Atomic Theory Review
Who was the Greek scientist who started the atomic theory? What was his statement about the atom?
Dalton picked up the theory of the atom in the 1800’s. What were his five principles of atomic theory?
What is the law of definite proportions?
What is the law of multiple proportions?
What is the Law of Conservation of Matter?
How was the cathode ray used to discover the electron? Include a simple sketch.
What was Rutherford’s experiment, and what did he conclude from it?
How did Bohr extend the atomic theory?
What are the masses, charges, and positions of electrons, neutrons, and protons?
What is an isotope? Give examples of multiple isotopes of the same element and explain how they are different.
What are the parts of the nucleus and what holds them all together?
In general, what would make the nucleus of an atom unstable?
Write the symbol and name formats for the following atoms
Aluminum with 16 neutrons and 10 electrons
Rubidium with 49 neutrons and 36 electrons
Bromine with 49 neutrons and 36 electrons
Draw a Bohr model for the following elements
+2
12Mg 26
33
P15 -3
17
Cl36
Determine the molar mass for the following
Vanadium
Indium
Zirconium
C6H12O6
H2O2
Fe2(SO4)3
212.45 g C6H12O6
189.01 g Fe2O3
How many atoms or molecules in
87.13 g Silicon
What is the name of a positive ion? a negative ion?
What is the average atomic mass of Tungsten if the following is true; Tungsten 182 is 12%, Tungsten 183 is 79%, and
Tungsten 185 is 9%?
What are the percentages for Calcium 40 (39.978) and Calcium 42 (41.969)?
How many electrons can each energy level hold?
How are atomic mass and mass number similar? Different?
Explain what physical change is and give an example.
Explain what chemical change is and give an example.
If there is a sample with 6.7X1024 atoms of Neon, how much mass does this have? Use significant figures in your answer.
What is Avagadro’s number? What is it used to calculate?
Explain fusion and give an example of a fusion reaction.
Explain fission and given an example of humans using fission.
Explain what is meant by half-life.
Draw a simple graph of typical nuclear decay (using half-lifes as the time unit and grams as the sample size)
If the half-life of Carbon-14 is 5,730 years, how long will it take for a 20 g sample to decay to less than 1 g of carbon-14?
Atomic Theory Review - KEY
Who was the Greek scientist who started the atomic theory? What was his statement about the atom?
Democritus – he said that you can keep cutting until you reach a point where it can’t be cut anymore, not because of
size, but because it can’t be cut – “atomos” in Greek
Dalton picked up the theory of the atom in the 1800’s. What were his five principles of atomic theory?
1)all matter is made of atoms
2) all atoms of the same element are identical
3) atoms of different elements are different
4) atoms can not be broken
5) chemical reactions are combining, separating, or rearranging atoms
What is the law of definite proportions?
Atoms combine in whole number ratios (or proportions). Some atoms only combine in one ratio – NaCl, MgO – they
have a definite proportion
What is the law of multiple proportions?
Some elements can combine in more than one set of whole number ratios – H2O and H2O2, CO2 and CO
What is the Law of Conservation of Matter?
Matter (or mass) can not be created or destroyed
How was the cathode ray used to discover the electron? Include a simple sketch.
The ray in the cathode ray tube was attracted or repelled by ends of a magnet – scientists determined it had a
negative charge. Scientists put a paddlewheel in the tube and made the ray hit it. When this happened, the wheel
spun, so the ray had to have some mass.
The object with very little mass and a negative charge was named an electron
What was Rutherford’s experiment, and what did he conclude from it?
Rutherford shot alpha particles at a sheet of gold foil. Most of the particles passed straight through. A few were
deflected, and even fewer bounced back. Rutherford determined that an atom is mostly empty space with a very
small, dense, positive core he called the nucleus. He thought all the electrons were in one circle or orbit around the
nucleus
How did Bohr extend the atomic theory?
Bohr came up with “boring rings” or energy levels. Electrons are in many orbits, not just one as Rutherford thought.
What are the masses, charges, and positions of electrons, neutrons, and protons?
