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Brief Timeline of Atomic Theory
Democritus
• 400BC• Greek philosopher
Hard Particle (Cannonball)Theory
• Proposed that they world was made up of tiny, indivisible particles moving through a void of empty space
• “atom” comes from the Greek word “atomos”, meaning indivisible (cannot be divided)
John Dalton
• 1808 AD• First modern atomic theory
Daltons Atomic Theory
1. All matter is composed of tiny, indivisible particles called atoms
2. All atoms of an element are identical
3. Atoms of different elements are all different
4. Atoms combine in simple ratios to form compounds
J.J. Thomson
• 1897-1904• “Plum Pudding Model”• Cathode Ray tube experiment
• demo
Cathode Ray Tube
• Thompson showed that cathode rays (electrons) were composed of negatively charged particles that separated from the gas atoms inside the tube
• Significant because: this meant that atoms are not hard, indivisible particles. Atoms are composed of smaller “subatomic” particles
Thomson’s Plum Pudding Model
• The atom was a hard sphere that was positively charged with negatively charged electrons that “dotted” the atom like raisins in plum pudding
The discovery of radioactivity
• Henri Becquerel– 1896– Discovered that uranium ore released rays that could expose photographic film
The discovery of radioactivity
• Marie & Pierre Curie– Extracted 2 new elements from uranium (U)ore: radium (Ra) and polonium (Po)
Marie Curie
Ernest Rutherford
Magnetic Field Experiment• Was able to separate
radioactive rays into 2 types: alpha (a) & beta (B)
• Determined that a rays were composed of helium nuclei (He +2 charge)
Gold Foil Experiment (1911)• Lead to discovery of the
nucleus, as a positively charged center of atom, containing the mass
• Most of the atom is negatively charged empty space, electrons are outside the nucleus
Magnetic Field Experiment
Gold Foil Experiment
Gold Foil Experiment
Rutherford’s Atomic Model
Rutherford’s “Nuclear Model”
• Most of the atom is negatively charged empty space, surrounding a small, positively charged nucleus, containing most of the mass of the atom
Modern Theory of Atomic Structure
• Developed by Niels Bohr, based on the science of nuclear physics
• Bohr determined that an element's position on the periodic table was related to its electron configuration.
Electron configuration
Electron configuration – shows how many electrons are in each energy level or “ring”
• Ex: Carbon 2-4
Bohr’s Planetary Atomic Model
• Niels Bohr (1922)• Determined that electronsrotate around the nucleusin discrete paths or rings
Planetary Model of Atomic Structure
Wave-Mechanical Model
• Current (modern) theory of atomic structure
• Moseley used x-ray analysis to calculate an integer for each element: these integers are the atomic numbers
Wave-Mechanical Model
• There is a tiny, dense positively charged nucleus at the center of a huge negatively charged electron cloud
Wave-Mechanical Model
Orbital
• Region of probability of finding an electron
“The whole point:”
• The modern model of the atom is the result of many investigations that have been revised over a long period of time by many scientists
• Atomic theory song
Place the models of atomic structure in order from earliest to the modern theory:
Basic Atomic Structure
• The nucleus occupies less than 0.01% of the total volume of an atom but accounts for 99.97% of its mass. Thus most of an atom is EMPTY SPACE where the ELECTRONS are found, this is called an ELECTRON CLOUD.
• One atomic mass unit is 1/12TH THE MASS OF A CARBON-12 ATOM. This is the standard by which the masses of all other elements are determined. It is abbreviated “u”.
Subatomic Particles
Atomic Number
Mass Number NuclearCharge
# ofProtons
# of Neutrons # of electrons
2713Al
3517Cl
11H
20782Pb
Use your Periodic Table to complete the following:
The only number that never changes for an element is
ATOMIC NUMBER
!!
