CP Chemistry Chapter 8 Atomic Theory

Subatomic Particles Protons Protons Neutrons Neutrons Electrons Electrons

Early Models Democritus – 4 th century Democritus – 4 th century First use of word “atoms” First use of word “atoms” No experimentation – just philosophy No experimentation – just philosophy

Dalton’s Atomic Theory He performed experiments He performed experiments Pg. 306 main ideas Pg. 306 main ideas Model similar to a solid rubber ball Model similar to a solid rubber ball Exactly the same throughout Exactly the same throughout

Electrons J.J. Thomson Cathode ray tube – pg. 307 Studying electricity Glowing beam called “cathode rays” Deflected by a magnet

Thomson concluded that the cathode ray was made of MATTER, not energy Proposed that the rays were made of negatively charged particles Later, particles named electrons

This flow of electrons is ELECTRICITY!!!!!

Words to know Anode + electrode Cathode - electrode

Millikan ( ) CCCCALCULATED ELECTRON MASS AND CHARGE OOOONE UNIT OF NEGATIVE CHARGE 1111/2000 MASS OF A PROTON (HYDROGEN ATOM) DDDDisproved one of Dalton’s ideas (atoms ARE made of smaller particles)

 Thomson’s “Blueberry Muffin” model of the atom  Ball of positively charged matter with electrons scattered throughout

After Thomson’s work  Scientists identify positively charged particles called protons  Mass 2000 times that of an electron  MUCH LARGER than electrons

Rutherford’s Gold Foil Experiment

Concluded: ► Atom mostly empty space ► Dense central core – positively charged ► Called the nucleus

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Niels Bohr Electrons move around the nucleus in planetary orbits “Planetary Model” Not true

Protons and electrons have equal but “opposite” charges Scientists realized something was wrong Must be another particle to account for mass of atom

Neutron ► Chadwick discovered ► Neutral charge (no charge) ► Located in the nucleus ► Mass of 1 amu (same as proton)

Atomic number – number of protons in the nucleus Neutral atom #p = #e

Atoms can form ions (charged particles) by gaining or losing electrons Atoms can form ions (charged particles) by gaining or losing electrons Gain electron(s) – negative charge – ANION Gain electron(s) – negative charge – ANION Lose electron(s) – positive charge – CATION Lose electron(s) – positive charge – CATION Bromine gains an electron becomes Br- bromide ion (anion) Bromine gains an electron becomes Br- bromide ion (anion) Sodium loses an electron becomes Na+ sodium ion (cation) Sodium loses an electron becomes Na+ sodium ion (cation)

In both cases, the number of protons DOES NOT CHANGE!!!!! In both cases, the number of protons DOES NOT CHANGE!!!!! Overhead examples Overhead examples

Isotopes Atoms of the same element that have different number of neutrons Atoms of the same element that have different number of neutrons Shows that all atoms of the same element are not identical Shows that all atoms of the same element are not identical Distinguish isotopes of same element by MASS NUMBER Distinguish isotopes of same element by MASS NUMBER

Mass Number # Protons + # Neutrons = mass number # Protons + # Neutrons = mass number Isotope Notation on the board (Pg. 319) Isotope Notation on the board (Pg. 319)

Calculating average atomic mass  Weighted average of the naturally occurring isotopes of that element. (always carried to a few decimal places)  Similar idea to “weighted” class average.

Average atomic mass  amu - atomic mass unit  1/12 of a carbon-12 isotope  C-12 weighs 12 amu