First Year in Dentistry First Semester Al-Azhar University - Gaza Lama El Banna general chemistry

1. Chapter 1
Introduction: Matter &
Measurement
CHEMISTRY
6th
Edition

2. • Chemistry is the study of the properties of materials and
the changes that materials undergo.
• Chemistry is central to our understanding of other
sciences.
• Chemistry is also encountered in everyday life.
Why Study Chemistry

3. The Molecular Perspective of Chemistry
• Matter is the physical material of the universe.
• Matter is made up of relatively few elements.
• On the microscopic level, matter consists of atoms and
molecules.
• Atoms combine to form molecules.
• As we see, molecules may consist of the same type of
atoms or different types of atoms.
The Study of Chemistry

4. Molecular Perspective of Chemistry

5. • Pure
Substances
and Mixtures

7. Property
physical : no change in composition
chemical : change in composition
• Intensive physical properties do not depend on how
much of the substance is present.
– Examples: density, temperature, and melting point.
• Extensive physical properties depend on the amount of
substance present.
– Examples: mass, volume, pressure.
States of matter
Solid: crystal - amorphous (glass)
Fluid: liquid - gas

8. Physical and Chemical Changes
Properties of MatterProperties of Matter

9. SI Units
• There are two types of units:
– fundamental (or base) units;
– derived units.
• There are 7 base units in the SI system.
Units of MeasurementUnits of Measurement

10. Units of MeasurementUnits of Measurement
Base SI Units

11. SI Units
• Note the SI unit for length is the meter (m) whereas the SI
unit for mass is the kilogram (kg).
– 1 kg weighs 2.2046 lb.
Temperature
There are three temperature scales:
• Kelvin Scale
– Used in science.
– Same temperature increment as Celsius scale.
– Lowest temperature possible (absolute zero) is zero Kelvin.
– Absolute zero: 0 K = −273.15 o
C.
Units of MeasurementUnits of Measurement

12. Temperature
• Celsius Scale
– Also used in science.
– Water freezes at 0 o
C and boils at 100 o
C.
– To convert: K = o
C + 273.15.
• Fahrenheit Scale
– Not generally used in science.
– Water freezes at 32 o
F and boils at 212 o
F.
– To convert:
( )32-F
9
5
C °=° ( ) 32C
5
9
F +°=°
Units of MeasurementUnits of Measurement

13. Derived Units
Density
• Used to characterize substances.
• Defined as mass divided by volume:
• Units: g/cm3
.
• Originally based on mass (the density was defined as the
mass of 1.00 g of pure water).
Units of MeasurementUnits of Measurement
volume
mass
Density =

14. • All scientific measures are subject to error.
• These errors are reflected in the number of figures
reported for the measurement.
• These errors are also reflected in the observation that two
successive measures of the same quantity are different.
Precision and Accuracy
• Measurements that are close to the “correct” value are
accurate.
• Measurements that are close to each other are precise.
Uncertainty in MeasurementUncertainty in Measurement

15. Precision and AccuracyPrecision and Accuracy

16. Significant Figures
• The number of digits reported in a measurement reflect
the accuracy of the measurement and the precision of the
measuring device.
• All the figures known with certainty plus one extra figure
are called significant figures.
• In any calculation, the results are reported to the fewest
significant figures (for multiplication and division) or
fewest decimal places (addition and subtraction).
Uncertainty in MeasurementUncertainty in Measurement

17. Significant Figures
• Non-zero numbers are always significant.
• Zeros between non-zero numbers are always significant.
• Zeros before the first non-zero digit are not significant.
(Example: 0.0003 has one significant figure.)
• Zeros at the end of the number after a decimal place are
significant.
• Zeros at the end of a number before a decimal place are
ambiguous (e.g. 10,300 g).
Uncertainty in MeasurementUncertainty in Measurement

18. Uncertainty in MeasurementUncertainty in Measurement
Significant Figures
not significant:
zero for "cosmetic"
purpose
not significant:
zero used only to
locate the decimal
point
significant:
all zeros between
nonzero numbers
significant:
all nonzero integers
significant:
zeros at the end of a
number to the right of
decimal point
0.005008600
The number of
significant figures
in this example is 7

19. Significant figures in numerical calculations:
Significant Figures
Uncertainty in MeasurementUncertainty in Measurement
(1) Addition/Subtraction: The answer must be expressed with the same
number of decimal places as the quantity carrying the smallest number
of decimal places.
89.332
1.1+
90.432
one significant figure after decimal point
round off to 90.4

20. (2) Multiplication/Division/Taking Roots: The number of significant
figures in the final answer is determined by the original number that has
the smallest number of significant figures.
4.51 x 3.6666 = 16.536366 = 16.5
3 sig figs round to
3 sig figs
6.8 ÷ 112.04 = 0.0606926
2 sig figs round to
2 sig figs
= 0.061
Significant figures in numerical calculations:
Uncertainty in MeasurementUncertainty in Measurement
Significant Figures

21. Significant Figures
Exact Numbers
Numbers from definitions or numbers of objects are considered to
have an infinite number of significant figures
The average of three measured lengths; 6.64, 6.68 and 6.70?
6.64 + 6.68 + 6.70
3
= 6.67333 = 6.67
Because 3 is an exact number
= 7
Uncertainty in MeasurementUncertainty in Measurement

22. • Method of calculation utilizing a knowledge of units.
• Given units can be multiplied or divided to give the
desired units.
• Conversion factors are used to manipulate units:
• Desired unit = given unit × (conversion factor)
• The conversion factors are simple ratios:
unitgiven
unitdesired
factorConversion =
Dimensional AnalysisDimensional Analysis

23. Using Two or More Conversion Factors
• Example to convert length in meters to length in inches:
( ) ( )
( )
( )
cm2.54
in1
m
cm100
mofnumberinofNumber
incmconversion
cmmconversionmofnumberinofNumber
××=
→
×→×=
Dimensional AnalysisDimensional Analysis

24. • A person’s height is measured to be 67.50 in. What is
this height in centimeters?
• Perform the following conversions: (a) 2 days to s; (b)
20 Kg to g.
Class Practice ProblemClass Practice Problem

25. Using Two or More Conversion Factors
• In dimensional analysis always ask three questions:
• What data are we given?
• What quantity do we need?
• What conversion factors are available to take us from
what we are given to what we need?
Dimensional AnalysisDimensional Analysis