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.

Johann Dobereiner

1780 - 1849

Model of triads

In 1829, he classified some elements into groups of three, which he called triads.�The elements in a triad had similar chemical properties and orderly physical properties.

(ex. Cl, Br, I and� Ca, Sr, Ba)

John Newlands

1838 - 1898

Law of Octaves

In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) 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.

John Newlands

1838 - 1898

Law of Octaves

His law of octaves failed beyond the element calcium.

WHY?

Would his law of octaves work today with the first 20 elements?

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

• Both Mendeleev and Meyer arranged the elements in order of increasing atomic mass.
• Both left vacant spaces where unknown elements should fit.

So why is Mendeleev called the “father of the modern periodic table” and not Meyer, or both?

• 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 K

Co and Ni

Te and I

Th and Pa

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.”

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. Seaborg

After 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 known�as the Actinide series.

1912 - 1999

Glenn T. Seaborg

He 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, than�winning the Nobel Prize."

Periodic Table Geography

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!

Periodic Law

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

Hydrogen

• The hydrogen square sits atop Family AI, but it is not a member of that family. Hydrogen is in a class of its own.
• It’s a gas at room temperature.
• It has one proton and one electron in its one and only energy level.
• Hydrogen only needs 2 electrons to fill up its valence shell.

Alkali Metals

• The alkali family is found in the first column of the periodic table.
• Atoms of the alkali metals have a single electron in their outermost level, in other words, 1 valence electron.
• They are shiny, have the consistency of clay, and are easily cut with a knife.

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Alkali Metals

• They are the most reactive metals.
• They react violently with water.
• Alkali metals are never found as free elements in nature. They are always bonded with another element.

What does it mean to be reactive?

• We will be describing elements according to their reactivity.
• Elements that are reactive bond easily with other elements to make compounds.
• Some elements are only found in nature bonded with other elements.
• What makes an element reactive?
• An incomplete valence electron level.
• All atoms (except hydrogen) want to have 8 electrons in their very outermost energy level (This is called the rule of octet.)
• Atoms bond until this level is complete. Atoms with few valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

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Alkaline Earth Metals

• They are never found uncombined in nature.
• They have two valence electrons.
• Alkaline earth metals include magnesium and calcium, among others.

Transition Metals

• Transition Elements include those elements in the B families.
• These are the metals you are probably most familiar: copper, tin, zinc, iron, nickel, gold, and silver.
• They are good conductors of heat and electricity.

Transition Metals

• The compounds of transition metals are usually brightly colored and are often used to color paints.
• Transition elements have 1 or 2 valence electrons, which they lose when they form bonds with other atoms. Some transition elements can lose electrons in their next-to-outermost level.

Transition Elements

• Transition elements have properties similar to one another and to other metals, but their properties do not fit in with those of any other family.
• Many transition metals combine chemically with oxygen to form compounds called oxides.

Boron Family

• The Boron Family is named after the first element in the family.
• Atoms in this family have 3 valence electrons.
• This family includes a metalloid (boron), and the rest are metals.
• This family includes the most abundant metal in the earth’s crust (aluminum).

Carbon Family

• Atoms of this family have 4 valence electrons.
• This family includes a non-metal (carbon), metalloids, and metals.
• The element carbon is called the “basis of life.” There is an entire branch of chemistry devoted to carbon compounds called organic chemistry.

Nitrogen Family

• The nitrogen family is named after the element that makes up 78% of our atmosphere.
• This family includes non-metals, metalloids, and metals.
• Atoms in the nitrogen family have 5 valence electrons. They tend to share electrons when they bond.
• Other elements in this family are phosphorus, arsenic, antimony, and bismuth.

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Oxygen Family

• Atoms of this family have 6 valence electrons.
• Most elements in this family share electrons when forming compounds.
• Oxygen is the most abundant element in the earth’s crust. It is extremely active and combines with almost all elements.

Halogen Family

• The elements in this family are fluorine, chlorine, bromine, iodine, and astatine.
• Halogens have 7 valence electrons, which explains why they are the most active non-metals. They are never found free in nature.

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Halogen atoms only need to gain 1 electron to fill their outermost energy level.

They react with alkali metals to form salts.

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Noble Gases

• Noble Gases are colorless gases that are extremely un-reactive.
• One important property of the noble gases is their inactivity. They are inactive because their outermost energy level is full.
• Because they do not readily combine with other elements to form compounds, the noble gases are called inert.
• The family of noble gases includes helium, neon, argon, krypton, xenon, and radon.
• All the noble gases are found in small amounts in the earth's atmosphere.

Rare Earth Elements or Inner Transition elements

• The thirty rare earth elements are composed of the lanthanide and actinide series.
• One element of the lanthanide series and most of the elements in the actinide series are called trans-uranium, which means synthetic or man-made.

Mendeleev

• In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table.
• He grouped elements according to their atomic mass, and as he did, he found that the families had similar chemical properties. 
• Blank spaces were left open to add the new elements he predicted would occur. 

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Matter

• All matter is composed of atoms and groups of atoms bonded together, called molecules.
• Substances that are made from one type of atom only are called pure substances.
• Substances that are made from more than one type of atom bonded together are called compounds.
• Compounds that are combined physically, but not chemically, are called mixtures.

Elements, Compounds, Mixtures

• Sodium is an element.
• Chlorine is an element.
• When sodium and chlorine bond they make the compound sodium chloride, commonly known as table salt.

▪Compounds have different properties than the elements that make them up.

▪Table salt has different properties than sodium, an explosive metal, and chlorine, a poisonous gas.

Elements, Compounds, Mixtures

• Hydrogen is an element.
• Oxygen is an element.
• When hydrogen and oxygen bond they make the compound water.
• When salt and water are combined, a mixture is created. Compounds in mixtures retain their individual properties.

The ocean is a mixture.

Elements, compounds, and mixtures

• Mixtures can be separated by physical means.
• Compounds can only be separated by chemical means.
• Elements are pure substances. When the subatomic particles of an element are separated from its atom, it no longer retains the properties of that element.

Alkali Metals

Alkaline Earth Metals

Transition Metals

InnerTransition Metals

These elements are also called the rare-earth elements.

Halogens

Noble Gases

The s and p block elements�are called�REPRESENTATIVE ELEMENTS.

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