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The Development of the Periodic Table Chapter 7 Section 1 Timeline of Development… 1790’s Antoine Lavoisier: compiled a list of elements (about 23) Mid-1800’s Scientists developed a way to determine atomic mass 1870 Ah Ha! My life has purpose again About 70 known elements Organization Meyer, Mendeleev & Moseley Mendeleev gets most of the credit Organized by atomic mass (just as Newlands) but changed columns Organized into columns with similar properties Left blank spaces for places where he thought elements should be, but weren’t discovered yet Table 7.1? Mendeleev’s Predictions Why not atomic #? It was found that some of Mendeleev’s elements were incorrectly placed Why didn’t he use atomic number instead of atomic mass? Answer: atomic #’s weren’t discovered until the early 1900’s Moseley’s Adaptation After Henry Moseley discovered protons (and atomic number) he changed the organization and fixed Mendeleev’s problems Periodic Law: Periodic repetition of chemical and physical properties of the elements when arranged by increasing atomic number Parts of the Periodic Table Columns = Groups (or families) Rows = Periods Sections of the PT Transition Elements Inner Transition Elements Other periodic tables… Why? Why do things behave the way they do? The best predictor/explanation of why elements react are found in: Their # of electrons The way their electrons are organized The size of the atoms How much they want electrons or how much they want to get rid of electrons Valence Electrons Electrons in the outermost energy level of an atom Core Electrons: all electrons that are not in the valence shell Na 1s22s22p63s1 Electron Shielding Positives & Negatives are attracted to each other Effective Nuclear Charge: describes the pull on the electrons by the nucleus Zeff = Z - S Effective Nuclear Charge Shielding constant (# of non-valence electrons) Nuclear Charge (# of protons) Atomic Size 50ml + 50ml = ? Atomic Size Atoms of different elements have different sizes What happens to Zeff as we go down a group? As we go across a period? Atomic Radius What is it? Atomic Radius Trend Increases Increases Increases Atomic Radius Trend Increases Why? 1) As you go down a group, principle energy levels are added (n=1, n=2, n=3) This increases the radius Increases Atomic Radius Trend Why? 2) As you go across a period: No energy levels are added Protons are added Increases Ionic Radius Ions: An atom that has an overall positive or negative charge Examples: Cl-1 (Chlorine with 17 protons and 18 electrons) Mg2+ (Magnesium with 12 protons and 10 electrons) What happens to size when atoms do this? Ionic Radius Trend Positive Atoms To become positive, atoms lose electrons What happens to size if you lose electrons? Hint: You now have more positives pulling in less negatives Positive Nucleus Ionic Radius Trend Negative Atoms To become negative, atoms gain electrons What happens to size if you gain electrons? Hint: out You now have more negatives pulling Positive Nucleus Chapter 7 Test Monday – January 7th Development of the Periodic Table Periodic Trends (what & why) Atomic radius Ionic radius Ionization energy Electron Affinity Isoelectronic Ions Groups of the Periodic Comparing Atomic Size Remember isoelectronic When atoms have the same electron configuration, which one is bigger? Example: a) Na+ b) F-1 c) O-2 Radius decreases with increasing nuclear charge (# of protons) O-2 > F-1 > Na+ Na = +11 F = +9 O = +8 Sample 7.6 Ionization Energy The energy required to remove an electron from an atom 1st IE: Energy to remove the first electron Na Na+ + e 2nd IE: Energy to remove the 2nd Na+ Na2+ + e 3rd IE, 4th IE etc… Hard to steal electrons Easy to steal electrons Increases Increases Trend in 1st Ionization Energy IE Equations & Energies We show the change through an equation: Na Na+ + e- E=+495 Na+ Na+2 + e- E= +4562 Why is the 2nd IE so much bigger? Spikes in IE Sample 7.7 Electron Affinity The measure of how much an atom wants to gain an electron For most atoms, energy is released when this happens Delta E = negative Affinity vs Ionization Ionization energy Cl Cl+ + e- DE = 1251 kJ/mol Electron Affinity Cl + e- Cl- DE = -349 kJ/mol More negative = more energy given off = more favorable Fluorine has the most electron affinity Increases Increases Electron Affinity