March 26:
HW3 was collected. SOLUTIONS ARE POSTED -
access them! Ch. 8.6 Lewis structures continued:
NH4+ and C
2H2, CH3COOH, SO2, O3
; Ch. 8.7 New terms: Resonance and resonance structures;
resonance hybrid. If there are 2 or more different possibilities of of accomodating
electrons in a molecule (or ion), several valid Lewis structures can be
drawn. The one(s) with the best (closes to zero) formal charges will be
the best and will contribute the most to the resonance hybrid.
March 21: EXAM 2 INFORMATION Ch. 8.4-8.5 More about bond polarity
- we looked at electronegativity differences as a rough estimate of bond
polarity. A true measure of a bond polarity is a DIPOLE MOMENT,
m, which is a vector (has both length and direction). At this point,
we will deal with dipole moments qualitatively only (no calculations). If you have done any vector
algebra before, review it. We will need it in the near future to determine
molecular polarities. Ch. 8.6 Lewis structures - RULES!!!!!!!
Know them. Formal charges -
know how to calculate them. Following the rules for writing
(drawing) Lewis structures may give us a correct (valid) Lewis structure,
which may not necessarily be the BEST possible Lewis structure. Formal charges
allow to find the best Lewis structure among several valid ones. March 19:
Quiz 4! Ch. 8.2: Electron configurations
of transition metal (TM) cations and post-TM cations. Ch. 8.3: Sizes of ions. You can
compare isoelectronic ions in terms of their sizes:
the larger the positive charge,
the smaller the cation
the larger the negative
charge, the larger the anion
Otherwise, we can compare ions
with the same charges for atoms from the same group in the periodic table
and use common sense (that is F- is expected do be smaller than
Cl -, or Mg2+ is expected to be smaller than Ca
2+ , just like RA(F) < RA(Cl) and RA
(Mg) < RA(Ca)) NOTE: IONIC COMPOUNDS OCCUR AS
IONIC LATTICES - there are no individual molecules of ionic compounds. Instead,
in order to MAXIMIZE ATTRACTIONS between oppositely charged ions, and MINIMIZE
REPULSIONS between same charge ions, ions are arranged in 3D lattices (Fig.
8.3) Ch.8.4 - Covalent bonds - typical
among NOMETALS Electrons are shared between atoms,
and sharing can be: 1) EQUAL - if atoms in a bond
are the same. The bond is pure covalent (or nonpolar) 2) UNEQUAL - of atoms in a bond
are DIFFERENT (most common scenario). The bond is polar covalent. New term: ELECTRONEGATIVITY The degree to which electrons
are shifted towards towards the more electronegative atom (ie. bond polarity)
depends on the electronegativity difference between atoms in a bond.
Know the electronegativity trends in the periodic table. March 14:
Ch. 7.5 Comparison of major physical and chemical properties of metals
and nonmetals. Associate metals with bases
and nonmetals in acids (this will come handy in CHEM 1202). Ch. 7.6 Group trends - group 1A
(1) We have analyzed, starting with
the electron configurations) trends in atomic sizes and first ionization energy. Reactivity (the ease with which
+1 cations were formed when elements in the group 1A react) was related to
the trends in the first ionization energy (the lower the I1
, the more reactive the element towards species which gladly accept an
electron, eg. halogens) Implications the high reactivity
of elements in group 1A in the natural occurrence (we always find them in
salts or minerals, and never as pure metals). Read Ch. 7.6 to the end and
Ch. 7.7 on your own and try to analyze information in a similar way we did
in class for group 1A metals. Ch. 8.1 OCTET RULE revisited,
Lewis electron dot symbols. Ch. 8.2 Ionic Bonds: which atoms
form which kind of ions? Lewis electron dot symbols were used to show the
formation of Al3+ and Cl- ions, and subsequently the
formation of AlCl3 (an ionic salt) Lattice energy (see Table 8.2) March 12:
Ch. 7 - PERIODIC PROPERTIES Ch. 7.2 Sizes of Atoms (Bonding
Atomic Radius, RA); trends: increases from top to bottom within
a group, and decreases from left to right within a row (period).
Can you explain these trends using electron configurations, concept of
screening and Coulomb's law (electrostatics) in your arguments? Ch. 7.3 First Ionization Energy
( I1); trends are OPPOSITE to those for RA.
Why? Ionization energy increases from
bottom to top within a group and from left to right within a period. Within periods, the largest ionization
energies can be found for noble gases. Why? Within periods, the lowest ionization
energies can be found for the alkali metals.
Why? Second ionization energy is always
higher than the first ionization energy, etc.: I1 <
I2 < I3 < ... Be able to to analyze and draw
conclusions from the following: Figure 7.5, Table 7.2 and Figures 7.6 and
7.7 If ever in doubt, write anelectron
configuration, focus on the valence electrons, and judge what is to be accomplished
by an atom losing, or gaining (next class) an electron. Electron affinity -
know the basic facts (trends are less clear) OCTET RULE - satisfied if an element
has ns2 np6
(or ns2
(n-1)d10 np6
) valence electron
configuration. Satisfying the octed rule is VERY
OFTEN a driving force behind atoms either losing or gaining electrons. Be able to explain, using previously
acquired knowledge, why certain trends, especially those in RA
and I1 are seen. A very good place to start would be the electron
configurations of atoms. Keep asking yourself questions about what you have
already learnt in this course that would allow you to explain the trends. March 7:
HW2 was collected as well as an in-class Quiz3 was administered. Electron configurations for elements
in the first two rows in the periodic table, noble gases up to Xe, and selected
other elements. New concept:
VALENCE electrons -
know the rules of which electrons in the entire electron configuration
belong to the valence! Writing and drawing full electron
configurations, eg. for potassium, K: 1s2 2s2 2p
6 3s2 3p6 4s
1and short-hand electron configurations,
eg.: [Ar] 4s1 Remember - you can only
use the preceding noble gas when writing short-hand electron configurations. In the above example, K is in
the 4th period (row), and the preceding noble gas closed the
3 rd period and is Ar. Valence electrons determine the
chemistry of the element, that is the types of reactions elements enter,
the kind of ions they form or oxidation numbers they adopt. Introduction to Ch. 7.
Please read Ch. 7.1. I will start with
7.2 on March 12.
March 5: You
can still pick it HW2 (due March 7) from me or
ACCESS IT ON-LINE Significance of quantum numbers:
n, l, and ml Different methods of orbital representation:
charge clouds, plots of Y2, and "balloon"
pictures Be able to draw 2D renderings
of the balloon pictures for s, p and d type orbitals Spin quantum number, m
s Pauli's Exclusion Principle Comparison of energy diagrams
for H atom and many-electron atoms: For the H atom - orbitals are
DEGENERATE as long the principle quantum number, n, is the same. eg. E(3s) = E(3p) = E(3d) In many electron atoms, orbitals
are only DEGENERATE if the azimuthal quantum number, l, is the same. eg. E(3s) < E(3p) < E(3d) Why? Screening (aka shielding)
- "inner electrons" screen outer electrons from the full charge (and attraction)
of the nucleus. The less attration, the higher the energy. Eg. 3p electrons
are screened better than 3s electrons, and hence are less attracted to the
nucleus (see less of the nuclear charge), and have higher energy than the
3s electrons which tend to be closer to the nucleus and experience its larger
charge. Mnemonic for relative sublevel
energies (energies of orbitals within a subshell are the same as energy of
the subshell). Hund's Rule
