The document provides a timeline of atomic models from 400 BC to 1932 AD. It summarizes the key contributions of 5 scientists: 1) Democritus proposed in 400 BC that all matter is made of indivisible "atoms" that come in different shapes and sizes. 2) In 1803, Dalton developed his atomic theory that elements are made of atoms of a single type that differ in atomic weight. 3) Thomson discovered electrons in atoms in 1904 using deflection experiments with electric fields. 4) Rutherford showed in 1911 through gold foil experiments that atoms have a small, dense nucleus surrounded by space. 5) Bohr incorporated electron shells into his 1913 model of the atom.

1. Earth Air Fire Water
History of the AtomChemistry I

2. --------------- 400 BC: Democritus
----------------1803: Dalton
----------------1904: Thompson
----------------1911: Ernest Rutherford
----------------1915: Niels Bohr
----------------1927: Louis de Brogile
----------------1932: James Chadwick
Atomic Model TimelineAtomic Model Timeline

3. Democritus Model and His Ideas
• born around 460 BC in north Greece
• rejected the Eleatic school hypothesis that “everything is
one” and change and motion is an illusion
 everything consists of an infinite amount of very small
particles called “atoms” and space
• atoms can be physically divided, are indestructible,
contain no space, and are eternal
• many types of atoms having
different sizes and shape
• atoms move at random like gases

4. Dalton Model
• born in England in 1766
• wanted to take up law or medicine but his family didn’t approve
• after being laid off he began keeping a record of meteorology
and air circulation
• he then became a secretary to a philosophical society where he
presented his essays on gas laws
 is now most known for theory
his theory that all atoms of a given element
are exactly alike and atoms of a different
element have different atomic weights and
the plum pudding model

5. Thomson Model
• born in England in 1856
• was always interested in science
• disproved the assumption that atoms were clear
• discovered that atoms contain electrons
after deflecting rays from the electric field

6. Rutherford Model
• born in 1871
• came up with the terms alpha and beta during his
research of radioactivity and discovered the half-life
• shot alpha and beta particles through gold foil and
discovered that most went through, indicating that
atoms are mostly space
• some particles bounced back,
providing proof of the positive
nucleus
• suggested Thompson’s plum pudding
model was incorrect

7. Bohr Model
• born in 1885 in Denmark
• Helped found the Institute of Theoretical
Physics
• worked on the Manhattan Project in the U.S.
• Determined that electrons orbit the
nucleus in shells and can be moved
to other shells