Download UNIT 2 ATOMS, MATTER, AND THE MOLE

UNIT 2 ATOMS, MATTER, AND THE MOLE
I. CHEMISTRY - The study of matter and the changes it undergoes.
A. . Matter is categorized into two types:
1. Heterogeneous –“not the same throughout”. Each part has
different
physical properties. Most mixtures fall into this category. EX:
milk is a
heterogeneous mixture made up of water, fats (cream), protein
(casein and whey) and lactose and can be separated into its components.
2. Homogeneous – “the same throughout”. Compounds and elements
are pure substances and are homogeneous. Solutions are
homogeneous
mixtures that have a uniform, though varying, distribution of
particles
(solute) in a dissolving material (solvent).
B. MATTER is anything that has mass and occupies space. It is further
subdivided
into three general classes, based on chemical or physical properties:
1. Compound – a pure substance composed of 2 or more elements
which has
new properties of its own unlike the properties of the original
substances.
EX: table salt is sodium chloride-a white crystalline substance with a
high melting point. Sodium is a metallic element and chlorine is a
yellowgreenish gas.
2. Element – a substance composed of only one kind of atom that can
no
longer be decomposed by ordinary chemical means. EX: silver,
nitrogen.
3. Mixture – a material composed of 2 or more substances, each of
which
retains its own physical properties. Mixtures can be heterogeneous
or
homogeneous (also called a solution).
II. THE CHANGES THAT MATTER UNDERGOES
A. PHYSICAL PROPERTIES – characteristics that undergoes no change
in
composition. EX: mass, length, volume, density, solubility, melting
and
boiling point, conductivity, color, hardness. Mixtures are separated
using
their physical properties.
B. PHYSICAL CHANGE- changes in which no new kinds or matter are
formed.
EX: phase changes (freezing, boiling and melting), grinding,
dissolving.
Mixtures can be separated by physical separation-filtration,
evaporation,
thawing, distillation, precipitation, boiling.
C. CHEMICAL PROPERTIES- describes how a substance changes into
something new. By asking questions such as does it burn or react with
acids
helps determine the chemical properties of a substance.
D. CHEMICAL CHANGES – changes that produce new kinds of matter
that
show brand new properties. (ex.) Combustion (burning), composition
and
decomposition, color changes, energy changes, light emitted, gas
given off,
precipitation, pH changes.
Compounds are the products of chemical changes. They cannot be
broken
down physically, but can be separated chemically.
E. LAW OF DEFINITE COMPOSITION-states that a compound always
contains
elements in certain definite compositions by having the same
percentage by
mass of each element in the compound.
1. EX: water has the formula H2O, which means for one atom of
oxygen
there are two atoms of hydrogen.
2. H2O2 is not water. It is called hydrogen peroxide, has two atoms of
hydrogen for every two atoms of oxygen and behaves much
differently that
water. This brings us to the next law.
F. LAW OF MULTIPLE PROPORTIONS-states that there can exist two
or more
compounds with different proportions of the same elements.
1. EX: water and hydrogen peroxide both contain hydrogen and
oxygen in
definite composition, but in a different proportion to each other.
2. Methane (CH4) and butane (C4H10) are also good examples.
3. What are two compounds that contain carbon and oxygen?
III. THE STRUCTURE OF THE ATOM – smallest unit of an element
A. Consists of two main parts held together by an electro-magnetic force:
1. NUCLEUS-central (most dense) part that contains 2 types of
subatomic
particles.
a. Protons- have a positive (+) charge.
b. Neutrons-have a neutral (o) charge.
c. Both particles contribute the majority of the mass to the nucleus
and are
held together by the strong force.
2. ELECTRON CLOUD- surrounds the nucleus. It contains one type of
subatomic particle.
a. Electrons have a negative () charge.
b. Electrons are all identical.
c. The mass of an electron is negligible compared to the rest of the
atom.
d. They move about the atom with different energies that are
relative to
their distance from the nucleus,
e. If the nucleus were 1 cm. in diameter, the electrons would be
found
48 m or ½ football field away.
B. RULES CONCERNING CHARGES: opposite charges attract and like
charges
repel.
1. Particles with the same charge (+ and +) or ( and ) push each
other away.
