Atomic Number and Mass Number The Atom Atomic Number and Mass Number Isotopes

JJ Thomson Plum-Pudding Model Cathode Ray Tube http://www.youtube.com/watch?v=_nLESblUAHY

Rutherford Discovered atom is mostly empty space since most particles went through the foil. A few particles bounced back which meant there must be a nucleus.

Bohr

Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds

LecturePLUS Timberlake Subatomic Particles Particle Symbol Charge Relative Mass Electron e- 1- 0 Proton p+ + 1 Neutron n 0 1 LecturePLUS Timberlake

Location of Subatomic Particles

Atomic Number Counts the number of protons in an atom

Atomic Number on the Periodic Table 11 Na Atomic Number Symbol LecturePLUS Timberlake

All atoms of an element have the same number of protons 11 Na 11 protons Sodium LecturePLUS Timberlake

LecturePLUS Timberlake Learning Check State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons LecturePLUS Timberlake

LecturePLUS Timberlake Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Unless it is an ion. LecturePLUS Timberlake

LecturePLUS Timberlake Mass Number Counts the number of protons and neutrons in an atom LecturePLUS Timberlake

LecturePLUS Timberlake Atomic Symbols Show the mass number and atomic number Give the symbol of the element mass number 23 Na sodium-23 atomic number 11 LecturePLUS Timberlake

Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl 17 17 chlorine - 35 chlorine - 37

LecturePLUS Timberlake Atomic Mass Na 22.99 Listed on the periodic table Gives the mass of “average” atom of each element compared to 12C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number LecturePLUS Timberlake

Calculating Average Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = (mass isotope1)(%) + (mass isotope 2)(%) +… 100 100

Atomic Mass of Magnesium Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70% 25Mg = 25.0 amu 10.13% 26Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu Mg 24.3 LecturePLUS Timberlake

LecturePLUS Timberlake Learning Check Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the average atomic mass of gallium? LecturePLUS Timberlake

Solution Atomic mass Ga = 69.7 amu 68.9 amu x 60.2 = 41.5 amu for 69Ga 100 + Ga-71 70.9 amu x 39.8 = 28.2 amu for 71Ga Atomic mass Ga = 69.7 amu