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Course lecturer :

Jasmin Šutković

4th March 2015

Chemistry - SPRING 2015

Lecture 1:Introduction to Chemistry

Grading criteria

Quizzes ( 2 x 10% ) 20%

Midterm exam 20%

Tutorial / Homework assignments 10%

Project 10%

Attendance More then 70%required

Final exam 40%Total 100%

Link for the book: https://docs.google.com/file/d/0B1lV-EMiZm99OUFEeExHOERCLWs/edit

Contents International University of Sarajevo

1. Chemistry in modern world 1.1 Scientific method

2. What is MATTER?

3. Brief History of Chemistry3.1 Atomic theory of matter3.2 Law of multiple proportions3.3 Avogadros Hypothesis

4. The ATOM4.1 The electrons4.2 Radioactivity

5. Periodic system of elements

1. Chemistry in the modern World

Chemistry is the study of properties of substances and how they react with one another .

It is an experimental science based of the scientific method!

Hunderds of materials that we use EVERY DAY , directly and indirectly, are the products of chemical reseacrh.

For example: Plastics , Computer Chips, paper, fuels, cement, ceramics, sollar cells, Cosmetics and so on.........

WE NEED CHEMISTRY TO UNDERSTAND OUR ENVIRONMENT!!

International University of Sarajevo

Why we study Chemistry ?:

Important chemistry processess in our life !

Digestion..

Cooking..

When you write with ink on paper..!

Steel is 94% iron and 6% carbon. The carbon forms complex bonds making steel so strong that you can bend an iron crowbar, but not a steel one.

ANYTHING that burns is undergoing a chemical reaction and almost always creates some form of carbon as waste.

Figure1. Chemistry in every day life

1.1 Scientific method

Scientists (Chemists) increase – expend their knowledge through the process of making observations, using SCIENTIFIC METHODS through laboratory experiments, to answer scientific questions.

We first define the GOAL (formulate the question we wish to answer).

After the goal we collect data about the problem . We use two types of data : Qualitative data consists of descriptive observation Quantitative data consists of numbers obtained from

measurements .

Scientific method cont…

If we gather enough data about our subject we will be able to form a HYPOTHESIS. Hypothesis is a proposed explanation for an observation,

phenomenon, or scientific problem that can be tested by further investigation!

To test the hypothesis we perform EXPERIMENTS .If the experiments support the hypothesis we will perform another experiments(under various conditions) to verify our statement.

After many confirmed experiments( the results are reproducible) we can state a LAW or Scientific law . A law simply says what happens but doesn't explain it (why this

happens).

Scientific method cont….

Once a Law has been formulated, scientist try to develop a THEORY (unifying principle) that explains the law based on experimental methods( why nature behaved as it does ).

The theory can develop by time because new facts may arise.

Figure 2.The scientific method

2. What is Matter ?

Matter is anything that occupies space and possesses MASS. People, Gold, Smoke, Smog and so on….. NOT MATTER : light and sound! Many people mix-up MASS and Weight .

Object MASS is not its WEIGHT !!! MASS is a measurement of the amount of matter something

contains, while WEIGHT is the measurement of the pull of gravity on an object.

Matter does not depend on the location of an object but Weight does !!! Example: On the Moon, your MASS will be the same, but your WEIGHT will be

different since the Moon doesn't have the same gravity as the Earth.

States of Matter ?

Under normal conditions there are three distinct states of matter :1. Solids – rigid and fixes shape

2. Liquids – fixed volumes and take the shape of their containers

3. Gases – have neither fixed shape nor fixed volume and fill their container completely

Figure 3. Example of states of matter

Pure Substances and Mixtures

Pure Chemical Substance — any matter that has a fixed chemical composition and characteristic properties

Mixture — combinations of two or more pure substances in variable proportions in which the individual substances retain their identity 1. Homogeneous mixtures

a. All portions of a material are in the same state, have no visible boundaries

b. Also called SOLUTIONS

2. Heterogeneous mixtures a. Composition of a material is not completely uniform

The simplest substances are …

Most mixtures can be separated into pure substances - Elements or Compounds.

