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Unit 1: Stoichiometry and Gases By Alex and Maria Tour of the Periodic Table – Groups and Periods • Groups: vertical columns of elements with similar chemical and physical properties • Periods: Horizontal columns Element Groups • Groups 1A: Alkali Metals • Group 2A: Alkali Earth Metals • Group 3A-4A: unnamed • Group 5A: Pnictogens • Group 6A: Chalcogens • Group 7A: Halogens (salt) • Group 8A: Noble Gases Naming Ionic Compounds -Ite NO2- -Ate NO3- Per…Ate Hypo- Exceptions ClO2- ClO3- ClO4- OHCN- SO3- SO42- -Ide Monatomic ClO- •An ionic compound is a metal cation bonding to a non-metal anion •Binary compounds are two nonmetal compounds, like NF3 (add prefix) Protons, Neutrons, Electrons and Isotopes • • • • An Isotope is an atom with the same atomic number but different mass numbers because of a difference in the number of neutrons. The atomic number of an element is the number of protons Neutrons and Protons add up to the mass number of an ion/element The number of electrons is determined by the charge of the ion Example Element Atomic Mass # # of Protons # # of Neutrons # of Electrons Na 11 23 11 12 11 Na+ 11 23 11 12 10 Na 11 24 11 13 11 Percent Abundance • • • Percent Abundance is the percentage of atoms of each isotope in a sample % abundance= (# of atoms of given isotope) x 100% (total # of atoms of all isotopes of that element) Mass Mole Relationships/Percent Composition • Mass to Mole Relationships: Mass of A Moles of A Moles of B •Percent Composition= •(MA/MT) x 100% Mass of B Empirical and Molecular Formula • Empirical Formula: (HINT-Assume 100g sample) = % composition ÷ (Smallest number of moles) molar mass • Molecular Formula: (Mexp/Memp) x (Elements in Compound) Example (Empirical Formula) • You have a compound composed of 49.8% C, 5.15% H, 16.49% O, and 28.87% N. Find the empirical formula • 49.48g C x 1 mol C = 4.120mol C = 4 mol C 12.011g C 1.031 • 5.15g H x 1 mol H = 5.110 mol H = 5 mol H 1.0079g H 1.031 • 16.49g O x 1 mol O = 1.031 mol O = 1 mol O 15.9994g O 1.031 • 28.87g N x 1 mol N = 2.061 mol N = 2 mol N 14.0067g N 1.031 C4H5ON2 Example (Molecular Formula) • If the molar mass for the previous compound is 194.2 g/mol, what is its molecular formula? • Theoretical molar mass = 4(12.011 g/mol C) + 5(1.0079 g/mol H) + (15.9994 g/mol O) + 2(14.0067 g/mol N) = 97.0963 g/mol • 194.2 g/mol ~ 2 96.0963 g/mol • 2(C4H5ON2) = C8H10O2N4 Balancing Reaction Equations/ Stoichiometry • To balance a reaction equation be sure to have the same number of elements on the reactant and products side. • See mass to mole relationship for stoichiometry. Limiting Reactants/ Percent Yield • Using stoichiometry find which reactant produces less of either product. This reactant is the limiting reactant. • (Mexp/Mtheor) x 100% Hydrates • Hydrates are compounds which molecules of water are associated with the ions of the compound. • There is no simple way to predict how much water will be present in a hydrate compound; it must be determined experimentally. • Mass of Water=Mass of Hydrate Compound – Mass of anhydrous compound Partial Pressure • Partial pressure: PA=χAPTotal Ptotal=((nA+nb+nc…)RT)/V χA= na/ntotal • Mole fraction: Ratio of the number of moles of one substance to the total number of moles in a mixture of substances Ideal Gas Law PV = nRT P = Pressure (atm) 1atm = 760torr = 760mmHg V = Volume (L) N = # of moles R = Rate = .08206 (L∙atm/mol∙K) T = Temperature (K) K =°C + 273K m/v = (PM)/(RT) = ρ GAS…. Kinetic Molecular Theory • Tiny particles surrounded by much empty space • Constantly moving • Energy (speed2) proportional to temperature (T) in Kelvin • Particles collide without losing energy (preferably an elastic collision) R.M.S speed/Effusion/Diffusion • √(3RT)/M = √u2 R= 8.314 J/mol∙K (J=kg∙m2/sec2) T = Temperature (K) M = Molar Mass (kg/mol) • Effusion is going from a container into a vacuum • Diffusion is the mixing of two gases • rate1/rate2= √M2/M1 Non-Ideal Gas Law (Van der Waals) • • • • • • (Preal+a(n/v)2)(Vreal-bn)=nRT a= Attractive forces (atm∙L2/mol2) b= Molecular volume (L/mol) a(n/v)2 is the correction for intermolecular forces bn is the correction for molecular volume a and b are Van der Waals constants GAS!