ATOMIC STRUCTURE S.MORRIS 2006

(greek for indivisible) HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC 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)

HISTORY OF THE ATOM ATOMS John Dalton 1808 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 Atomic Theory All matter is composed of tiny particles called atoms. Atoms of the same element are identical in size, mass, and chemical properties. (*Has been disproved*) Atoms cannot be subdivided, created, or destroyed. (*Also disproved*) Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged.

HISTORY OF THE ATOM Joseph John Thompson 1898 Discovered the negtatively (-) chargered ELECTRON using a Cathode Ray Tube. Particles were attracted to (+) positively charged plates. What do we know about opposites?? http://www.youtube.com/watch?v=IdTxGJjA4Jw&feature=related

Thompson’s Cathode Ray Tube

HISTORY OF THE ATOM PLUM PUDDING MODEL 1904 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 like plums surrounded by pudding. PLUM PUDDING MODEL

HISTORY OF THE ATOM Ernest Rutherford 1910 Ernest Rutherford For his famous experiment he fired Helium nuclei at a piece of gold (Au) foil which was only a few atoms thick. He found that although most of the nuclei passed right through, about 1 in 10,000 hit something?? http://www.youtube.com/watch?v=wzALbzTdnc8&NR=1

HISTORY OF THE ATOM 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. http://micro.magnet.fsu.edu/electromag/java/rutherford/

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 Niels Bohr 1913 Niels Bohr He studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits called energy levels. Rather like planets orbiting the sun. Each energy level is only able to contain a set number of electrons. http://www.dnatube.com/video/2812/Bohrs-model-of-the-atom

Which Atom Model belongs to which Scientist?

Niels Bohr’s Work with Hydrogen Gas Bohr found that when electrons are excited they absorb energy and jump from their Ground State to a higher energy level. When they fall back down from this Excited State they give off energy in the form of Photons of light. Each energy level gives off its own color of light creating a Line Spectrum. http://www.youtube.com/watch?v=L0UJhSvPE5A

The Electromagnetic Spectrum There is an inverse relationship between Wavelength, Frequency, and Energy. The GREATER the Energy and Frequency the shorter the Wavelength. Visible light is a very small part of the EM Spectrum Violet has the smallest wavelength, highest energy, and highest frequency of the visible spectrum. Which color has the longest wavelength, lowest frequency, and lowest energy?

Dangers of Electromagnetic Radiation The least dangerous is Radio Waves The MOST dangerous is Gamma Waves

Wavelength (λ), Frequency (f) and Energy (E) Speed of Light Constant c = 3.0 x 108m/s Planks Constant h = 6.626 x 10-34 J s

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

Number of protons = Number of electrons ATOMIC STRUCTURE He 2 Atomic number the number of protons in an atom 4 Atomic mass the number of protons and neutrons in an atom Number of protons = Number of electrons

SUMMARY The Atomic Number of an atom = number of protons in the nucleus. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. The number of Protons = Number of Electrons in a neutral atom. Electrons orbit the nucleus in energy levels (shells). Each energy level can only carry a set number of electrons.