Atomic Structure: Bohr Model and Subatomic Particles

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Atomic Structure

• The Bohr model describes the structure of an atom.
• Subatomic particles include protons, neutrons, and electrons.
  • Protons are located in the nucleus, have a positive charge, and a mass of approximately 1 atomic mass unit (amu).
  • Neutrons are located in the nucleus, have no charge, and a mass of approximately 1 amu.
  • Electrons are located in electron shells outside the nucleus, have a negative charge, and negligible mass.
• Atomic number: the number of protons in an atom, defining element identity.
• Atomic weight (mass number): the total number of protons and neutrons in an atom's nucleus.
• Number of electrons equals the number of protons in a neutral atom.
• Electron configuration describes the arrangement of electrons in the different energy levels and sublevels within an atom.
• The periodic table organizes elements by their atomic number and electron configurations.
• Periods (rows) reflect the number of electron shells.
• Groups (columns) indicate the number of valence electrons and similar chemical properties.
• Four main groups on the periodic table:
  • Group 1 (Alkali Metals): Highly reactive metals with one valence electron.
  • Group 2 (Alkaline Earth Metals): Reactive metals with two valence electrons.
  • Group 17 (Halogens): Highly reactive nonmetals with seven valence electrons.
  • Group 18 (Noble Gases): Inert gases with a full valence shell (8 electrons, except for Helium which has 2).

Ions and Bonding

• Valence shell: the outermost electron shell of an atom, determining its bonding behavior.
• Valence electrons: electrons in the valence shell that participate in chemical bonding.
• Ions form when atoms gain or lose electrons to achieve a stable electron configuration.
  • Cations: positive ions formed when an atom loses electrons.
  • Anions: negative ions formed when an atom gains electrons.
• Common ions associated with each group:
  • Group 1 elements form +1 ions (e.g., Na+).
  • Group 2 elements form +2 ions (e.g., Mg+2).
  • Group 16 elements form -2 ions (e.g., O-2).
  • Group 17 elements form -1 ions (e.g., Cl-).
• Ionic bonds: formed by the electrostatic attraction between oppositely charged ions, electrons are transferred.
• Ion ratios in ionic compounds are determined by the charges of the ions to achieve electrical neutrality (e.g., Ca+2 and F- form CaF2).
• Naming ionic compounds: the cation name comes first, followed by the anion name (e.g., Calcium Fluoride).
• Covalent bonds: formed by the sharing of electrons between atoms.

Chemical Reactions

• Reactants: substances that undergo change in a chemical reaction.
• Products: substances that are formed as a result of a chemical reaction.
• Word equations: represent chemical reactions using the names of the reactants and products (e.g., Hydrogen + Oxygen → Water).
• Symbol equations: represent chemical reactions using the chemical formulas of the reactants and products (e.g., 2H2 + O2 → 2H2O).
• Balancing equations: ensuring that the number of atoms of each element is the same on both sides of the equation, obeying the law of conservation of mass.
• Types of chemical reactions: synthesis, decomposition, single replacement, double replacement, combustion, acid-base, redox.
• Rates of reactions: the speed at which a chemical reaction occurs.

Rates of Reaction

• Collision theory: states that for a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation.
• Factors affecting reaction rate:
  • Temperature: increasing temperature usually increases reaction rate.
  • Concentration: increasing reactant concentration usually increases reaction rate.
  • Surface area: increasing surface area of a solid reactant usually increases reaction rate.
  • Catalyst: a substance that speeds up a reaction without being consumed.
• Measuring rates of reaction: monitoring the change in concentration of reactants or products over time

Data Analysis

• Independent variable: the variable that is deliberately changed or manipulated.
• Dependent variable: the variable that is measured in response to changes in the independent variable.
• Constant variables: variables that are kept the same throughout the experiment.
• Graphing a table of results: plotting the independent variable on the x-axis and the dependent variable on the y-axis.
• Describing a graph: noting the overall pattern, trends, and relationships shown by the data.
• Identifying trends and relationships: positive, negative, linear, exponential, etc.
• Identifying meaning in slope of graph: the rate of change between the variables.
• Drawing data from a graph: reading specific values of the dependent variable for given values of the independent variable.
• Predicting possible continuation of graphs: using the observed trend to estimate values beyond the measured data points.
• Calculating values from set of data: determining averages, percentages, or other relevant quantities.