The History of the Modern

Periodic Table

Johann Dobereiner

1780 - 1849

Model of triads

In 1829, he classified some elements into groups of three, which he called triads.They had similar chemical and physical properties.

(ex. Cl, Br, I andCa, Sr, Ba)

John Newlands

1838 - 1898

Law of Octaves

In 1863, he suggested that elements be arranged in “octaves” because he noticed that certain properties repeated every 8th element.

John Newlands

1838 - 1898 Law of Octaves

Newlands' claim to see a repeating pattern was met with savage ridicule on its announcement. His classification of the elements, he was told, was as arbitrary as putting them in alphabetical order and his paper was rejected for publication by the Chemical Society.

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.

Elements known at this time

• stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)

• was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.

Mendeleev...

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.

However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined. By looking at our modern periodic table, can you identify what problems might have caused chemists a headache?

Ar and KCo and NiTe and I

Th and Pa

Henry Moseley

1887 - 1915

In 1913, 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.”

Henry Moseley

His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

Glenn T. SeaborgAfter co-discovering 10 new elements, in 1944 he moved 14 elements out of the main body of the periodic table to their current location below the Lanthanide series. These became knownas the Actinide series.

1912 - 1999

Glenn T. SeaborgHe is the only person to have an element named after him while still alive.

1912 - 1999

"This is the greatest honor ever bestowed upon me - even better, I think, thanwinning the Nobel Prize."

Periodic Table Geography

The horizontal rows of the periodic table are called PERIODS.

Horizontal rows arecalled periods

Period numbers correspond to the highest occupied energy level.

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!

For A family elements the valence electron configuration is the same in each column.

The chemical behavior and properties of elements in a family are associated with the electron configuration of its elements.

With the exception of helium which has a filled s orbital, the nobles gases have filled p orbitals.

10.17

The group numbers for the representative elements are equal to the total number of outermost electrons in the atoms of the group.

The elements of a family have the same outermost electron configuration except that the electrons are in different energy levels.

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

Elements in the A groupsare designated

representative elements

Properties of Metals

• Metals are good conductors of heat and electricity.

• are shiny• are ductile (can be stretched

into thin wires).• are malleable (can be pounded

into thin sheets).• Its reaction with water results in

corrosion.

Properties of Non-Metals

• Non-metals are poor conductors of heat and electricity.

• are brittle and break easily.

• They are dull.• Many are gases.

Sulfur

Properties of Metalloids• Metalloids (metal-like) have

properties of both metals and non-metals.

• They are: Boron, Silicon, germanium, arsenic, antimony, tellurium, astatine

Silicon

Alkali Metals

Alkaline Earth Metals

Transition Metals

InnerTransition Metals

These elements are also called the rare-earth

elements.

Halogens

Noble Gases

• Classwork: color code periodic table

Include: metals, nonmetals, metalloids, alkali metals, alkaline- earth metals, halogens, noble gases, transition metals, inner transition metals

Reading the Periodic Table

Metalloids-Appearance will vary- 3 to 7 valence electrons-Form positive and/or negative ions-Conduct better than nonmetals but nor as well as metals-Properties of metals and nonmetals-Often used in semi-conductors for computer chips-Separate metals from nonmetals; touching bold stair-step line

-They are: Boron, Silicon, germanium, arsenic, antimony, tellurium, astatine-Aluminum is a metal.

Categories of the Periodic Table

Metals – (specific)*Reactive metals (alkali and alkaline earth metals)- -Alkaline earth metals- very reactive and are found in the earth’s crust.-Alkali metals- soft and malleable & ductile ( bendable and can be reshaped)*Transition metals (includes poor metals)- -less reactive than most metals-found in foods we eat, for industry (steel, copper), modern technology catalytic converters, and incandescent light bulbs), and alloys (steel and brass). *poor metals- soft, low melting points, ex: lead*Rare earth metals (lanthanide series and actinide series)- -previously believed to be rare, however as mining improved, scientist realized that they are not rare, just hard to isolate.

Reading the Periodic TableNonMetals

*Noble gases- Group 18, almost never react with other elements-Some are used to make colorful lights*Halogens- Group 17, very reactive nonmetals that form salts when combined with many metals. -Uses: to kill harmful microorganisms in hospitals, to purify drinking water and prevent growth of algae in swimming pools.

Student Misconceptions

*All metals are not magnetic

*Iron is not the only metal that has magnetic properties

*Electrical conductivity is not a property of only metals

*Carbon rod (graphite) is actually an element with properties that are intermediate

between a metal and a nonmetal

*Not all elements are solids