22 November 2011
Take out your Problem Set (if you
haven’t already handed it in)
 Objective: You will be able to:
 describe, calculate and compare the
effective nuclear charge of elements

Agenda
Questions about electron configuration?
II. Effective nuclear charge notes and
problems
Homework: Quiz Monday
6-8 multiple choice, 2 multi-part free
response
I.
Periodic Properties of the Elements
Today
attraction between electrons and the
nucleus
 repulsion between electrons
 and some properties and their trends on
the periodic table that this
attraction/repulsion causes

Effective Nuclear Charge
kQ
Q
1
2
 First, some definitions:
F
2
d

force of attraction (between two charged
particles) where Q1 and Q2 are the charges of
the particles and d is the distance between them
 in general, electrons close to the nucleus will
be held with greater force than those that are
more distant from the nucleus!
 higher positive nuclear charges will draw
electrons closer to the nucleus and hold them
tighter.
Valence vs. Core Electrons
Valence electrons: electrons in the
outermost orbitals of atoms, farthest from
the nucleus
 Core electrons: inner electrons, include
electrons in completely full “d” orbitals

Effective Nuclear Charge
http://www.youtube.com/watch?v=MtP5
mWLB-ys
 Zeff, the net positive charge experienced by
an electron in an atom.
 Not the full nuclear charge because the
core electrons “shield” (cancel) part of the
positive nuclear charge.
 Valence electrons experience less-thanfull pull from the nuclear charge.

Shielding Effect

the reduction of the full nuclear charge
experienced by an outer electron as a
result of screening (cancelling) by inner
core electrons
Trends in Effective Nuclear Charge
Zeff increases from left to right across any
period
 core electrons maintain constant across
any row, but the nuclear charge
increases, so Zeff increases
 Zeff = Z – S
 S: screening constant, about equal to the
number of core electrons in an atom

Examples

Zeff is constant going down a group
because valence electrons going down a
group are constant, but there is an
increase in number of protons to balance
this
Problems
1.
2.
What is the approximate Zeff of
scandium?
Are the valence electrons of Sc held more
or less tightly than those of K?
Use scandium’s electron configuration
to explain your answer.
Zeff produces trends…
Sizes of atoms and ions
 Ionization energy
 Electron affinity (electronegativity)

29 November 2011
Objective: You will be able to: describe
trends on the periodic table caused by
effective nuclear charge.
 Do now: (On page 5, 3rd slide):
 How many energy levels do the
following atoms have?

a.

sodium
b. potassium
c. rubidium
Calculate Zeff for Na, Mg and Al.
Sizes of Atoms and Ions

atomic radius: an estimate of the size of
an atom
 atoms don’t have sharply defined
boundaries because orbitals are areas of
probability, so definite sizes can’t be
determined
Atomic Radius (size of the atom)
Atomic radius increases
Atomic radius increases
Atomic Radius
Increases top to bottom: outer
electrons are on higher energy levels,
which are further from the nucleus
 Decreases left to right: shielding
remains constant as nuclear charge
increases
 no more core electrons are added, but
more protons are, which pull the valence
electrons closer to the nucleus

Ionic Radius
http://www.youtube.com/watch?v=hkyxQj
KwBU4
 Cations (+) are smaller than their parent
atoms because the electron is lost from the
valence shell, and e--e- repulsions are
decreased
 Anions (-) are larger than their parent
atoms because additional electrons cause
increased e--e- repulsions, causing the
electrons to spread out more in space

Ionization Energy





first ionization energy (I1): the energy
required to remove the outermost electron
from the ground state of a gaseous atom.
Ex: 495 kJ + Na(g) → Na+(g) + e−
second ionization energy (I2): the energy
required to remove the second electron
etc.
I1<I2<I3 because with each successive
removal, an electron is pulled away from an
increasingly positive ion.

http://www.youtube.com/watch?v=6e4uo
WQeM4s&feature=related
Ionization Energy Increases
Ionization Energy Increases
Exceptions
I1 decreases from Be to B and Mg to Al
 electrons in filled s or d orbitals provide
limited screening for electrons in p
subshells
 I1 decreases from N to O, P to S and As to
Se
 due to repulsion of paired electrons in
the p4 configuration of group 16 atoms

Noble Gases
have the highest ionization energies of
their periods because their valence
electrons are poorly screened.
 very high Zeff
 They are also the smallest in their periods

