ATOMIC STRUCTURE AND PERIODICITY PART 2

PERIODIC TRENDS Atomic Radii Ionic Radii Electronegativity Ionization Energy Electron Affinity

ATOMIC RADIUS Definition: Half of the distance between nuclei in covalently bonded diatomic molecule. Radius decreases across a period Increased effective nuclear charge due to decreased shielding Radius increases down a group Each row on the periodic table adds a “shell” or energy level to the atom 2r

IONIZATION ENERGY Definition: the energy required to remove an electron from an atom **Increases for successive electrons taken from the same atom. (First Ionization Energy is lower than the second…and that lower than the third…etc) Tends to increase across a period (general pattern-valence e - ) Electrons in the same quantum level do not shield as effectively as electrons in inner levels. Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove Tends to decrease down a group Outer electrons are farther from the nucleus and easier to remove

IONIZATION ENERGY AND ORBITAL NOTATION Phosphorus vs. Sulfur Potassium 1 st Ionization vs. 2 nd

ELECTRON AFFINITY Definition: the energy change associated with the addition of an electron Affinity tends to increase across a period Affinity tends to increase up in a group Electrons farther from the nucleus experience less nuclear attraction Some irregularities due to repulsive forces in the relatively small “p” orbitals

ELECTRONEGATIVITY Definition: A measure of the ability of an atom in a chemical compound to attract electrons from another atom. Electronegativity tends to increase across a period As the radius decreases, electrons get closer to the bonding atom’s nucleus Electronegativity tends to increase up a group or remain the same. As radius increases, electrons are farther from the bonding atom’s nucleus

IONIC RADII Cations Positively charged ions formed when an atom loses one or more electrons SMALLER that the corresponding atom Anions Negatively charged ions formed when an atom gains one or more electrons LARGER than the corresponding atom

ANALYZING PERIODIC TABLE TRENDS WITH PEERS Explain why atomic radius increases going down a group and right to left in a period. Rank the following from largest to smallest. Explain why electronegativity, ionization energy, and electron affinity increase from left to right and from bottom to top. Rank the following from largest to smallest.

SPECTROSCOPY Photoelectron Spectroscopy (PES) Provides data for ionization energy trends and applications Mass Spectrometry Provides atomic/molar mass data as it ionizes

PHOTOELECTRON SPECTROSCOPY (PES) Atom e-e- E photon = hv KE = mv 2 2 IE electron = E photon - KE Monochromatic Beam of X-Rays

PHOTOELECTRON SPECTRUM 20 MJ/mol10 MJ/mol0 MJ/mol Relative Intensity = 1 Relative Intensity = 2 Each peak is relative to the others. This indicates the relative number of electrons. If the peak is twice as big, there are twice as many electrons.

PHOTOELECTRON SPECTRUM 20 MJ/mol10 MJ/mol0 MJ/mol 19.3 MJ/mol 1.36 MJ/mol 0.80 MJ/mol Valence RI = 2 RI = 1 Gap is due to increased energy of the orbital (decreased amount of energy to remove the electron)

PHOTOELECTRON SPECTRUM 20 MJ/mol10 MJ/mol0 MJ/mol 19.3 MJ/mol 1.36 MJ/mol 0.80 MJ/mol RI = 2 RI = 1 Analysis: 1)Valence has 2 values: 2)RI is 2 to 1 in valence: 3)Closest core has RI 2 not 6: 4)s 2 s 2 p 1 must be 1s 2 2s 2 2p 1 Boron (Z=5) 1s 2 2s 2 2p 1 Inner orbitals require the most energy Valence orbitals require the least energy

PHOTOELECTRON SPECTRUM Depending on the size of the table, 1s may be intentionally cut out of view because it’s too far away and makes the graph too long Remember IE is about REMOVING electrons, which means they are removed from the OUTSIDE to the INSIDE, and NOT in reverse order of energy! For example, 4s is removed BEFORE 3d.

