Chapter 2 Atoms, Molecules, and Ions
2.1- Atomic Theory
Dalton's Atomic Theory

  • "Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass, and chemical properties. The atoms of one element are different from the atoms of all other elements.
  • Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction.
  • A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction."
Joseph Proust's law of definite proportions
  • "Different samples of the same compound always contain its constituent elements in the same proportion by mass."
Law of multiple proportions
  • "If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers."
Law of conservation of mass
  • "Matter can be neither created nor destroyed."

2.2- Structure of the Atom

  • The basic unit of an element that can enter into chemical combination. It is made up of subatomic particles called protons, electrons, and neutrons.
  • “The emission and transmission of energy through space in the form of waves.”
  • Electron
    • “Negatively charged particle.”
    • The charge of all electrons is the same.
    • “A dense central core within the atom.”
    • Positively charged particle within the nucleus of an atom.
    • Electrically neutral particles with greater mass than protons
    • Exist within the nucleus of an atom.

  • “The spontaneous emission of particles and/or radiation.”
Three Types of Rays are Produced by the Decay of Radioactive Substances.
  • Alpha Rays
    • Positively charged particles
  • Beta Rays
    • Electrons
  • Gamma Rays
    • High-energy rays that have no charge and are not affected by an external field.
J.J. Thomson
  • Proposed the “plum pudding” model of the atom
    • This model states that “an atom could be thought of as a uniform, positive, sphere of matter in which electrons are embedded like raisins in a cake.”
Rutherford Gold Foil Experiment

2.3- Atomic Number, Mass Number, and Isotopes
Atomic Number

  • “The number of protons in the nucleus of each atom of an element.”
Mass Number
  • “The total number of neutrons and protons present in the nucleus of an atom of an element.”
  • Mass number = number of protons + number of neutrons = atomic number + number of neutrons
  • “Atoms that have the same atomic number but different mass numbers”
Periodic Table
  • “A chart in which elements having similar chemical and physical properties are grouped together.”
  • Organized by atomic number.
    • Periods- horizontal rows
    • Groups/Families- vertical columns according to similarities in their chemical properties.

2.4- The Periodic Table

  • "good conductor of heat and electricity"
  • "poor conductor of heat and electricity"
  • "has properties that are intermediate between those of metals and nonmetals"
Alkali Metals
  • Group 1A elements (Li, Na, K, Rb, Cs, and Fr)
Alkaline earth Metals
  • Group 2A elements (Be, Mg, Ca, Sr, Ba, and Ra)
  • Group 7A elements (F, Cl, Br, I, and At)
Noble Gases
  • Group 8A elements (He, Ne, Ar, Kr, Xe, Rn)

2.5- Molecules and Ions
  • "an aggregate of at least two atoms in a definite arrangement held together by chemical forces"
Diatomic molecule
  • contains 2 atoms (H2, N2, O2, Cl2)
Polyatomic molecules
  • molecules containing more than two atoms
  • H2O NH3
  • ion with a net positive charge
  • ion whose net charge is negative
Ionic Compound
  • formed from cations and anions
Monatomic Ions
  • contain only one atom (Mg, S, N, Na)
Polyatomic Ions
  • ions containing more than one atom

2.6- Chemical Formulas
Chemical Formulas
  • "express the composition of molecules and ionic compounds in terms of chemical symbols"
Molecular Formula
  • "shows the exact number of atoms of each element in the smallest unit of a substance"
  • Hydrazine for example, has a molecular formula of N2H4
  • "one of two or more distinct forms of an element"
  • O2 (oxygen) and O3 (ozone) are allotropes
Structural Formula
  • "shows how atoms are bonded to one another in a molecule"
  • H2O is shown as H-O-H with the "-" representing a chemical bond
Empirical formula
  • "tells us which elements are present and the simplest whole-number ratio of their atoms"
  • not necessarily the actual number of atoms in the given molecule
  • Hydrazine for example (N2H4), has a chemical formula of NH2

2.7- Naming Compounds

Fun Fact-





Chapter 2 Lab
For some naming practice- ****

In this exploration you will be observing reactions of a copper compound and aluminum.
After completing the lab complete the questions at the end.