Presentation on theme: "UNIT 1 Significant figures Uncertainty in measurement Percent error Separation Techniques for Mixtures (Lab activities once I open the Flinn boxes!)"— Presentation transcript:
UNIT 1 Significant figures Uncertainty in measurement Percent error Separation Techniques for Mixtures (Lab activities once I open the Flinn boxes!)
Class Groups Explain the distribution of class groups. Groups of Eight 4 Groups will perform lab and remaining 4 will study in their groups Switch around next day!
Atomic Structure Image courtesy of
Chemistry Timeline #1 B.C. 400 B.C. Demokritos and Leucippos use the term "atomos” 1500's Georg Bauer: systematic metallurgy Paracelsus: medicinal application of minerals 1600's Robert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements 1700s' Georg Stahl: Phlogiston Theory Joseph Priestly: Discovery of oxygen Antoine Lavoisier: The role of oxygen in combustion, law of conservation of mass, first modern chemistry textbook 2000 years of Alchemy
Chemistry Timeline #2 1800's Joseph Proust: The law of definite proportion (composition) John Dalton: The Atomic Theory, The law of multiple proportions Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic molecules Amadeo Avogadro: Molar volumes of gases Jons Jakob Berzelius: Relative atomic masses, modern symbols for the elements Dmitri Mendeleyev: The periodic table J.J. Thomson: discovery of the electron Henri Becquerel: Discovery of radioactivity 1900's Robert Millikan: Charge and mass of the electron Ernest Rutherford: Existence of the nucleus, and its relative size Meitner & Fermi: Sustained nuclear fission Ernest Lawrence: The cyclotron and trans-uranium elements
Dalton’s Atomic Theory (1808) Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties John Dalton
Modern Atomic Theory Several changes have been made to Dalton’s theory. Dalton said: Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties Modern theory states: Atoms of an element have a characteristic average mass which is unique to that element.
Modern Atomic Theory #2 Dalton said: Modern theory states: Atoms cannot be subdivided, created, or destroyed Atoms cannot be subdivided, created, or destroyed in ordinary chemical reactions. However, these changes CAN occur in nuclear reactions
Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
Link to Animations hill.com/sites/ /student_view0/chapt er2/animations_center.htmlhttp://highered.mcgraw- hill.com/sites/ /student_view0/chapt er2/animations_center.html
Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model. J.J. Thomson
Mass of the Electron 1909 – Robert Millikan determines the mass of the electron. The oil drop apparatus Mass of the electron is x kg Mass of the electron is x kg
Conclusions from the Study of the Electron Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons Electrons have so little mass that atoms must contain other particles that account for most of the mass
Questions for Homework Write a paragraph to explain the Millikan’s experiment. What all did he calculate from his experiment? How did he calculate the charge on an electron. Why is oil drop used in Millikan's oil drop experiment instead of water drop?
Rutherford’s Gold Foil Experiment Alpha particles are helium nuclei Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded
Try it Yourself! In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?
The Answers Target #1Target #2
Rutherford’s Findings The nucleus is small The nucleus is dense The nucleus is positively charged Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions:
The Atomic Scale Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space Helium-4 Image: User Yzmo Wikimedia Commons.
About Quarks… Protons and neutrons are NOT fundamental particles. Protons are made of two “up” quarks and one “down” quark. Neutrons are made of one “up” quark and two “down” quarks. Quarks are held together by “gluons” Images: Arpad Horvath, Wikimedia Commons.
GOD PARTICLE One year ago, several hours before cities across the United States started their annual fireworks displays, a different type of fireworks were set off at the European Center for Nuclear Research (CERN) in Switzerland. At 9:00 a.m., physicists announced to the world that they had found something they had been searching for nearly 50 years: the elusive Higgs boson.the elusive Higgs boson Today, on the anniversary of its discovery, are we any closer to figuring out what that particle's true identity is? What exactly is the Higgs boson?
Isotopes Isotopes are atoms of the same element having different masses due to varying numbers of neutrons.
Atomic Masses average Atomic mass is the average of all the naturally isotopes of that element. Carbon =
Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.
Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope. Mass # = p + + n Arsenic Phosphorus