CHEM 1331 First Exam Review
CHEM 1331 First Exam Review 1331
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This 5 page Study Guide was uploaded by gypsgirl on Wednesday September 21, 2016. The Study Guide belongs to 1331 at University of Houston taught by Mark A Smith in Spring 2015. Since its upload, it has received 126 views. For similar materials see Fundamentals of Chemistry in Chemistry at University of Houston.
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Date Created: 09/21/16
Chem 1331 First Exam Review Ch. 1 - Scientific Method Make observations Formulate hypotheses Perform experiments - Models/ Theories = explanations of nature’s behavior Subject to medication over time and aren’t always correct - Quantitave Observations= Measurements Consist of a number and a unit Have some uncertainty (ex. sig figs) SI is preferred - Fundamental Laws Conservation of Mass- mass is neither created nor destroyed Definite Proportion- a compound always has exactly the same proportion of elements by mass Multiple Proportions- when 2 elements bond to create a series of compounds, the ratios of the masses of the second element can always be reduced to small whole numbers when combined with one gram of the first element; basically you can combine two elements and get different molecules ex. SO and SO2 - Dalton’s Atomic Theory All elements are made of atoms All atoms of an element are identical Chem. Compounds formed by atoms combining Atoms do not change in chem. reactions, but the way they bond does - Early Atomic Experiments and Models Thomson Model- used cathode-ray tubes to discover the charge-to- mass ratio of electrons; plum pudding model- electrons are dispersed throughout a positive charge cloud Millikan Experiment- used charged oil drops to determine the mass of an electron- 9.11x 10^-31 kg. Rutherford Experiment- alpha particles were shot at a thin sheet of gold foil; many particles were deflected proving there was a nucleus in the atoms Nuclear Model- positively charged nucleus at center of atom, surrounded by negatively charged electron cloud - Atomic Structure Small, dense nucleus made of: protons (+ charge) and neutron (no charge) Electrons (- charge, mass= 1/1840 of a proton) hang out around the nucleus in the large amount of remaining atomic volume Isotopes have same atomic number as element but different mass number (# of protons (atomic number) + # of neutrons) Ch. 2 - Electromagnetic Radiation Defined by wavelength (upside down v with longer left leg) , frequency (v), and speed (c= 2.9979 x 10^8 m/s) (wavelength)v = c Viewed as a stream of “particles” (photons) Each particle as an energy of hv, h is Planck’s constant (6.626 x 10^-34 J. s) - Photoelectric Effect Electrons are emitted when light strikes a metal surface Einstein suggested electromagnetic radiation can be viewed as a stream of “particles” based on his analysis of emitted electrons’ amounts and kinetic energy - Hydrogen Spectrum Emission spectrum of hydrogen shows discrete wavelengths Says that hydrogen has discrete energy levels - Bohr Model of the Hydrogen Atom Bohr created a model using data from the hydrogen spectrum and angular momentum assumptions (that is quantized- energy can only occur in discrete units called quanta) in which electrons travel in circular orbits Completely wrong, however it is still important - Wave (Quantum) Mechanical Model Electrons are standing waves Square of the wave function (aka an orbital) shows the probability distribution for an electron’s position We can never know the EXACT position of an electron (consistent w/ Heisenberg’s uncertainty principle) Heisenberg’s Uncertainty Principle- you can’t accurately know the position and momentum of a particle at the same time Define orbital shapes with probability maps Orbitals characterized by quantum numbers: n, l, ml n- relates to the size and energy of an orbital, positive integer l- relates to the shape of the atomic orbital, 0 to n-1 ml- relates to orientation of orbital relative to same l orbitals, integer values of -l to l, ex. l= 2 so ml can be -2, -1, 0, 1, or 2 - Electron Spin Quantum number, ms (+ or – ½) Pauli Exclusion principle: no two electrons can have the same values of the quantum numbers n, l, ml, and ms An orbital holds two electrons that have opposite spins - Periodic Table The aufbau principle explains the way