Transcript Introduction to Chemistry and Measurement

Welcome to the
World of Chemistry
Mrs. Panzarella
Rm. 351
“The Central Science”
Astronomy
Nuclear Chemistry
Health and Medicine
Biology
Physics
Chemistry
Biology
Geology
Plant Sciences
Biochemistry
Environmental Science
The Language of Chemistry
• The elements, their names,
and symbols are given on
the PERIODIC TABLE (along
with reference Table S)
http://www.youtube.com/watch?v=6b2Uy1TDAl4
Dmitri Mendeleev
(1834 - 1907)
Chemical Symbols
• Each element on the periodic table
is represented by a chemical
symbol
Chemical Symbols
(continued)
NOTICE!!
The Chemical symbols with two letters are
written with a capital first letter and
lowercase second letter
ELEMENTS TO KNOW
Atomic numbers:
1-38, 47, 50-56, 74, 78-80, 82-84, 86, 92, 94
Mass Number
Atomic Number
•
•
•
•
A
X
Element Symbol
Z
LEARN the name and chemical symbol
spelling counts-use Table S or Agenda (pg R-7)
Complete pages 2-3 in Learning Guide
Quiz Thursday
Chemistry
• The study of matter, energy
and their interactions
Measurement
1) N3: No Naked Numbers.
All measurements and
answers to math problems
must have units written after
the numbers.
2) No Work, No Credit. You
must show the math set-up
when doing math problems.
Measurement
• Qualitative observation
– Focus on the qualities of an object.
– Ex. Color of an object
• Quantitative observation
– Characteristics of an object that can
be measured.
– Ex. Mass, Length
Accuracy vs. Precision
• Accuracy - how close a measurement is to the accepted
value
• Precision - how close a series of measurements are to
each other
ACCURATE = CORRECT
PRECISE = CONSISTENT
Can you hit the bull's-eye?
Three targets
with three
arrows each to
shoot.
How do
they
compare?
Both
accurate
and precise
Precise
but not
accurate
Neither
accurate
nor precise
Precision and accuracy in the laboratory.
Figure
1.16
precise and accurate
precise but not accurate
Significant Figures
Indicate precision of a measurement.
Includes all digits that can be known
precisely plus a last digit that must be
estimated
2.35 cm
Rules for Significant Figures
a. All non-zero digits are significant
b. Zeroes between non-zero digits are significant
c. In measurements containing an expressed decimal,
zeros to the right of NON-ZERO digits are significant.
http://www.youtube.com/watch?v=ZuVPkBb-z2I
Atlantic/Pacific Rule
Pacific = Decimal Present
Atlantic = Decimal Absent
Count from the ocean towards the coast starting with the first nonzero
digit, and include all the digits that follow
Significant Figures
Counting Sig Fig Examples
1. 23.50
4 sig figs
2. 402
3 sig figs
3. 5,280
3 sig figs
4. 0.080
2 sig figs
Significant Numbers in Calculations
An answer cannot be more
precise than the least
precise measurement
Adding and Subtracting
The answer has the same number of decimal
places as the measurement with the fewest
decimal places.
25.2
one decimal place
+ 1.34 two decimal places
26.54
answer 26.5 one decimal place
Learning Check
In each calculation, round the answer to the
correct number of significant figures.
A. 235.05 + 19.6 + 2.1 =
1) 256.75
2) 256.8
3) 257
B.
58.925 - 18.2 =
1) 40.725
2) 40.73
3) 40.7
Multiplying and Dividing
• Round to the calculated answer until you
have the same number of significant figures
as the least precise measurement.
(13.91g/cm3)(23.3cm3) = 324.103g
4 SF
3 SF
3 SF
324 g
Percent Error
• Indicates accuracy of a measurement
• Formula on Reference Table T
experim ent
al  literature
% error
 100
literature
your value
accepted value
Percent Error
• A student determines the density of a substance to
be 1.40 g/mL. Find the % error if the accepted value
of the density is 1.36 g/mL.
% error
1.40 g/m L 1.36 g/m L
1.36 g/m L
% error = 2.9 %
 100
DENSITY
Mercury
13.6 g/cm3
• an important and useful physical property
• standard values can be found on Table S
• Density usually decreases as temperature increases because volume
increases making the mass more spread out, but the total mass stays
the same.
One exception!!
WATER
• Density decreases as the temperature decreases in water
Density 
mass (g)
volume (cm3)
Density example
• An object has a volume of 825 cm3 and a
density of 13.6 g/cm3. Find its mass.
GIVEN:
WORK:
V = 825 cm3
D = 13.6 g/cm3
M=?
M = DV
M
D
V
M = (13.6 g/cm3)(825cm3)
M = 11,200 g
Metric System
• 1. length
– The meter is the basic unit of length. The meter
stick is divided into 100 equal parts each 1 cm
in length
» 1km = 103 micro meter – 10-6 m
• 2. Mass
– The kilogram is the basic unit of mass
– 1kg is equal to the mass of 1L of water at 4 C
therefore 1g of water equal to the volume of
1cm3(ml) at 4 C
• 3. Volume
– The space occupied by matter. Derived from
measurement of length.
– 1L = 1000cm3 1ml = 1cm3
Table 1.3
Common Decimal Prefixes Used with SI Units
• Based on powers of 10
Prefix
Prefix
Symbol
Word
tera
giga
mega
kilo
hecto
deka
----deci
centi
milli
micro
nano
pico
femto
T
G
M
k
h
da
---d
c
m

n
p
f
trillion
billion
million
thousand
hundred
ten
one
tenth
hundredth
thousandth
millionth
billionth
trillionth
quadrillionth
Conventional
Notation
1,000,000,000,000
1,000,000,000
1,000,000
1,000
100
10
1
0.1
0.01
0.001
0.000001
0.000000001
0.000000000001
0.000000000000001
Exponential
Notation
1x1012
1x109
1x106
1x103
1x102
1x101
1x100
1x10-1
1x10-2
1x10-3
1x10-6
1x10-9
1x10-12
1x10-15
The “Unit fraction” Method
aka Dimensional Analysis
Steps:
1. Identify starting & ending units.
2. Line up conversion factors so units cancel.
3. Multiply all top numbers & divide by each
bottom number.
4. Check units & answer.
g
cm 

3
cm
3
g
set up:
known value with unit
x
unknown unit
known unit
Ex. 1 A rattlesnake is 2.44 m long.
How long is the snake in cm?
2.44 m x ______cm
m
= cm
Solution :
A rattlesnake is 2.44 m long.
How long is the snake in cm?
2.44 m x 100 cm
1m
= 244 cm
Write and solve for the following problems using
the factor label method:
1) 20 cm to m
2) 500 ml to L
3) 0.032 L to mL
4) 45 m to km
5) 805 dm to km
6) 81 cm to mm
7) 5.29 cs to s
8) 3.78 kg to g
Scientific Notation
• Scientific notation is a way of
expressing really big numbers or
really small numbers.
65,000 kg  6.5 × 104 kg
Move decimal until there’s 1 digit to its left.
Places moved = exponent.
Large # (>1)  positive exponent
Small # (<1)  negative exponent
Graphs should contain the following features:
•
•
•
•
Independent variable in the X axis (with units)
Dependent variable on the Y axis (with units).
uniform numerical scale
Include a title: (Dependent Variable) vs. (Independent
Variable)
• Data points, circled with “point protectors”.
• Data points connected with a line or a best fit line
Done on
graph paper
in pencil or
on the
computer