Problem

Arrange the period 3 elements in order of
increasing first ionization energy, lowest
to highest. Note any anomalies.
Electron Affinity
a.k.a. electronegativity
 ∆Hea, the energy change when an electron
is added to a gaseous atom
 F(g) + e- → F-(g) ∆Hea = -328 kJ/mol
 Energy is released when an atom attracts
an electron.
 http://www.youtube.com/watch?v=scvNY
ZD3jrI

Electronegativity Increases
Electronegativity Increases
Trend in Electron Affinity
Increases from left to right along a
period
 Increases from bottom to top within
a group
 smaller atoms are less shielded and
attract electrons more easily
 Exception: F has less electron affinity
than chlorine because of the small size of
F causes greater e--e- repulsion

Summary of Exceptions
Periodic Property
Periodic Anomaly
Explanation
Atomic radius
First ionization
energy
none
B<Be, Al<Mg
First ionization
energy
O<N, S<P, Se<As,
Te<Sb
Electron-electron
repulsion in p4
configurations of
Group 16 atoms
Electron affinity
F<Cl
Small size of
fluorine contributes
to strong electronelectron repulsion
Partial shielding by
s valence electrons
decreases Zeff
30 November 2011
Objective: You will be able to describe and
write chemical questions for patterns in
reactivity on the periodic table.
 Homework quiz (week of Nov. 28)
 Compare the radius and ionization
energy of oxygen and sulfur. Explain
your answer.

Agenda
Homework Quiz
II. Homework answers
III. More trends on the periodic table:
reactivity and compounds formed
Homework: Read lab – be familiar with the
procedure for tomorrow!
p. 359 #61, 72, 73, 74, 82, 86, 95: Mon.
I.
Metals, Non-Metals, Metaloids



Metals: low ionization energy, lose electrons
readily
 have luster, conduct heat and electricity,
malleable, ductile
Metallic character increases right to left
along a period and top to bottom within a
group
Metal hydrides, oxides and nitrides are basic
 Li2O(s) + H2O(l) → 2Li+(aq) + 2OH-(aq)

Non-metals have high electron affinity
and gain electrons readily
 form negative ions
 do not have luster, and are poor
conductors of heat and electricity
 form molecular compounds
 non-metal oxides are acidic
SO2(g) + H2O(l) → H2SO3(aq)

metalloids have properties intermediate
between those of metals and non-metals
Trends for Group 1 and 2 Metals
Group 1
 alkali metals (group 1): soft, metallic
solids
 s1 valence electron configurations
 lose one electron to form 1+ cations
 become more reactive moving down the
group
 http://www.youtube.com/watch?v=uixxJt
JPVXk

Alkali metal + Water
all alkali metals react with water to produce
hydrogen gas
2Na(s) + 2H2O(l) → 2Na+(aq) + 2OH-(aq) + H2(g)

Alkali metal + H2 gas
all alkali metals react with hydrogen gas to
form hydrides
 2Li(s) + H2(g) → 2LiH(s)

Alkali metals + Non-metals
all alkali metals react with most nonmetals
 2K(s) + S(s) → K2S(s)
 6Li(s) + N2(g) → 2Li3N(s)

Forming Peroxides
Na, K, Rb and Cs form peroxides
 2Na(s) + O2(g) → Na2O2(s)

oxide ion: O2peroxide ion: O22superoxide ion: O2-
Forming Superoxides
K, Rb and Cs form superoxides
 K(s) + O2(g) → KO2(s)

When burned
Li: crimson-red
 Na: yellow
 K: violet

Practice
a.
b.
c.
Write and balance a chemical equation to
describe what happens when solid
potassium is added to water.
Classify as acid-base, redox, or
precipitation reaction.
Describe what you would observe when
the reaction takes place.
6 December 2011
Objective: You will be able to:
 Describe trends in alkaline earth metals,
some non-metals, allotropes, halogens
and noble gases
 Do now: Find the final mass of your
copper + filter paper.