Name Symbol Atomic Number
Mass Number
Charge # ofProtons
# of Neutrons
# of electrons
199F 0
Helium-4 0
11 23 0
Nitrogen-14 0
0 14 14
32 0 16
6429Cu 0
25 0 35
0 81 56
53 131 0
0 53 74
Atomic Structure 1
Name-mass Symbol Atomic Number
Mass Number
Charge # ofProtons
# of Neutrons
# of electrons
Flourine-19 199F 9 19 0 9 10 9
Helium-4 42He 2 4 0 2 2 2
Sodium-23 2311Na 11 23 0 11 12 11
Nitrogen-14 147N 7 14 0 7 7 7
Silicon-28 2814Si 14 28 0 14 14 14
Silicon-32 3216Si 16 32 0 16 16 16
copper-64 6429Cu 29 64 0 29 35 29
Manganese-60 6025Mn 25 60 0 25 35 25
Barium-137 13756Ba 56 137 0 56 81 56
Iodine-131 13153I 53 131 0 53 78 53
Iodine-127 12753I 53 127 0 53 74 53
Atomic Structure 1
Phosphorus-32 0
146C 0
Potassium-39 0
16 0 8
5626Fe 0
18 40 0
0 29 35
79 197 0
2412Mg 0
**Shade the columns representing the nucleons light blue
ISOTOPE
• Forms of the same element having different mass due to different number of neutrons.
• Indicated by “element name-mass”
158O 16
8O
Name: _______________
Mass: ________________
Protons: ______________
Neutrons: _____________
Name: _______________
Mass: ________________
Protons: ______________
Neutrons: _____________
Practice:Name Symbol Atomic # Mass # # Protons # Neutrons # Electrons
235U
238U
Carbon-12
Carbon-13
The mass number on the periodic table indicates the weighted average of all the naturally occurring isotopes of an element
To calculate a weighted average:
% X mass + % X mass + …..100 100
Neon is naturally found in nature having 90.51% mass of 20.00u, 0.24% mass of 21.00u and 9.22% mass of 22.00u. Calculate the weighted atomic mass of neon.
1.) Uranium is found naturally in nature as 3 isotopes: isotope mass % abundance U-238 238.05g 99.28 U-235 235.04g 0.7110 U-234 234.04g 0.0054
Calculate the weighted average atomic mass of the elements below. Show all work, round to the nearest hundredth.
a.)99.63%14N & 0.37%10N
b.)69.1%63Cu (actual mass of 63.93g) & 30.9%65Cu (actual mass of 64.93g)
c.)78.9%24Mg, 10.00%25Mg & 11.01%26Mg
You can estimate which isotope is found in the highest abundance as the one with a mass closest to the mass
listed on the periodic table
Example: Chlorine-35 mass 34.969g Chlorine-37 mass 36.966g
Look on the periodic table for the mass of chlorine ____________________________
The more abundant isotope has a mass closer to the mass given on the periodic table:_____________
Practice: Which isotope of silicon would be found in the highest percentage?
2814Si, mass 27.977 29
14Si, mass 28.976 3014Si, mass 29.974
Why?
Atomic Structure 2Isotopic Notation Number of
protonsNumber of neutrons
Number of electrons
Mass number
1.Oxygen-16 O-16 16O 2.Oxygen-18 3. Ar-40 4. 18 18 5. 16 326. 34S 7. 19 20 8. 19 419. Iron- 10. 57Fe 11. 26 32 12. Ne-20 13. 10 2214.Hydrogen- 115. H-2 16. 3H
2.) Calculate the weighted average of the following naturally occurring isotopes. SHOW ALL WORK!
a.) 95.50%7Li & 7.50% 6Li d.) 99.63%14N & 0.37%15N
b.)80.20%11B & 19.80%10B e.) 78.9%24Mg, 10.00%25Mg, & 11.01%26Mg
c.)95.02%32S, 0.75%33S, & 4.21%34S f.) 92.23%28Si, 4.67%29Si, & 3.10%30Si
Changes in number of subatomic particles
Isotopes• Change in number of
neutrons• Same atomic number,
different mass• Same number protons,
different number neutrons
Ions• Change in number of
electrons
• A cation is positive ion, results from loss of electrons, reducing radius
• An anion is negative ion, results from gain of electrons, increasing radius
IONS
• A charged part of an atom, resulting from the loss or gain of electrons
• VALENCE electrons: outermost electrons, the last number in an electron configuration
• KERNEL electrons: all electrons except valance electrons
Electron configuration
Electron configuration – shows how many electrons are in each energy level or “ring”
• Ex: Carbon 2-4
Electron configuration of sodium:
2 diagrams of atomic structure:Bohr diagrams Lewis electron dot diagrams
Bohr realized that the rows on the periodic table corresponded to the number of shells of electrons
Lewis realized that the groups/families on the periodic table correspond to the number of valence electrons
This model shows the nucleus, indicating the number of protons and neutrons, surrounded by rings, representing each energy level
This model shows the element symbol surrounded by dots, representing the valence electrons. You must place one dot at each (3, 6,9,12 o’clock) location before “doubling up” (exception: Helium)
18
9F electron configuration 2-7
F electron configuration 2-7
1 18
1 Bohr Atomic Structures tables to fill in the electron 4
configurations, as shown, then
draw the Bohr Atomic Structure
for each element 1-20.
