Atomic Structure and the Periodic Table Chapter 5 By Beth McKee
Early Models of the Atom Democritus of Abdera 4 th century B.C.- Greece 1 st to suggest particles fundamentally indivisible and indestructible, called atomos Lacked experimental support and did not explain chemical behavior John Dalton 1766 – 1844 Studied ratios that elements combined in chemical reactions Formulated Dalton’s atomic theory
The Principles of Chemistry by Stewart R. Brinkley, ©1926
Dalton’s Atomic Theory All elements are composed of tiny indivisible particles called atoms Atoms of the same element are identical. The atoms of any one element are different from those of any other element
Dalton’s Atomic Theory cont’d Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction
How Small is an Atom? Smallest particle of an element that retains the properties of that element Scanning Tunneling microscope can give a visual image of indivi- dual atoms even though they are extremely small
Writing with atoms
STRUCTURE OF THE NUCLEAR ATOM
Atoms Can Be Subdivided Into Many Subatomic Particles Electrons discovered by Thomson in 1897 Used cathode ray tube to show that electrons were negatively charged
Cathode Ray Tube "To the electron -- may it never be of any use to anybody." -- JJ. Thomson's favorite toast
Slide 6 of 20 Notes: DEMO: cathode ray tube w/ Tesla coil.
Slide 7 of 20
Slide 8 of 20
Atoms Can Be Subdivided Into Many Subatomic Particles Robert Millikan- calculated electron carries 1 unit of negative charge Mass of electron is 1/1840 of the mass of a hydrogen atom
Matter and Electrical Charges Atoms have no electrical charge Electric charges are carried by particles of matter Electric charges always exist in whole- number multiples of a single base unit X # of – charged particles + X # of + charged particles forms electrically neutral particle
Protons and Neutrons Eugene Goldstein (1886) observed another ray is given off in the cathode ray tube- he called it a canal ray These positively charged subatomic particles are called protons James Chadwick (1932) confirmed the existence of neutrons which have no charge or a neutral charge Chadwick
Nucleus of the Atom Rutherford (1911) discovered that positive and negative charges not evenly spaced throughout the atom
Slide 9 of 20
Directed a stream of -particles (He +2 ) through a thin sheet of gold foil Majority of -particles passed through without deflection Few were deflected by the positive charge within the atoms Led to theory of positive nucleus and much empty space between it and the electrons
Slide 11 of 20 Notes: Prediction based on Rutherford’s nuclear atom: number of scattered alpha particles is proportional to: thickness of foil square of the charge on the nucleus 1/sin4(theta/2) 1/velocity4
Simplest Model of the Atom Don’t be mistaken about the paths of electrons. They are not on rings and rotating in one direction. They form a cloud around the nucleus and can be found in many different locations.
This illustrates the size of a neutron star which has the same density as that of the nucleus of an atom. Our sun could hold 333,000 earths to show a relative volume to that of a neutron star.
Atomic Number Protons and Neutrons are in nucleus Atomic number = # of protons in nucleus All atoms of an element contain same # of protons Atoms are electrically neutral so protons equal the electrons also.
Mass Number Mass number is total number of protons and neutrons it is a whole # Calculate number of neutrons by subtracting the atomic number from the atomic mass Gold-197 or Au-197 denotes both the name of the element and the mass number
Mass Number
Components of the elements on the Periodic Table Atomic
Work problems, page p , #35-42, 45
Isotopes Have the same # of protons but different # of neutrons different mass # Chemically alike b/c the subatomic particles responsible for chemical behavior are the same 3 known isotopes of hydrogen: hydrogen-1 (hydrogen), hydrogen-2 (deuterium), and hydrogen-3 (tritium)
Atomic Mass Mass of atoms was calculated in the 1920’s using a mass spectrometer Masses were so small that it is not practical to use the actual #’s We use relative masses based on a reference isotope, carbon-12
Carbon-12 was assigned a mass of 12 atomic mass units (amu) 1amu = 1/12 mass of a carbon-12 atom Mass of electron is practically negligible compared to the mass of a proton or neutron the mass of a proton or neutron = 1 amu In nature, most elements occur as 2 or more isotopes Mass on periodic table is a weighted average based on relative abundance of the isotope
Calculations of Atomic Mass Numbers based on Percent Abundance The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for mass amu, and 30.8% for mass = amu. Calculate the average atomic mass of copper.
(62.93)(.692) + (64.93)(.307) = 63.5 amu mass x percent plus mass x percent, etc. = abundance abundance (in decimal form) average atomic mass
Work problems, page p , #50, 51, 53, 55, 59, 60
The Periodic Table Organizing the Elements
Periodic Table Development Dimitri Mendeleev ( ) arranged the ~70 known elements by increasing atomic masses and grouped them according to the similarity of their properties Could predict properties of elements yet to be discovered
Henry Moseley ( ) arranged the elements by atomic # Solved the problem of I and Te not having similar properties that other elements in their group had b/c they switch places when ordered by atomic #
Glenn Seaborg was responsible for the latest version of the periodic table. His work was a result of the Manhattan Project during WWII. Glenn Seaborg is the only person ever to patent any elements, curium and americium. He is also listed in the Guinness Book of World Records as having the longest biography in Who's Who in America. He also is the only person to have an element named for him, while alive.
Important components and terms of the Periodic Table Alkali Metals Alkaline Earth Metals Transition Metals Inner Transition Metals or Lanthanide and Actinide Series Halogens Noble or Inert Gases Group or Family (numbers) Periods (numbers) Metals Nonmetals Metalloids or Semimetals
An expanded version of the Periodic Table.
Work problems, page p , #62, 65-70