the periodic table is organized The Aufbau Principle (wave mechanical model)- protons are added one by one to the nucleus to build elements, electrons are similarly added Atoms in a given group have the same valence electron configuration Trends in the periodic table (ex. Ionization energies and atomic radii) are explained by the concepts of nuclear attraction, shielding, penetration, and electron repulsions Ch. 3 - Chemical Bonds Hold atoms in molecules together Occur when some atoms can lower their total energy by bonding Types: Ionic- electrons are transferred to make ions (Nonpolar) Covalent- equal sharing of electrons Polar Covalent- unequal sharing of elections Percent ionic character of a bone X-Y ((Measured dipole moment of X-Y)/(Calculated dipole moment for X+ Y-))x 100% Electronegativity- relative ability of an atom to attract shared electrons Polarity of a bond depends on electronegativity difference of bonded atoms Spatial order of polar bonds determines whether a molecule has a dipole moment Dipole moment- the mathematical product of the separation of the ends of a dipole and the magnitude of the charges - Ionic Bonding Ion has a different size than the normal atom Anion- larger, negative Cation- smaller, positive Lattice energy: change in energy when ions group together to create an ionic solid (ex. salt) - Bond Energy Energy needed to break a covalent bond Increases as # of shared pairs goes up Used to estimate energy change in chemical reactions - Lewis Structures Illustrate how valence electron pairs are arranged among atoms in molecules or polyatomic ions Most stable molecules have atoms with filled valence orbitals Dual rule for hydrogen Octet rule for second row elements Atoms in the third row and beyond can go past the octet rule Resonance- multiple ways the atoms can bond in the same molecule Formal charge is used to choose which resonance structure is best - Compounds named depending type and other rules Binary Compounds Type 1- has a metal that always makes the same cation Type 2- has a metal that can make more than one cation Type 3- has two nonmetals Compounds containing a polyatomic ion Ch. 4 - VSEPR Model Based on the fact that electron pairs can be arranged around a central atom so that electron repulsions are minimized Used to predict geometric structure of most molecules - Dipole Moment Spatial arrangement of polar bonds determines whether the molecule has a dipole moment - Two Widely Used Bonding Models Localized electron model Molecular orbital model - Localized Electron Model Molecule is pictured as a group of atoms sharing electron pairs between atomic orbitals Hybrid orbitals (combos of native atomic orbitals) required to explain the molecular structure d2sp3- octahedral, 6 e- pairs dsp3- trigonal bipyramidal, 5 e- pairs sp3- tetrahedral, 4 e- pairs sp2- trigonal planar, 3 e- pairs sp- linear, 2 e- pairs - Two Types of Bonds Sigma- electrons shared via area shared by two electron clouds of two atoms, centered on a line that joins the atoms Pi- shared electron pair from two parallel electron clouds of two atoms, space above and below a line that joins the atoms - Molecular Orbital Model Molecule assumed to be a new thing containing positively charged nuclei and electrons Electrons in molecule contained in molecular orbitals (constructed from atomic orbitals of the atoms in the molecule) Correctly predicts relative bond strength, bond polarity, and magnetism Correctly shows electrons as delocalized in polyatomic molecules Main disadvantage: difficult to apply to polyatomic molecules qualitatively - Molecular Orbitals Classified by Energy and Shape Energy Bonding MO- lower in energy than its original atomic orbital, lower in molecule than in separated atoms, favor molecule formation Antibonding MO- higher in energy than its original atomic orbital, higher in molecule than in separated atoms, do not favor molecule formation Shape/ Symmetry Sigma MO- centered electron probability on line passing through nuclei Pi MO- electron probability concentrated above and below line passing through nuclei - Bond Order is Index of Bond Strength Bond order= ((# of bonding electrons) – (# of antibonding electrons))/2 - Resonance Molecules Best Described by Combining LEM and MOM Sigma bonds- localized Pi bonds- delocalized
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