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CHE1031
CHE1031: Atoms, Isotopes, Ions & Molecules: Practice Quiz 2 Key
Dalton’s atomic theory
1. Which is NOT a postulate of Dalton’s atomic theory?
a. a) Atoms are composed of protons, neutrons and electrons.
b. b) All atoms of an element are identical.
c. c) Atoms of an element are not changed by chemical reaction.
d. d) Compounds form when elements combine at a constant ratio.
e. e) Elements are made up of tiny particles called atoms.
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2. Methane and ethane are both made of only carbon and hydrogen. In methane there are
12.0 g of carbon for every 4.00 g of hydrogen, a 3:1 mass ratio. In ethane, there are 24.0 g
of carbon for every 6.00 g of hydrogen, a 4:1 mass ratio. This is an example of:
a. Law of constant composition
b. b) Law of multiple proportions

c. Law of conservation of mass
d. Law of conservation of matter
e. Octaves
Molecules & formulas
3. Write formulas for three molecular compounds whose empirical formula is CH3.
C2H6, C3H9, C4H12
4. Give an example of a pair of molecules with the same empirical formula that are also an
example of the law of multiple proportions.
C2H4, C4H8
Discovery of atomic structure
5. Which form of radiation has no mass?
Gamma – energy only
6. What did Rutherford’s gold-foil experiment:
a. Prove?
Atoms have a dense central nucleus of protons & neutrons
b. Disprove?
Thompson’s plum pudding model of the atom
7. What three physical forces act at the atomic level? Define each and be sure that your
reader can see the differences between the forces.
1) EM force
2) Strong nuclear force
3) Weak nuclear force
Sub-atomic particles & the periodic table
8. How many protons, neutrons and electrons are there in an atom of polonium?
Atomic number 84, atomic mass 209
So 84 protons & 84 electrons; neutrons = 209 – 84 = 125
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CHE1031
Atomic weight
9. The element X has three isotopes whose masses and abundances are shown below.
Calculate the average atomic mass of element X.
isotope
abundance (%) mass (amu)
15
X
28.60
15.33
17
X
16
X
13.30
17.26
58.10
18.11
Avg = (0.2860)(15.33) + (0.1330)(17.26) + (0.5810)(18.11) = 17.20 amu
Periodic table
10. Name three elements most similar to magnesium.
Berylium, calcium and strontium
11. When samples are placed in a mass spectrometer they are bombarded with _________ to
change the samples from ______________ to _____________ before they are
accelerated through the instrument.
Electrons, atoms or molecules, ions
Ions & ionic compounds
12. Non-metals tend to ____________ electrons to form __________ charged __________.
gain
negatively
anions
13. Show how the compound Na2O forms from two sodium atoms and a single oxygen atom.
Show this formation in three steps and show valence electrons in each step: show all
atoms; show how ions form by movement of electrons; show how ions are attracted to
form a compound.
 2 Na atoms, each with a single ve- and 1 O atom with 6 ve Nas’ ve- move to oxygen creating atoms: Na+1 with no ve- & O-2 with 8 ve Oppositely charge ions are attracted by EM force to create the compound, or
aggregate, Na2O
Naming chemical compounds
14. The formulas of some compounds are shown below. FOR EACH, identify it as an
ionic, molecular or acidic compound AND name the compound.
Type?
Name?
a. N3O5
molecular
trinitrogen pentoxide
b. AlBr3
ionic
aluminum bromide
c. H(NO2)
acidic
nitrous acid
d. SO
molecular
sulfur monoxide
e. Mo(SO4)
ionic
molybdenum (II) sulfate
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CHE1031
Ionic compounds
15. Write formulas for these compounds:
a. nickel (II) cynanide
Ni(CN)2
b. sodium peroxide
Na2O2
c. phosphoric acid
H3(PO4)
d. magnesium nitride
Mg3N2
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