2. Particles with opposite charges (+ and ) are drawn to each other.
3. Two questions:
a. What keeps the electrons from falling into the positively
charged nucleus?
b. What keeps the protons in the nucleus from repelling each other?
IV. “ATOMIC FACTS” FROM THE PERIODIC TABLE
A. TERMS YOU MUST KNOW:
1. Atomic number-number of protons in the nucleus
2. Mass number- number of protons and neutrons in the nucleus. It is
always a
whole number. Have you ever heard of 2/3 of a neutron?
3. Atomic mass-the mass of an atom expressed in atomic mass units
(AMU’s), a
very tiny weighing scale for atoms.
B. DETERMINING THE ATOMIC NUMBER, MASS NUMBER AND
ATOMIC
MASS NUMBER FROM THE PERIODIC TABLE.
1. Atomic number- on the periodic table, it is the whole number listed.
2. Atomic mass number – on the periodic table, it is the larger
number listed
with a decimal because it is an average of all isotopes of that
element.
3. Mass number – not directly found on the periodic table, but is may
be
determined by rounding the atomic mass number to the nearest
whole number.
C. DETERMINING THE NUMBER OF NEUTRONS: not given directly
on the
periodic table.
1. Subtract the atomic number from the mass number.
Mass number (protons and neutrons)
 atomic number (protons)
=
[larger number]
[smaller number]
number of neutrons
D. EXAMPLE:
1.
2.
3.
4.
5.
6.
mass number
neutrons
electrons
protons
mass in AMU’s
atomic number
11
6
5
5
10.81 amu
5
E. CONVENTIONAL WAY OF WRITING ELEMENT WITHOUT USE
OF
PERIODIC TABLE
Mass number
39
K
Atomic number
19
EX: the whole numbers indicate the mass numbers
oxygen-17,
iron-56,
25
magnesium-
Indicate the number of protons, electrons, and neutrons for the elements
above.
O:
Fe:
Mg:
F. ISOTOPES: Atoms of the same element that have different masses
(different
number of neutrons, same number of protons).
1. All elements have 2 or more isotopes. The atomic mass is the
average of all
the different isotopes. It is not a simple average. The average
takes into
account the percentage of occurrence of the isotopes considered.
2. Isotopes have different mass numbers but the same atomic number.
3. EX: protium, deuterium, and tritium
1
2
H
1
3
H
1
a. All have one proton and one electron.
H
1
b. Protium has no (0) neutrons (99.985% of all H), deuterium has
one
neutron (0.015% of all H) and tritium has two neutrons (very
small and
very radioactive).
V. AVOGADRO’S NUMBER
ATOMIC MASS-the mass of an atom in amu’s (atomic mass units).
EX: carbon
=
12.0111 amu
hydrogen =
1.007825 amu
chlorine
=
35.453 amu
B. AVOGADRO’S NUMBER = 6.02 x 1023 atoms in WHAT?
1. You took the mass of 1 atom in amu’s and converted it to grams,
then
found that for every element there is the same number of atoms in
that mass.
2. 1 dozen = 12
1 case
= 24
1 mole
= 6.02 x 1023
atoms
[Instead of saying, “Give me a dozen eggs, the chemist says, “Give
me a mole
of carbon.]
VI. MOLE = THE AMOUNT OF A SUBSTANCE THAT CONTAINS 6.02
x 1023
OF ANY KIND OF CHEMICAL UNIT ( atoms, molecules, ions).
A. MOLAR MASS- the mass in grams of one mole of naturally occurring
atoms of
an element. Its unit is grams/mole (g/mol).
1. EX. Give the molar mass of:
Fluorine______________, Magnesium_____________,
Silver_____________
2. Give the grams in one mole of:
Fluorine______________, Magnesium_____________,
Silver_____________
3. Give the number of atoms in one mole of:
Fluorine______________, Magnesium_____________,
Silver_____________
4. If you have 18.998 grams of fluorine, how many moles is this?
5. If you have 48.610 grams of magnesium, how many moles is this?
VII. MOLE PROBLEMS: Use the “canceling units” method.
A. START WITH WHAT IS GIVEN (INCLUDING UNITS) AND TRY
TO END
UP WITH WHAT YOU WANT (INCLUDING UNITS).
Space has been left you to complete the problems. Use these
conversions.
