Topic 1- development of the periodic table

Relative atomic mass

The average mass of one atom of an element

Isotope

A form of chemical element that has the same number of protons but a different number of neutrons

How was the periodic table arranged in the early 1800s?

Via atomic mass

How is the periodic table organised today?

• their relative atomic mass

• Their physical and chemical properties

Which scientist overcame errors in the early periodic tables?

Dimitri Medeleev

What did Mendeleev do

Ensured that each element was organised by both relative atomic mass AND their chemical and physical properties + leaving gaps for those undiscovered

What discovery proved that Mendeleevs idea of ordering by properties is correct?

The discovery of isotopes in the 20th century

How are elements arranged in the modern periodic table?

Via increasing atomic number

On the left side of the staircase, the elements are

Metals, with the centre being transition metals

On the right side of the staircase are

Nonmetals

Before atomic structure was discovered,

Atomic weight was used to order elements