Presentation on theme: "First 5 min of class Identify the following as a molecule, compound, element, or/and an atom. KCl 200 copper atoms O2 C2H4 He."— Presentation transcript:
1 First 5 min of classIdentify the following as a molecule, compound, element, or/and an atom.KCl200 copper atomsO2C2H4He
2 RiddleIf 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”)
3 History of the Atomic Model Over 2000 years of science
4 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.
5 Aristotle, and therefore everyone, believed that the universe was made of Earth, Fire, Wind, Water, and Aether.
6 John DaltonAll matter is made up of tiny indivisible particles called atomsAtoms cannot be created or destroyedAll atoms of a particular element are identicalCompounds are formed through the combination of elementsAtoms combine in whole number ratios to form compounds
7 J.J. ThomsonHe shot cathode rays between two electrically charged plates. The cathode rays always bent towards the positive plate.He concluded thatCathode rays consist of negatively charged particles he called electronsElectrons are much smaller than the smallest atom
12 Results of Rutherford’s Experiment Note: alpha particles are positive particles1) He found that most of the alpha particles went straight through the foil unaffected2) A very few particles were deflected slightly from their path3) 1 in particles were strongly deflected from their path (90o or more)
15 Rutherford’s Conclusions Most of the atom is empty spaceThe centre of the atom, the nucleus, is positively charged and contains most of the mass of the atomSince only a very few alpha particles were affected by the nucleus, it must very smallHis model is often called the “nuclear model of the atom”atom
16 1918Rutherford discovers that atoms contain positively charged particles calledprotons
17 Electromagnetic Radiation Waves of energy travelling through space at the speed of lightThe shorter the wavelength the higher the energyMore importantly: the bluer the colour of light, the more energetic it is.
18 Bohr’s Model of the Atom Bohr’s model suggests that electrons orbit in rings around the nucleusElectrons can exist in these orbits, and not in betweenThe lower the orbit, the lower the energy
19 Bohr’s Model of the Atom Ground state = when an electron is in the lowest energy level that it can occupyExcited state = when an electron is in any energy level higher than ground stateElectrons jump from ground state to excited state when they absorb energy from heat or electricityElectrons release energy when they fall from the excited state back to ground state