ELEMENTS is any substance that CANNOT be broken down into simpler substances . Many definition of Elements exists but the modern one is :

An element is a substance that consists only of atoms with the same nuclear charge .

99.99% of all substances are made of only 40 elements .

COUMPOUNDS are substances that can be broken into two or more elements.

Properties of Matter

· Properties used to describe material substances can be classified as either physical or chemical.

· Physical properties: Characteristics that scientists can measure without

changing the composition of the sample under study (mass, color, volume, amount of space occupied by the sample).

· Chemical properties: Describe the characteristic ability of a substance to react

to form new substances (flammability and corrosion).

Properties of Matter cont…

· Physical properties can be extensive or intensive 1. Extensive properties a. Vary with the amount of the substance, b. Include mass, weight, and volume.

2. Intensive properties a. Do not depend on the amount of the substance, b. Include color, melting and boiling point, electrical

conductivity, and physical state at a given temperature, c. Determine a substance’s identity, d. Have an important intensive property called density (d), a

ratio of two extensive properties, mass and volume

density = mass / volume d = m/V (g/cm3)

3. Brief History of Chemistry

In fourth century B.C., ancient Greeks proposed that matter consisted of fundamental particles called ATOMS.

Over the next two millennia, major advances in chemistry were achieved by alchemists. Their major goal was to convert certain elements into others by a process called transmutation.

MODERN CHEMISTRY

Beginnings in the sixteenth and seventeenth centuries, where great advances were made in metallurgy, the extraction of metals from ores.

In the seventeenth century, Boyle described the relationship between the pressure and volume of air and defined an element as a substance that cannot be broken down into two or more simpler substances by chemical means.

Modern Chemistry cont….

In the 18th century Priestley discovered oxygen gas and the process of combustion

Father of modern chemistry -- Lavoisier discovered respiration and wrote the first modern chemistry text. His famous law says that the mass is always conserved during

the chemical reaction  the mass of the products equals the mass of the reactants.

3.1 Atomic theory of matter

In 1803, Dalton proposed that elements consist of individual particles called atoms.

His atomic theory of matter contains four hypotheses:

1. All matter is composed of tiny particles called atoms. 2. All atoms of an element are identical in mass and fundamental

chemical properties. 3. A chemical compound is a substance that always contains the

same atoms in the same ratio. 4. In chemical reactions, atoms from one or more compounds or

elements redistribute or rearrange in relation to other atoms to form one or more new compounds.

Atoms themselves do not undergo a change of identity in chemical reactions.

Atomic theory of matter cont..

Dalton’s atomic theory is essentially correct, with four minor modifications:

1. Not all atoms of an element must have precisely the same mass

2. Atoms of one element can be transformed into another through nuclear reactions.

3. The composition of many solid compounds are somewhat variable

4. Under certain circumstances, some atoms can be divided (split into smaller particles).

3.2 Law of multiple proportions

Dalton could not use his theory to determine the elemental compositions of chemical compounds because he had no reliable scale of atomic masses.

Dalton’s data led to a general statement known as the law of multiple proportions.

If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element, will be ratios of small whole numbers!

3.3 Avogadro's hypothesis

Gay-Lussac attempted to establish the formulas of chemical compounds by measuring volumes of gases under constant temperature and pressure conditions, that react to make a chemical compound.

Exp: One volume of chlorine gas always reacted with 1 volume of hydrogen gas (HCl) or 1 volume of oxygen gas always reacted with two volume of hydrogen gas (H2O).

Gay-Lussac’s results were explained by Avogadro’s hypothesis, which proposed that equal volumes of different gases contain equal numbers of gas particles when measured at the same temperature and pressure.

Figure 4. Gay Lussacs eexperiments with chlorine gas and hydrogen

4. The ATOM

Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components.

