Module 2 Chemistry Review - CHM 104 (Atoms, Isotopes, and Periodic Families)

Atomic structure: subatomic particles and atomic numbers

  • Subatomic particles

    • Proton: charge = +1; located in the nucleus.

    • Neutron: charge = 0; located in the nucleus.

    • Electron: charge = −1; located in the electron cloud (around the nucleus).

  • Key charges and locations

    • Proton: +1, in nucleus.

    • Neutron: 0, in nucleus.

    • Electron: −1, in electron cloud/orbitals.

  • Atomic number and mass concepts

    • Atomic number (Z): number of protons in the atom.

    • Mass number (A): total number of protons and neutrons; A = Z + N.

    • Neutron number (N): N = A - Z.

Isotopes, isotones, isobars, and atomic mass

  • Isotopes

    • Definition: atoms with the same number of protons (Z) but different numbers of neutrons (N).

    • Example from the transcript: Uranium-238 vs Uranium-235 differ in neutrons.

  • Related concepts

    • Isotones: atoms with the same neutron number (N) but different Z.

    • Isobars: atoms with the same mass number (A) but different Z and N.

  • Weighted atomic mass (modern concept)

    • The atomic mass of an element is a weighted average of the masses of its isotopes.

    • Formula: ext{Atomic mass} = ar{A} = \sumi fi Ai, where fi is the fractional abundance of isotope i and A_i is its mass number.

    • Example (Uranium): if U-238 is 98% and U-235 is 2%, the atomic mass is
      M_U = 0.98 imes 238 + 0.02 imes 235 = 237.94 ext{ amu}.

  • Important note on notation

    • Mass number (A) is the superscript; atomic number (Z) is the subscript in the nuclear symbol: ^{A}_{Z} ext{X}.

The modern atomic theory and the atomic mass concept

  • Which statement is consistent with modern atomic theory?

    • Correct: Atoms combine in whole-number ratios to form compounds (law of definite proportions / law of multiple proportions).

    • Other statements in the quiz (e.g., all atoms of a given element are always the same, or all matter is composed of isotopes) are not accurate descriptions of the theory as presented.

  • Atomic mass concept

    • Atomic mass is not a whole number; it is a weighted average reflecting isotope abundances across naturally occurring samples.

    • Relationship to isotopes: mass values are the isotopic masses, and their natural abundances determine the weighted average.

Nuclear notation and counting subatomic particles

  • Write the nuclear symbol for isotopes (examples from the short-answer task):

    • Strontium-88: ^{88}_{38}Sr

    • Bromine-82: ^{82}_{35}Br

    • Boron-10: ^{10}_{5}B

    • Neon-20: ^{20}_{10}Ne

  • Counting protons, neutrons, and electrons for neutral atoms (from Sr-88, Br-82, B-10, Ne-20):

    • Strontium-88: Z=38 o p^+ = 38; ext{ } e^- = 38; ext{ } n^0 = A - Z = 88 - 38 = 50.

    • Bromine-82: Z=35 o p^+ = 35; ext{ } e^- = 35; ext{ } n^0 = 82 - 35 = 47.

    • Boron-10: Z=5 o p^+ = 5; ext{ } e^- = 5; ext{ } n^0 = 10 - 5 = 5.

    • Neon-20: Z=10 o p^+ = 10; ext{ } e^- = 10; ext{ } n^0 = 20 - 10 = 10.

Element classification and periodic table concepts

  • Metals, nonmetals, and metalloids (classifications from the practice set):

    • Sodium: metal

    • Chlorine: nonmetal

    • Oxygen: nonmetal

    • Copper: metal

    • Silicon: metalloid

    • Potassium: metal

    • Selenium: nonmetal

  • Element identifications from descriptions:

    • a) In period 5 and a transition metal with 2 valence electrons → Strontium

    • b) A metalloid in period 3 → Silicon

    • c) A noble gas in period 6 → Radon

    • d) A nonmetal with 5 valence electrons in period 2 → Nitrogen

    • e) An element in period 4 and group 17 → Bromine

    • f) An element in group 15 and period 4 → Arsenic

  • Family names (from element names):

    • Helium → noble gas

    • Sulfur → chalcogen

    • Sodium → alkali metal

    • Magnesium → alkaline earth metal

    • Iron → transition metal

    • Bromine → halogen

    • Phosphorus → pnictogen

Quick reference: Practice Test – Answer key (as provided in the transcript)

  • 1. A

  • 2. A

  • 3. B

  • 4. B

  • 5. B

  • 6. D

  • 7. Proton; charge = +1; located in the nucleus; Neutron; charge = 0; located in the nucleus; Electron; charge = -1; located in the electron cloud

  • 8. ^{88}{38}Sr s, ^{82}{35}Br s, ^{10}{5}B s, ^{20}{10}Ne s

  • 9. a) Sr-88: 38 p+, 38 e-, 50 n0; b) Br-82: 35 p+, 35 e-, 47 n0; c) B-10: 5 p+, 5 e-, 5 n0; d) Ne-20: 10 p+, 10 e-, 10 n0

  1. a) metal, b) nonmetal, c) nonmetal, d) metal, e) metalloid, f) metal, g) nonmetal

  1. a) strontium, b) silicon, c) radon, d) nitrogen, e) bromine, f) arsenic

  1. a) noble gas, b) chalcogen, c) alkali metal, d) alkaline earth metal, e) transition metal, f) halogen, g) pnictogen

Note: All chemical symbols, isotopes, and related quantities align with the content given in the transcript and its answer key. If you’d like, I can turn these notes into a printable study sheet or create flashcards for quick review.