Presentation on theme: "First 5 min of class Identify the following as a molecule, compound, element, or/and an atom. KCl 200 copper atoms O 2 C 2 H 4 He."— Presentation transcript:
First 5 min of class Identify the following as a molecule, compound, element, or/and an atom. KCl 200 copper atoms O 2 C 2 H 4 He
Riddle If a pen and a pencil cost a pound and ten pence and the pen is a pound more than the pencil, how much does the pen cost? (A pound is a UK “dollar” and a pence is a UK “cent”)
History of the Atomic Model Over 2000 years of science
Democritus, 400 BC He was the first to suggest the idea of the atom He presumed there must be a “stopping point” when you’re cutting something, where it is “indivisible”…where it is “atomos” Unfortunately he was laughed at by all the other mean philosophers who followed Aristotle. So atomic science became stagnant for 2000 years.
Aristotle, and therefore everyone, believed that the universe was made of Earth, Fire, Wind, Water, and Aether.
John Dalton All matter is made up of tiny indivisible particles called atoms Atoms cannot be created or destroyed All atoms of a particular element are identical Compounds are formed through the combination of elements Atoms combine in whole number ratios to form compounds
J.J. Thomson He shot cathode rays between two electrically charged plates. The cathode rays always bent towards the positive plate. He concluded that Cathode rays consist of negatively charged particles he called electrons Electrons are much smaller than the smallest atom
Thomson’s Model of the Atom
Ernest Rutherford 1911
Rutherford’s Gold Foil Experiment
Results of Rutherford’s Experiment Note: alpha particles are positive particles 1) He found that most of the alpha particles went straight through the foil unaffected 2) A very few particles were deflected slightly from their path 3) 1 in particles were strongly deflected from their path (90 o or more)
Rutherford’s Results Explained
Thomson’s model vs Rutherford’s
Rutherford’s Conclusions Most of the atom is empty space The centre of the atom, the nucleus, is positively charged and contains most of the mass of the atom Since only a very few alpha particles were affected by the nucleus, it must very small His model is often called the “nuclear model of the atom”
1918 Rutherford discovers that atoms contain positively charged particles called protons
Electromagnetic Radiation Waves of energy travelling through space at the speed of light The shorter the wavelength the higher the energy More importantly: the bluer the colour of light, the more energetic it is.
Bohr’s Model of the Atom Bohr’s model suggests that electrons orbit in rings around the nucleus Electrons can exist in these orbits, and not in between The lower the orbit, the lower the energy
Bohr’s Model of the Atom Ground state = when an electron is in the lowest energy level that it can occupy Excited state = when an electron is in any energy level higher than ground state Electrons jump from ground state to excited state when they absorb energy from heat or electricity Electrons release energy when they fall from the excited state back to ground state