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Monday, October 15 •  Lecture 12 (Thursday) –  Electron Arrangement in Atoms (3.6) –  Orbital Diagrams and Electron ConfiguraEons (3.7)
•  Lecture 13 (Today) –  Orbital Diagrams and Electron ConfiguraEons (3.7) –  Trends in Periodic ProperEes (3.8) –  Exam 1 –  RadioacEvity (4.1) Fixing Clicker Issues •  When you click in during class, make sure that your clicker shows a green light •  Check the list of working and non-­‐working clickers •  If you are in the “not working” column, re-­‐register your clicker •  double-­‐check that your Device ID has been submiWng responses (boXom of file) Energy Levels, Sublevels, and Orbitals
•  Electrons can be in different energy levels (n = 1 - 7)
•  Each energy level contains n sublevels (1 - 4) labeled s, p,
d, or f.
–  energy level 2 contains 2 sublevels
–  energy level 4 contains 4 sublevels
•  Each sublevel is made up of 1, 3, 5, or 7 orbitals
•  Each orbital can hold up to 2 electrons (of opposite spin)
Electron Spin •  In a magneEc field, electrons behave in 2 different ways! •  The electron behaves as if it were a bundle of “spinning” charge “spin up”
“spin down”
Order of Filling
Energy levels are filled with electrons
§  in order of increasing energy.
§  beginning with quantum number n = 1.
§  within an energy level, the
orbitals are filled in the order
s, p, d, f
n = 7 n = 6 n = 5 n = 4 n = 3 n = 2 n = 1 Electron-Dot Symbols
An electron-dot symbol
§  indicates valence electrons
as dots around the symbol of the
element.
§  of Mg shows two valence
electrons as single dots on the
sides of the symbol Mg.
Mg
Mg
Mg
Mg
Mg
Writing Electron-Dot Symbols
The electron-dot symbols for
§  Groups 1A (1) to 4A (14) use single dots:
Na
Mg
Al
C
§  Groups 5A (15) to 7A (17) use pairs and single dots:
P
O
Cl
•  Single/paired dots ARE NOT the same as paired/
unpaired electrons in orbital filling diagrams! # e− 6 1s 2s 2p C Groups and Electron-Dot Symbols
In a group, all the electron-dot symbols have the same
number of valence electrons (dots).
Example: Atoms of elements in Group 2A (2) each have
2 valence electrons.
Group 2A (2)
· Be ·
· Mg ·
· Ca ·
· Sr ·
· Ba ·
Atomic Size
Atomic size §  is described using the atomic radius. §  is the distance from the nucleus to the valence electrons. §  increases going down a group. §  decreases going across a period from le^ to right. Atomic Radius
Ionization Energy
Ionization energy
§  is the energy it takes to remove a valence electron from
an atom in the gaseous state.
Na(g) + Energy (ionization)
Na+(g) + e–
§  decreases down a group, increasing across the periodic
table from left to right.
§  The electron is removed from the last orbital in the
electron configuration
Na: 1s22s22p63s1 C: 1s22s22p2 Ionization Energy and Valence Electrons
• 
E
n
e
r
g
y
The e− in 2p orbitals are: •  aXracted to nucleus •  repelled by 2s (and 1s) e− e− are “shielded” from the nucleus by the e− in lower energy orbitals •  can also think about this as e−-­‐e− repulsion ? 2pz ? 2s nuc Ionization Energy
Increasing Atomic Radius; Decreasing IonizaEon Energy IonizaEon Energy Increases Decreasing Atomic Radius; Increasing IonizaEon Energy The ionization
energies of
§  metals are low.
§  nonmetals are high.
Ionization Energy
•  The ionization energy of Li
> Na > K
•  It is very easy to remove
an e- from K: it is the most
reactive!
