The Periodic Table

Bringing order to the chemical world.

Dmitrii Mendeleev

Called the Father of the Periodic Table.

Said to have created the first Periodic Law while playing chemical solitaire on a long train ride.

Found that when the elements were arranged in order of increasing atomic mass the properties of the elements repeated.

http://en.wikipedia.org

Mendeleev’s Periodic Law

The physical and chemical properties of the elements

are periodic functions of their atomic masses.

(When the elements are arranged in order of their masses their properties repeat)

Mendeleev’s Original Table

Mendeleev’s attempt to organize the elements in order of increasing atomic mass led him to create holes (in red) in his tables.

He predicted that elements would be discovered that would fill the holes.

Mendeleev predicts existence of two new elements.

In 1869, Mendeleev called these undiscovered elements eka-Aluminum and eka-Silicon and predicted their properties.

Chemists began a search for these elements. Today these elements are know as Gallium (Ga), discovered in 1875, and Germanium (Ge), discovered in 1885.

A problem?!When Mendeleev got to Tellurium (Te) and Iodine (I) a problem arose. Iodine appeared to have an atomic mass less than Tellurium. Yet, based on their properties, it seemed that Iodine should have a heavier mass than Tellurium.

What Mendeleev thought

Mendeleev thought that the problem was that the atomic mass of Tellurium was not correct. He predicted that future determinations of the atomic mass of Te would show that Tellurium’s atomic mass was actually less than Iodine’s mass.

He was wrong! Further studies confirmed that Tellurium was heavier than Iodine.

Henry Mosely solves the problem

Mosely was a student of Rutherford who developed the concept of atomic number. Based on his studies, it was determined that Tellurium comes before Iodine because the atomic number of Tellurium is less than the atomic number of Iodine.

Mosely was killed by a sniper at the age of 28 during World War I. Since that time Great Britain and many other countries have not allowed scientists to serve in the front lines.

http://www.answers.com/topic/henry-moseley

The Modern Periodic Law

Based on Mosely’s discovery of the concept of atomic number, the modern Periodic Law now states:

The chemical and physical properties of the elements are periodic functions of atomic number.

Regions of the Periodic Table

Comparison of Metals & Non-metals

Metals Non-Metals

Chemical properties Lose electrons in chemical reactions

Gain electrons in chemical reactions

Physical Properties •Good conductors•Shiny (luster)•Ductile (can be drawn into wire)•Malleable (hammered flat)

•Often gases at room temperature•Poor conductors•Brittle

The Periods (Rows)The horizontal rows in the Modern Periodic Table are called Periods

As you go across a period from left to right, the properties of the elements change in a regular manner:

metals metalloids non-metals Noble gases

Groups or Families (Vertical columns)

Elements that are located in the same column of the Periodic Table are called Groups or Families. Elements in the same Family have similar chemical and physical properties. There are four common families:

•The Alkali Metals

•The Alkaline Earth Metals

•The Halogens

•The Noble Gases

The Alkali Metals

Column 1 in the Periodic Table.

Alkali Metals:

•React with air and water (they are never found uncombined in nature)

•Very Soft

•Good conductors of electricity

•Form compounds in 1:1 ratios with chlorine (LiCl, NaCl, KCl, etc.)

The Most Reactive Metals

This is the picture of a piece of sodium that was dumped into a bucket of water. The Na reacts with water to produce hydrogen and heat. The heat ignites the hydrogen gas causing a hydrogen explosion.

The Alkaline Earth Metals

Column 2 in the Periodic Table.

Alkaline Earth Metals are:•Very reactive with air and water (they are rarely found uncombined in nature)

•Soft

•Good conductors of electricity

•Form compounds in 1:2 ratios with chlorine (BeCl2, MgCl2,CaCl2, etc.)

The HalogensColumn 17 in the Periodic Table.

Halogens are:•Very reactive with most metals and non-metals (they are never found uncombined in nature)

•Have low melting and boiling points (F and Cl are gases at room temp.)

•Form diatomic molecules (F2, Cl2, Br2, I2)

•Poor conductors of electricity

•Form compounds in 1:1 ratios with hydrogen (HF, HCl, HBr, etc)

The Noble Gases

Column 18 in the Periodic Table.

Noble Gases are:•Very unreactive. At one time they were called the Inert Gases.

•Have low melting and boiling points (They are all gases at room temp.)

Other Areas in the Periodic Table

The Transition Elements (Groups 3-12) – hard, metallic elements with high melting points. Transition elements tend to form colored compounds.

Other Areas in the Periodic TableThe Inner-Transition Elements – elements in Periods 6 and 7 that are

inserted between Group 3 and 4. The elements in Period 6 are called the Lanthanide Series (since they follow Lanthanum), while the elements in Period 7 are called the Actinide Series (since they follow Actinium).

Quick Quiz1. The Modern Periodic Table is organized based on

_________________ and _______________.2. Iodine belongs to the ____________Family.3. The rows in the Periodic Table are called _____________.4. Elements that form colored compounds are classified as

________________ metals.5. Family of elements that almost never react is called

_______________________.6. Barium (Ba) belongs to the ____________ Family.7. What Alkali metal is found in Period 5?8. How did Mendeleev’s Periodic Law differ from the Modern

Periodic Law? 9. How many sodium atoms are present in a 46 gram sample of

sodium?

Atomic number Chemical & physical propertieshalogen

Periods

transition

Noble gasesAlkaline Earth

Rubidium (Rb)

Mendeleev based his law on atomic mass, modern law is based on atomic number.