Chem presentation1 introduction By: Sir PJ De Castro

SCIENTIFIC METHOD 1. FACT : An observable event; indisputable evidence which does not explain but simply is. 2. HYPOTHESIS: A guess to try to explain an observation. 3. EXPERIMENT: A systematic exploration of an observation or concept. 4. THEORY: An explanation of the facts; it can be proven by experiment and it confirms an hypothesis. 5. LAW: A theory which has undergone rigorous experimentation and no contradiction can be found. Note: MODEL: A visual or mathematical device or method used to demonstrate a theory or concept.

EXPERIMENTS In ancient Greece philosophers, like Aristotle, did very little physical experimentation. Mental exercises were the preferred method for solving problems. SCIENTIFIC METHOD depends on experimentation therefore the ability to make measurements is vital when using scientific method .

THE DEVELOPMENT OF MODERN CHEMISTRY

Practical arts (----to 600B.C.) Egypt and Mesopotamia Metal from ore Pottery Brewing Baking Preparation of dyes THE DEVELOPMENT WAS EMPIRICAL AND BASED ON PRACTICAL EXPERIENCE

Greek theory (600 B.C. to 300 B.C.) Two theories: A concept that al substances found on earth are composed of four elements (earth, fire, air, and water) in various proportions. A theory that matter consists of separate and distinct units called atoms was proposed by Leucippus and extended by Dimocritus in the 5 th Century BC.

Greek theory (600 B.C. to 300 B.C.) Plato proposed that the atom of one element differ in shape from the atom of another. He further believed that atom of one element could be changed into atoms f another by changing the shape of the atom. The concept of transmutation also found in Aristotle's theories. However, he did not believed in the existence of atom.

Greek theory (600 B.C. to 300 B.C.) To Aristotle, the form included not only shape but also qualities such as color and hardness that distinguish one from others. Throughout the Middle ages, it was believed that mineral could grow and that mines would be replenished after minerals were removed from them.

Alchemy (300BC to 1650 AD) The philosophical tradition of the Ancient Greece and the craft tradition of the Ancient Egypt met in Alexandria. Alchemy was the result of the union. The philosophical content of alchemy incorporated elements of astrology and mysticism into the theories of the earlier Greeks.

Alchemy (300BC to 1650 AD) Alchemist believed that a metal could be change by changing its qualities and that such change occur in nature-the metal strives from the perfection represented by gold.

Alchemy (300BC to 1650 AD) In the 7 th century AD, the Arabs conquered the centers of Hellenistic civilization and alchemy passed into their hands. The Arabs called the philosopher’s “ aliksir ” (which was later corrupted into “ elixir ”. Arab alchemists believed that this substance could not only ennoble metals by transmuting them into gold but could also ennoble life by curing all diseases.

For centuries afterwards, the two principal goals of alchemy were the transmutation of base metals into gold and the discovery of the elixir of life that could make human s immortal by preventing death.

A school of iatrochemistry, a branch of alchemy concerned with medicine into the 16 th and 17 th centuries. Alchemy lasted until the 17 th century. Gradually the theories and attitudes of the alchemists began to be questioned. The work of Robert Boyle, who published The Sceptical Chymist in 1661 is noteworthy. Boyle emphasized that chemical theory should be drieved from experimental evidence.

PHLOGISTON THEORY Involved a weightless or nearly weightless substance known as phlogiston. Metals and fire were considered to be rich in phlogiston and earth was considered oxygen poor.

When metal is calcined, or roasted in the presence of air, it turns to a powdery substance called a calx (now known as an oxide). This reduction in weight was explained as a loss of phlogiston into the air. For the smelting of an ore, the process reversed. Charcoal was believed to be rich in phlogiston and so, when charcoal was burned with this powdery calx, phlogiston supposedly passed from the charcoal to the calx restoring the metal. It was believed that….

The Phlogiston Theory Explained... Weight loss when combustibles are burned because they lose phlogiston Fire burns out in an enclosed space because it saturates the air with phlogiston Charcoal leaves very little residue when burned because it is made mostly of phlogiston Animals die in an airtight space because the air becomes saturated with phlogiston Some metal calxes turn to metals when heated with charcoal because the phlogiston from the charcoal restores the phlogiston in the metal

MAJOR PROBLEM The problem was that when some metals were calcined, the resulting calx was heavier than the initial metal. Some proponents of the phlogiston theory tried to explain this phenomena by saying that in some metals, phlogiston has negative weight. It was discovered that mercury could be turned back into a metal simply by heating it, that is without a phlogiston rich source such as charcoal. Rather than except this theory that phlogiston could have positive weight, negative weight, and sometimes no weight at all,

Lavoisier suspected and later proved that the weight increase was a result of the metal combining with air. In 1777 Lavoisier presented his theory that combustion and related processes were reactions in which oxygen combines with other elements in a paper entitled Memoir on Combustion in General.

SOLUTION : LAW OF CONSERVATION OF MASS Laviosier changed chemistry from a qualitative to a quantitative science. He freed society from the disillusionment of the phlogiston theory by showing that the mass of the products in a reaction are equal to the mass of the reactants. The following diagram uses the example of mercury calx to show the major difference between the mental model used by Priestly and the one developed by Lavoisier. Therefore, Lavoisier proved that oxygen played the major role in the differences in weight associated with combustion, disproving the accepted view of the Phlogiston Theory.

Welcome to the World of Chemistry

The Language of Chemistry CHEMICAL _____________ - pure substances that cannot be decomposed by ordinary means to other substances. Sodium Bromine Aluminum

The Language of Chemistry The elements, their names, and symbols are given on the PERIODIC TABLE How many elements are there? 117 elements have been identified 82 elements occur naturally on Earth Examples: gold, aluminum, lead, oxygen, carbon 35 elements have been created by scientists Examples: technetium, americium, seaborgium

The Periodic Table Dmitri Mendeleev (1834 - 1907)

Glenn Seaborg (1912-1999) Discovered 8 new elements. Only living person for whom an element was named.

Branches of Chemistry Many major areas of study for specialization Several career opportunities Also used in many other jobs

1. Organic Chemistry Organic is the study of matter that contains carbon Organic chemists study the structure, function, synthesis, and identity of carbon compounds Useful in petroleum industry, pharmaceuticals, polymers

2. Inorganic Chemistry Inorganic is the study of matter that does NOT contain carbon Inorganic chemists study the structure, function, synthesis, and identity of non-carbon compounds Polymers, Metallurgy

3. Biochemistry Biochemistry is the study of chemistry in living things Cross between biology and chemistry Pharmaceuticals and genetics

4. Physical Chemistry Physical chemistry is the physics of chemistry… the forces of matter Much of p-chem is computational Develop theoretical ideas for new compounds

5. Analytical Chemistry Analytical chemistry is the study of high precision measurement Find composition and identity of chemicals Forensics, quality control, medical tests

Chem presentation1 introduction By: Sir PJ De Castro

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Chem presentation1 introduction By: Sir PJ De Castro