上海交通大学：《大学化学》教学资源_加州理工课件学习_Series05LewisDotStructures

0 O 0 Lewis O o Dot ● Structures O O 0 Reading:Gray:(2-1),(2-7),(2-11)to(2-13) OGC:(3.5)to(3.8) 0 -1

Lewis Dot Structures Reading: Gray: (2-1), (2-7), (2-11) to (2-13) OGC: (3.5) to (3.8) V-1

Periodic Chemical Reactivity Reactions with hydrogen to form hydrides: LiH vs.HF (notice electronegativity difference) Reactions with fluorine: -HF VS.F2 ionic covalent Reactions with oxygen: -Li2O vs.CO2 vs.F2O Can we predict these structures? Can we understand their properties? Yes,we can!We use Lewis dot structures based on valence electrons. V-2

Periodic Chemical Reactivity Reactions with hydrogen to form hydrides: Reactions with fluorine: Reactions with oxygen: Can we predict these structures? Can we understand their properties? Yes, we can! We use Lewis dot structures based on valence electrons. HF vs. F2 LiH vs. HF (notice electronegativity difference) ionic covalent Li2O vs. CO2 vs. F2O V-2

Person of the Day ©1998H.MITCHELL G.N.Lewis V-3

G.N. Lewis Person of the Day V-3

GILBERT NEWTON LEWIS (1875-1946) "Heavy Water" Gilbert Newton Lewis,one of the most influential and admired scientists of the twentieth century,was a pioneer in both chemistry and physics.Born in Weymouth Landing,Massachusetts in 1875,Lewis was reading by the age of 3.He entered college at age 15,then transferred to Harvard University,where he earned a B.S.(1896)and Ph.D.(1899).His research concentrated on thermodynamics and valence theory (on the behavior of electrons when atoms combine).From this early work on valence,Lewis developed the concept of the covalent bond,and invented the "Lewis symbols"which are still used to describe ways in which atoms bond. Lewis taught at Harvard and MIT before becoming a Professor and Dean at the University of California at Berkeley,whose then languishing College of Chemistry he single-handedly transformed into one of the nation's best.Lewis became the mentor to 290 Ph.D.recipients and 20 Nobel Prize winners For example,he directed the experiments that resulted in the discovery of elements 93-106. In his own work,Lewis combined strict discipline in collecting and organizing data with innovative interpretation of the results.In the early 1930s,he became the first scientist to produce "heavy water," with double-weight hydrogen atoms,which was essential to early experiments in atomic energy.He also worked with Ernest Lawrence in the invention of the cyclotron and in early atom-smashing experiments. From the late 1930s to his death in 1946,Lewis focused on photochemistry.In fact,it was he who coined the term "photon." Gilbert Newton Lewis won numerous honors for his work,including the Society of Arts and Sciences Medal as "the outstanding chemist in America"(1930).He was nominated for the Nobel Prize in chemistry over 30 times,and still today,many scientists believe he well deserved it. V-4

GILBERT NEWTON LEWIS (1875-1946) "Heavy Water" Gilbert Newton Lewis, one of the most influential and admired scientists of the twentieth century, was a pioneer in both chemistry and physics. Born in Weymouth Landing, Massachusetts in 1875, Lewis was reading by the age of 3. He entered college at age 15, then transferred to Harvard University, where he earned a B.S. (1896) and Ph.D. (1899). His research concentrated on thermodynamics and valence theory (on the behavior of electrons when atoms combine). From this early work on valence, Lewis developed the concept of the covalent bond, and invented the "Lewis symbols"which are still used to describe ways in which atoms bond. Lewis taught at Harvard and MIT before becoming a Professor and Dean at the University of California at Berkeley, whose then languishing College of Chemistry he single-handedly transformed into one of the nation's best. Lewis became the mentor to 290 Ph.D. recipients and 20 Nobel Prize winners. For example, he directed the experiments that resulted in the discovery of elements 93-106. In his own work, Lewis combined strict discipline in collecting and organizing data with innovative interpretation of the results. In the early 1930s, he became the first scientist to produce "heavy water,” with double-weight hydrogen atoms, which was essential to early experiments in atomic energy. He also worked with Ernest Lawrence in the invention of the cyclotron and in early atom-smashing experiments. From the late 1930s to his death in 1946, Lewis focused on photochemistry. In fact, it was he who coined the term "photon." Gilbert Newton Lewis won numerous honors for his work, including the Society of Arts and Sciences Medal as "the outstanding chemist in America" (1930). He was nominated for the Nobel Prize in chemistry over 30 times, and still today, many scientists believe he well deserved it. V-4