Two Kinds of Atomic Symbols
Isotope symbol describes a single atom mass number •  idenEfies the isotope •  gives the mass of the atom 12
6
symbols found in periodic table describes a typical sample made of many atoms 6
C
atomic number C
12.01
Isotopes are a big part of Chapter 4… atomic mass Exam #1: Tuesday, Oct. 23rd •  Exam 1 = 13% of class grade •  Unexcused absence = big problems! •  don’t be late •  don’t miss the exam •  bring a non-­‐graphing, non-­‐phone calculator (see syllabus) CHEM 120 So Far: The Rest of CHEM 120: • 
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Sig Figs Units Atoms Elements Phases of MaXer Periodic Table •  RadioacEvity (Ch.4) •  Chemical Bonds (Ch.5) •  Chemical ReacEons (Ch.6) •  Gases & SoluEons (Ch.7, 8) •  ReacEon Rates (Ch.9) •  Acids & Bases (Ch.10) •  CHEM 220 & 221! Chapter 4: Nuclear Chemistry What is radioacEvity? What makes a substance radioacEve? How do we put radioacEve chemicals to use? Will radioacEve substances give me superpowers? (No) Radioactive Isotopes
A radioactive isotope
§  has an unstable nucleus and usually has an
atomic number above 20.
§  emits radiation to become more stable.
§  can be one or more of the isotopes of an element.
§  is identified by writing the mass number after the
element symbol, such as iodine-131 or I-131.
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Four Types of Radiation (#1 & 2)
Radiation is the energy emitted by an unstable atom
in the process of becoming more stable. It takes the
form of
§  alpha particles, which are identical to a helium
nucleus,
§  beta particles, which are high-energy electrons with
a charge of 1− and a mass number of 0,
© 2013 Pearson EducaEon, Inc. Chapter 4, Section 1
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Four Types of Radiation (#3 & 4)
§  positron, similar to a beta particle with a charge of
1+ and mass number of 0
§  gamma rays, which are high-energy radiation
often emitted with other types of radiation. They
are written with a mass and atomic number of 0.
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Six Types of Radiation Summarized
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Radiation Protection
§  paper and clothing for alpha particles,
§  a lab coat or gloves for beta particles,
§  a lead shield or a thick concrete wall
for gamma rays,
§  limiting the amount of time spent near
a radioactive source, or
§  increasing the distance from the
source.
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Clicker Ques-on: •  Which of the following types of radia-on is the most penetra-ng (the hardest to protect yourself against)? a)
b)
c)
d)
Alpha particles
Beta particles
Positrons
Gamma rays
Fiesta Ware: RadioacEve?! •  The “fiesta red” (orange-­‐red) color was colored by uranium oxide •  Uranium (U) has two major naturally occurring isotopes: 238 U 92 235 U 92 Fiesta Ware: colorful ceramic dinnerware 99.3 % natural abundance 0.7 % natural abundance Both U isotopes emit alpha parEcles (They undergo alpha decay) DetecHng RadiaHon: The Geiger Counter A Geiger counter
§  detects beta and gamma radiation.
§  uses ions produced by radiation to create an
electrical current.
•  If both natural U isotopes undergo a decay, how did we detect them with the geiger counter? TOPICS U-­‐238 Nucleus •  U-­‐238 and U-­‐235 are converted to Th-­‐234 and Th-­‐231 by α decay! •  Thorium-­‐234 and Thorium-­‐231 both undergo β-­‐
decay! Alpha Decay
When a radioactive nucleus
emits an alpha particle, a
new nucleus forms that has
§  a mass number 4 less
than that of the original
nucleus, and
§  an atomic number that
has decreased by 2 from
that of the initial nucleus.
Completing Nuclear Equations
In a completed nuclear equation,
§  the sum of the mass numbers of the unstable
isotope and the products are equal, and
§  the sum of the atomic numbers of the
unstable isotope and the products are equal.
Sum of Mass Numbers
Sum of Atomic Numbers
Beta Decay
When a radioactive
nucleus
emits an beta particle, a
new nucleus forms that
has
§  a mass number equal
to that of the original
nucleus, and
§  an atomic number that
is 1 larger than that of
the initial nucleus.
Gamma Radiation
In gamma radiation,
§  energy is emitted from an unstable
nucleus, indicated by m following the mass
number:
technetium-99m,
§  the mass number and the atomic number
of the new nucleus are unchanged
Gamma radiaEon is the result of “nuclear reorganizaEon”