1 mole of an element
element
the molar mass of the element
1 mole of an element
6.02 x 10 23 atoms
the molar mass of the
1mole of an element
6.02 x 10 23 atoms
1 mole of an element
1. What is the mass of 3.50 moles of copper?
2. What is the mass of 5.75 moles of copper?
3. How many moles are there in 6.195 grams of phosphorus?
4. How many moles are there in 0.0400 grams of copper?
***check answers to make sure your resulting unit is correct!!
B. One and/or two step problems
1. How many atoms are in 36.0 grams of carbon?
2. How many grams are in 1.90 x 10 24 atoms of copper?
How many moles are in 1.90 x 10 24 atoms of copper?
4. How many atoms are in 245.0 grams of gold?
***Are units included in your work? Do the units cancel? Are there units in
your answer?
If the answer to any of these is NO, go back and include them!!
SIGNIFICANT FIGURES
A measurement can only be as accurate and precise as the instrument that is
used for measuring. A scientist needs to understand and document the
accuracy of a number, not just the set of numbers. The accuracy of a
number can be determined by looking at the number of significant figures
that it contains. There are three rules to determine the significant figures in a
number.
1. If an answer starts with a digit 1-9 and has a decimal point
anywhere within the number, all figures are significant.
2. If an answer starts with a zero and decimal point, look to the
first digit 1-9. That digit and all digits that follow (including
zeros) are significant.
3. If an answer starts with a digit 1-9 and does not have a decimal
point, all digits are significant unless the answer ends in zeros.
Then all digits are significant except the last zero(s).
I. Determine the number of significant figures in the following set of
numbers and state which rule applies.
1. 0.04
_____
_____
2. 6,000.
_____
_____
3. 0.050
_____
_____
4. 3,042.00
_____
_____
5. 205
_____
_____
6. 0.0008
_____
_____
7. 205.0
_____
_____
8. 0.3010
_____
_____
9. 6,000
_____
_____
10. 20,002
_____
_____
11. 7030
_____
_____
12. 80,200
_____
_____
13. 0.400
_____
_____
14. 4.7 x 108
_____
_____
15. 788.5
_____
_____
16. 20,300,000.
_____
_____
17. 0.090200_____
_____
18. 2.000 x 104
_____
_____
19. 0.000420_____
_____
20. 2.04 x 10 20
_____
_____
Significant Figures with addition, subtraction, multiplication and division
If the question involves addition or subtraction, line the columns up so the
decimal points are in alignment. The data with the least number of decimal
points decides the number of decimal points in the answer.
9.985 The datum with the least number of decimal points is 11.0,
therefore the
10.05
answer can only have one decimal point, because the least
accurate number,
11.0
11.0, has only one decimal point. The answer would be rounded
to 31.0.
31.035
When multiplying or dividing data, the answer contains the same number of
sig figs as the datum with the least number of sig figs.
35.0 x 32.75 x 28 = 32095
because 28 has
100.35
100.35
= 319.8305929 = 3.2 x 102 2 sig figs
2 sig figs.
Add or subtract the following sets of data:
1.005 + 1.253 + 1.14 = _____________
0.04560 + 0.0325 + 0.26 =
____________
3.9 – 2.803 = _____________
249.035  248.98 = _____________
Multiply or divide the following sets of data:
