Some elements exhibit similar chemical and physical properties. For example, lithium (Li), sodium (Na), and Potassium (K) can all combine in a 1:1 ratio.

Periodic Table

Patterns in Element Properties

Some elements exhibit similar chemical and physical properties. For example, lithium (Li), sodium (Na), and Potassium (K) can all combine in a 1:1 ratio easily with Chlorine.

Elements With Similar Properties

The elements chlorine, bromine, and iodine look very different from each other. But each forms a similar-looking while solid when it reacts with sodium.

John Newlands Noticed a Periodic Pattern

In 1865, an English chemist, John Newlands, arranged the known elements according to their properties and in order of increasing atomic mass.

He noticed that all of the elements in a given row had similar properties, and they repeated every 8 elements (he called this the law of octaves).

Newlands’ Table

In Newland’s time, determining atomic weights was based on comparing other

elements to the lightest element (hydrogen). Some of the elements were given inaccurate values. . Newland was ridiculed by other chemists

who felt the table he created was not reliable. He could not get his papers published and returned as chief chemist in a sugar factory and later opened a chemical business with his brother.

Dmitri Mendeleev Invented the First Periodic Table

In 1869, a Russian chemist, Dmitri Mendeleev produced the first orderly arrangement (periodic table) of all 63 elements known at the time.

Mendeleev—the Father ofthe Periodic Table

Mendeleev (1834-1907) rose from very poor beginnings to a position of a renowned Russian chemist in the 19th century. He wrote down information on each element on cards. He ranked the elements from lightest to heaviest.

Mendeleev also put the elements into a table according to their properties. He started a new row each time he noticed that the chemical properties of the elements repeated.

Mendeleev Correctly Predicted the Gaps

Mendeleev’s Table contains gaps that elements with particular properties should fill.

He correctly predicted the properties of the missing elements. He even gave them provisional names. These elements were eventually discovered.

Henry Moseley

A young English chemist, Henry Moseley, discovered that the elements should be organized according to their atomic numbers, not their atomic weights as was done before.

When Moseley studied the lines in the X-ray spectra of 38 different elements, he found that the wavelength of the lines decreased in a regular manner as atomic number increased.

Henry Moseley

Henry Moseley lost his life in 1915 during World War I at the Gallipoli battle in Turkey at the age of 27 and is buried there. His death has been called one of the greatest tragedies of WWI because he was such a brilliant chemist.

The Periodic Law

The Periodic Law states that when the elements are arranged according to their atomic numbers, elements

with similar properties

appear at regular intervals.

Organization of the Periodic Table

Elements in each column of the table have the same number of electrons in their outer energy level.

These electrons are called valence electrons.

Valence Electrons

The outer energy level electrons in an atom are the ones that participate in chemical reactions with other atoms.

Elements with the same number of valence electrons react in similar ways.

Groups

A vertical column on the periodic table is called a group. (These are also called families.) These exhibit similar properties.

Relationship between Groups and Electron Configuration:

The group an element belongs to is determined by the last notation in its’ electron configuration.

For example, all elements that end in s1

have the same properties and are in the same group.

Periods

A horizontal row on the periodic table is called a period. Elements in the same period have the same number of occupied energy levels.

Blocks of Elements

The Periodic Table is organized into blocks—each corresponding to the sublevels. (S, P, D, and F)