1 2
1 2 13 14 15 16 17 2
7 9 11 12 14 16 19 20
3 4 5 6 7 8 9 10
2-1 2-2 2-3 2-4
23 24 27 28 31 32 35 40
11 12 13 14 15 16 17 18
2-8-1 2-8-2 2-8-3 2-8-4
39 40 Rules:
1.) Show placement 2.) The nucleus is 3.) Indicate the number
of ALL electrons represented by a center of electrons in each
circle showing the energy level, by writing
*use atomic # # of protons & the the number on each ring.
19 20 OR the entire # of neutrons
2-8-8-1 2-8-8-2 electron configuration ** closest to nucleus is 1st
1 Directions:use your reference 181 LEWIS Electron Dot Structures tables to fill in the electron 2
configurations, as shown, then
draw the Lewis Dot Structure
for each element 1-20.
1 2 13 14 15 16 173 4 5 6 7 8 9 10
2-1 2-2 2-3 2-411 12 13 14 15 16 17 18
2-8-1 2-8-2 2-8-3 2-8-419 20 Rules:
1.) Only show 2.) Electrons are represent- ex: 3.) You must place 1 dot(e-) 4.) Exception is row 1:
outermost(VALENCE) ed as dots, placed at the at each location before for element #2, indicate
electrons 12 you double up. both electrons at the 12
*use group # 12,3,6,9 o'clock location.
or the last # in the around the
2-8-8-1 2-8-8-2 electron configuration element symbol.
2 Main Types of Ions:
anion
A negative ion
Ex: Cl-, O-2
cation
A positive ion
Ex: Na+, Al+3
The octet rule
Atoms will gain or lose electrons in order to have a full valence shell of 8 electrons.
Exception: Helium can have a maximum of 2 valance electrons
When an atom gains 1 or more electrons
It becomes a negative ion and it’s radius increases. A negative ion is an anion.
When an atom loses 1 or more electrons
It becomes a positive ion and it’s radius decreases. A positive ion is a cation.
CATION ANION Definition
Results from
Indicated by What happens to radius???
Na Na+
Naming
Lewis Dot Structure
CATION ANION
Definition
positive ion negative ion
Results from
Loss of electron(s) Gain of electron(s)
Indicated by (+) charge (-) charge
What happens to radius???
Gets smaller Gets bigger
Na Na+
Naming
“Element name-ion” Change ending of element to “-ide”
Lewis Dot Structure [Na] + ..
[:.F.:]-
How to predict if an element will form an anion or cation:
The “electron clock”:
8/07 16 25 3
4
# valance electrons
Atomic Structure 3: Predicting Ions
ElementElectron
configuration
Lewis dot structure of
atomLose or gain electrons?
How many electrons lost
or gained?Ionic Charge
**
Lewis dot structure of
ion
Radius increase or decrease?
F 2-7 F gain 1 -1 F increase
Mg 2-8-2 Mg lose 2 +2 Mg decrease
O
Al
N
Fr
C
2-8-8-1
2-8-7
2-8-18-18-8-2
2-8-6
2-8-5
2-3
**In the “ionic charge” column only: shade the cation charges red and the anion charges blue
ElementElectron
configuration
Lewis dot structure of atom
Lose or gain
electrons?
How many electrons
lost or gained?
Ionic Charge
**
Lewis dot structure of
ion
Radius increase or decrease?
