Atoms, Ions and the Periodic Table
Chemistry 131Chapter 2
Dalton’s Atomic Theory
Structure of the Atom
Atomic Mass
Periodic Table
Ions
Dalton’s Atomic Theory
Two Key Ideas led to Atomic Theory
Law of Conservation of Mass
1787 - Lavoisier
Law of Definite Proportions
1804 - Proust
Dalton’s Atomic TheoryPublished in 1808 with Four Postulates
All matter is composed of exceedingly small, invisible particles called Atoms.
Atoms of an element have a given mass and properties, atoms of differing elements differ in mass and properties.
Atoms are not created or destroyed in a chemical reaction.
Atoms combine is simple, fixed, whole-number ratios to form compounds
Structure of the Atom
Dalton perceived Atoms as the smallest unit of matter.
Thomson’s discovery of the electron posited a different model.
Positive Charge
Negative ChargeElectron
Rutherford’s Gold Foil experiments led to yet another revision
The Nuclear Model of the Atom
Even atoms have sub-structure.
Hydrogen
ProtonMass = 1.6726×10-24
g Charge = +1.6022×10-19 C
NeutronMass = 1.6749×10-24 gCharge = 0
ElectronMass = 9.1094×10-28
gCharge = -1.6022×10-19 C
Atomic Number = Number of protons
Mass Number= # Protons + # Neutrons
Hydrogen
Also Hydrogen
Isotopes
Ions
Number of Electrons = Number of Protons, if the atom is neutral.
Li +1Ions
Atomic Mass
1.6749×10-24 g isn’t a lot
Atomic Mass Unit (amu)
1 amu = 1/12 the mass of 1 Carbon-12 atom
All atomic masses are therefore relative to Carbon-12
The atomic masses on the periodic table are relative atomic masses
Relative Atomic Mass=(Isotope 1 mass × Abundance 1) + (Isotope 2 mass × Abundance 2)+…
Example (Silver)107Ag 106.9051 amu is 51.82%109Ag 108.9048 amu is 48.18%
106.9051 amu × 0.5182 = 55.40 amu108.9048 amu × 0.4818 = 52.47 amu55.40 amu+52.47 amu =107.87 amu
ProblemGiven the following information, calculate the relative atomic mass of Magnesium.24Mg = 23.985 amu at 20.00%25Mg = 24.985 amu at 20.00%26Mg = 25.983 amu at 60.00%
ProblemThe copper mined on Earth consist of 63Cu (62.93 amu) and 65Cu (64.93 amu). Which isotope is more abundant? Why?
Periodic Table
Review Problems
Review Problem 1How many carbon atoms are present in each sample?(a)120 amu(b)12,000 amu(c)7.22 × 1024 amu
Review Problem 2During a typical physical exam blood tests measure the cholesterol level. A high result is anything over 240.0 mg/dL. What is this in pounds/fluid ounce? If a typical human has 5.000 L of blood, how many pounds of cholesterol are present in the blood of a patient with a total cholesterol of 260.0 mg/dL?