CHEMISTRY TIMELINE

TIMELINE ATOMIC MODEL

EXPERIMENT

CONCLUSION

THE ELECTRON AND THOMPSN'S MODEL

Dalton's model

bohr's model

THE NEUTRON

1913

1897

1803

1932

1920

1909

1886

Rutherford's model

THE GOLDFOIL EXPERIMENT

E. GOLDSTEIN THEORY

(by Rutherford)

DALTON'S MODEL

He proposed some ideas: • Matter=made up of atoms • Atoms cannot be divided into smaller pieces • All the atoms of an element are exactly alike • Different elements are made of different kinds of atoms • Combination of atoms of diferent elements form compounds He indicated that atoms have an: • Atomic weight • A diameter • Certain properties.

Introduction

Early philosophers speculated about matter over 2500 years ago. They proposed the existence of tiny, indivisible particles called "atoms. They had limited technology so, they ideas were mainly based on their reasoning. Finally, in the 18th century, scientists were able to ideate several models that proved the atoms existence. On the laboratories, chemists began experiments with matter, discovering elements made of atoms of only one kind, such as iron, silver, carbon, gold, and oxygen.

BOHR'S MODEL

Problems with Ritherford's model: it could not explain the observation that atoms only emot light light at certain wevelengths or frequecies. Bohr's solved by proposinf that electrons could only orbit the nucleus in certain special orbits at different energy levels around the nucleus.

E.GOLDSTEIN'S MODEL

• E. Goldstein (physicist): discoevred PROTON in cells
• Used: Hydrogen gas-filled tube (similar to Thomson's tube)
• The (+) charge particles: PROTONS
• Mass=1,837 · electron's mass
• CONCLUDED: electrons (-) travel from the negative charge cathode toward the positive charge anode and opposite direction

GOLDFOIL EXPERIMENT

- Rutherford + his team: bombarded a sheet of gold foil with PARTICLES - Expectations: alpha particles pass through the foil (with no defection accordin to plum puddling atom model) - What happened: particles deflected at many angles (few bounced back) - This helped to propose a new atom model --> small + dense NUCLEUS (center) + electrons around

CONCLUSION

• If all atoms contain - charges, but not all matter is - charged…
• 'Are there atoms containing + charge?'
• Yes, so that the – and + charges can balance each other.
• + CHARGE ALSO INCLUDED IN MODEL.

EXPERIMENT:

• Constructed a glass tube --> Partially evacuated.
• Applied a high electrical voltage btw 2 electrodes at each end of the tube.
• Detected a stream of particle which was coming out
• From: - electrode (cathode)
• To: + electrode.
• Construction: Cathode ray tube.

RUTHERFORD'S MODEL

• Showed (+) charge existed in an atom's region
• HYPOTHESIS: all mass of atom and (+) charge: center of atom (NUCLEUS) --> proved TRUE
• scientists: (+) charge: PROTONS
• PROTON (+): present in nucleus of all atoms
• REST OF ATOM: occupied by atom's mass less ELECTRONS (-)

THE NEUTRON

• Rutherford deduced a neutral charge in 1920 (info in the grey arrow)
• 1932: James Chadwick (physicist) discovered Neutron
• measured its mass (same as proton)
• electrically neutral

THE NEUTRON BY RUTHERFORD (1920)

• Thought: only protons in the nuecleu (+) it should break into bits (repulsive forces)
• To make sure ATOM stays NEUTRAL, the particle would have to be neutral itself with a neutral charge element

ATOM'S MASS

• Electron
• Proton
• Neutron