CI

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

Particle

Symbol

Mass (u)

Mass (g)

Charge (C)

Neutron

n

1.00867

1.67493 x 10^{-24}

0 (neutral)

Proton

p+

1.00728

1.67262 x 10^{-24}

+1 (1.602 x 10^{-19})

Electron

e-

0.000549

9.10939 x 10^{-28}

-1 (1.602 x 10^{-19})

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.