# of
Protons# of
Neutrons# of
ElectronsNuclear Charge
Bohr Diagram of Atom
Lewis Dot of Atom
PredictIonic
Charge
Lewis Dot of
IonName of Ion
ex 3517Cl 17 18 17 +17 Cl -1 Chloride
1 2311Na
2 94Be
3 6530Zn
4 147N
5 3216S
6 2010Ne
7 12753I
8 10847Ag
9 7031Ga
10 126C
Atomic Structure 4
Atomic Spectra
Radiant Energy
• Energy that travels through space as electromagnetic waves at the speed of light
Electromagnetic Spectrum• Includes all types of radiant energy from
gamma rays (hi E) to radiowaves (lo E)• Visible light is only a small portion of the
spectrum
1 photon = 1 quantum
Quanta: tiny packets of energy released or absorbed by objects
*Einstein and Plank determined that energy is released or absorbed in a continuous flow of small packets or quantum/photons
Release or Absorption of Energy:
Higher energy levels(excited state)
Electrons absorb energy when jumping to
Electrons release energy when falling to
Lower energy levels(ground state)
Bohr used the emission spectrum as proof of planetary model
But his model only works for hydrogen because he didn’t account for electrons moving between energy levels
Spectral Lines
Characteristic wavelengths (l) of photons of energy released as electrons fall from hi to lo energy
Spectral lines demo:Salt of Element Color of Flame
Strontium Chloride
Barium Chloride
Copper (II) Chloride
Lithium Chloride
Potassium Chloride
Identity
Unknown Element
Unknown Mixture
Emission Spectrum:
Each element has it’s own characteristic spectrum:
Compare H & He:
hydrogen helium
Because electrons do move between energy levels, emitting “spectral lines”, we had to change our view of atomic structure:
Excited State Electron ConfigurationsOccurs when elements absorb energy and jump to a higher energy level.
** it will not look like it is written on periodic table, be sure they add to the correct number!
Ground state: 2-8-1Excited state : 2-7-2
“Crib Sheet”• #p+ = atomic number *#n0 = mass-atomic
number• #e- = #p+ - charge (use the sign of the charge)• Isotope: same #p+, different #no OR same
atomic number, different mass• To calculate weighted average: (%/100 x atomic
mass) + (%/100 X atomic mass) + …..• *Ion: same # p+, different #e-
• Charge= #p+ - #e-
Atomic Structure Review p. 17
1. 112. 93. 434. 925. 1186. 137. 118. 4
9. Br10. C11. Sn12. Zn13. Cl14. 4015. 16
Atomic Structure Review p. 17
16.)
=(.925x7) + (.0750x6)
=6.475 + .45
=6.925
=6.93g
17)
=(.789x24)+(.10x25)+(.1101x26)
= 18.936 + 2.5 + 2.8626
= 24.2986
= 24.30g
Atomic Structure Review p. 18
18.) 2-8-119.) Na20.) 2-7-221.) 1922.) 123.) Y24.) Ar25.) Not possible
27.) as electrons fall from excited state to ground state energy is released as radiant energy (spectral lines).28.) you can ID the gas element using spectral line analysis.29.) electrons are negatively charged particles. B has 5 e-, its e-config. is 2-3, with 2 e- in the 1st energy level and 3 e- in the 2nd (valence) level
Atomic Structure Review MC?s1.) 2 13.) 12.) 4 14.) 43.) 1 15.) 14.) 1 16.) 35.) 3 17.) 46.) 1 18.) 37.) 4 19.) 28.) 2 20.) 29.) 4 21.) 310.) 311.) 412.) 3 pg 19-20
1.) 4 13.) 22.) 3 14.) 43.) 2 15.) 34.) 3 16.) 35.) 2 17.) 26.) 3 18.) 17.) 1 19.) 18.) 2 20.) 49.) 3 21.) 410.) 1 22.) 211.) 3 23.) 312.) 1 pg 21-22
Atomic Structure Review p. 23
1.) 19p, 20n, 18e 2.) 9p,10n,10e3.) 5p,6n,2e 4.) 15p,16n,18e5.) 16p,16n,18e 6.) 14p,14n,10e7.) 7p,7n,10e 8.) 20p,20n,20e9.) 37p,48n,36e 10.) 53p,75n,54e11.) 30p,35n,28e 12.) 6p,6n,10e