CHEM131 2/3

Chapter 1: Introduction

• People achieving scores around 12 or 13 lower than a baseline of 25 should focus on past skills, data, and verification practices for improvement.

• Important schedule announcements:

  • Discussion with Michael starts tomorrow at 8 AM and additional sessions at 9 and 10:30 AM.

  • Lauren's session is from 5 to 6 PM, with a leadership session beginning this week.

• Teaching methodologies include overlap between successive classes to maintain continuity.

Oil Droplets Experiment

• The oil droplets in the experiment absorb electrons:

  • Variability in electron absorption leads to uncertainty in determining how many electrons each droplet contains (e.g., one droplet may have 3 electrons, while another has 2, etc.).

• To ascertain the number of electrons per droplet, extensive data collection is required, yielding charges that are all multiples of a fundamental unit.

Fundamental Charge Discovery

• The fundamental unit of charge is the charge of an electron:

  • Charge of an electron (q) = -1.60 x 10^-19 C.

• Example of mass calculation:

  • Multiple bags of guavas with different masses (21 g, 35 g, 56 g) demonstrate identifying one fundamental mass unit (7 g) through similar principles.

Chapter 2: Mass Of Atom

• Most alpha particles in Rutherford's gold foil experiment passed through the foil.

  • A small fraction of alpha particles were reflected at large angles, indicating a concentrated mass at the center of the atom.

• Pre-gold foil model:

  • Plum pudding model depicted atoms as solid spheres with embedded electrons.

• Rutherford's conclusions:

  • Most of the atom's mass and positive charge reside in the nucleus.

  • Electrons occupy most of the atomic volume, making atoms predominantly empty space.

  • The nucleus is much smaller than the atom, with diameters of atoms approximately 100,000 times that of the nucleus.

Chapter 3: Mass Or Number

• The concept of foil thickness influences the results of alpha particle reflection.

  • Thinner foils produce similar observations regardless of the element used.

• Nucleus vs. alpha particles:

  • When alpha particles approach the nucleus, they experience strong deflection due to the nucleus's mass.

  • A high mass ratio between the alpha particle and nucleus explains why most alpha particles pass through without deflection.

Chapter 4: Number Of Protons

• Understanding the relative masses, charges, and locations of subatomic particles:

  • Protons: Mass = 1 AMU, Charge = +1, Location = Nucleus.

  • Neutrons: Mass = 1.008 AMU, Charge = 0, Location = Nucleus.

  • Electrons: Mass = 1/1837 AMU, Charge = -1, Location = Outside Nucleus.

• The concept of nuclear symbols:

  • Atomic number (Z) indicates the number of protons (and electrons in neutral atoms).

• Example: For oxygen (O), Z = 8 (atomic number).

Chapter 5: Number Of Protons

• Mass number (A) is the sum of protons and neutrons.

• Charge of an atom refers to the number of electrons in relation to protons:

  • An atom becomes positive or negative if it has fewer or more electrons than protons, respectively.

• Examples of atomic composition:

  • Cobalt with mass number 162 and atomic number 27 results in specific numbers of neutrons and electrons.

Chapter 6: Conclusion

• The atomic mass listed on the periodic table includes both protons and neutrons, with electron mass often neglected due to its insignificance.

• Isotopes: Atoms with the same number of protons but different numbers of neutrons lead to different mass calculations.

  • Example: Carbon has isotopes with varying neutron counts (e.g., 6 protons, differing neutrons).

• Summary: Atomic structure knowledge is pivotal in understanding chemical behavior and the physical properties of elements.