PHOTOELECTRON SPECTRUM 104 MJ/mol 6.84 MJ/mol 0.50 MJ/mol 8 MJ/mol4 MJ/mol0 MJ/mol Sodium (Z=11) 2p 6 2s 2 3s 1 { } 3.67 MJ/mol 1s 2

html Online PES Resources

From the AP Sample Questions…

Which peaks in the photoelectron spectrum are representative of the binding energy of p orbital electrons? a.C onlyc. C and E b.D onlyd. B, C and D

Mass Spectrometry Mass spectrometry gives the mass to charge ratio Like PES, the relative size of the peaks indicates the relative number of particles Separates isotopes according to mass Used to find relative abundance and atomic/molar mass of unknown samples

Mass Spectrometry

From the AP Sample Questions… The elements I and Te have similar average atomic masses. A sample that was believed to be a mixture of I and Te was run through a mass spectrometer, resulting in the data above. All of the following statements are true. Which one would be the best basis for concluding that the sample was pure Te?

From the AP Sample Questions… a.Te forms ions with a -2 charge, whereas I forms ions with a -1 charge. b.Te is more abundant that I in the universe. c.I consists of only one naturally occurring isotope with 74 neutrons, whereas Te has more than one isotope. d.I has a higher first ionization energy than Te does.

Based on the mass spectrum of atom Y, which of the following statements is false? a. peak A and peak D come from atoms that have the same number of electrons b. there are seven isotopes of atom Y c. peak C comes from the most abundant isotope of atom Y d. peak D comes from an atom with 4 more protons than the atom that gave peak B

PREPARATION OF A STANDARD SOLUTION A chemist whishes to prepare 1.00L of a M sodium hydroxide solution. Describe the steps, with calculations, necessary to complete this task starting with solid sodium hydroxide and distilled water.

DILUTION OF SOLUTIONS- M 1 V 1 = M 2 V 2 You’ve been asked to prepare 150 ml of a 0.035M solution of sodium hydroxide from the 0.200M stock sodium hydroxide solution prepared earlier. Detail the steps necessary to complete this task. (a)A Measuring Pipet (b) A Volumetric (transfer) Pipet

BEER- LAMBERT LAW Relates the amount of light being absorbed to the concentration of the substance absorbing the light A=abc A = measured absorbance a = molar absorptivity constant (a characteristic of the substance being monitored). b = path length through which the light must pass. c = Molar concentration of the absorbing substance.

BEER’S LAW SAMPLE PROBLEMS 1. A solution with a concentration of 0.14M is measured to have an absorbance of Another solution of the same chemical is measured under the same conditions and has an absorbance of What is its concentration? 2. The following data were obtained for 1.00 cm samples of a particular chemical. What is the concentration of a 1.00 cm sample that has an absorbance of 0.60? Conc. (M) Abs The absorptivity of a particular chemical is 1.5/M·cm. What is the concentration of a solution made from this chemical if a 2.0 cm sample has an absorbance of 1.20?

BEER’S LAW SAMPLE PROBLEMS 4. Using the data from the graphing example in question #2, what are the concentrations of solutions with absorbances of 0.20, 0.33, and 0.47? 5. A solution is prepared to be 0.200M. A sample of this solution 1.00 cm thick has an absorbance of measured at 470nm and an absorbance of measured at 550nm. Calculate the concentrations of the following solutions: SampleAbsorbanceWavelengthPath length nm1.00cm nm1.00cm nm1.00cm nm5.00cm

GATORADE LAB/INVESTIGATION What is the relationship between the concentration of a solution and the amount of transmitted light through the solution? Video Spectrophotometer See Pre-lab and Report Sheet for support. **Dilution calculations MUST be done prior to data collection!!** (Due Monday!) –complete first 3 columns in data table prior to entering lab.

LAB PARTNERS AND DILUTION ASSIGNMENTS 2 ND BLOCK Dilution Assignments (mL of stock/ mL of water) Group 1: Jackson and Kenny 10mL/0mL; 6mL/4mL 9mL/1mL; 3mL/7mL Group 2: Garrett and Nelson 5mL/5mL; 0mL/10mL 8mL/2mL; 1mL/9mL Group 3: Ashley and Taylor 2mL/8mL; 4mL/6mL, 0mL/10mL, 7mL/3mL Will share class data for plots.

UNIT 3 REVIEW Now available on the blog!! (Practice Tab) Begin working through. BRING QUESTIONS TOMORROW!!!!