chem notes chapter 4

Democritus

First to say that everything is made of small particles

Aristotle

Matter is continuous

Law of constant composition

A given compound always contains the same proportions (by mass) of elements

Daltons atomic theory

Elements are made up of tiny particles called atoms

Daltons atomic theory

All atoms of a given element are identical. Atoms of one element are different from atoms of another element

Daltons atomic theory

Atoms of one element combine with atoms of another element in simple whole number ratios to form compounds

Daltons atomic theory

Atoms cannot be broke into smaller particles

JJ Thompson

Concluded that all atoms contain negatively charged particles that we call electrons

JJ Thompson

Used a cathode ray to determine the charge to mass ratio of electrons

JJ Thompson

Credited with the plum pudding model of the atom - negative charges surrounded by a uniform “pudding” of positive charge

Ernest Rutherford

Gold Foil experiment

Ernest Rutherford

In terms of a nuclear atom - dense center of a positive charges (nucleus) around which tiny electrons move in a space that is otherwise empty (planetary model)

Robert Millikan

Obtained first accurate measurements of an electrons charge (oil drop experiment)

James Chadwick

Discovered high energy particles with essentially the same mass as protons and no charge (neutrons)

Protons

+1 positive charge and 1amu

Electrons

Essentially no mass and -1 charge

Electrons

no charge and 1amu

All atoms of one element

Have the same number of protons

Free atom

Neutral charge

Atomic number

Z - number of protons in an atom

Mass number

A - number of protons and neutrons in an atom

number of protons =

Number of electrons