Transcript 1-Introduction

General Chemistry
Chem111
Dr. Karim M. ElSawy
Assistant professor of physical chemistry
Department of Chemistry
Qassim University
Contents
 Introduction
 Chemical calculation
 Thermodynamics
 Solutions
 Bohr Theory Periodic table
 Chemical bonding
 gases
 liquids
 kinetics
 Chemical and ionic equilibrium
References
1- Chemistry a Basic Introduction, G. Tyler Miller, Wadsworth, 1984, Inc..
2- General Chemistry: principles and modern applications, Ralph H. Petrucci, William S. Harwood,
2002, Prentice –Hall.
3- General Chemistry, Whitten, Davis, Peck, and Stanley, General Chemistry, 7th Edition
4- General_Chemistry, Ebbing, Gammon 9th Edition, 2007
Lectures:
Quiz1
4
40
1st midterm
12
Quiz 2
4
2nd midterm
12
Attendance
3
Report & contribution
5
Final
40
40
Quiz 1
2.5
20
Quiz 1
2.5
Final (lab; sheet)
5
Final (lab)
10
Lab:
Total
100
Chemistry?????????
All of the objects around you—your pen or pencil, and the things of
nature such as rocks, water, plant and animal substances—constitute the
matter of the universe.
Matter is anything that has mass and volume
We can define chemistry as the study of matter and its properties, the
changes that matter undergoes, and the energy associated
with those changes.
matter
properties
Combustion of coal
changes
energy
The Properties of Matter
We learn about matter by observing its properties, the characteristics that
give each substance its unique identity.
To identify a substance, chemists observe two types of properties,
physical and chemical
Physical properties: are those that a substance shows by itself, without
changing into or interacting with another substance.
e.g. colour, melting point, electrical conductivity and density
Center: Sulfur. From upper
right, clockwise:
Arsenic, magnesium,
bismuth,
mercury.
Classifying matter
Solid
Elements
Compounds
chemical
constitution
Matter
Physical
State
Liquid
Gas
Mixtures
There are two ways of classifying matter;
I) by its physical state as a solid, liquid, or gas
A solid is the form of matter characterized by rigidity; a solid is
incompressible and has fixed shape and volume.
A liquid is the form of matter that is a relatively incompressible fluid;
a liquid has a fixed volume but no fixed shape.
A gas is the form of matter that is a easily compressible fluid; a given
quantity of gas will fit into a container of almost any size and shape.
II) Matter can also be classified by its chemical constitution
as an element, compound, or mixture.
1) An element is a substance that cannot be decomposed by
any chemical reaction into simpler substances.
E.g. Na, H, O
elements
2) A compound is a substance composed of two or more
elements chemically bonded (combined).
E.g. H2O, NaCl
A pure compound always contains constant proportions of
the elements by mass (Law of constant composition).
The physical and chemical properties of a compound are
different from the properties of its constituent elements.
compounds
Sodium (Na)
Chlorine (Cl)
Sodium chloride (NaCl)
shinny
a poisonous,
Ordinary table salt,
extremely reactive
metal.
greenish –yellow gas
a white unreactive solid.
The properties of compounds are very different from
those of the elements they contain.
9
Compounds are formed of elements through chemical reactions (chemical
change). This change follows the Law of Conservation of Mass
The total mass remains constant during a chemical change (chemical reaction).
E.g.
TOTAL MASS BEFORE REACTION = TOTAL MASS AFTER REACTION
Mass of mercury + Mass of oxygen = mass of mercury oxide
A physical change leads to a different form of the same substance (same
composition),
Water (solid form) → water (liquid form)
A chemical change leads to a different substance (different composition).
Water current
→
Electric
hydrogen gas + oxygen gas
The law of conservation of mass, illustration
AgNO  NaCl  AgCl  NaNO
3
3
→
Note: the balance reading (total mass) has not changed despite
change in chemical composition due to reaction.
Note: Mass and weight are different
The weight of an object is the force of gravity exerted on it.
It changes from one place to another. An object weighs more at the North
Pole, where it is closer to the centre of the earth, than at the equator.
Weight is measured in Newton
The mass of an object is the amount of matter it contains, it does not
change from one place to another. It is measured in grams.
We use a set of symbols to represent the elements. These symbols can be
written more quickly than names, and they occupy less space. The symbols
consist of either a capital letter or a capital letter and a lowercase letter, such
as C (carbon) or Ca (calcium).
3) A mixture is a material that can be separated by physical means into two or more
substances.
Unlike pure compounds, a mixture has variable composition, so it does not follow
the law of constant composition
mixture
Mixtures are classified into two types.
a) A heterogeneous mixture is a mixture that
consists of physically distinct parts, each with
different properties.
E.g. a mixture of iron filings and copper
b) A homogeneous mixture (also known as a
solution) is a mixture that is uniform in its
properties throughout.
E.g. When sodium chloride (salt) is dissolved in
water, you obtain a homogeneous mixture, or
solution.
Classification of matter
solid
element
compound
‫مخلوط‬
mixture
Chemical
consitution
Matter
Physical
state
liquid
gas
USE OF NUMBERS:
In chemistry, we measure and calculate many things, so we must be sure we
understand how to use numbers. In scientific context, numbers are of two
types:
1) Exact numbers:
Numbers obtained by counting or from definitions.
