Chemistry Chapter 2: Atoms and Elements

Study Notes

Chapter 2: Atoms and Elements

Law of Conservation of Mass: Matter cannot be created or destroyed in a chemical reaction; the mass of reactants equals the mass of products.
Plum-Pudding Model: Proposed by J.J. Thomson, this model depicts the atom as a sphere of positive charge with negatively charged electrons embedded within it, resembling a "plum pudding."
Rutherford’s Gold Foil Experiment: Demonstrated that atoms have a small, dense nucleus; most of the atom's volume is empty space, as most alpha particles passed through gold foil, while some were deflected.
Subatomic Particles:
- Protons: Positive charge, mass of approximately 1 amu.
- Neutrons: No charge, mass of approximately 1 amu.
- Electrons: Negative charge, negligible mass (approximately 1/1836 amu).
Atomic Number (Z) vs. Mass Number (A): Z indicates the number of protons in an atom; A is the sum of protons and neutrons.
Isotopes: Atoms of the same element that have different numbers of neutrons, resulting in different mass numbers.
Percent Natural Abundance of Isotopes: The relative percentage of each isotope found in nature, usually determined by mass spectrometry.
Average Atomic Mass Calculation: Use the masses and natural abundances of isotopes to compute the weighted average atomic mass of an element.
Ions: Charged particles formed when atoms gain or lose electrons; can be cations (positively charged) or anions (negatively charged).
Predicting Ion Charges: Generally, main-group elements form ions that achieve a stable electron configuration, typically resembling the nearest noble gas.
Mole Concept: A mole is 6.022 x 10²³ particles (atoms, molecules) of a substance. Calculations can involve converting between mass, moles, and number of atoms.
Mass Variability Between Elements: Each element has a unique atomic mass due to differences in the number of protons and neutrons.

Chapter 3: Matter, Measurement, and Problem Solving

Chemical Bonds:
- Ionic Compounds: Formed between metals and non-metals where electrons are transferred, resulting in attraction between oppositely charged ions.
- Molecular (Covalent) Compounds: Composed of two or more non-metals sharing electrons to form molecules.
Ionic Compound Neutrality: Ionic compounds must have overall neutral charge, determined by the charges of contributing ions.
Nomenclature:
- Covalent Compounds: Use prefixes (mono-, di-, tri-, etc.) to indicate the number of each element present.
- Acid Naming Rules:
  - Binary acids: Prefix “hydro-” + root of element + “-ic acid.”
  - Oxoacids: “-ate” becomes “-ic acid,” “-ite” becomes “-ous acid.”
Molar Mass Calculation: The sum of the atomic masses of all atoms in a compound, calculated from periodic table values.
Chemical Composition:
- Molecular Formula: Shows the actual number of each type of atom in a molecule.
- Empirical Formula: Represents the simplest whole-number ratio of different atoms in a compound.
Empirical Formula Problems: Can be derived from given masses or percent by mass of elements in a compound; involves converting mass to moles.