Atoms consist of electrons, protons, and neutrons.

1. Electrons and protons have electrical charges that are identical in magnitude but opposite in sign. Relative charges of 1 and +1 are assigned to the electron and proton, respectively.

2. Neutrons have approximately the same mass as protons but no charge—they are electrically neutral.

3. The mass of a proton or a neutron is about 1836 times greater than the mass of an electron. Protons and neutrons

constitute the bulk of the mass of the atom.

4.1 Electrons

In 1897, Thomson demonstrated that cathode rays could be deflected, or bent, by magnetic or electric fields, which indicated that the cathode rays consisted of charged particles.

Measuring the extent of the deflection of the cathode rays, Thomson calculated the mass-to-charge ratio of the particles.

Since like charges repel each other and opposite charges attract, Thomson concluded that the particles had a net negative charge. These particles are called electrons.

4.2 Radioactivity

In 1896, Hanry Becquerel discovered that certain minerals emitted a new form of energy.

Becquerel’s work was extended by Pierre and Marie Curie, who used the word radioactivity to describe the emission of energy rays by matter.

Ernest Rutherford, building on the Curies’ work, showed that compounds of elements emitted at least two distinct types of radiation. These particles were called α particles. Particles in the second type of radiation were called β particles and had the same charge and mass-to-charge ratio as electrons.

A third type of radiation, γ rays, was discovered later and found to be similar to a lower energy form of radiation called X -rays.

Radioactivity cont…

So we have four kinds of radiation :

α particles, β particles and x and γ rays (gamma)

Distinguished by the way they are deflected by an electric field and by the degree to which they penetrate matter ( ionizing radiation)

α particles and β particles are deflected in opposite directions. Most α rays can not go through (penetrate) the human skin and they are

ejected by He (Helium) nucleus . β particles are actually ejected by electrons and if high radiation exist it

may penetrate through the skin and damage it.

γ rays have no charge and are not deflected by electric or magnetic fields.

α particles have the lowest penetrating power, and γ rays are able to penetrate matter readily.

X rays are like gamma rays (Y rays). X rays and Y rays are very energetic and dangerous to humans .

The Atomic model

Rutherford’s results strongly suggested that both the mass and positive charge are concentrated in a tiny fraction of the volume of the atom, called the nucleus.

Rutherford established that the nucleus of the hydrogen atom was a positively charged particle, which he called a proton.

Also suggested that the nuclei of elements other than hydrogen must contain electrically neutral particles with the same mass as the proton.

The neutron was discovered in 1932 by Rutherford’s student Chadwick.

Because of Rutherford’s work, it became clear that an α particle contains two protons and neutrons—the

5. Periodic system of elements

Periodic system of elements cont..

The single most important learning aid in chemistry!!!

Summarizes huge amounts of information about the elements so that you can predict many of their properties and chemical reactions.

Elements are arranged in seven horizontal rows, in order of increasing atomic number from left to right and from top to bottom.

Rows are called periods and are numbered from 1 to 7. Elements with similar chemical properties form vertical columns, called groups,

which are numbered from 1 to 18. Groups 1, 2, and 13 through 18 are the main group elements. Groups 3 through 12 are in the middle of the periodic table and are the transition

elements. The two rows of 14 elements at the bottom of the periodic are the lanthanides and

actinides.

Periodic system of elements…

Elements with similar chemical behavior are in the same group.

Elements of Group 1 are alkali metals.

Elements of Group 2 are the alkaline earths.

Elements of Group 17 are the halogens.

Elements of Group 18 are the noble gases.

Guidelines for reading …..

Book chapter 1 (page 1- 60) Book - Electronic format :

https://docs.google.com/file/d/0B1lV-EMiZm99OUFEeExHOERCLWs/edit

Prepare yourself for tutorial (5th Mar.2015) and revise UNITS OF MEASUREMENTS (starting page 55)..

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Prepared by Jasmin Šutković