Chapter 3 – Atomic Structure Development of the Atomic Theory

Democtritus Greek First coined the term “Atom” which means invisible and indivisible. Came up with the theory while trying to starve himself to death. Aristotle had opposing theory which was believed for 2000 years

Boyle & Newton Robert Boyle Isaac Newton Began ‘experimental chemistry’ Studied gases Worked with Newton to bring alchemy out of the “dark ages” . Eventually became Chemistry. Isaac Newton was one of the first people to propose a “mechanical universe.” He believed that the universe is made up of small solid masses that are constantly in motion. This idea is known as “The Mechanical Universe” idea. Wrote article “Skeptycal Chemyst”

John Dalton John Dalton formulated the Atomic Theory which states that: atoms cannot be divided or separated atoms of one element are the same atoms of an element are different than atoms of other elements atoms of different elements can be combined in whole number ratios to form compounds Used actual experimental work from Antoine Lavoisier (Law of conservation of Mass) and Joseph Proust (Law of Definite Proportions) to support his theory.

Atomic Mass The atomic mass on the Periodic Table of Elements is a WEIGHTED AVERAGE. Measured in atomic mass units (amu) The amu is based on 1/12 the mass of a carbon-12 atom 1 amu = 1.66 x 10-27 kg

The Mole SI unit for amount of a substance is the mole 1 mole = 6.02 x 1023 particles A particle can be an atom, ion, molecule, compound or formula unit This is called Avogadro’s Constant 1 mole of a substance = mass of substance from PTE in grams 6.02 x 1023 particles of a substance = mass of substance from PTE in grams

Modern Atomic Structure

JJ Thomson Experimented with Cathode rays. Based on the work that he did, he discovered electrons, the first subatomic particle He also developed a model of the atom called the “plum pudding” model. Because of Thomson’s work, Dalton’s theory was adjusted. http://www.youtube.com/watch?v=RW_zfKOU9uM

Rutherford Student of Thomson. Designed gold Foil Experiment to prove Thomson’s model. His experiment disproved Thomson and he proposed his own theory, the nuclear model of the atom. http://www.youtube.com/watch?v=bSEOOMs5VNU

Modern Atomic Structure Scientists now know that there are three major subatomic particles: protons, neutrons and electrons. Particle Location Mass Charge proton nucleus 1 amu + neutron none electron orbit nucleus (in the electron cloud) 1/2000 amu -

How does this relate to the PTE? You can use the periodic table of elements (PTE) to figure out how many protons, neutrons and electrons are in any atom on the table. Neutrons can be found by subtracting the atomic mass from the atomic number: N = A - Z Atomic mass (A) = p + n in the nucleus Au 197 79 Atomic number (Z) = number of protons in the nucleus

Atoms, Ions and Isotopes The number of protons in an atom NEVER changes. This is how you identify an element. If the number of protons are changed, you have a whole new element. Atoms are electrically neutral (protons = electrons). If an atom is heavier/lighter than expected (greater or lower atomic mass than on the PTE), neutrons have been added or lost. This is now an isotope. If an atom becomes charged, it has lost (+) or gained (-) electrons. It is now an ion.

Rb+1 Ni Name Symbol A Z P N E Atom, Ion or Isotope? uranium 92 148 50 46 85 37 59 28 48 62 Rb+1 Ni

Name Symbol A Z P N E Atom, Ion or Isotope? carbon 8 54 33 40 28 gold 207 43 19 18

ELEMENT SYM A Z P N E ATOM, ION OR ISOTOPE 13 14 79 114 48 17 18 197 80 7 3 2 83 130 240 92 74 58 88 38 36 24 25 19 20 51 54

ELEMENT SYM A Z P N E ATOM, ION OR ISOTOPE Aluminum Al 27 13 14 Atom Gold Au 197 79 118 Cadmium Cd 114 48 66 Isotope Chlorine Cl 36 17 19 18 Ion Mercury Hg 80 117 Lithium Li 7 3 4 2 Bismuth Bi 213 83 130 Uranium U 240 92 148 Tungsten W 184 74 110 Cerium Ce 140 58 82 Strontium Sr 88 38 50 Chromium Cr 49 24 25 Potassium K 39 20 Antimony Sb 122 51 71 54 ion 27 13 197 79 114 48 36 17 -1 197 80 7 3 +1 213 83 240 92 184 74 140 58 88 38 +2 49 24 39 19 122 51 -3