They are known to be absolutely accurate.
For example,
• The exact number of people in a closed room can be counted, and there is
no doubt about the number of people.
• A dozen eggs is defined as exactly 12 eggs, no more, no fewer
•
•
•
an inch is defined to be exactly 2.54 centimetres
1 meter is defined to be exactly 100 cm
1 km is defined to be exactly 1000 m
2. Numbers obtained from measurement:
They are not exact, every measurement involves an estimate (uncertainty).
In order to measure a property we need two things; some unit of measurement
and a device to measure this property.
Length is measured in cm by a ruler
Volume is measured
in ml by a buret
e.g. We can measure length in cm using a ruler; we could say that the length of
the rod is 9.1 cm
But how certain (precise) are we about this measurement?
Suppose you measure the length of this rod three times using the same device
(the ruler). With care, you find the values to be 9.1 cm, 9.13 cm and 9.14 cm.
Thus, you record the length of the rod as being somewhere between 9.1 cm
and 9.14 cm.
Obviously we are certain about only two digits but not certain about the
third. The third digit is a best estimate. In reporting numbers obtained from
measurements, we report one estimated digit, and no more
So how can we express uncertainty in measurement?
We deal with this problem using significant figures.
Significant figures are those digits in a measured number (or in the result
of a calculation with measured numbers) that include
all certain digits and a final digit having some
uncertainty.
Say we want to record the average of the previous length measurements,
9.10  9.12  9.14
 9.12333
3
It will be wrong to say that the average length is 9.12333, because this would
mean that we are certain about the length up to five digits (9.12333) whereas
we are certain about individual measurement just up to two digits.
So, using significant figures, we should report the average length of the rod as
two digits (certain) and an extra digit (uncertain)
The average length would then be
9.12
In significant figure terminology, the reader will then understand that we are
certain about the first two digits (9.12) but we are not certain about third (9.12)
Significant figures in calculations:
When you take measurements or use them in calculations,
The results of the calculation cannot be more precise than the
measurements,
9.10  9.12  9.14
 9.12333 (more precise than measurments )
3
9.10  9.12  9.14
 9.12
3
So you must know the number of digits that are significant in each
measurement.
In general, all digits are significant, except zeros that are not measured
but are used only to position the decimal point.
How many significant figures in a number?
All digits are significant except zeros which may or may not be significant:
1. zeros at the beginning (left) of the number are not significant
E.g. 9.12 cm, 0.912 cm, and 0.00912 cm all contain three significant
figures.
2. Terminal zeros ending at the right of the decimal point are significant.
E.g. Each of the following has three significant figures: 9.00 cm, 9.10 cm,
90.0 cm.
3. Terminal zeros in a number without an explicit decimal point may or may
not be significant.
E.g.
If someone gives a measurement as 900 cm, you do not know whether one,
two, or three significant figures are intended.
But, if a person writes 900. cm (note the decimal point), the zeros are
significant.
More generally, you can remove any uncertainty in such cases by
expressing the measurement in scientific notation.
Number of significant figures; examples
1.234 g
1.2 g
3.07 mL
0.001 oC
0.012 g
0.0230 mL
0.20 g
190 miles
50,600 calories
has 4 significant figures,
has 2 significant figures.
has 3 significant figures.
has only 1 significant figure,
has 2 significant figures.
has 3 significant figures,
has 2 significant figures.
may be 2 or 3 significant figures,
may be 3, 4, or 5 significant figures.
So, if the number ends with zeros and there is no decimal points, the number
of significant figures cannot be determined.
This ambiguity can be avoided if we use scientific notation.
n
Scientific notation ( A x10 )
n
It is the representation of a number in the form A x10 , where
A is a number with a single nonzero digit to the left of the decimal point
n is an integer.
5.06 × 104 calories
5.060 × 104 calories
5.0600 × 104 calories
(has 3 significant figures)
(has 4 significant figures),
(has 5 significant figures).
The conventions of significant figures used for measured numbers
do not apply to exact numbers.
Thus, the 2.54 in the expression “1 inch equals 2.54 centimetres” should
not be interpreted as a measured number with three significant figures.
An exact number has no uncertainty; therefore, it has an infinite number
of significant figures
Calculation with measured numbers
When adding or subtracting numbers, the end result should have the same amount
of decimal places as the number with the least amount of decimal places
Y = 232.234 + 0.27 Find Y.
3 decimal places
2 Decimal places
Y = 232.50
2 Decimal places
When multiplying or dividing numbers, the end result should have the same
amount of significant digits as the number with the least amount of significant
digits.
Y = 28 x 47.3 Find Y
2 significant figures
3 significant figures
Calculator Display: Y=1324.4
We have to express this as 2 significant figures
We use scientific notation
Correct answer Y=1.3x103
2 significant figures
Calculate the length in cm of a piece of wood 1.245 inches long
1 inch = 2.54 cm
Definition (exact number)
Length = 1.245 inches
=1.245 x 2.54 cm
4 significant figures
3 significant figures
Exact number (definition)
Calculator Display: Length = 3.1623
We have to express this as 4 significant figures
Length = 3.162
SI Base Units and SI Prefixes
In 1960 the General Conference of Weights and Measures adopted the
International System of units (or SI, after the French le Système
International d’Unités), which is a particular choice of metric units. This
system has seven SI base units, the SI units from which all others can be
derived.