Ch2

Chapter 2: Atoms, Ions, and Molecules

Structure of Atom

• Components of an Atom:

  • Proton: Positively charged particle.

  • Neutron: Neutral particle, no charge.

  • Electron: Negatively charged particle.

• Significant Formulas:

  • Avogadro's Number: 6.02214179 x 10^23 ( \text{SO CALL ME MAYBE} )

Atomic Structure: Electrons

• Discovery of Electrons:

  • Conducted by J.J. Thomson in 1897.

  • Experiment involved a cathode ray tube that showed electrons being deflected towards a positively charged plate.

• Characteristics:

  • Atoms contain negatively charged particles (electrons) which have a consistent mass-to-charge ratio.

Cathode Rays

• Statements about Cathode Rays:

  • A. They originate from the negative electrode in a cathode ray tube.

  • B. They travel in straight lines in the absence of electric or magnetic fields.

  • C. They are made up of electrons.

  • D. The properties of cathode rays are dependent on the cathode material.

  • Correct Answer (Not True): D

Mass of an Electron

• Robert Millikan's Oil-Drop Experiment (1909):

  • Determined the mass and charge of an electron.

  • Charge of an electron: 1.602 x 10^-19 C.

  • Mass of an electron: 9.109 x 10^-28 g.

Thomson's Model of the Atom

• Plum-Pudding Model:

  • Proposed that electrons (negative charge) are distributed throughout a diffuse, positively charged sphere.

• Conclusion: Positive charge is distributed throughout the spherical atom.

Radioactivity and the Nuclear Atom

• Henri Becquerel: Discovered that some materials emit invisible radiation consisting of charged particles.

• Marie and Pierre Curie: Confirmed that these emissions consist of small particles.

• Radioactivity: Is defined as the spontaneous emission of high-energy radiation and particles, including:

  • Beta particles (( \beta )): High energy electrons.

  • Alpha particles (( \alpha )): +2 charge, with mass equivalent to Helium nucleus.

Atomic Structure: The Nucleus

• Ernest Rutherford’s Gold Foil Experiment:

  • Used alpha particles to test Thomson’s model of the atom.

The Nuclear Atom

• James Chadwick's Discovery:

  • Bombarded beryllium with alpha particles and emitted high-energy radiation containing electrically neutral particles, called neutrons.

Nucleus Characteristics

• Nucleus:

  • The positively charged center of an atom.

  • Contains nearly all of the atom’s mass.

  • Composed of:

    • Protons: Positively charged subatomic particles.

    • Neutrons: Electrically neutral subatomic particles.

Atomic Mass Units (amu)

• Definition:

  • The unit used to express the relative masses of atoms and subatomic particles.

• Measurement:

  • Equal to 1/12 of a carbon atom.

  • Example: 6 protons + 6 neutrons = 12 amu.

  • 1 amu = 1 Dalton (Da), named after John Dalton.

Subatomic Particles Summary

Isotopes and Average Atomic Mass

Isotopes Definition

• Isotopes: Atoms with the same number of protons but different numbers of neutrons.

• Example with Neon Gas:

  • Two types: 90% with mass 20 amu and 10% with mass 22 amu.

Nuclide Symbols

• Format:

  • Representation: A (mass number) Z (atomic number / protons) X (element symbol).

• Example:

  • Isotope with 11 protons and 12 neutrons:

    • Have to calculate mass number A = 11 + 12.

Average Atomic Mass Calculation

• Definition: It's the weighted average of masses of all isotopes of an element.

• Common Calculation Method:

  • Multiply the natural abundance of each isotope by its mass in amu and sum these products.

Mendeleev’s Periodic Table

• Dmitri Mendeleev:

  • Organized elements by atomic mass and similar properties.

  • Left spaces for undiscovered elements.

The Modern Periodic Table

• Structure:

  • Horizontal rows = Periods.

  • Vertical columns = Groups.

• Element Categories:

  1. Metals (left/bottom)

  2. Nonmetals (right/top)

  3. Metalloids (between metals/nonmetals)

Groups of Elements

Common Groups

1. Group 1: Alkali metals

2. Group 2: Alkaline earth metals

3. Group 17: Halogens

4. Group 18: Noble gases

• Transition metals: Found in between groups in the periodic table.

Transition Metal Example

• Questions about Transition Metals:

  • Which of the following is a transition metal?

    • A. Silver [CORRECT ANSWER]

    • B. Sodium

    • C. Lead

    • D. Tin

Significant Chemistry Equations to Know

1. Avogadro's Number:

   • 6.02214179 x 10^23

2. Charge of an Electron:

   • 1.602 x 10^-19 Coulombs

3. Mass of an Electron:

   • 9.109 x 10^-28 grams

4. Atomic Mass Units (amu):

   • 1 amu = 1 Dalton (Da), equal to 1/12 of a carbon atom.

5. Average Atomic Mass Calculation:

   • Average Atomic Mass = (Natural Abundance of Isotope 1 × Mass of Isotope 1) + (Natural Abundance of Isotope 2 × Mass of Isotope 2) + ...

6. Nuclide Symbols Format:

   • Representation: A (mass number) Z (atomic number / protons) X (element symbol).

These equations are foundational for understanding atomic structure, electron properties, and elemental calculations.