The Periodic Table

Inert

Unreactive

Element

A substance that cannot be split into simpler substances by chemical means

Atomic number

The atomic number of an atom is the number of protons in the nucleus of that atom

Mass number

The mass number of an atom is the number of protons and neutrons in the nucleus of that atom

Dobereiner's Triads

A triad is a group of three elements with similar properties in which the atomic weight (relative atomic mass) of the middle element is approximately equal to the average of the other two

Newlands' Octaves

Newlands' Octaves are arrangements of elements in which the first and eighth element, counting from a particular element, have similar properties

Mendeleev's Periodic Law

When elements are arranged in order of increasing atomic weight (relative atomic mass), their properties recur periodically

Modern Periodic Table

The modern periodic table is an arrangement of elements in order of increasing atomic number

Modern Periodic Law

When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically

Isotopes

Atoms of the same element (same atomic number) that have different mass numbers due to different numbers of neutrons in the nucleus

Relative Atomic Mass (RAM)

The average mass of the isotopes of an element, taking their abundances into account, compared with 1/12 of the mass of a carbon-12 atom

Ion

A charged atom or group of atoms

Mass spectrometer

Measures masses of atoms and abundances of isotopes

Robert Boyle

Gave the first accurate definition of an element

Humphry Davy

Discovered many elements by passing electricity through them

Johann Dobereiner

Discovered triads which didn't work for all the elements

John Newlands

Arranged elements by increasing atomic mass and created the Law of Octaves

Dmitri Mendeleev

Arranged elements by increasing atomic mass. Elements with similar properties under each other in groups. Space for undiscovered elements.

Henry Mosely

Showed Mendeleev's reversals were correct. He showed that elements could be arranged by atomic number instead of atomic mass.