2. A single gram of hydrogen contains about:
602,000,000,000,000,000,000,000 hydrogen atoms
Writing such a number like this will be confusing and there
will be a big probability for making mistakes.
To make our life easier, we can use the scientific notation,
which is a product of two numbers:
The first one is a coefficient and the other is 10 raised to
a power.
e.g. the number which is written above can be written as follows:
23
10X6.02
3. Significant Figures
All of the digits that are known and the last digit that is estimated.
Rules for determining whether a digit is significant:
1. Every nonzero digit is significant.
2. Zeros appearing between nonzero digits are significant.
3. Leftmost zeros appearing in front of nonzero digits are
not significant.
4. Zeros at the end of a number and to the right of a
decimal point are significant.
5. Zeros at the rightmost end that lie to the left of a
decimal point are not significant.
43.1 , 0.546
3004 , 20.9
0.0097 , 0.0201
12.00 , 1.030
300 , 5000
4. If the next place value is 5 or more, increase
the value in the last retained place by 1
If the next place value is less than 5, the value
in the last retained place stays the same.
How to Round Numbers
Addition & Subtraction:
Round the answer to the least decimal place.
Multiplication & Division:
Round the answer to the least significant figures.
7. The Five SI basic units commonly used by chemists are:
Meter
Kilogram
Kelvin
second
mole
m
kg
mol
K
s
Length
Mass
Temperature
Time
Amount of substance
Unit Symbol Quantity
9. Units of Temperature
Scientists commonly use two equivalent units of temperature,
the degree Celsius and the Kelvin.
The Celsius scale sets the freezing point of water at 0°C
and the boiling point of water at 100°C.
The Kelvin scale sets the freezing point of water at 273 K
and the boiling point is 373 K
K = °C + 273
°C = K - 273
The zero point on the Kelvin scale, 0 K is called, absolute zero.
°C = (°F - 32) ÷ 1.8
°F = (°C x 1.8) + 32
12. Density is the ratio of the mass of an object to its volume.
Density =
volume
mass
It is an intensive property that depends only on the
composition of a substance, not on the size of the sample.
What do you think will happen if the corn oil is poured into
a beaker of water?
The oil floats on the top of water, why??
The density of oil is less than the density of water.
Look at Table 3.6 on page 90
13. If you heat an object, like a piece of iron, what do you notice?
It increases in volume, but the mass remains the same.
According to the density law, Density =
volume
mass
So when the temperature increases, the volume will increase
and as a result the density will decrease.
Exception for this conclusion is water
By decreasing the temperature the volume will increase. So
the density will decrease.
e.g. ice water floats on liquid water. Why??
