The second section of the course focuses on matter at the chemical level: atoms, their variant isotopes and ions, and the molecules they form by combining. We'll take a brief tour of the history of atomic discovery and learn how atoms are built and how molecules are formed and named. Supporting material is found in Brown's chapter 2.
Topics for Lecture 2 [Links to PowerPoint slide sets]
1. Atoms are the fundamental unit of matter for chemists.
2. Isotopes are atoms with a variant number of neutrons.
3. Ions are atoms that have lost of gained valence electrons.
a. Atoms are made of subatomic particles: protons, neutrons & electrons.
b. Compounds are formed when 2 or more atoms combine at a constant ratio (law of constant
c. Combining any 2 atoms at a series of ratios produces a wide variety of compounds (law of multiple
d. Atoms have a tiny, dense central nucleus of protons & neutrons surrounded by massive but diffuse
cloud of electrons (Rutherford’s nuclear model).
e. Isotopes are atoms with a variant number of electrons.
f. The periodic table organizes elements on the basis of their atomic number (#p) and the principle energy
levels of their electrons.
g. Formation of cations and anions is inextricably linked and simultaneous.
h. Chemical compounds are named as ionic compounds, molecular compounds, or acids.
i. Dalton’s atomic theory: 1) all matter is atoms; 2) atoms of a single element are identical; 3) chemical
reactions don’t change atoms but rearrange them; 4) compounds form when atoms combine at
ii. Molecular formulas list types and numbers of atoms in a molecule while empirical formulas give the
simplest ratio of atoms in a molecule.
iii. JJ Thompson discovered electrons by using electricity to separate the particle from atoms of one
element. Proposed the plum pudding model.
iv. Radioactivity: alpha particles (2 + nuclei); beta particles (high energy electrons); gamma rays (pure
energy w/o particles).
v. Atoms can be identified by the number of protons in their nuclei (ie atomic number).
vi. Atoms are uncharged & have equal numbers of protons & electrons.
vii. Number of neutrons = atomic mass – atomic number (#p).
viii. Average atomic mass is calculated by summing the product of the mass of each isotope multiplied by
the frequency or abundance of that isotope.
ix. Mass spectroscopy is able to identify chemical make up by separating atoms & isotopes on the basis of
x. Within each row (aka period) of the periodic table all elements that have the same number of principle
xi. Within each column (aka group) of the periodic table, elements share 1) similar chemical & physical
properties, and 2) valence electron configuration.
xii. Electropositive metals are found in columns 1A & 2A (and Al in 3A). Transition metals are found in the
“B” columns (mid-table). Non-metals are found above the “staircase”. Noble elements (or gases) are
found in column 8A. Metalloids are found on the staircase and have properties between metals & non-
xiii. Cations are positively charged ions formed when metals lose valence electrons.
xiv. Anions are negatively charged ions formed when non-metals gain valance electrons.
xv. Ions and the atoms they are formed from have very different physical & chemical properties.
xvi. Ionic compounds form large, repeating crystal lattice structures held together by electrostatic
xvii. Cations are named as “element + ion”. Names of transition metal ions must include charges (iron (I),
or iron (II) or iron (III)).
xviii. Anions are named as “root_ide + ion”. Polyatomic anions combine a non-metal with some number of
oxygen (or sometimes nitrogen) atoms. Polyatomic anions are named as “root_ate (more oxygens)
or root_ite (less oxygens)” ions.
xix. Ionic compounds are named by combining cation & anion names. If the cation is a transition metal,
the charge must be shown: (I) or (II) or (III). Subscript numbers are NOT included in the names of ionic
xx. Molecular compounds are named for the first & second elements as “element root_ide” and subscript
numbers become prefixes using for each element: P2O5 is diphosphorous pentoxide. Exception: when
there is only one of the first element, the mono prefix is not used: CO2 is carbon dioxide.
xxi. Monoatomic acids are named for the root of their non-metal: hydro_root_ic acid. Polyatomic acids are
named without the prefix and the suffix of their non-metal changes from –ate to –ic or from –ite to
–ous: root_ic or root_ous acid.
Resources for students:
Links and items of interest: