Chem 103, Section F0FUnit II - Quantum Theory and Atomic StructureLecture 9•The periodic trends for three key properties of the elements•How the electronic structure of the elements affects their chemical reactivity.Lecture 9 - Electron Configuratioin•Reading in Silberberg-Chapter 8, Section 4 Trends in Three Key atomic Properties-Chapter 8, Section 5 Atomic Structure and Chemical Reactivity2Lecture 9 - IntroductionIn lab we compared the chemical reactivity for elements at different locations on the periodic table.•We defined chemical reactivity for metals as a willingness to give up electrons.3Lecture 9 - IntroductionIn lab we compared the chemical reactivity for elements at different locations on the periodic table.•We defined chemical reactivity for nonmetals as a willingness to accept electrons.4Lecture 9 - IntroductionToday we will discuss the question: What does the electron configuration of a element tell us about the its physical and chemical properties?•We will focus on trends for three properties:-Trends in atomic size-Trends in ionization energy!The energy required to remove an electron form an atom in the gaseous state.-Trends in electron affinity!The energy change when an electron is added to an atom in the gaseous state.5Lecture 9 - Trends in Atomic SizeThere are different ways to measure size, we will use the following definitions:•For metals-1/2 the distance between one atom and its neighbor in a metallic crystal6Lecture 9 - Trends in Atomic SizeThere are different ways to measure size, we will use the following definitions:•For nonmetals, which typically form covalent bonds with other nonmetals-1/2 the distance between one one atom and the neighbor it is bonded to.78Atomic SizeLecture 9 - Trends in Atomic SizeTrends among the main-group elements:•As n (the period) increases, the radius increases.-Each shell places the electrons further from the nucleus.-There are also more inner electrons, which shield the outer electrons, lowering the Zeff.9Lecture 9 - Many-Electron AtomsThe effect of electron repulsions and shielding on orbital energy •The electrons feel not only the attraction of the nucleus, but also the repulsion of the other electrons.•Shielding by inner elecrons greatly lowers the effective nuclear charge (Zeff).10Electron shieldingLecture 9 - Trends in Atomic SizeTrends among the main-group elements:•As n (the period) increases, the radius increases.-Each shell places the electrons further from the nucleus.-There are also more inner electrons, which shield the outer electrons, lowering the Zeff.•As you move across a period, the size decreases.-The added electrons are in the same shell, but the Zeff increases, pulling these electrons closer to the nucleus.11Lecture 9 - Many-Electron AtomsThe effect of nuclear charge (Z)•Higher nuclear charge lowers the energy of an energy level.12Comparing the 1s orbital of H and He+Lecture 9 - Trends in Atomic SizeTrends among the main-group elements:•As n (the period) increases, the radius increases.-Each shell places the electrons further from the nucleus.-There are also more inner electrons, which shield the outer electrons, lowering the Zeff.•As you move across a period, the size decreases.-The added electrons are in the same shell, but the Zeff increases, pulling these electrons closer to the nucleus.•We will focus on the main group elements and not worry about the subtleties of the transitions metals (pp318-320).13Lecture 9 - Trends in Atomic SizeMoving through the periodic table, we see the atomic size is periodic14Lecture 9 - Trends in Ionization EnergyThe ionization energy (IE) is the energy required to completely remove 1 electron from an atom in its gaseous state.•Because energy is entering the atom (system), it is positive.•The energy for removing a second electron (IE2) is always greater than the energy for removing the first electron (IE1)15Atom(g)Ion+(g)+ e-!E = IE1 > 0Ion+(g)+ e-!E = IE2 > IE1Ion+2(g)Lecture 9 - Trends in Ionization Energy•For the hydrogen atom, the ionization energy (IE) can be calculated by combining Rydberg’s equation with Planck’s equation and finding the energy it takes to move the electron from n = 1 to n = !.16 1!= R1n12"1n#2$%&'() (Rydberg's Equation)E = h* (Planck's Equation)=hc!= hcR1n12"1n#2$%&'()Lecture 9 - Trends in Ionization Energy•For the hydrogen atom, the ionization energy (IE) can be calculated by combining Rydberg’s equation with Planck’s equation and finding the energy it takes to move the electron from n = 1 to n = !.17 E = hcR1n12!1n"2#$%&'(= 6.626 x 10-34 J•s( )2.998 x 108 m/s( )1.097 x 107 1/m( )112!1"#$%&'(= 2.179 x 10-18 JFor 1 mole of atoms= 2.179 x 10-18 J( )6.022 x 1023 1/mol( )= 1,312,00 J/molE = 1,312 kJ/molLecture 9 - Trends in Ionization EnergyAtoms with low IE’s tend to form cations (lose electrons), Atoms with high IE’s tend to form anions (gain electrons)18Lecture 9 - Trends in Ionization EnergyAtoms with low IE’s tend to form cations (lose electrons), Atoms with high IE’s tend to form anions (gain electrons)•Like the atomic sizes, the IE’s vary periodically:19Lecture 9 - Trends in Ionization EnergyTrends•As n increases ionization energies decrease- As the atoms get larger, the electrons removed are located further from the nucleus.20Lecture 9 - Trends in Ionization EnergyTrends•From left to right in a period, ionization energies increase.-The Zeff is increasing while the atoms are getting smaller, so the electrons are held more strongly.21Lecture 9 - Clicker Question 1Rank the elements Potassium (K), Argon (Ar) and Neon (Ne) in order of increasing IE1, based on their position in the periodic table.A) Ar < Ne < KB) Ar < K < NeC) K < Ar < NeD) Ne < Ar < K22Lecture 9 - Trends in Ionization EnergySuccessive ionizations•Successive ionizations show increasing ionization energies-This is because the resulting ion becomes increasingly positively charged.•There is also a substantial jump in IE when dropping down to a lower energy level to remove one of the inner (core) electrons.23Berylium (Be)Lecture 9 - Trends in Ionization EnergySuccessive ionizations•There is also a substantial jump in IE when dropping down to a lower energy level to remove one of the inner (core) electrons.24Lecture 9 - Clicker Question 2Element Q is in Period 3 and has the following ionization energies (in kJ/mol):Element Q is A) AlB) BeC) BD) CE) N25IE1IE2IE3IE4IE5IE65771816274411,57614,82918,375Lecture 9 -