# S.MORRIS 2006. Papercuts This piece of paper is 28cm x 2.5 cm How many times would you have to cut this piece of paper to be the same width as an atom?

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S.MORRIS 2006

Papercuts This piece of paper is 28cm x 2.5 cm How many times would you have to cut this piece of paper to be the same width as an atom? Once you cut a piece in half, you have to discard one half and then use the other piece to continue this process Repeat this until you can no longer cut the paper. How many cuts did you make?

Width of an Atom The average width of an atom is 130 picometers 1pm = 10 -12 m = 1/1 000 000 000 000 of a meter 1 millimeter = 1 000 000 000 picometers That’s teeny tiny !

Who are these dead dudes? How did they contribute to our present day model of an atom?

HISTORY OF THE ATOM 460 BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible)

This theory was ignored and forgotten for more than 2000 years!

HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

Dalton’s Theory 1.all elements are composed of atoms. 2.atoms of the same element are exactly alike. 3.atoms of different elements are different. 4.compounds are formed by the joining of atoms of two or more elements. Fill this in on your Notes sheet Dalton’s Atom

HISTORY OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

HISTORY OF THE ATOM Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge 1904 like plums surrounded by pudding. PLUM PUDDING MODEL

HISTORY OF THE ATOM 1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit

HISTORY OF THE ATOM gold foil helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back. helium nuclei

HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.

HISTORY OF THE ATOM 1913 Niels Bohr studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

 The Bohr model was a modification of the Rutherford model.  Bohr the electrons in certain circular orbits around the nucleus called shells. Bohr’s Atomic Theory +

Scientists had learned a lot about the atom, but couldn’t figure out what made it so heavy. In 1932 James Chadwick solved the mystery by coming up with the idea of neutrons, neutral particles that live in the nucleus with protons. The new improved Bohr model includes these particles. 0 Neutrons

Bohr Model of a HELIUM ATOM + N N + - - proton electron neutron Shell New Bohr Model

ATOMIC STRUCTURE Particle proton neutron electron Charge + charge - charge No charge 1 amu nil Mass

Use your periodic table to help you find the ATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom He 2 4 Atomic mass Atomic number Charge = # of protons + # of electrons = (+ number) + (- number) If the number of protons is the same as the number of electrons, what is the charge of the atom?

ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shella maximum of 2 electrons second shella maximum of 8 electrons third shella maximum of 8 electrons

Nucleus 1 st shell 2 nd shell 3 rd shell Adapted from http://www.sciencespot.net/Media/atomsfam.pdf

Created by G.Baker www.thesciencequeen.net So let’s try it…. How to draw a Lithium atom First, look at the Periodic Table Second, How do you find the number of protons? Then determine the number of neutrons Then determine the number of electrons 3 Li Lithium 7

Created by G.Baker www.thesciencequeen.net So let’s try it…. 3 Li Lithium 7 + + + Protons = 3 Neutrons = 4 (7-3=4) - - - Electrons = 3 2 in the 1 st shell, 1 in the 2 nd shell

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