chemistry Unit 1 atomic models

Dalton’s Atomic Theory - 1808 (1st)

Matter are composed of atoms, atoms of the same element are identical in size, mass and properties. Atoms of different elements are different in size, mass and properties

Atoms of different element combine in simple ratios to make compounds Exp:H2S

In chemical reactions, atoms are combined, separated, or rearranged (No atoms are

created or destroyed)

So at this point we believe that an atom is like a small solid ball of matter that cannot be split up

C. J.J. Thomson- 1904 (2nd)

Discovered electrons in atoms in 1897, the “plum pudding” model of the atom.

Shows the atom as composed of electrons scattered throughout a spherical cloud of positive charge.

J.J. Thomson using the cathode ray tube led to the discovered of the electron

Cathode Ray tube (2nd)

cathode ray tube led to the discovered of the electron (J.J tomson)

Rutherford -1911 (3rd)

Atoms have mostly empty space

(This is why most rays went straight through)

There must be a dense positive center to an atom (discovery of nucleus)

This is why the positive rays deflected. (Positive rays are repelled by

positive charged objects)

Gold foil experiment (3rd)

Fired + charged alpha rays at a very thin piece of gold (Gold foil)

Put a screen behind the foil to determine what happens to the rays

Discovered empty space and positively charged nucleus

Bohr -1913 (4th)

Electrons exist in orbits around nucleus, discovered energy levels/ shells, planetary model

Wave Mechanical Model-1926

Electrons exist in orbitals around nucleus not orbits, energy levels have subunits