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Coulombic Attraction (between + and – charges)
Periodic Trends Coulombic Attraction (between + and – charges) + - Attracts (electrons with protons, i.e. the nucleus) - - Repels (electrons with electrons, i.e. electrons in shells) (of course + + repels as well… that rhymes!) Attraction or Repulsion increases as things get closer together and decreases as they get farther apart (as 1 𝑟 2 )
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We will explain observed trends in
Atomic Radius Ionization Energy Electronegativity size ability to lose e– ability to gain e–
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The atomic radius of a chemical element is the distance from the center of the nucleus to the boundary of the surrounding cloud of electrons (valence electrons).
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decreases across period
Atomic Radius decreases across period -more nuclear charge (more attraction) -due to increasing shielding (more energy levels) increases down group Note: covalent or metallic radius of bonded atoms vs. van der Waals radius of nonbonded atoms (Noble Gases)
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increases across period
Ionization Energy (IE): + energy required to remove an e– increases across period -more nuclear charge (more attraction) -due to increasing shielding (more energy levels) decreases down a group
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Electronegativity (EN) Trends
atom’s ability to attract bonded electrons increases across period -more nuclear charge (more attraction) -due to increasing shielding (more energy levels) decreases down group
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nuclear charge & shielding
Atomic Radius Ionization Energy Electronegativity size ability to lose e– ability to gain e– explained by: nuclear charge & shielding atomic # / protons electrons in filled energy levels
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Nuclear Charge & Shielding
protons(+) attracting e–’s(–) shielding: inner e– levels block nuclear charge decreases Ne Li across a period +10 +3 What happens to atomic radius? Na Ar down a group increases +11 +18 WHY?
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Periodic Trends (Summary)
ATTRACTION INcreases so…Atomic Radius __________ decreases so…Ionization Energy _________ increases so…Electronegativity _________ increases ATTRACTION DEcreases so…Electronegativity _________ so…Ionization Energy _________ so…Atomic Radius __________ All explained by ATTRACTION: nuclear charge shielding increases decreases decreases
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Ions & Ionic Radius Cations from metals: e–’s removed
positive (+) charge smaller outer shell lost Anions from nonmetals: e–’s added negative (–) charge larger more e– repulsions
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WHY? Quick Quiz! Atoms get ________ down a ________. bigger, period
smaller, group bigger, group smaller, period WHY? more energy levels more shielding less attraction
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WHY? Quick Quiz. Atomic radii _________ across a period? get bigger
get smaller stay the same size are weird WHY? more protons more nuclear charge more attraction
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Quick Quiz. Which of the following correctly orders atomic size from largest to smallest? F > Cl > Br Li > Na > K F > N > B Mg > Al > S
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Quick Quiz. Metals tend to ________ electrons to form _________ cations. gain, positive gain, negative lose, negative lose, positive
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(same energy level/shielding)
Quick Quiz. As you go across period 3 from Mg to Cl, the energy needed to remove an electron from an atom ______________. A. generally increases B. generally decreases C. does not change D. varies unpredictably. WHY? more protons more nuclear charge more attraction (same energy level/shielding)
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Quick Quiz. Which of the following is the most electronegative? Cl Se Na I
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Quick Quiz. The noble gases have _____________. A. high ionization energies. B. high electronegativities. C. large atomic radii. D. a tendency to form both cations and anions.
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Quick Quiz. Alkali metals have lower ionization energies than halogens because _______________. A. alkali metals are smaller with more protons. B. halogens are larger with more protons. alkali metals are larger with lower nuclear charges. D. halogens are smaller with fewer protons.
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Quick Quiz. Fluorine is the most electronegative halogen because it is ___________________. A. larger with more energy levels (shielding) B. smaller with more energy levels (shielding) C. smaller with fewer energy levels (shielding) D. larger with fewer energy levels (shielding)
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