CHM 101 1st Edition Lecture 18Last Lecture OverviewI. Core Electrons and Outer Shell ElectronsII. Valence ElectronsIII. Electron Configurations continuedCurrent Lecture OverviewI. Development of the Periodic TableII. Effective Nuclear Charge III. Periodic trendsDevelopment of the Periodic Table- Physical and chemical properties are a result of their electron configurations- Elements from the same group have similar valence electron configurationsEffective Nuclear Charge (Zeff)- Net positive charge “felt” by a valence electron in a many electron atom- This is always less than the charge of the nucleus (Z) because the core electrons partially shield the attraction- Zeff < Z- Zeff is the effective nuclear charge- Z is the nuclear charge- Zeff = Z – S- S is the screening constant (the number of core electrons)- Example: Nao 11-10 = +1 o The valence electron in Na only feels a +1 charge of the nucleus - Valence electrons of elements in the same group experience similar ZeffThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Periodic Trends I. Atomic sizeII. Ionization Energy – energy associated with the removal of an electron from an elementIII. Electron Affinity – energy change associated with the addition of an electron to an element- The patterns in these properties can be explained by effective nuclear charge Size of Atoms- Even though the valence electrons of elements in the same group experience a similar Zeff they are in orbitals of increasing n.- Going down a group of the periodic table the atomic size increases- Other valence electrons are not effective at screening nuclear charge- When the number of protons increases across a row so does Zeff. As a result valence electrons are pulled toward the nucleus more and atomic size decreases.- Going across a row of the periodic table from left to right atomic size decreasesSizes of Ions- Cations – lose valence e- - Na  Na+ + 1e-- Smaller than parent ion (neutral ion)- Anions gain e-- Anions are larger than the parent atom- When ions have the same number of electrons (isoelectric) the species with more protons will be smallerIonization Energy - Energy required to remove an electron from an isolated gaseous atom or ion- The IE is always positive- Na  Na+ + e-o IE = 496 kJ- Na  Na+2 + e- o IE = 4580 kJ- It’s harder to take the second electron because it has to be taken from the coreTrends - Going down a group IE decreases because atoms increase in size. Electrons that are far from the nucleus are easier to removeExcept when removing an electron results in valence orbitals being exactly filled or half