Chem 1ALecture 2Introduction2Instructor: Dr. Crisjoe A Joseph Office: Chem 1204Office Hours: W 9:00 am – 10:30 am R 12:00 pm – 1:30 pmEmail: [email protected] Course Website: https://gauchospace.ucsb.edu/HomeworkStart reading chapter 1 & 2 Start with your ALEKS homework: XM4NG-QNDN6Start chapter 2 book problemsCrashingYou have to show up everyday and sign in.You are expected to keep up with everything (iClickers, ALEKs, etcs). I will not be waving anything.You can not be enrolled in another Chem 1A class.• Learn: LanguageConceptsProblem Solving• Apply learned concepts to new problems• Multiple concept problems• Problems without a simple formulaGeneral ChemistryHow Chemist View the World• Chemistry – is the study of the properties of materials and the change that materials go through.• Qualitative Analysis – determination of the presence or absence of a particular characteristic. • Quantitative Analysis – determination of the amount (numerical value) of a particular characteristic. • Chapter 1 – Gets a bit philosophical, talks about the goals, dilemmas, integrity of science. General ChemistryExperimental Result:Weight of Reactants = Weight of ProductsLaw of Conservation of MassIn a chemical reaction we can not create or destroy mass.Early ExperimentsA mixture This balloon is filled with a mixture of hydrogen and oxygen gas. The relative amounts of hydrogen and oxygen are variable.A chemical compound This balloon is filled with water, composed of molecules that have a fixed ratio of hydrogen to oxygen. (Source:JoLynn E. Funk.)Constant Composition of Compounds• Joseph Proust (1754–1826) formally stated the idea that elements combine in fixed proportions to form compounds.• The law of constant composition states:All samples of a given compound have the same proportions of their constituent elements.Constant composition of compoundsNaCl always 1:1 ratio of Na and ClCarbon dioxide always CO2, 1:2 ratio of C and O Carbon monoxide always CO1:1 ratio of C and OProust’s StatementWhen two elements form a series of compounds, the ratio of the masses of the second element that combined with 1 gram of the first element can always can be reduced to small whole numbers.Law of Multiple Proportions1) Each element is composed of tiny particles called atoms.2) Atoms of a given element are identical; atoms of different elements are different in a fundamental way.3) Atoms combine in simple, whole-number ratios to form compounds. A given compound has the same relative numbers and types of atoms.4) Chemical reactions involve reorganization of atoms: changes in the way they are bound together. The atoms themselves are not changed.Dalton’s Atomic Theory (page 19)A. –1,+1,+1B. –1,+1,–1C. –1, 0,+1 D. –1,+1, 0E. +1,+1, 0What is the charge on the electron, the proton, and the neutron, respectively?A. –1,+1,+1B. –1,+1,–1C. –1, 0,+1 D. –1,+1, 0E. +1,+1, 0What is the charge on the electron, the proton, and the neutron, respectively?Electrons discovered only ~100 years agoJ.J. Thomson determined: e/m = 1.76 × 108C/gR.Millikan determined: e = 1.602 × 10–19C ElectronsThomson discovered the following:• Electrons are negatively charged.• Electrons are much smaller and lighter than atoms.• Electrons are uniformly present in many different kinds of substances.• He proposed that atoms must contain positive charge that balances the negative charge of electrons. Plum pudding model of the atom: In the model suggested by J. J. Thomson, negatively charged electrons (yellow) were held in a sphere of positive charge (red).Electrons• Discovery of the atomic nucleus(a) Expected result of Rutherford’s gold foil experiment:• If the plum pudding model were correct, the alpha-particles would pass right through the gold foil with minimal deflection. (b) Actual result of Rutherford’s gold foil experiment: • A small number of alpha-particles were deflected or bounced back.Atomic Theory of RutherfordSizesNucleus: 2 – 7 fmAtom: 30 – 300 pmImagine nucleus the size of a golf ball – 1.68 inchesAtomic Structure1. Most of the atom’s mass and all of its positive charge are contained in a small core called the nucleus.2. Most of the volume of the atom is empty space through which the tiny, negatively charged electrons are dispersed.3. The number of negatively charged electrons outside the nucleus is equal to the number of positively charged particles (protons) inside the nucleus, so that the atom is electrically neutral. In this image, the nucleus is greatly enlarged and the electrons are portrayed as particles. The electrons are dispersed throughout a large volume but weigh almost nothing. Atomic Theory of RutherfordQuantum ModelAtoms are the basic building blocks of matter. They are the smallest particles of an element that retains the chemical identity of the element.Atomic mass unit (u) is one twelfth of the mass of an atom of carbon with six protons and six neutrons.A proton is about 1836 times more massive than an electron.Atomic StructureFor each of the following substances indicate whether it is a compound or element.H2(g) CaCl2(s) Na(s) CH4(g)H2O(l) He(g) O2(g)Elements and CompoundsFor each of the following substances indicate whether it is a compound or element.H2(g) CaCl2(s) Na(s) CH4(g)H2O(l) He(g) O2(g)Elements can not be decomposed into simpler substances by chemical or physical processes (elements are made of one kind of atom)Compounds can be broken down into elements by chemical processesElements and CompoundsPure SubstancesPure substance - matter that has fixed composition and distinct properties.eg Table Salt, Water, Copper…• Elements – substances that can not be decomposed into a simpler substance. Each element is composed of only one kind of atom.• Compounds – are composed of two or more elements, and thus composed of two or more kinds of atoms.Pure SubstancesPure substance - matter that has fixed composition and distinct properties.eg Table Salt, Water, Copper…Atomic elements are those that exist in nature with single atoms as their basic units. Most elements fall into this category.Molecular elements do not normally exist in nature with single atoms as their basic units.KNOW the seven diatomics!H2 (g) N2 (g) O2 (g) F2 (g)Cl2 (g) Br2 (l) I2 (s)Diatomic MoleculesSymbolic RepresentationHow many protons, electrons and neutrons are there in the aluminum atom,27Al?Symbolic RepresentationHow many