The Atom protons, neutrons, and electrons oh my!
What s an Atom? An atom is the smallest physical particle of an element that still retains the properties of that element.
How Big is an Atom? At sea level, one cubic centimeter of air (size of a sugar cube, or marble) will have 45 billion atoms within it. 45,000,000,000,000,000,000 How many atoms would it take to fill this room? The universe?
Where Did Atoms First Begin? First scientist to suggest atoms: Democritus Everything that is must be eternal. Democritus believed that there were basic things that always exist, but can be rearranged; he called these atomos.
What They Used to Think About Atoms The following ideas are now known as untrue wrong! All atoms are identical. Chemical reactions occur when atoms of one element are changed into atoms of another element.
Laws Law of Conservation of Mass Law of Constant Composition Law of Multiple Proportions Cr 2 O 3 CrO 3
What does an atom look like? ATOMIC STRUCTURE
Where s the Proof? One century after Dalton, Viennese scientist Ernst Mach wrote that atoms cannot be perceived by the senses they are things of thought. Many scientists that made contributions to atomic structure John Dalton, J.J. Thomson, Robert Millikan, Ernest Rutherford, Niels Bohr, Erwin Schrödinger and James Chadwick.
John Dalton s Atomic Theory 1803 1. All elements are composed of tiny particles called atoms. 2. Atoms of the same element are identical. Atoms of different elements are always different. 3. Atoms of different elements can chemically combine in fixed ratios to form compounds.
John Dalton 4. Chemical reactions occur when atoms are joined, separated, or rearranged. Atoms of one element are NEVER changed into another during a chemical reaction.
John Dalton s Atom Atoms are solid and indivisible.
Robert Millikan 1908 Oil Drop Experiment For more information on how this experiment works go to http://www.kentchemistry.com/links/atomicstructure/ Millikan.htm Measured the charge on an electron as 1.6 x 10 19 coulombs
J.J. Thompson 1897 Particles deflected in Cathode Ray tubes
J.J Thompson Thompson passed electric current through gases in a glass tube. The result was a glowing beam flowing from the negative side to the positive side. Since the glowing ray (cathode ray) was attracted to a positive magnet on the side of the tube the beam must be negatively charged.
J.J Thompson Results of the experiment Electrons are negatively charged. Electrons have very small mass. 1/2000 that of the lightest atom.
J. J. Thompson s Atom Thompson hypothesized that all atoms had such negative charges within. Plum pudding model
Ernest Rutherford 1911 Born in New Zealand Terrible at mathematics Diligent problem solver First to discover the power of the atom, power to make bombs that could make this old world vanish in smoke.
Rutherford s Experiment Gold Foil Experiment Shot radioactive alpha particles through thin sheets of gold foil. Most went straight through, but other were knocked off course or bounced back. Like shooting a fifteen-inch shell at a sheet of paper and having it bounce off.
Rutherford s Experiment Nucleus - used alpha particles and discovered a high concentration of mass and positive charge at the nucleus of the atom with the very light electrons distributed throughout. This led to a new model of the atom.
Rutherford s Atom Nucleus compact center of the atom where protons and neutrons are located. Nucleus has very little of the atom s volume, but contains most of the atom s mass.
James Chadwick 1932 The mass of an atom is greater than the mass of protons plus electrons. Because of this he was able to determine a 3 rd particle of the atom with no charge neutrons. Protons, neutrons, and electrons are called subatomic particles.
An Overview of Subatomic Particles Proton Mass equal to H Positive one charge Found in the nucleus Neutron Mass equal to H No charge Found in the nucleus Electron Mass 1/2000 of H Negative one charge orbits the nucleus
amu
Niel Bohr s Atom 1922 Electrons orbit the nucleus in orbits, like a solar system. Planetary Model or Bohr s Model
Erwin Schrödinger 1930 Born in Vienna, Austria University of Berlin professor Nobel Prize 1933 Work based on waves of light and probability Quantum Mechanical Model like a shot gun blast
How do Atoms Differ? ATOMIC PROPERTIES
Atomic Number Atoms of different elements have different structures. Elements differ because their atoms contain different numbers of protons! Atomic Number number of protons or electrons in the atom
Mass Number atomic mass Electrons have negligible mass compared to protons and neutrons. Mass of a neutron is approximately equal to mass of a proton. Mass Number number of protons plus number of neutrons in an atom. Atomic mass average mass number of atoms of the same element. measured in amu (atomic mass units) not grams!
Using the Periodic Table
Nuclear Symbol When not given the number of neutrons round the amu to the nearest whole number to find mass number of the average isotope.
Let s Practice! Find the mass number and write the nuclear symbol! Beryllium 5 neutrons Mass Number = Atomic Number = Sodium 12 neutrons Mass Number = Atomic Number = Gold 118 neutrons Mass Number = Atomic Number =
IONS AND ISOTOPES
Vocabulary Ion: same number of protons, different number of electrons. Cation: positively charged ion Anion: Negatively charged ion Isotope: Same number of protons, different number of neutrons
Ions Ions is an atom whose electrons do not equal the total number of protons. This gives the atom a positive or negative electrical charge. Cation - Positive charge (more protons than electrons) Anion Negative charge (more electrons than protons)
Let s Practice How would I write the following using the nuclear symbol? Lithium atom with 3 protons, 4 neutrons and 2 electrons. Oxygen atom with 8 protons, 7 neutrons and 10 electrons. Carbon atom with 6 protons, 5 neutrons, and 6 electrons.
Isotopes Atoms of the same element (same number of protons) with different number of neutrons Chemically equivalent (same element) Most elements occur as a mixture of isotopes
Isotopes of Hydrogen Write the correct nuclear symbol for each!
Calculating Atomic Mass in a Mass Spectrometer Mass of a proton is more than 1800 times the mass of an electron A Mass Spectrometer is used to find masses of atoms Masses of subatomic particles too small to work with, so a reference isotope is used
How a mass Spectrometer Works Charged atoms fly towards a magnet. Where they hit the wall (detection screen) determines their mass. How many hit a certain spot determines the abundance (percent) of each isotope. magnet WALL
Calculating Atomic Mass Atomic masses found on periodic table are averages of all isotopes of that element based on abundance To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance (expressed as a decimal), and then add the products.
Calculating Atomic Mass Chlorine is a mixture of Cl-35 and Cl-37. 75.77% Cl-35 (35) 24.23% Cl-37 (37) 0.7577 x 35 amu = 26.50 amu 0.2423 x 37 amu = 8.957 amu + Added together 35.45 amu
Example Silicon-28 93.37% Silicon-29 4.63% Silicon-30 2.00% Atomic Mass?
How do they get that atomic mass? ISOTOPE LAB!