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Atomic Theory Timeline

Science 9, Period #7

Rachel Yen

on 12 October 2012

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Transcript of Atomic Theory Timeline

The History of Atomic Theory By: Rachel Yen
Science 9, Block # 7 Introduction Early Greek Philosophers and Alchemists researchers that worked in Europe and Middle East
wanted to turn common metals into gold-> tried for a long time but weren't successful Alchemists: Greek Philosophers believed matter was made of atomos (atoms)->means no cut
many Greek philosophers trying hard to figure out the nature of matter
believed that atoms were the smallest pieces of matter - the Atomic Theory is a theory about the nature of matter
-lots of scientists contributed to developing this theory such as Democritus, Aristotle, JJ Thompson, etc... Democritus (around 460 BC- around 370 BC) Greek philosopher His theory: all matter is made of atoms that are indistructable
atoms remain unchanged
the characteristic of an object is determinded by its atoms
Had weak evidence that atoms even existed Aristotle (384 BC-322 BC) Greek philosopher
disagreed with Democritus' theory His theory: matter was made of different combinations of earth, air, fire and water
for the next 2000 years, people followed Aristotle's theory ex. fire would have the characteristics of being hot and dry, water being wet and cold, etc John Dalton (1766-1844) British school teacher His theory (known as Dalton's Atomic Theory): All matter is made of small particles called atoms
atoms cannot be created, destroyed or divided into smaller particles
all atoms of the same element are identical in mass and size, but they are different in mass and size from the atoms of other elements
compounds are created when atoms of different elements link together in definite proportions Dalton's model of an atom J.J. Thompson (1856-1940) British physicist who studied electric currents His discoveries he found out that the currents were streams of negatively charged particles, later called electrons
from results of experiments, he reasoned that all atoms must contain electrons
hypothesised that atoms are made up of much smaller particles
startling because most scientists believed particles were indivisible
created raisin bun theory Thompson's "raisin bun" model of an atom Negatively charged particles are imbedded in an atom (positive)
Positively charged ball-> the bun
Negatively charged particles-> raisins Democritus vs. Aristotle all matter was made of atoms
characteristics of an object was determined by its atoms matter was made of different combinations of earth, air, fire and water
characteristics defined by texture, temperature, etc., then after categorized into earth, air, fire or water Dmitri Mendeleev (1834-1907) Russian chemist and inventor His discovery: created the first periodic table of elements
arranged elements into their atomic weights
organized them into groups of similar properties Mendeleev's Periodic Table (groups are horizontal) Ernest Rutherford (1871-1937) student of J.J. Thompson
from New Zealand What he discovered: designed "gold foil experiment" to probe inside atoms
his results indicated that the majority of the alpha particles went right through gold atoms->atoms weren't effected
discovered nucleus
decade later, he established that there must be two kinds of particles inside the nucleus
discovered proton (positive charge) and neutron (neutral charge Gold Foil Experiment exposed thin sheet of gold foil to alpha particles (which are high speed, heavy particles that are positive)
Rutherford wanted to see what would happen to alpha particles
placed detector sceen around gold which made an alpha particle visible whenever it struck the screen Neils Bohr (1885-1962)
studied results of experiments on light released by gaseous samples of atoms
in experiments, gases had been made to glow by passing electric currents through them
proposed electrons surround nucleus in specific energy "shells" or "levels" Danish scientist working under Rutherford
studied regions surrounding nucleus His discoveries: 400 B.C. 300 B.C. 1700 A.D. 1800 2000 500 B.C. 1900 Thanks for watching :)
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