37.0970 x 2.09 = ___________________
______________
28.605 x 2.00 x 0.0004560
0.002480  0.000470 =
= _____________
3.0
MATTER, ATOMS, MOLES ASSIGNMENT-UNIT 2
I. Isotopes:
A. What is an
isotope?________________________________________________
_____________________________________________________________
__
_____________________________________________________________
__
B. For 235U, determine: Number of
protons______electrons______neutrons_____
92
C. For 238U, determine: Number of
protons______electrons______neutrons_____
92
D. Are B and C isotopes? Why or why not?
______________________________
_____________________________________________________________
___
_____________________________________________________________
___
II. Define:
A. molar
mass:______________________________________________________
_____________________________________________________________
___
B. mass
number:____________________________________________________
_____________________________________________________________
___
C. atomic mass:
_____________________________________________________
_____________________________________________________________
___
D. atomic
number:___________________________________________________
_____________________________________________________________
___
III. Using a periodic table, determine:
A. number of protons in F_________
Ar_________
C. number of neutrons in He_______
Fe______________
E. atomic number of Zn___________
Cl_________
G. number of neutrons in Pt________
Ni________________
IV. Three isotopes of carbon are:
12
6
C
B. number of electrons in
D. mass number of
F. atomic mass number of
H. molar mass of
13
6
C
14
C
6
A. They are the same in
that:___________________________________________
_____________________________________________________________
___
B. They are different in that:
___________________________________________
_____________________________________________________________
__
V. Suggest a way to separate the following mixtures:
A. salt dissolved in
water_____________________________________________
_____________________________________________________________
__
B. sugar and powdered
glass___________________________________________
_____________________________________________________________
__
C. alcohol and
water_________________________________________________
_____________________________________________________________
__
D. pieces of iron and
wood____________________________________________
_____________________________________________________________
__
VI. Classify the following as elements (E), compounds (C), homogeneous
mixtures (S) or heterogeneous mixtures (HM).
_____1. CH3OH
_____11. table salt (NaCl)
_____2. CaCO3
_____12. copper
_____3. C8 H16
_____13. sugar water
_____4. oxygen
_____14. raisin bread
_____5. vitamin C
_____15. wood
_____6. dry ice (CO2 )
_____16. sulfur dioxide (SO2)
_____7. hamburger
_____17. milk
_____8. after-shave lotion
_____18. mercury
_____9. aluminum foil
_____19. smog
_____10. iron nail
_____20. clear sea water
# elements_________
mixtures________
# of compounds________
# of
VII. Does the law of definite composition apply to mixtures? Why or why
not?
_____________________________________________________________
_
_____________________________________________________________
__
VIII. Classify the following as physical property (P) or chemical property
(C).
_____1. blue color
_____9. reacts with water to form a
gas
_____2. density
____10. reacts with a base to form a
precipitate
_____3. flammability
____11. hardness
_____4. solubility
____12. boiling point
_____5. can neutralize a base
____13. reacts with acid to form
hydrogen gas
_____6. supports combustion
____14. luster
_____7. tastes sour
____15. stinks
_____8. melting point
____16. malleability
IX. Classify the following as a physical change (P) or chemical change (C).
_____1. wood rotting
_____9. pH changes
_____2. ice melting
____10. bromothymol blue changes
to yellow
_____3. evaporation
____11. baking soda and vinegar
reacts
_____4. milk sours
____12. salt dissolves in water
_____5. rain
____13. pepper suspended in water
_____6. water changing to steam
____14. crushing an Alka Seltzer
tablet
_____7. sugar changing to caramel
____15. Alka Seltzer tablet dropped
in water
_____8. iron rusts
____16. metal is pulled into a wire
X. Mole problems-show all work including units for credit. Use canceling
units method.
1. How many moles are in 0.7500 grams of sodium?
2. How many grams are in 2.50 moles of gold?
3. How many grams are in 1.80 x 1023 atoms of silver?
4. How many moles are in 4.50 x 1015 atoms of silicon?
5. Indicate the number of moles in 24.50 grams of chlorine.
6. What is the mass in grams of 0.500 moles of magnesium?
7. How many atoms are in 3.00 moles of tungsten?
8. How many moles are in 4.10 x 1021 atoms of platinum?
9. How many atoms are in 10.00 moles of potassium?
10. How many moles are in 0.150 grams of aluminum?
11. How many grams are in 5.00 x 1025 atoms of helium?
12. How many atoms are in 45.00 grams of cobalt?
13. How many atoms are in 3.50 grams of hydrogen?
14. How many moles are in 0.56 grams of boron?
15. How many grams are 5.00 moles of arsenic?
16. How many atoms are in 5.00 moles of phosphorus?
17. How many atoms are in 76.4 grams of iron?
18. How many grams are 0.083 moles of helium?
19. How many atoms are in 3.20 moles of lithium?
20. How many grams are in 3.10 x 1011 atoms of chlorine?
21. How many moles are in 0.152 grams of zinc?
22. How many atoms are in 2.00 moles of gallium?
23. How many atoms are in 76.4 grams of iron?
24. How many moles are in 12.2 grams of tungsten?
25. What is the mass in grams of 5.0 moles of magnesium?
26. How many moles are in 3.7 x 10 23 atoms of sodium?
27. How many atoms are in 10.0 moles of platinum?
28. How many moles are in 0.152 grams of gold?
29. How many atoms are in 4.8 grams of cobalt?