2. A whole number representing the atomic number. The atomic number is not always in the same place on every periodic table - but it is ALWAYS a whole number.

2. A whole number representing the atomic number. The atomic number is defined as the number of protons in the atom.

2. A whole number representing the atomic number. Normal atoms have an equal number of protons and electrons - so, the atomic number is also equal to the electrons in an atom.

2. A whole number representing the atomic number. Chemists can change the number of electrons in an atom, but they can NOT change the number of protons in an atom.

2. A whole number representing the atomic number. Changing the number of protons changes the element into another element - this can only happen in a nuclear reaction.

3. A decimal fraction number representing the element's average atomic mass.

3. A decimal fraction number representing the element's average atomic mass. The atomic mass of an element is the sum of its protons and neutrons.

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3 How many neutrons?

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3 0

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3 How many neutrons?

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3 1

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3 How many neutrons?

Atoms of an element all have the same numbers of protons, but they can have different numbers of neutrons. H Hydrogen-1 Hydrogen-2 Hydrogen-3 2

Atoms of the same element with different numbers of neutrons are called isotopes. H Hydrogen-1 Hydrogen-2 Hydrogen-3

Which of hydrogen's three isotopes is the most common? H Hydrogen-1 Hydrogen-2 Hydrogen-3

Which of hydrogen's three isotopes is the most common? H Hydrogen-1 Hydrogen-2 Hydrogen-3

Round off all mass numbers to the nearest WHOLE number.

Isotopes

More information on the Periodic Table

The Nobel Gas Family is chemically inactive.

Fluorine is the most active nonmetal Francium is the most active metal

The oxidation number of an element indicates the number of electrons gained or lost when forming compounds.

Elements with positive oxidation numbers lose electrons.

Elements with negative oxidation numbers gain electrons.

+1

+2

+1, +2, +3

+3

+4 or -4

-3

-2

Electron energy levels, from 1 to 7

Electron energy sublevels

Electron energy sublevel p

Electron energy sublevel d

Electron energy sublevel f

Each "pair" of boxes in a sublevel indicates an orbital.

Vertical columns are Families - elements with similar properties.

Alkali Metals

Alkaline Earth Metals

Transition Metals

Rare Earth Metals

Boron Family

Carbon Family

Nitrogen Family

Oxygen Family

Halogen Family

Nobel Gas Family

The Periodic Table - 27 min

Size of a Molecule

An Electron Configuration shows the exact location of every electron in an atom. With very few exceptions, the electron configuration of an atom can be read directly from the Table.