Mrs. Howell’s Grade 9 Science: Acton District High School

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1903AD1898AD1897AD1911AD1922ADBeyond

The idea started around.. About 450 BC The Greek philosopher Empedocles stated that matter consists of four elements -earth, air, fire & water- 450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1903AD1898AD1897AD1911AD1922AD

But about… About 400 BC The Greek philosopher Democritus developed the first atomic hypothesis. - All matter be subdivided only to a certain point, at which only atoms remain. “Atomos”- Greek word for indivisible 450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1903AD1898AD1897AD1911AD1922AD

Unfortunately... About 350 BC The Greek philosopher Aristotle opposed Democritus' idea of atoms and dismissed it as worthless and promoted the 4 element model. Because of Aristotle’s great influence in the science world, this concept about matter lasted for more than 2000 years. 450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1903AD1898AD1897AD1911AD1922AD

A.D Arabian, Chinese and European Alchemists studied matter, experimenting with different chemical substances. They devised the system chemical symbols. -but they still used the four element system- 450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1903AD1898AD1897AD1911AD1922AD

A.D ’s Robert Boyle Antoine Lavoisier Joseph Priestley Henry Cavendish Found that matter such as air and water were made of a mixture of pure substances. Their research promoted the idea of matter being made of ‘elements’ and disproved the idea of the four element system. 450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1897AD1911AD1922AD

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1855AD1879AD1898AD1897AD1911AD1922AD 1808 A.D. British scientist John Dalton Pictured the atom as a tiny, indivisible sphere much like a billiard ball. Further developed the idea of ‘atom particles’ in his atomic theory.

Dalton's Atomic Theory All elements are composed of atoms (indivisible particles) All atoms of the same element are identical - in particular they have the same mass. The atoms of one kind of element are different from the atoms of all other elements - in particular the atoms of one element have a different mass than those of other elements. Atoms are indestructible and retain their identity in chemical reactions. Compounds are formed by joining atoms in specific whole number ratios.

1855 A.D. German scientist Heinrich Geissler A glassblower and inventor of the sealed glass tubes that pumped out air and discharged electricity through gases. -his invention helped lead to the next two atom discoveries- -his invention helped lead to the next two atom discoveries- 450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1855AD1879AD1903AD1898AD1897AD1911AD1922AD

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1855AD1879AD1898AD1897AD1911AD1922AD 1879 A.D. British scientist William Crookes Discovered as the pressure was lowered in a electric gas discharge tube, the negative end appeared to emit rays, now known to be a stream of free electrons. This stream also could push a tiny windmill in the tube. Discovery of charged particles and that they had mass.

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1911AD1922AD 1897 A.D. British scientist J.J. Thomson Experimented on the streams of particles using magnets and electric current and discovered the pieces of atoms we know as electrons and protons. - Proposed the “raisin bun” model of the atom. Positive charged sphere with negatively charged particles embedded in it- - Proposed the “raisin bun” model of the atom. Positive charged sphere with negatively charged particles embedded in it- 1897AD

A.D. French (Polish) scientists Henri Becquerel Pierre & Marie Curie Experimented with natural radioactivity. - Their work and the materials they discovered greatly helped the next proposed model of the atom - - Their work and the materials they discovered greatly helped the next proposed model of the atom BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1911AD1922AD1897AD

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1911AD1922AD1897AD 1911 A.D. New Zealand scientist Ernest Rutherford Experimented with a radiation source that sent out alpha particles through a thin piece of gold foil to a detector screen that glowed when it was hit. Most particles passed through the foil, but 1 in 8000 bounced back!

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1911AD1922AD1897AD 1911 A.D. Ernest Rutherford Proposed that if the particles bounced back that the atom must consist of a tiny, dense, positive core called a nucleus and is surrounded by a cloud of moving negative electrons, and not a sphere with embedded electrons (JJ.Thomson’s idea). -Discovered the second sub- atomic particle of the atom: the proton (+) & new model for the atom - -Discovered the second sub- atomic particle of the atom: the proton (+) & new model for the atom -

450 BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1897AD1911AD1922AD 1922 A.D. Danish scientist Niels Bohr Came up with experimental evidence proving that electrons exist in energy levels (shells) orbiting around a positively charged nucleus. -Orbital electron energy shells - -Orbital electron energy shells AD

1932 A.D. English scientist James Chadwick Using alpha particles discovered a neutral atomic particle with a mass close to a proton. What he discovered was the neutron. -Discovered the third sub- atomic particle of the atom: the neutron - -Discovered the third sub- atomic particle of the atom: the neutron BC400 BC350 BC AD1808AD1650 ADLate 1700’s1831AD1879AD1898AD1897AD1911AD1922AD1932AD

History of the Atomic Theory (see text pg 82 through pg 85 and 91) A. Fill in the Blank areas in this table during the lesson or review the presentation on our class’ website. B. Draw the Atom Models of: DaltonJ.J. ThomsonRutherford Bohr Time Perio d ScientistsAtomic ModelWhat discovery they made Ancien t Greec e Empedocles Ancien t Greec e Democritus A.D AlchemistsFour element model Elements like Zinc, Bithmuth, Phosphorous, and Arsenic late 1700’ Robert Boyle Antoine Lavoisier Joseph Priestley Henry Cavendish 1808John Dalton 1879William Crookes 1897J.J. Thomson (Nobel prize 1906) 1911 Ernest Rutherford (Nobel prize 1908) 1922Niels Bohr (Nobel prize 1922) 1932 James Chadwick (Nobel prize 1935) Your task: Work on filling out the worksheet on the history of the atom table as well as drawing the examples of the models of the atom on the bottom of the sheet. And

Thank you!