Chapter 1 Molecular Reasons

1. Chapter 1Molecular Reasons

2. Firesticks • A chemical reaction is an extraordinary transformation. • Microscopic versus Macroscopic Worlds • Interpretation of a situation depends on the manner in which it is framed. • And so, why should nonscience majors study science (chemistry in particular)?

3. Molecular Reasons • Chemistry is a world that is not readily apparent to the naked eye, yet it is the cause of all that is around us. • Chemists examine the molecular reasons for our macroscopic observations.

4. The Scientist and the Artist • In a chemical reaction, matter is neither created nor destroyed. • Antoine Lavoisier • Father of modern chemistry • Unfortunate end • Law of conservation of mass • Capable of summary and prediction

5. The Scientific Method • A process by which a set of observations leads to a model of reality. • Iterative process

6. The Scientific Method: Structure • Hypothesis • Experiment • Theory • Further experimentation • John Dalton’s formulation of atomic theory is an application of the scientific method.

7. Concept Check 1.1 • A newly discovered aqueous extract of a berry grown in southeast Asia is claimed to cure malaria. How would you classify this claim? Is this an example of a (a) fact, (b) theory, (c) hypothesis, or (d) myth?

8. Concept Check 1.1 Solution Concept Check: A newly discovered aqueous extract of a berry grown in southeast Asia is claimed to cure malaria. How would you classify this claim? Is this an example of a (a) fact, (b) theory, (c) hypothesis, or (d) myth? Solution: The claim that the extract cured malaria is classified as a (c) hypothesis. No evidence had been provided to prove or disprove the claim.

9. First Wonderers • Greek philosophers • Plato • Democritus • Thales • Empedocles • Aristotelian logic • Reigned for 2000 years

10. Alchemy • Goal: transmutation of base metals into gold and discovery of the “elixir of life” • Metallurgy • Mysticism and secrecy slowed any real scientific progress.

11. An Understanding • The scientific revolution • Publications by Copernicus and Vesalius emphasized observation and experimentation. • Galileo Galilei’s ideas contradicted the teachings of Aristotle and the Catholic Church. • Robert Boyle’s Skeptical Chymist criticized Greek ideas centered on four elements while further developing the concept of elements.

12. Classification of Matter Boyle’s Approach

13. Classification by Composition: • Pure substance • Elements cannot be decomposed to simpler forms by any amount of chemical transformation. • Compounds are composed of two or more elements in definite proportions.

14. Classification by Composition: Mixtures are combinations of two or more pure substances in variable proportions. They are classified as homogeneous and heterogeneous. • Homogeneous: A mixture that has the same composition throughout. • Heterogeneous: A mixture that is separated into two or more regions with different composition.

15. Concept Check 1.2 Determine whether each of the following is an element, a compound, or a mixture. If it is a mixture, classify it as homogeneous or heterogeneous. • 14 carat gold ring • sand • carbon dioxide • diamond

16. Concept Check 1.2 Solution • 14 carat gold 24 carat gold is pure gold. 14 carat gold is a homogeneous (solid-solid) mixture of gold and other elements such as copper or nickel. • sand Sand is heterogeneous mixture of quartz and other minerals. The composition of sand changes depending on sample location. • carbon dioxide Carbon dioxide is pure compound. • diamond Diamonds are a form of elemental carbon.

17. Classification by Phase: Solid, Liquid, and Gas

18. Classification by Phase: Solid, Liquid, and Gas

19. Concept Check 1.3 • Classify a cup of grape juice in terms of its state and composition.

20. Concept Check 1.3 Solution Classify a cup of grape juice in terms of its state and composition. • State: At room temperature, a cup of grape juice is a liquid. If the liquid were cooled below 0°C, a grape popsicle (solid) results. • Composition: Grape juice is a clear purple liquid indicating a homogeneous solution of water with molecules that bring color (pigments) and sweetness (sugar). Included in this solution are vitamins and other nutrients.

21. Properties of Matter • Physical properties: those properties that a substance displays without changing its composition. • Chemical properties: those properties that a substance displays only when changing its composition.

