Transcript AP Chemistry – Chapter 2

AP Chemistry – Chapter 2
Atoms, Molecules and Ions
The Atomic Theory
• John Dalton’s Postulates:
– Each element is composed of atoms.
– All atoms of an element are identical to each
other, but different than atoms of other
elements.
– Atoms of one element cannot be changed into
atoms of different elements by chemical
reactions; atoms are neither created or
destroyed in reactions.
– Compounds are formed when atoms of
different elements combine.
Laws!
• Law of Constant Composition – In a given
compound, the relative numbers and kinds of
atoms are constant. (CO2 and H2O)
• Conservation of Mass – The total mass of
products equals the mass of the reactants.
Mass is not created or destroyed in a reaction.
• Law of Multiple Proportions – If 2 elements
combine to form more than one compound, the
masses exist in small whole number ratios.
Developing the Current Atomic
Theory
• J. J. Thomson and the cathode ray tube lead
to the discovery of the electron and its charge
to mass ratio.
• Millikan’s Oil Drop experiment calculated the
mass of an electron.
• Rutherford’s Gold Foil Experiment determined
the atom is mostly empty space with a small
dense nucleus at the center of the atom.
Thomson’s
Plum Pudding
Model
Atomic Structure
Average Atomic Mass
The average atomic mass is determined by
multiplying the abundance by the mass, and adding
these values for all isotopes of that given atom.
The Periodic Table
• Metals lose electrons and become positive
ions (cations)
• Non-metals gain electrons and become
negative ions (anions)
The Periodic Table of Elements