22 November 2011
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Transcript of 22 November 2011
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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
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Agenda
I. Questions about electron configuration?
II. Effective nuclear charge notes and problems
Homework: Quiz Monday6-8 multiple choice, 2 multi-part free response
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Periodic Properties of the Elements
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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
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Effective Nuclear Charge First, some definitions:
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.
221
dQkQF
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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
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Effective Nuclear Charge
http://www.youtube.com/watch?v=MtP5mWLB-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-than-full pull from the nuclear charge.
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Shielding Effect
the reduction of the full nuclear charge experienced by an outer electron as a result of screening (cancelling) by inner core electrons
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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
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Examples
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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
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Problems
1. What is the approximate Zeff of scandium?
2. Are the valence electrons of Sc held more or less tightly than those of K?
Use scandium’s electron configuration to explain your answer.
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Zeff produces trends…
Sizes of atoms and ions Ionization energy Electron affinity (electronegativity)
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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.
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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
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Atomic radius increases
Atomic radius increases
Atomic Radius (size of the atom)
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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
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Ionic Radius
http://www.youtube.com/watch?v=hkyxQjKwBU4
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
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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.
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http://www.youtube.com/watch?v=6e4uoWQeM4s&feature=related
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Ionization Energy IncreasesIo
niza
tion
Ene
rgy
Incr
ease
s
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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
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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
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Problem
Arrange the period 3 elements in order of increasing first ionization energy, lowest to highest. Note any anomalies.
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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=sc
vNYZD3jrI
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Electronegativity IncreasesEl
ectr
oneg
ativ
ity
Incr
ease
s
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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
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Summary of Exceptions
Periodic Property
Periodic Anomaly
Explanation
Atomic radius noneFirst ionization energy
B<Be, Al<Mg Partial shielding by s valence electrons decreases Zeff
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 electron-electron repulsion
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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.
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Agenda
I. Homework QuizII. Homework answersIII. More trends on the periodic table:
reactivity and compounds formedHomework: Read lab – be familiar
with the procedure for tomorrow!p. 359 #61, 72, 73, 74, 82, 86, 95:
Mon.
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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)
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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)
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metalloids have properties intermediate between those of metals and non-metals
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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=ui
xxJtJPVXk
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Alkali metal + Water
all alkali metals react with water to produce hydrogen gas
2Na(s) + 2H2O(l) → 2Na+(aq) + 2OH-(aq) + H2(g)
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Alkali metal + H2 gas
all alkali metals react with hydrogen gas to form hydrides
2Li(s) + H2(g) → 2LiH(s)
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Alkali metals + Non-metals
all alkali metals react with most non-metals
2K(s) + S(s) → K2S(s) 6Li(s) + N2(g) → 2Li3N(s)
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Forming Peroxides
Na, K, Rb and Cs form peroxides 2Na(s) + O2(g) → Na2O2(s)
oxide ion: O2-
peroxide ion: O22-
superoxide ion: O2-
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Forming Superoxides
K, Rb and Cs form superoxides K(s) + O2(g) → KO2(s)
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When burned
Li: crimson-red Na: yellow K: violet
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Practice
a. Write and balance a chemical equation to describe what happens when solid potassium is added to water.
b. Classify as acid-base, redox, or precipitation reaction.
c. Describe what you would observe when the reaction takes place.
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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.
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Agenda
I. Do nowII. Trends in alkaline earth metals,
some non-metals, allotropes, halogens and noble gases
Homework: problem set due MondayQuiz Monday, Lab notebook due
monday
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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
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http://www.youtube.com/watch?v=kNA2ZDonFmE
http://www.youtube.com/watch?v=pPnnXD_K0BU
http://www.youtube.com/watch?v=QhYpEY2A1hg&feature=related
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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)
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Reaction with O2(g)
Mg and Ca form oxides: 2Ca(s) + O2(g) → 2CaO(s)
http://www.youtube.com/watch?v=m2i9jLPXprQ
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Reaction with Non-metals
3Mg(s) + N2(g) → Mg3N2(s)
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When burned
Ca: brick red Sr: crimson red Ba: green-yellow http://www.youtube.com/watch?v=d
8hpUtRnsYc
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Practice
a. Write and balance a chemical equation to describe what happens when solid calcium oxide is added to water.
b. Classify as acid-base, redox, or precipitation.
c. What color would a drop of phenolphthalein turn? Why?
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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
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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)
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Halogens (Group 17)
diatomic molecules: F2(g), Cl2(g), Br2(l), I2(s)
s2p5 valence electron configuration gain one electron to form 1- ion http://www.youtube.com/watch?v=y
P0U5rGWqdg
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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=HGUyH6zG7_U&feature=related
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Homework
p.
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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.
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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.
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Reagents
Measure 2 mL nitric acid using the transfer pipette 2 times.
Use a graduated cylinderfor other reagents. Use the graduated cylinders only aslabeled to avoid cross-contamination! Use distilled water from your wash bottle
1 mL mark
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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.
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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!
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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.
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Observations?
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Today’s goals
1. Record observations2. Mass filter paper and initial it3. Filter solution, picking out unreacted Al4. Place filter paper on a watch glass in
the drying oven5. Finish writing and balancing molecular
and net ionic equations6. Lab notebooks due Monday (we’ll find
final mass tomorrow)
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Homework
p. 359 #61, 72, 73, 74, 82, 86, 95: Tuesday
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8 December 2011
Objective: You will be able to: write and balance molecular and
net ionic equations review periodic properties of the
elements
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Your options
a. Work with a partner on the problem set
b. Work with your lab partner to complete the copper cycle lab
Both are due MondayQuiz on The Periodic Properties of the
Elements Monday
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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