Agenda
Do now
II. Trends in alkaline earth metals, some
non-metals, allotropes, halogens and
noble gases
Homework: problem set due Monday
Quiz Monday, Lab notebook due monday
I.
Alkaline Earth Metals (Group 2)
s2 valence electron configuration
 lose 2 electrons to make 2+ cations
 low ionization energy (but higher than
corresponding alkali metal)
 less reactive than alkali metals, but are
more reactive moving down the group

http://www.youtube.com/watch?v=kNA2
ZDonFmE
 http://www.youtube.com/watch?v=pPnn
XD_K0BU
 http://www.youtube.com/watch?v=QhYp
EY2A1hg&feature=related

Reaction with H2O
Mg reacts with steam
 Mg(s) + 2H2O(g) → H2(g) + MgO(s)
 Ca, Sr, Ba and Ra react with liquid water:
Ca(s) + H2O(l) → H2(g) + Ca2+(aq) + 2OH-(aq)

Reaction with O2(g)
Mg and Ca form oxides:
 2Ca(s) + O2(g) → 2CaO(s)


http://www.youtube.com/watch?v=m2i9j
LPXprQ
Reaction with Non-metals

3Mg(s) + N2(g) → Mg3N2(s)
When burned
Ca: brick red
 Sr: crimson red
 Ba: green-yellow
 http://www.youtube.com/watch?v=d8hp
UtRnsYc

Practice
a.
b.
c.
Write and balance a chemical equation to
describe what happens when solid
calcium oxide is added to water.
Classify as acid-base, redox, or
precipitation.
What color would a drop of
phenolphthalein turn? Why?
Trends for Some Non-Metals
Hydrogen: 1s1 configuration puts it in
group 1, BUT it doesn’t really belong in
any group.
 Extremely high ionization energy – no
shielding
 Can share electrons, so it is classified as a
non-metal

Allotropes

Allotropes: different forms of the same
element in the same state
 Carbon: C(s, graphite), C(s, diamond)
 Phosphorus: P4(s, white), P(s, red)
 Oxygen: O2(g), O3(g) ozone
 Sulfur: S(s), S8(s)
Halogens (Group 17)
diatomic molecules:
 F2(g), Cl2(g), Br2(l), I2(s)
2 5
 s p valence electron configuration
 gain one electron to form 1- ion
 http://www.youtube.com/watch?v=yP0U
5rGWqdg

Noble Gases (Group 18)
nonmetallic, monatomic gases at room
temperature
 completely filled s and p sublevels
 form a limited number of compounds:
 XeF2, XeF4, XeF6, KrF2, HArF
 http://www.youtube.com/watch?v=HGUy
H6zG7_U&feature=related

Homework

p.
1 December 2011
Objective: You will be able to:
 write and balance equations for the
reaction of copper through a series of
reactions.
 Do now: Grab a pair of goggles and sit
next to your lab partner.

Copper cycle lab
Overview
 Location of reagents
 fume hood
 Please leave reagents IN the fume hood.
 Conduct the reaction with HNO3 in the
fume hood until brown gas dissipates
completely.

Reagents
Measure 2 mL nitric acid using the
transfer pipette 2 times.
 Use a graduated cylinder
1 mL mark
for other reagents.
 Use the graduated cylinders only as
labeled to avoid cross-contamination!
 Use distilled water from your wash
bottle

Today
Complete this procedure through the set
up for step 14
 Your solution should be slowly reacting
with the aluminum.
 Label this beaker and set it at the back of
your lab bench
 You should have a filtration setup with a
massed filter paper ready for Monday.

A few notes
Use a professional, quiet tone of voice
 Avoid unnecessary movement around the
room and unnecessary discussion with
people across the room
 Work carefully on your lab notebook,
making qualitative observations and
recording each reaction. Find a neat way
to organize and label data!

5 December 2011
Objective: You will be able to:
 write and balance equations for the
reaction of copper through a series of
reactions.
 Do now: Grab a pair of goggles and your
beaker, and sit down next to your lab
partner silently.

Observations?
Today’s goals
1.
2.
3.
4.
5.
6.
Record observations
Mass filter paper and initial it
Filter solution, picking out unreacted Al
Place filter paper on a watch glass in the
drying oven
Finish writing and balancing molecular
and net ionic equations
Lab notebooks due Monday (we’ll find
final mass tomorrow)
Homework
p. 359 #61, 72, 73, 74, 82, 86, 95: Tuesday
8 December 2011

Objective: You will be able to:
 write and balance molecular and net
ionic equations
 review periodic properties of the
elements
Your options
Work with a partner on the problem set
b. Work with your lab partner to complete
the copper cycle lab
Both are due Monday
Quiz on The Periodic Properties of the
Elements Monday
a.
Criteria for your work
Work with 1 or 2 individuals
 Sit at a table with only those individuals
 Use a tone and volume of voice
appropriate to the situation and
environment
 Be equally engaged in your work
 Work consistently and efficiently for the
length of the class