Lewis Dot Structures How to:1)Write down configuration 2)Draw the structure (each valence e-gets a dot) Neon:(1s)2(2s)?(2p) valence level“n”is2 2+6=8 electrons on the valence level So Ne gets 8 dots: :Ne: Fluorine:(1s)2(2s)2(2p)5 What if we put 2 fluorines together? n=2 :F·+.F :F:F: 2+5=7 valence electrons for F Look！They both have8 So F gets 7 dots: electrons:so we predict F,is a stable molecule V-5

2 + 5 = 7 valence electrons for F So F gets 7 dots: Lewis Dot Structures How to: 1) Write down configuration 2) Draw the structure (each valence e– gets a dot) Neon: (1s)2 (2s)2 (2p)6 valence level “n” is 2 2 + 6 = 8 electrons on the valence level So Ne gets 8 dots: Ne Fluorine: (1s)2 (2s)2 (2p)5 n = 2 F What if we put 2 fluorines together? F + F F F Look! They both have 8 electrons: so we predict F2 is a stable molecule V-5

Each Atom Wants 8 Valence Electrons Chlorine is similar to fluorine:(1s)2(2s)2(2p)6(3s)2(3p)5 Valence level is now 3,but number of valence electrons is still 7.So,the structure is: We can also make Cl2::cl·+.Ci:一：Ci:Ci: Same thing with Br2,12,and the other column VII elements: Br:Br:> which can be rewritten as:Br-Br: The purple line is a single bond,and it stands for 2 electrons If each atom has eight dots,then the molecule is stable V-6

Each Atom Wants 8 Valence Electrons Chlorine is similar to fluorine: (1s)2 (2s)2 (2p)6 (3s)2 (3p)5 Valence level is now 3, but number of valence electrons is still 7. So, the structure is: Cl We can also make Cl2: Cl + Cl Cl Cl Same thing with Br2, I2, and the other column VII elements: Br Br which can be rewritten as: Br Br The purple line is a single bond, and it stands for 2 electrons If each atom has eight dots, then the molecule is stable V-6

Multi-Element Molecules Oxygen:(1s)2(2s)2(2p)4-n=2;6 valence electrons: Fluorine we already know: (n =2;7 valence e) To put 8 electrons on each atom,we need two fluorines and one oxygen:F: :0-f: 。 :F: F: Note:The dot diagram tells us nothing about structure V-7

Multi-Element Molecules Oxygen: (1s)2 (2s)2 (2p)4 → n = 2; 6 valence electrons: O Fluorine we already know: F (n = 2; 7 valence e- ) To put 8 electrons on each atom, we need two fluorines and one oxygen: O F F O F F Note: The dot diagram tells us nothing about structure V-7

Lewis's Dot Structures 便 a lt F a)克--拉+ 侧霜污 a 私0 Gilbert Newton Lewis's memorandum of 1902 showing his speculations about the role of electrons in atomic structure. From Valence and the Structure of Atoms and Molecules (1923),p.29. V-8

Gilbert Newton Lewis's memorandum of 1902 showing his speculations about the role of electrons in atomic structure. From Valence and the Structure of Atoms and Molecules (1923), p. 29. Lewisʼs Dot Structures V-8

More Multi-Element Molecules Nitrogen:(1s)2(2s)2(2p)3-5 valence electrons Nitrogen needs 3 fluorines to get octets on each atom :F:N:F: EN-E Carbon:(1s)2(2s)2(2p)2-4 valence electrons Carbon needs 4 fluorines to get octets on each atom V-9

Nitrogen needs 3 fluorines to get octets on each atom More Multi-Element Molecules Nitrogen: (1s)2 (2s)2 (2p)3 → 5 valence electrons N F F N F F F F Carbon: (1s)2 (2s)2 (2p)2 → 4 valence electrons Carbon needs 4 fluorines to get octets on each atom C F F C F F F F F F V-9

The Duet Rule H,He,Li,and Be only need 2 valence electrons H20 > :0:H 0-H H H .They are trying to "be like He",the nearest inert gas So,we predict NH3 and PHa to be stable compounds H-N-H H-P-H H H V-10

The Duet Rule H, He, Li, and Be only need 2 valence electrons H2O O H H O H H So, we predict NH3 and PH3 to be stable compounds N H H H P H H H •They are trying to “be like He”, the nearest inert gas V-10