CHEM 151 1st EditionExam #2 Study Guide Lectures: 10-20Lecture 10 (September 23)How to calculate an empirical formula:Example:Given40.0% C 6.71% H 53.3% O*percents based on mass*Calculate moles of each component.40.0 g C (1 mol/12.01 g C) = 3.33 mol C 6.71 g H (1 mol/1.008 g H) = 6.66 mol H53.3 g O (1 mol/16.00 g O) = 3.33 mol ODivide by lowest amount of moles.3.33 mol C / 3.33 = 1 6.66 mol H / 3.33 = 23.33 mol O / 3.33 = 1Answer: CH2OHow to calculate a molecular formula (from an empirical):Given 90.08 (g/mol) CxHyOzFind molar mass of empirical formula.1 C = 1(12.01 g/mol)2 H = 2(1.008 g/mol)1 O = 1(16.00 g/mol)Total = 30.026 g/molDivide the given molar mass by the empirical formulas molar mass.(90.08 g/mol) / (30.026 g/mol) = 3Multiply the subscripts of the empirical formula by answer.C3H6O3Lecture 11 (September 25)Protons are positive (+).Electrons are negative (-).Neutrons are neutral (no charge).Atomic Number: the number of protons(protons and electrons are equal in a neutral atom)Mass Number: protons + neutrons*If there are more electrons than protons, the ion will have a negative charge.**If there are more protons than electrons, the ion will have a positive charge.*Lecture 12 (September 27)Protons and neutrons are located in the nucleus in the center of the atom and are heavy.Electrons are tiny and orbit in the large area surrounding the nucleus.Lecture 13 (September 30)What does light do?- Y-ray destroys tissue- X-ray penetrates tissue and knocks electrons out- UV moves electrons and breaks bonds- Visible moves electrons inside atoms (jumps)- IR causes molecules to vibrate; no electron jumping- Microwaves spin molecules and rotate bonds- Radio/TV passes through tissue - Long waves communicate through earthLecture 14 (October 2)Photoelectron spectroscopy measures the energy levels of electrons.- can be used to determine the number of electrons with a determined energy in an atom- measures energy to remove one electron from any shell of a neutral atomLecture 15 (October 4)Orbitals:Orbitals with lower energy are filled first. *trend on the periodic table for electron configuration:1A: 1s12A: 2s23A: p14A: p25A: p36A: p47A: p58A: p6 Lecture 16 (October 7)Anions: add electronsCations: remove electronsQuantum Mechanical Model predicts:- Line spectra for individual atoms- Organization of periodic table- Trends in 1st ionization energies- Trends in size- Magnetic behavior of individual atoms- Formation of ions from atoms with correct charge for metals reacting with non-metalsLecture 17 (October 9)Ions vs. Neutral AtomsExample: Li vs. Li+Li has 3 electrons and 3 protons which cancel each other out to make it a neutral atom.Electronegativity: 1s22s1Radius: 152 pmLi+ has 2 electrons and three protons which results in a net charge of +1.Electronegativity: 1s2Radius: 76 pm***A negative charged ion has a larger radius than a positively charged ion.Lecture 18 (October 11)Ionic FormulasWhen writing the formula of an ionic compound, use the lowest possible whole numbers for each ion. (empirical formula)The charge must cancel to ensure that the ratio of positive and negative ions is correct.Example: Magnesium and ChlorineMg has a charge of +2Cl has a charge of -1So, you need 2 chlorine atoms for every 1 magnesium ion. The lowest possible whole number ratio would be 1:2. Therefore, the ionic formula is MgCl2.Lecture 19 (October 14)Ionic CompoundsProperties:- Hard- High melting point- Very high boiling point- Do not conduct electricity as solids, but conduct when melted - Shatter when struckMetalsProperties:- Hard- High melting point- Very high boiling point- Conduct electricity- Can be pounded into shapes (malleable)- Can be pulled into wires (ductile)Covalent CompoundsProperties:- Sof- Much lower melting and boiling points- Don’t conduct electricity in water- Not very soluble in waterLecture 20 (October 16)Electronegativity increases as you go up and to the right on the periodic table.Greater difference in electronegativity equals a more polar bond.>1.7 = mostly ionic >0.4-1.7 = polar covalent < (or equal to) 0.4 = nonpolar