Item
Electron
Mass
Zero
Charge
Negative
Neutrons
Proton
1 amu
1 amu
Neutral
Positive
Position
Around the nucleus in
energy levels
Nucleus
Nucleus
What is an isotope? Give examples of multiple isotopes of the same element and explain how they are different.
Carbon-12 and Carbon-14 are isotopes. Carbon-12 has a mass of 12, Carbon-14 has a mass of 14. They both have 6
protons. Carbon 12 has 6 neutrons while Carbon-14 has 8 neutrons.
What are the parts of the nucleus and what holds them all together?
The nucleus is made of protons and neutrons. The strong nuclear force is what holds them all together.
In general, what would make the nucleus of an atom unstable?
Stable atoms have a proton:neutron ratio of 1:1 to 1:1.5. either side of this ratio is not stable.
Write the symbol and name formats for the following atoms
Aluminum with 16 neutrons and 10 electrons
+3
13Al29
Aluminum 29 with a charge of +3
Rubidium with 49 neutrons and 36 electrons
37
Rb86+1 Rubidium 86 with a charge of +1
Bromine with 49 neutrons and 36 electrons
94
Br35-1 Bromine 94 with a charge of -1
Draw a Bohr model for the following elements
+2
12Mg 26
-8e-2e12 P
14N
33
P15 -3
17
Cl36
-8e-8e-2e15P
18N
-7e-8e-2e17P
19N
Determine the molar mass for the following
Vanadium
Indium
Zirconium
50.94 g/mol
114.82 g/mol
91.22 g/mol
C6H12O6
H2O2
Fe2(SO4)3
180.18 g/mol
34.02 g/mol
399.73 g/mol
87.13 g Silicon
212.45 g C6H12O6
189.01 g Fe2O3
1.87E24
7.10E23
7.13E23
How many atoms or molecules in
What is the name of a positive ion? a negative ion?
Positive ion is a cation, negative ion is an anion
What is the average atomic mass of Tungsten if the following is true; Tungsten 182 is 12%, Tungsten 183 is 79%, and
Tungsten 185 is 9%?
182 x .12
183 x .79
185 x .09
183.06 amu
What are the percentages for Calcium 40 (39.978) and Calcium 42 (41.969)?
X(39.978) +(1-x)(41.969) = 40.078\
X=.9498
Calcium 40 is 94.98%
Calcium 42 is 5.02%
How many electrons can each energy level hold?
1st = 2e
2nd = 8e
3rd = 18e
4th = 32e
How are atomic mass and mass number similar? Different?
Both are the result of protons and electrons. Atomic mass is the average for all isotopes, mass number is the mass on
one particular atom or isotope.
Explain what physical change is and give an example.
Physical change is a change in size, shape, or phase. It does not change what the material is. Phase change, cutting,
flattening – all change what it looks like without changing what the material is.
Explain what chemical change is and give an example.
Chemical change changes what a material is, atoms have changed their bonds. Burning, reacting with acid, rusting,
leaves decomposing – all change what atoms are bonded to, change the material into a different chemical.
If there is a sample with 6.7X1024 atoms of Neon, how much mass does this have? Use significant figures in your answer.
(6.7X1024 atoms Ne)(1 mol Ne/6.022X1023 atoms Ne)(20.18 g Ne/1 mol Ne) = 224.52 g Ne
Only 2 significant figures (use the measurement) = 220 g Ne
What is Avagadro’s number? What is it used to calculate?
6.022X1023 atoms/1 mol – this is used to convert between atoms and moles
Explain fusion and give an example of a fusion reaction.
Fusing or combining two or more atoms into one atom – happening in stars
Our sun takes 4 hydrogen atoms and fuses them into 1 helium atom
Explain fission and given an example of humans using fission.
Splitting of atoms – nuclear bombs and nuclear power plants
We split uranium or plutonium
Explain what is meant by half-life.
The amount of time it takes for ½ of a sample to decay
Draw a simple graph of typical nuclear decay (using half-lifes as the time unit and grams as the sample size)
Exponential curve – like the skittle lab
If the half-life of Carbon-14 is 5,730 years, how long will it take for a 20 g sample to decay to less than 1 g of carbon-14?
It takes 5 half lives, so it would take 28,650 years.