22. Physical and Chemical Properties • Differentiating between physical and chemical properties (and/or changes) is NOT trivial for the inexperienced observer. • The evaporation of alcohol is a physical change. The alcohol does not change composition upon vaporization.

23. Concept Check 1.4 Classify the following as a physical change or a chemical change. • Iron rusting • sugar dissolving in water • paper burning in air • ice melting

24. Concept Check 1.4 Solution • Iron rusting is a chemical change. Elemental iron is converted to iron(III) oxide (rust) upon exposure to oxygen. • Sugar dissolving in water is a physical change. Both the sugar and the water are unchanged by the process and can be separated into their pure form by evaporation of water. • Paper burning is a chemical change. The paper is converted to carbon dioxide and water when ignited in the presence of oxygen. • Ice melting is a physical change. Both ice and water are H2O, which is not altered by the phase change of a solid to a liquid.

25. Atomic Theory Develops • Lavoisier- Law of Conservation of Mass • Matter is neither created nor destroyed in a chemical reaction. • Father of Modern Chemistry • Studied combustion in closed containers • Proust – Law of Constant Composition • All samples of a compound have the same proportions of their constituent elements.

26. Concept Check 1.5 Oxygen and hydrogen combine in a mass ratio of 8:1 respectively to form water (H2O). Hydrogen peroxide (H2O2) forms from the combination of 2.0 grams of hydrogen and 32 grams of oxygen. • What is the mass ratio combination of oxygen to hydrogen in hydrogen peroxide? • The combining oxygen to hydrogen mass ratio for water is different than that for hydrogen peroxide. Is this observation consistent with the law of constant composition?

27. Concept Check 1.5 Solution • 32 grams of oxygen combine with 2.0 grams of hydrogen to form 34 grams of H2O2. • Both hydrogen peroxide and water are composed of hydrogen and oxygen atoms. All water is composed of oxygen and hydrogen combined in a 8:1 mass ratio. All hydrogen peroxide is composed of oxygen and hydrogen combined in a 16:1 mass ratio. Even though they are composed of the same elements, they are different compounds. Both are following the law of constant composition.

28. Dalton’s Atomic Theory • All matter is composed of particles called atoms. • All atoms of a given element are alike in mass and other properties. • Atoms differ from one element to another. • Atoms of different elements combine to form compounds in simple whole number ratios. • Dalton’s theory is synthesized from MANY different sources of information.

29. Rutherford’s Nuclear Theory • Gold Foil Experiment • Directed alpha particles at gold foil • Some alpha particles were “deflected” by something in the atom • Devised a theory to explain the experimental results • Demonstrated that the nucleus consists of particles: positively charged protons and neutral neutrons

30. Rutherford’s Nuclear Theory • Most of an atom’s mass is contained in a small space called the nucleus. • Most of an atom’s volume is empty space occupied by very tiny negative charged particles called electrons. • The number of negatively charged electrons outside of the nucleus is the same as the number of positively charged particles in the nucleus for electrically neutral atoms.

31. Rutherford’s Nuclear Theory • The graphite in pencil “lead” is made of carbon atoms. • Each carbon atom consists of a nucleus surrounded by a diffuse cloud of electrons. • The nucleus is composed of positively charged protons and neutral neutrons.

32. Concept Check 1.6 A neutral carbon atom has six electrons outside the nucleus. • How many protons must be in the nucleus? • What other atomic particle is found in the nucleus of an atom other than protons?

33. Concept Check 1.6 Solution • A neutral carbon atom must have an equal number of protons and electrons, therefore, with six electrons outside the nucleus, there must be six protons in the nucleus. • The other basic atomic particle found in the nucleus of an atom is the neutron, which is uncharged.

34. Molecular Concept The scientific method Classifying matter John Dalton’s atomic theory Rutherford’s Nuclear atom Societal Impact Chemistry deepens our understanding of the world. Technology has grown and continues to grow as we apply the knowledge acquired through the scientific method. Chapter Summary