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

Problem

Given 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%

Problem

The 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 2

During 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?