Atoms, Molecules, and Ions Chapter 2

Dalton’s Atomic Model First model - early 1800’s Developed through experiments All elements are composed of tiny indivisible particles called atoms All atoms of the same element are identical.

Discovery of Electron 1897 – JJ Thomson, using cathode ray tube, discovered the charge to mass ratio of negatively charged particles, later called electrons, to be 1.76 x 108 C/g

Millikan’s Oil Drop Experiment 1909 – Robert Millikan discovered the charge of an electron, 1.6 x 10-19 C Mass of electron = 9.1 x 10-28 g

“Plum Pudding” Model Uniform positive sphere with negatively charged electrons embedded within.

Radiation Late 1800’s – discovery of radiation Three Types Alpha Beta Gamma

Rutherford Gold Foil Experiment - 1909 Shot alpha particles at gold foil Most went through foil with little or no deflection. Some were deflected at large angle and some straight back.

Rutherford Gold Foil Experiment - 1909

Rutherford Model Conclusions from Gold Foil Experiment Atom is Mostly Empty Space Dense positive nucleus Electrons moving randomly around nucleus

Bohr Model Dense positive nucleus Electrons in specified circular paths, called energy levels

Wave Mechanical Model More detailed view of the Bohr Model Energy levels are divided into sublevels Electrons are found in Orbitals (in the sublevels) region of space with a high probability where electron COULD be. Modern Model AKA Quantum Mechanical Model, Electron Cloud Model

Subatomic Particles Electron Discovered in 1897 by JJ Thomson Negative charge (-1) Mass = 9.109389*10-28g Approx mass ~ 0 Found outside of nucleus

Subatomic Particles Proton Discovered in 1919 by Rutherford Positive charge (+1) Mass = 1.672623*10-24g Approx mass ~ 1 atomic mass unit (u) Found inside nucleus

Subatomic Particles Neutron Discovered in 1932 by James Chadwick No charge (0) Mass = 1.6749286*10-24g Approx mass ~ 1 atomic mass unit (u) Just slightly larger than a proton Found inside nucleus

Atomic Structure Atomic Number - number of protons in an element All atoms of the same element have the same number of protons Mass Number - number of protons and neutrons in an atom Isotope – atoms of the same element with different number of neutrons

Chemical Symbols Mass Number Cl-35 Chlorine-35 Atomic Number

Ion Atom or group of atoms that have gained or lost one or more electrons Have a charge Example: H+, Ca2+, Cl-, OH-

Average Atomic Mass Atomic Mass Example Weighted average based on the relative abundance and mass number for all naturally occurring isotopes Example C-12 12.00 u 98.9% 12.011u C-13 13.00 u 1.1%

Periodic Table

Molecular Formula Chemical Formula used to represent a molecule Usually contain nonmetals Give exact number of atoms of each element in a compound H2O

Empirical Formula Gives the lowest whole-number ratio of atoms of each element in a compound C6H12O6 CH2O

Structural Formula Shows order in which atoms are bonded O H O=C=O

Ionic Compounds Usually contains a metal and a nonmetal or polyatomic ions Ionic formula is an empirical formula NaCl

Naming Ions and Ionic Compounds Name positive ion first, then negative ion. NaCl, Sodium Chloride Ions of metals that have more than one positive oxidation number need a roman numeral

Oxyanions Polyatomic ions often contain oxygen The most common combination of oxygen and another ion will end with –ate Nitrate (NO3-), Sulfate (SO42-), Chlorate (ClO3-) The anion with one less oxygen will end with –ite Nitrite (NO2-), Sulfite (SO32-), Chlorite (ClO2-)

Oxyanions An anion with two less oxygens will start with Hypo- and end with –ite Hypochlorite (ClO-) An anion with one more oxygen that the most common ion will start with Per- and end with –ate Perchlorate (ClO4-)

Naming Acids Acid names are based on the anion in the acid Anions that end with –ide become hydro_____ic acid HCl Chloride  Hydrochloric acid

Naming Acids Anions that end with –ate become _____ic acid HNO3 Nitrate  Nitric acid H2SO4 Sulfate  Sulfuric acid

Naming Acids Anions that end with –ite become _____ous acid HNO2 Nitrite  Nitrous acid H2SO3 Sulfite  Sulfurous acid

Naming Molecular Compounds Use a prefix to indicate the number of atoms for each element Binary Covalent System Second element ends in –ide Exceptions When there is only one atom of the first element, do not use mono- prefix. When an element starts with a vowel, drop any o or a at the end of a prefix