Download Unit 4 Study Guide (Test on Friday 3/10) ANSWER

Unit 4 Study Guide (Test on Friday 3/10) ANSWER KEY
History of the Atomic Theory
1. For each Theorist, explain what they contributed to the discovery of the atom (major discoveries).
ALSO, draw or explain their model of the atom.
DemocritusFirst to propose the atom existed. He called it “atomos,” and claimed they were small particles of matter
that there indivisible and indestructible. He did not have scientific basis for his theory.
DaltonAgreed with Democritus on atoms being indivisible and indestructible. HIs theory stated that atoms of
the same element are all similar, elements can combine to form compounds, and that atoms were tiny
and spherical.
ThomsonFirst to propose that atoms were NOT indestructible (they could be split or separated). He discovered
the electron as a negatively charged particle using cathode rays. Proposed the plum pudding model of
the atom in which electrons were scattered throughout the atom like seeds in a watermelon.
RutherfordPerformed gold foil experiment and discovered two important things about the atom: the nucleus was
positively charged. And atoms were made up of mostly empty space. This would lead him to the
conclusion that protons (being positively charged) and neutrons were in the center of the atom and
made up most of the atom’s mass. And that electrons were spaced out on the outside of the atom,
similar to planets being a certain distance away from the sun and from each other.
BohrProposed a more modern model of the atom in which the electrons were orbiting around the outside of
the nucleus in different energy levels. This model is similar to the planetary model, in which the
electrons represent planets at different distances from the sun. And the nucleus represents the sun.
Higher energy levels are further from the nucleus.
2. For the following elements, identify the atomic number, atomic mass, number of protons, number of
neutrons, and number of electrons.
Fe (Iron)- A.N- 26; A.M- 55.85 amu; Protons- 26; Neutrons- 30; Electrons- 26
Cl (Chlorine)- A.N- 17; A.M- 35.45 amu; Protons- 17; Neutrons- 18; Electrons- 17
Pd (Palladium)- A.N- 46; A.M- 106.42 amu; Protons- 46; Neutrons- 60; Electrons- 46
Rb (Rubidium)- A.N- 37; A.M- 85.47 amu; Protons- 37; Neutrons- 48; Electrons- 37
3. For the following isotopes of each element, label the number of protons, number of neutrons, and
number electrons. ALSO, draw a Bohr model (planetary model) for at least one of each isotope.
●
12
C
13
C
14
C
C-13 would have 6 protons and 7 neutrons in the center closely packed together. There would be 2
electrons in the first energy level and 4 electrons in the second energy level.
The only number of particles that changes is neutrons!!! Electron and proton numbers stay the same
with each isotope!
47
48
● 46Ti
Ti
Ti
Ti-47 would have 22 protons and 25 neutrons in the center closely packed together. There would be 2
electrons in the first energy level, 8 electrons in the second energy level, and 12 electrons in the third
energy level.
The only number of particles that changes is neutrons!!! Electron and proton numbers stay the same
with each isotope!
4. What changes with each isotope?
ONLY NEUTRONS
5. How do you know which isotope will be labeled on the periodic table?
The atomic mass that appears on the periodic table for each element is a weighted average of all
isotopes. The most common isotope is more likely to appear than one that is least common or least
abundant.
6. Convert the following using dimensional analysis. Label units and elements. And show ALL work!
●
Convert 3.55 moles of NaCl to atoms.
3.55 x (6.01 x 10^23) = 2.13 x 10^24 atoms NaCl
●
What is the mass of 9.30 moles of SiH4? (molar mass of 32 g)
9.30 x 32 = 297.6 g SiH4
●
Convert 3.00 moles of As2S3 to grams. (molar mass of 246 g)
3.00 x 246 = 738 g As2S3
●
Convert 8.00 x 1020 molecules of H2 to moles.
(8.00 x 10^20) / (6.02 x 10^23) = 0.0013 molecules H2 (1.3 x 10^-3 molecules H2)
●
How many molecules of tin are found in 3.50 moles of tin?
3.50 x (6.02 x 10^23) = 2.11 x 10^24 molecules Sn
7. What are valence electrons? How many electrons can fit in the first 3 energy levels?
Valence electrons are electrons in located in the outermost shell or energy level. For example: Chlorine
has 17 electrons but only 7 valence electrons because only 7 are located in its outermost shell or third
energy level.
**2 electrons can fit in the first energy level, 8 in the second energy level, 18 in the third energy level,
and 32 in the fourth energy level.