Presentation on theme: "The History of Atomic Structure. Democritus Named the atom from the Greek word “atomos” meaning indivisible. Wrote that atoms were the smallest unit."— Presentation transcript:
Conclusions? The stream of particles was … Negative Overall, atoms are... Neutral Therefore, atoms must also contain charges that are... Positive
Plum Pudding Model Thomson figured out that atoms contained positive and negative charges but had no idea how they were arranged. He guessed there was a diffuse positive cloud with negative charges randomly distributed
Marie & Pierre Curie Provided evidence for the existence of protons and neutrons. Discovered radium and polonium. Marie Curie was the first female winner of the Nobel prize and the first double winner.
Ernest Rutherford Discovered that the nucleus was positively charged and very tiny. Found that the atom is mostly empty space.
Ernest Rutherford Rutherford found the positive particles called alpha particles. He shot these particles at a piece of gold foil and found that many particles went straight through the foil and some were deflected backwards. This does not fit the plum pudding model! There must be a concentrated positive charge that was repelling his rays!
HOLY ATOMS! What conclusions can be drawn here? There is something inside an atom that is heavy enough to deflect a particle straight back. That “something” must be positively charged. It must also be very small.
Conclusions? Heavy, dense, positively charged, small piece of the atom is…. The nucleus!! Lets watch this animated Lets watch this animated
Niels Bohr Developed the “solar system” model of the atom. The nucleus in the center of the atom is made of protons (+) and neutrons. Electrons (-) orbit the nucleus like the planets around the sun.
Electron Cloud Model The current model of the atom. Electrons do not orbit the nucleus in orderly paths. Electrons move around the nucleus at near the speed of light in a general area. Research continues.
Electron Cloud Model Nucleus e-e- e-e- e-e- e-e-
Proton Don says “If all the elements are on the periodic table, where’s the cheese?”
Protons Found inside the nucleus of the atom. Have a charge of +1 Have a mass of 1 atomic mass unit (amu)
Neutrons Found inside the nucleus of the atom. Mass of 1 amu Neutrons have no charge.
Electrons Found in orbits (energy levels or shells) around the nucleus. Travel at near the speed of light. Charge is –1 Mass is 1/1800 th amu.
What makes one element different from another? The number of protons is always the same as the atomic number. The number of electrons is usually the same as the atomic number. To find the number of neutrons: take the atomic mass, rounded to the nearest whole number, and subtract the atomic number.
Finding the number of neutrons The mass number of this isotope of lithium is 7. Notice that 7 is equal to the total number of protons and neutrons. If you remove the protons (atomic number), the neutrons are left.
Isotopes of Hydrogen What do they have in common? What are the differences?