Early Ideas in Atomic Theory

Electrons, neutrons, and protons

Three fundamental particles that an atom is composed of

Mass number

Sum of the protons and neutrons in the atom.

Located as the left superscript of the element symbol in the nuclide notation

Atomic number

Number of protons in an atom

Located as the left subscript of the element symbol in the nuclide notation.

Determines the identity of an atom

11

Atomic number of sodium

23

Mass number of sodium

9.109×10^-31 kg

Mass of an electron

1.673×10^-27 kg

Mass of a proton

1.675×10^-27 kg

Mass of a neutron

Atomos

The Ancient Greek adjective from which the word atom is derived from

Indivisible

Meaning of the word “atomos”

John Dalton

Individual to propose Dalton’s Atomic Theory

And the law of multiple proportions

1807

Year when the Dalton’s Atomic Theory was proposed

Leucippus and Democritus

Two ancient Greek philosophers to propose/work around the idea of “atomos”

Dalton’s Atomic Theory

1) All matter is made up of tiny, indivisible particles called atoms

2) Atoms of the same element have the same mass and same properties

3) Atoms combine in simple, whole-number ratios to form compounds

4) Chemical reactions involve the rearrangement of atoms

Law of conservation of matter

1) Atoms are not created nor destroyed during the chemical change.

2) The total mass present when matter changes from one type to another type will remain constant.

3) Atoms are just getting rearranged to yield substances that are different from previous

Joseph Proust

The French chemist who came up with the law of definite proportion.

Law of Constant Composition

Another name for “Law of Definite Proportions”

Law of Definite Proportions

All samples of a pure compound contain the same elements in the same proportion by mass.

An idea that the number of atoms of the elements in a given compound always exist in the same ratio

Isooctane

A component of gasoline and one of the standards used in the octane rating system.

5.33:1

Carbon-to-hydrogen mass ratio found in the samples of isooctane

The Law of Multiple Proportions

States that when two elements react to form more than one compound

Then a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers