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Transcript of Chapter 4: Glow in the Dark. Glow in the dark This chapter will introduce the chemistry needed to...
Glow in the dark
This chapter will introduce the chemistry needed to understand how glowing things workSection 4.1: History of the atomSection 4.2: Atomic Structure/Bohr ModelSection 4.3: Electron StructureSection 4.4: Periodic tableSection 4.5: PeriodicitySection 4.6: Light & Matter
Section 4.2 Atomic Structure
The atom is defined as the smallest particle of an element that retains the properties of that element.
It consists of 2 regions & 3 sub-atomic particles
What’s in an atom?
An atom is made of three sub-atomic particles
Particle Location
Nucleus
Nucleus
Outside the nucleus
Mass
1 amu = 1.6710-27 kg
1 amu = 1.6710-27 kg
0.00055 amu
9.1010-31 kg
Charge: Fix
+1
0
-1
Proton
Neutron
Electron
1 amu (“atomic mass unit”) = 1.66 10-27 kg
The TWO Regions of the Atom
Electron Cloud: contains electrons and mostly empty space
: dense center containing the protons & neutrons
Counting Subatomic Particles: Mass Number
The total number of protons + neutrons in the nucleus is called the mass number.
To calculate mass number: 2 options
1. Round atomic mass from periodic table
to a whole number Nitrogen’s atomic mass = 14.01 amu
mass # = 14
2. Add the # protons and # neutrons of an
atom together
Mass # = protons + neutrons
Counting Subatomic Particles: Atomic Number
Every atom has a different number of protons which determines the identity of the atom
The atomic number shows the number of protons. Atomic number = protons
To get the Atomic Number: Find the whole number of the element from the periodic table
Nitrogen’s Atomic # = 7
Counting Subatomic Particles: Number of Neutrons
To calculate the number of neutrons: 2 options
1. Subtract the atomic number from the mass number
2. Subtract the proton# from the mass #
# Neutrons = Mass # - Atomic #
14 -7 = 7 neutrons
Neutral Atoms vs Charged Atoms (IONS)
A neutral atom has the same number of protons and electrons
A ion has a different number of protons and electrons leaving it with a charge.
How to calculate number of electrons:Subtract electron number from proton
number.
Overall Charge = protons - electrons
-1 = 35 - electrons
Atomic number for Br = 35 = # of protons
Charge = -1
Electrons = 36
Determining the Number of Electrons
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:How many electrons does Br-1
have?
+3 = 13 - electrons
Atomic number for Al = 13 = # of protons
Charge = +3
Electrons = 10
Determining the Number of Electrons
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:How many
electrons does Al+3 have?
XA C
Z
Displaying Information of atoms: Nuclear Symbol
Charge# protons - # electrons(assumed to be “0” if blank)
Element Symbol1 or 2 letters, found on
the periodic table
Mass number# protons + # neutrons
Atomic number # of protons
Example: Nuclear symbol
O16 -2
8
Charge-2
Element SymbolO = Oxygen
Mass number16
Atomic number 8
8 p
10 e
8 n
Self Check
What are the number of protons, neutrons & electrons in each atom?
19F-1 57Fe 204Hg 9 26 80
9 p10 e10 n
26 p26 e31 n
80 p 80 e124 n
Displaying Information of atoms: Hyphen notation
NuclearSymbol
Hyphen Notation
Atomic #
Mass #
Charge Proton Neutron Electron
Magnesium-25 +2
82 126 82
copper – 65 mass number
Element Name
Find the Missing Values
Let’s Practice
Nuclear Symbol
Hyphen Notation
Atomic #
Mass #
Charge Proton Neutron Electron
Magnesium -25 +2
82 126 82
Remember: Atomic number is the identityAtomic number = protonsCharge = proton - electronsMass # = protons + neutrons
12 25 12 13 10
Lead-208 208 0 82
22512
Mg
Pb20882
How do Atoms Differ?
Isotopes– are atoms of the same element with a different number of neutrons or mass number
Some isotopes are radioactive—but not all…many are quite stable!
Most elements contain a mixture of 2 or more isotopes. Each one having its own
mass and abundance.
Identifying Isotopes
12C 13C
Carbon-12 Carbon-13
Isotopes can be differentiated by their different mass numbers in the element symbol
Or by the mass number following their name.
Mass Number versus Atomic Mass
Mass Number Average Atomic Mass
# of protons + # of neutrons Average of actual masses
For one specific isotope only
Is not found on the periodic table
Weighted average of all isotopes
Is found on the periodic table
Always a whole number Not a whole number
Calculating aWeighted Average!
Practice Problems:(1) Mrs. Soto’s chemistry semester grades are calculated using a
weighted average of three category scores: Major Grades= 60% of your gradeMinor Grades= 30% of your gradeSemester Exam=10% of your grade
• If a student had the following scores, what would they receive for the semester?
Major= 80 Minor= 60
Semester Exam=65
Weighted AverageStep (1): Multiply each score by the % that it is weighted.Step (2): Add these products up, and that is the weighted average!
60% x 80 = 48.030% x 60 = 18.0
10% x 65 = 6.5 Add them up!!
A “normal average” would be calculated by simply adding the raw scores together and dividing by 3…
80 + 60 + 65 = 205 ÷ 3 = 68.3 = D
+
72.5
Calculating Average Atomic Mass
Average atomic mass
= Abundance of isotope
Mass of isotope
( )
Average atomic mass is a weighted average of the masses of all naturally occuring isotopes.
“Sum of”
What fraction of the time is that isotope present?
Actual mass (not mass number)
Example of Finding Average Atomic Mass
966.362422.0969.347578.0 amuMassAvg
Example:Find the atomic mass of
chlorine Chlorine-35 has a mass of 34.969 amu.Chlorine-37
has a mass of 36.966 amu & is 24.22% abundant.
Remember that percents add up to 100.
So they said the second isotope is present 24.22% of the time.
This means that the first isotope is present 100 -24.22 = 75.78% of the time
Isotope Mass Percent Decimal
1 34.969 amu 75.78 0.7578
2 36.966 amu 24.22 0.2422
This chart summarizes the information in the problem:
= 35.45 amu (this is what’s on the periodic table for Cl!)
SELF CHECK! Example:Element X has 2 natural isotopes. Calculate the average atomic mass. 1st isotope has a mass of 10.012 a.m.u with 19.91% abundance. 80.09% of the 2nd element has a mass of 11.009 a.m.u.
Isotope Mass Percent Decimal
1 10.012 amu 19.91 .1991
2 11.009 amu 80.09 .8009
This chart summarizes the information in the problem:
= 10.81 amu (Element X is Boron!)
SELF CHECK !
Example:Calculate the average atomic mass of copper if it has 2 isotopes. 69.11% has a mass of 62.93 a.m.u and the rest has a mass of 64.93 a.m.u.
Remember that percents add up to 100.
So they said the first isotope is present 69.11% of the time.
This means that the second isotope is present 100-69.11 = 30.89% of the time
Isotope Mass Percent Decimal
1 62.93 amu 69.11 .6911
2 64.93 amu 30.89 .3089
This chart summarizes the information in the problem:
= 63.55 amu
Lets focus in on the electrons in the electron cloud!
Niehls Bohr performed experiments with hydrogen & light.
Electron are in ENERGY LEVELS according to how much energy they have. Only certain energy amounts are allowed.
Think of the energy levels as rungs of a ladder. The farther away an energy level is from the nucleus, the more Energy it attains!
Electrons can move from one energy level to the next by gaining or losing energy (quanta).Ground State: An electron is as close to the nucleus as it can get.
Excited State: An electron in a higher energy level than it should be.
Bohr believed electrons were located in Energy Levels (SHELLS)
“excited state”
“groundstate”
Bohr Models: show how the electrons are situated within the energy levels
http://www.youtube.com/watch?v=Cn6v5ygyZHQ A maximum of 2 electrons are placed in the first shell. A maximum of 8 electrons are placed in the second shell. A maximum of 18 electrons are placed in the third shell. Only 8 electrons can be placed in the 3rd shell at first, then 2 electrons will move into the 4th shell and remaining electrons will be placed back in the 3rd shell until the max of 18.
**(Just know this : it will be explained in the next section)** A maximum of 32 electrons are placed in the 4th shell.
***Valence Electrons are the outermost electrons found in the highest, outermost energy level of the atom***
Lewis Dot DiagramsA way to show the valence electrons in an atom. The symbol represents the nucleus and inner core
electrons. The dots represent the valence electrons.
Only 2 dots per side. Only 4 sides. Maximum of 8 valence electrons.
Add dots one at a time on each side until each side is full. Then add a second dot to make a pair when needed. Exception is Helium. It can look like this:
He: or He
1920: Bohr Models are not accurate! Let me introduce you to the Quantum Mechanical Model
Bohr Models are still used to simplify the atom. HOWEVER
Modern atomic theory uses calculus equations to show how the subatomic electrons act as both particles and waves
These equations show the most probable location of electrons in the atom (known as atomic orbitals)
Quantum Mechanical Model
In theory, we really don’t know the exact location of an electron. We can only estimate the likelihood of it being in a certain region ofspace called an orbital
Protons, Neutrons & Electrons Wksht
Symbol Atomic# Protons Neutrons Electrons Mass #
B 5 5 6 5 11
Na 11 11 13 11 24
Ga 31 31 37 31 68
Y 39 39 50 39 89
Cu 29 29 35 29 64
Tc 43 43 57 43 100
Pb 82 82 125 82 207
Protons, Neutrons & Electrons Wksht
Symbol Atomic# Protons Neutrons Electrons Mass #
Yb 70 70 102 70 172
Ac 89 89 136 89 225
Mo 42 42 53 42 95
Tl 81 81 125 81 206
Fm 100 100 159 100 259
No 102 102 159 102 261
Yb 70 70 102 70 172
Sg 106 106 159 106 265
Atom Wksht : Isotopes
Hyphen Notation Nuclear Symbol
Atomic #
Mass #
protons electrons Neutrons
Carbon-13 C 6 13 6 6 7
Sodium-23 11 23 11 11 12
Iodine-126 53 126 53 53 73
Neon-20 10 20 10 10 10
Phosphorus-31 15 31 15 15 16
Magnesium-25 12 25 12 12 13
Atom Wksht : Isotopes
Hyphen Notation Nuclear Symbol
Atomic #
Mass # protons electrons Neutrons
Lead-206 Pb 82 206 82 82 124
Mercury-202 Hg 80 202 80 80 122
Strontium-90 Sr 38 90 38 38 52
Hydrogen-1 H 1 1 1 1 0
Hydrogen-2 H 1 2 1 1 1
Uranium-238 U 92 238 92 92 146
Uranium 235 U 92 235 92 92 143
Ion Wksht: Part III
Ion Symbol Atomic Number
Mass # protons electrons neutrons Nuclear charge
F-1 9 19 9 10 10
Al-+3 13 27 13 10 14
Ca+2 20 40 20 18 20
S-2 16 32 16 18 16
P-3 15 31 15 18 16
K+1 19 39 19 18 20
Br-1 35 80 35 36 45
Se-2 34 79 34 36 45
Fe+3 26 56 26 23 30
Atomic Dimensions: Element Sym
bolAtomic #
Mass # P+ N e- Isotope, ION, or Neutral atom
Aluminum Al 13 27 13 14 13 n. atom
Bromine Br 35 80 35 45 36 ion
Uranium U 92 238 92 146 92 N atom
Helium He 2 4 2 2 2 isotope
Helium He 2 5 2 3 2 isotope
Lithium Li 3 7 3 4 2 ion
Tungsten W 74 184 74 110 74 N atom
Xenon Xe 54 133 54 79 54 Neutral Atom
Magnesium Mg+2 12 24 12 12 10 Positive ion
Atomic Dimensions: Element Symb
olAtomic #
Mass # P+ N e- Isotope, ION, or Neutral atom
Carbon C 6 12 6 6 6 Neutral atom
Carbon C 6 14 6 8 6 isotope
Nitrogen N 7 14 7 7 7 N atom
Restaurant
The story of the Electron Hotel
A man built an hotel for electrons with a restaurant next door.
But he was making so much money that he decided to add on with some more rooms and a parking garage.
He still had high demand and decided to add on some more rooms and a shopping center.
He used the last space he could to put some rooms above the shopping center.
Parking GarageShopping Center
Restaurant
How the Electron Hotel Fills
This man had some very strange ideas about how to run his hotel. He insisted four things:
• The lowest possible must be used first (actually it was the fire inspector that insisted on this one)
• There can only be one person in a room until all rooms at that level have someone
• No more than 2 people to a room• When two people are in a room, they must be of opposite sex
If 8 people come to the hotel, where would he put them?
Parking GarageShopping Center
RestaurantParking Garage
Another Example
This man had some very strange ideas about how to run his hotel. He insisted four things:
• The lowest possible must be used first (actually it was the fire inspector that insisted on this one)
• There can only be one person in a room until all rooms at that level have someone
• No more than 2 people to a room• When two people are in a room, they must be of opposite sex
If 21 people come to the hotel, where would he put them?
Shopping Center
RestaurantParking Garage
Shopping Center
SELF CHECK!
This man had some very strange ideas about how to run his hotel. He insisted four things:
• The lowest possible must be used first (actually it was the fire inspector that insisted on this one)
• There can only be one person in a room until all rooms at that level have someone
• No more than 2 people to a room• When two people are in a room, they must be of opposite sex
If 42 people come to the hotel, where would he put them?
Electron Clouds
They don’t live in a hotel…They are in the area outside of the nucleus where the electrons reside.
Electron Clouds
Electron cloud
Principal energy levels
(shells)
Sublevels(subshells)
Orbitals
The electron cloud is made of energy levels.
Energy levels are composed of sublevels.
Sublevels have orbitals.
Electron Hotel
Which floor of the hotel
Which area of the hotel?
Which room?
Energy Levels
There are 7 energy levels. The period number on the periodic table
correlates to the energy level
Ca has electrons up to energy level 4
Cl has electrons up to energy level 3
Sublevels(subshells): a set of orbitals with equal energy
“S” subshell
Spherical shapedOnly 1 orbital (orientation/position) in 3-D spaceFirst seen in the 1st energy levelCan hold a maximum of 2 electronsRepresented on the periodic table as groups 1A and 2A + helium
“P” Subshell
Dumbbell shapedThere are 3 orbitals(positions in 3-D space)First seen in the 2nd energy levelCan hold a maximum of 6 electronsRepresented on the periodic table as groups 3A -6A
“D” Subshell
Four lobed shapedThere are 5 orbitals First seen in the 3rd energy levelCan hold a maximum of 10 electronsRepresented on the periodic table as the transition metals (group B)
“F” Subshell
Too complex to name shapeThere are 7 orbitalsFirst seen in the 4th energy levelCan hold a maximum of 14 electronsRepresented on the periodic table as the inner transition metals (lower block)
The Most Probable Location for an Electron!
Orbital– Area of high probability of the electron being located.
Each orbital can hold 2 electrons
To calculate the total number of orbitals in an energy level, use 2(n)2
Electron Configuration
Is an address of an electronElectrons must be placed in the lowest energy levels first (ground state)
4p1
Energy Level
# of electrons
subshell
Energy and Subshells
1s
2s
3s
4s
5s
2p
3p
4p
5p
3d
4d
6s
6p5d
4f
Ene
rgy
Subshells are filled from the lowest energy level to increasing energy levels.
Does this look familiar? Electron Hotel!
3 rules that govern electron configurations
Aufbau Principle:Electrons must fill the lowest available subshells and orbitals before moving on to the next higher energy subshell/orbital.
1
Filling order is: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
Can use the periodic table as a guide to fill from lowest to highest sublevels or memorize filling order
An orbital can overlap within different energy levels, such as 4s is lower in energy than 3d
Hund’s Rule
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.
2
How does this work?
If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up.
Pauli Exclusion Principle
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have opposite spins.
3
“Spin” is designated with an up or down arrow.
How does this work?
If you need to add 4 electrons to a p subshell, you’ll need to double up. When you double up, make them opposite spins.
Electron Configurations
Determine the number of electrons to place1
Fill in subshells until they reach their max (s = 2, p = 6, d = 10, f = 14) or use periodic table as a guide.3
Follow Aufbau Principle for filling order2
The total of all the superscripts is equal to the number of electrons.4
0 = 16 - electrons
No charge written Charge is 0
Atomic number for S = 16 = # of protons
Electrons = 161s 2s 2p 3s 3p2 2 6 2 4
2 2 6 2 4+ + + + = 16
Example:Write
electron configuration
for S
Electron Configurations
0 = 19 - electrons
No charge written Charge is 0
Atomic number for K = 19 = # of protons
Electrons = 19
1s 2s 2p 3s 3p62 2 6 2 4s1
2 2 6 2 6 + 1+ + + + = 19
Example:Write electron configuration for K
Electron Configurations
0 = 22 - electrons
No charge written Charge is 0
Atomic number for Ti = 22 = # of protons
Electrons = 22
1s 2s 2p 3s 3p62 2 6 2 4s2
2 2 6 2 6 + 2 + 2+ + + + =22
Example:Write electron configuration for Ti
3d2
What is Orbital Notation?
It shows the grouping and position of electrons in an atom.
The number and configuration of electrons determines how something glows…so it’s important to know “where the electrons live” for an atom!
Orbital Notation use boxes or lines for orbitals and arrows for electrons.
Drawing Orbital Notation (boxes & arrows)
Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum1
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.3
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.2
Example:Write the
orbital notation for
Cl
Drawing Orbital Notations
Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum1
0 = 17 - electrons
No charge written Charge is 0
Atomic number for Cl = 17 = # of protons
Electrons = 17
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.3
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.2
1s 2s 2p 3s 3p
4231567910111213141516178
Example:Write the
orbital notation for
Cl
Drawing Orbital Notations
0 = 7 - electrons
No charge written Charge is 0
Atomic number for N = 7 = # of protons
Electrons = 7
1s 2s 2p
42315679101112131457
Example:Write the
orbital notation for N
Drawing Orbital Notations
0 = 26 - electrons
No charge written Charge is 0
Atomic number for Fe = 26 = # of protons
Electrons = 26
1s 2s 2p 3s 3p4231567910111213141526
Example:Write the
orbital notation for
Fe
4s 3d
Shorthand Notation (Noble Gas Notation)
Noble Gas– Group 8 of the Periodic Table. They contain full valence shells.
Noble Gas Notation– Noble gas is used to represent the core (inner) electrons and only the valence shell is shown.
1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 5
4s 2 3d 10 4p 5[Ar]
BrComplete electron configuration
Noble gas
The “[Ar]” represents the core electrons and only the valence electrons are shown
How do you know which noble gas to use to symbolize the core electrons?
Which Noble Gas Do You Choose?
Think: Price is Right.
How do you win on the Price is Right?
By getting as close as possible without going over.
Choose the noble gas that’s closest without going over!
Noble Gas # of electrons
He
Ne
Ar
Kr
Xe
2
10
18
36
54
Noble Gas Notation Example
Determine the number of electrons to place1
Start where the noble gas left off and write electron configuration for the valence electrons3
Determine which noble gas to use2
Example:Write noble gas notation
for Fe
Noble Gas Notation Example
Determine the number of electrons to place1
Start where the noble gas left off and write spectroscopic notation for the valence electrons3
Determine which noble gas to use2
0 = 26- electrons
No charge written Charge is 0
Atomic number for Fe= 26= # of protons
Electrons = 26
[Ar] 4s 3d2 6
18 2 6+ + = 26Closest noble gas: Ar (18)
Ar is full up through 3p
Example:Write noble gas notation
for Fe
Noble Gas Notation Example
0 = 56 - electrons
No charge written Charge is 0
Atomic number forBa= 56 = # of protons
Electrons = 56
[Xe] 6s 2
54 2+ = 56
Closest noble gas:Xe (54)
Xeis full up through 4p
Example:Write noble gas notation
forBa
Exceptional confuguration
Half-filled or completely filled d & f sublevels have ________ energies and are more stable than partially filled d’s and f’s.
This means that an atom can “borrow” one of its “s” electrons from the previous orbital to become more stable.
___ __ __ __ __ __
5s 4d
becomes
___ __ __ __ __ __
5s 4d
Because the 4d sublevel is now full, the atom is at a lower energy state and therefore more stable.
↓↑ ↓↑ ↓↑ ↓↑ ↓↑ ↑
↑ ↓↑ ↓↑ ↓↑ ↓ ↑ ↑↓
Electron Configuration for Ions
Determine the number of electrons to place. Positive ions lose electrons; negative ions gain electrons.
1
Fill in subshells until they reach their max (s = 2, p = 6, d = 10, f = 14) or use periodic table as a guide.3
Follow Aufbau Principle for filling order2
The total of all the superscripts is equal to the number of electrons.4
-2 = 16 - electrons
Atomic number for S = 16 = # of protons
Electrons = 181s 2s 2p 3s 3p2 2 6 2 6
2 2 6 2 6+ + + + = 18
Example:Write
electron configuration
for S-2