Developing the periodic table

• All elements are arranged in a chart called the periodic table.
• The arrangement of elements is based on their structure and properties.
• A Russian scientist named Dmitri Mendeleev produced one of the first practical periodic tables in the 19th century.

Watch this video to learn about the development of the periodic table.

In the 1800s, scientists had discovered many new elements, but no system existed to organise them. Scientists were trying to look for similarities in their properties to arrange them in a meaningful way.

Early attempts to organise the elements

John Newlands noticed that if the elements were ordered by atomic weights, every eighth element had similar properties. For example, sodium is the eight places further on than lithium and reacts in a very similar way.

For example, lithium (Li), sodium (Na) and potassium (K) all have the same kind of reaction with water.

Julius Meyer arranged elements by atomic weight and by the number of atoms the element usually combined with.

The group of elements below were grouped together because they tended to combine with two other atoms. For example, one oxygen atom combines with two hydrogen atoms to make water (H₂O).

A Russian scientist called Dmitri Mendeleev produced one of the first practical periodic tables in the 19th century.

The modern periodic table is based closely on the ideas he used.

These ideas were:

• The elements are arranged in order of increasing atomic mass
• The horizontal rows are called periods
• The vertical columns are called groups
• Elements in the same group are similar to each other

Mendeleev's ideas are still in use today. However, the modern periodic table arranges the elements by increasing atomic number, rather than atomic mass.

How did Mendeleev produce the periodic table?

Mendeleev wrote the names of elements onto cards to help him look for patterns. He put the cards in order of lightest to the heaviest element and made groups based on the chemical and physical properties of each element.

Mendeleev recognised that not all elements had been discovered yet. He left gaps in his table to place elements that scientists didn't yet know.

By looking at the physical properties and chemical properties of elements next to gaps, he could even predict the properties of these undiscovered elements.

These correct predictions increased the confidence in Mendeleev's periodic table.

Did you know?

Mendeleev’s work is the basis of the modern periodic table we use today.

He is often referred to as the 'father of the periodic table', but he didn’t achieve a Nobel Prize for his work.

The periodic table is a good example of how scientific ideas develop over time.

Mendeleev left gaps in his table when he drew it up in 1869, using his insights to predict that scientists would discover more elements. Since the 19th century, more elements have been discovered that fit these gaps, further confirming that Mendeleev’s understanding was correct.

The modern periodic table has no gaps and has extended beyond what Mendeleev predicted. There were 64 elements when Mendeleev was working on his table and he predicted 4 more. Now the periodic table has 118 elements.

Did you know?

The most recent element to be discovered is Tennesine which was made in a laboratory in 2009.

This element only exists for fractions of a second, because it is unstable meaning it breaks apart very quickly.