3. Democritus Aristotle -400 B.C. - Coined the term “atom” -384-322 B.C. - Believed matter is continuous

4.  1627 – 1690 A.D.  Introduced a scientific approach to chemistry

5.  All matter is composed of tiny particles called atoms.  Atoms of the same element have the same properties. (mass, size, etc.)  In a chemical reaction, matter cannot be created or destroyed – Law of Conservation of Mass  Compounds always contain elements in the same ratio by mass – Law of Definite Proportions Dalton 1810

6.  A penny contains 2.4 x 10 22 atoms.  The radius of a single atom is around 2 x 10 -10 m or 0.2 nm.  Scanning tunneling microscopes can generate images of individual atoms.

7.  Showed electrons are negatively charged  Every atom’s electrons have same charge

9.  Conclusion: most of an atom is empty space

11.  Thomson’s Model (1897)  Bohr’s Model (1913)  Electron-cloud Model (present)  Rutherford’s Model (1909)  Dalton’s Model (1803)

12.  Robert Millikan  Oil Drop Experiment  Determined charge of electron  Max Planck  E = h v  Defined a quantum of energy

13.  James Chadwick  Discovered Neutron in 1932

14.  Nucleus ◦ Contains protons and neutrons ◦ Makes up most of an atom’s mass ◦ Is positively charged  Proton (+ charge)  Neutron (0 charge)  Electron Cloud ◦ Contains electrons ◦ Makes up most of an atom’s volume

15. Subatomic Particles ChargeLocationMassOther Feature Proton + Nucleus1 amuDefines the element -Atomic # Neutron 0 Nucleus1 amuChange # to form isotopes Electron - Electron Cloud ~0Atom’s volume -dictate’s reactivity

16.  Short-ranged forces that hold the nuclear particles together  Between electrically charged particles  Like charges repel  Opposite charges attract

17.  Atoms of the same element that differ in mass ◦ Atomic # = # protons ◦ # protons = # electrons ◦ Mass # = # protons + # neutrons

18. NuclideProtonsNeutronsMassNumberProtium101 Deuterium112 Tritium123

19. Silver - 108 Lead - 207 Bromine - 80

20.  Found in an e- cloud outside of the nucleus ◦ But NOT in paths like the planets  1 st nrg level holds up to 2 e-  2 nd nrg level holds up to 8 e-  3 rd nrg level holds up to 18 e-

21.  Arranged by increasing atomic #  Rows = Periods  Columns = Groups OR Families