General ChemistryChem111

Dr. Karim M. ElSawyAssistant professor of physical chemistry

Department of ChemistryQassim University

Introduction Chemical calculation Thermodynamics Solutions Bohr Theory Periodic table Chemical bonding gases liquids kinetics Chemical and ionic equilibrium

References

Contents

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 Edition4- 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

Lab:

Quiz 1 2.5 20

Quiz 1 2.5

Final (lab; sheet) 5

Final (lab) 10

Total 100

All of the objects around you—your pen or pencil, and the things ofnature 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 associatedwith those changes.

Chemistry?????????

matter properties changes energy

Combustion of coal

The Properties of Matter

We learn about matter by observing its properties, the characteristics thatgive 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.

Physical State

Solid

Liquid

Gas

chemical constitution

Elements

Compounds

Mixtures

Matter

Classifying matter

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

2) A compound is a substance composed of two or more elements chemically bonded (combined).

E.g. H2O, NaCl

elements

compounds

The physical and chemical properties of a compound are different from the properties of its constituent elements.

A pure compound always contains constant proportions of the elements by mass (Law of constant composition).

9

The properties of compounds are very different from those of the elements they contain.

Sodium chloride (NaCl)

Ordinary table salt,

a white unreactive solid.

Sodium (Na)

shinny

extremely reactive metal.

Chlorine (Cl)

a poisonous,

greenish –yellow gas

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 REACTIONMass 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 → hydrogen gas + oxygen gasElectric current

→

33NaNOAgClNaClAgNO

Note: the balance reading (total mass) has not changed despite change in chemical composition due to reaction.

The law of conservation of mass, illustration

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

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.

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

Physical state

solid

liquid

gas

Chemical consitution

element

compound

مخلوط

Matter

Classification of matter

mixture

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.

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 be9.12

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)

Say we want to record the average of the previous length measurements,

12333.93

14.912.910.9

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,

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.

12.93

14.912.910.9

)(12333.93

14.912.910.9

smeasurmentthanprecisemore

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 significantE.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.

1.234 g has 4 significant figures,1.2 g has 2 significant figures. 1002 kg has 4 significant figures,3.07 mL has 3 significant figures. 0.001 oC has only 1 significant figure,0.012 g has 2 significant figures. 0.0230 mL has 3 significant figures,0.20 g has 2 significant figures. 190 miles may be 2 or 3 significant figures,50,600 calories may be 3, 4, or 5 significant figures.

Number of significant figures; examples

5.06 × 104 calories (has 3 significant figures)5.060 × 104 calories (has 4 significant figures), 5.0600 × 104 calories (has 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.

Scientific notation ( A x10n ) It is the representation of a number in the form A x10n, where

A is a number with a single nonzero digit to the left of the decimal point n is an integer.

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

Y = 232.234 + 0.27 Find Y.

2 Decimal places3 decimal places

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 = 232.50

Calculation with measured numbers

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

3 significant figures2 significant figures

Correct answer Y=1.3x103

Calculator Display: Y=1324.4

2 significant figures

We have to express this as 2 significant figures

We use scientific notation

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

Exact number (definition)

4 significant figures 3 significant figures

Calculator Display: Length = 3.1623

We have to express this as 4 significant figures

Length = 3.162

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.

SI Base Units and SI Prefixes