Chapter 4.1-Lewis-structure.ppt - CHEMICAL BONDING CHAPTER 4 1 2 CONTENTS 4.1 Lewis Structure 4.2 Molecular Shape Polarity 4.4 Intermolecular Forces 4.5

Chapter 4.1-Lewis-structure.ppt - CHEMICAL BONDING CHAPTER...

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Unformatted text preview: CHEMICAL BONDING CHAPTER 4 1 2 CONTENTS 4.1 Lewis Structure 4.2 Molecular Shape & Polarity 4.4 Intermolecular Forces 4.5 Metallic Bond Subtopic 4.1 LEWIS STRUCTURE 3 4 LEWIS STRUCTURE Concept of Resonance 6 Exception to 5 Octet Rule Lewis structure & 4 Formal Charge 1 Topic Outline Lewis Symbol 2 3 Octet Rule Formation of Chemical Bond 5 LEWIS STRUCTURE LEARNING OUTCOMES At the end of the lesson student should be able to: (a) (b) (c) (d) Write the Lewis symbol for an atom. State the octet rule and describe how atoms obtain the octet configuration. Describe the formation of the following bonds using Lewis symbol. i. Ionic bond or electrovalent bond ii. Covalent bond iii. Dative or coordinate bond Draw Lewis structure of covalent species with single, double and triple bonds. 6 LEWIS STRUCTURE LEARNING OUTCOMES At the end of the lesson student should be able to: (e) Compare the bond length between single, double and triple bonds. (f) Determine the formal charge and the most plausible Lewis structure. (g) Explain the exception to the octet rule: incomplete octet, expanded octet and odd number electrons. (h) Explain the concept of resonance using appropriate examples. 7 LEWIS STRUCTURE CHEMICAL BONDS The forces of attraction that holds the atoms together in new species Involved only electrons in the outermost orbital or _______________ Three type of bonds : ionic, covalent and metallic The outermost orbital or valence shell valence electrons LEWIS STRUCTURE 8 LEWIS SYMBOLS Also known as Lewis structure or Lewis diagram Consists of : Symbol of an element Pb or x x Pb x One dot or cross for each valence electron x 9 LEWIS STRUCTURE Lewis symbol for Main Group Atoms Group Electronic configuration 1 ns1 2 ns2 13 ns2np1 14 ns2np2 15 ns2np3 16 ns2np4 17 ns2np5 18 ns2np6 Period 2 Period 3 10 LEWIS STRUCTURE EXERCISE 1 Write Lewis dot symbols for the following atoms: (a) K (b) Ca (c) Be (d) Ga (e) O (f) Br (g) N (h) I (i) As (j) F (k) Mg (l) S 11 LEWIS STRUCTURE EXERCISE 2 Write Lewis dot symbols for the spesies according to the following electronic configuration: (a)P : 1s2 2s2 2p6 3s1 (b) Q : 1s2 2s2 2p6 3s2 3p6 4s2 (c) R : 1s2 2s2 2p6 3s2 3p4 (d) S : 1s2 2s2 2p3 (e) T : 1s22s22p1 (f) U : 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 (g) V : 1s2 2s2 2p6 3s2 3p2 (h) W : 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 12 LEWIS STRUCTURE THE OCTET RULE The tendency of molecules and polyatomic ions to have structures in which ______ electrons surround each atom To achieve ___________ electronic configuration which is stable Hydrogen atom achieve electronic configuration of 2 electrons (duplet) 13 LEWIS STRUCTURE THE OCTET RULE Transfer (lose/gain) of electron + 1s2 2s1 Atoms achieve noble gas configuration by: F 1s2 2s2 2p5 [Li]+ [ F ] 1s2 1s2 2s2 2p6 [He] [Ne] Sharing of electron F + F 1s2 2s2 2p5 1s2 2s2 2p5 F F 1s2 2s2 2p6 [Ne] 14 LEWIS STRUCTURE STABILITIES OF IONS Noble gas Stable electronic configuration of ions Pseudo noble gas Half-filled orbital 15 LEWIS STRUCTURE STABILITIES OF IONS Form stable ions (duplet/octet) Noble Gas Configuration Valence electronic configuration: ns2np6 Example: 1) Na → Na+ + e1s22s22p63s1 _____________ 2) F + e- → F1s22s22p5 _____________ 16 LEWIS STRUCTURE STABILITIES OF IONS A completely filled orbital but not the noble gas configuration Pseudo Noble Gas Configuration Valence electronic configuration: ns2np6nd10 or ns2np6nd10nf14 Example: 1) 31Ga : 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p1 Ga3+: ______________________ 2) 29Cu : 1s2 2s2 2p6 3s2 3p6 3d10 4s1 Cu+: 1____________________ 17 LEWIS STRUCTURE STABILITIES OF IONS A special stability of half-filled d orbital Half-filled Orbital Configuration Valence electronic configuration: nd5 Example: 1) 25Mn : 1s2 2s2 2p6 3s2 3p6 3d5 4s2 Mn2+: ____________________ 2)26Fe : 1s2 2s2 2p6 3s2 3p6 3d6 4s2 Fe3+: ____________________ 18 LEWIS STRUCTURE EXERCISE 3 Write the electron configuration and state the type of stability of the ions formed from the following atom. (a) 13Al Ion Al3+ ClIn3+ (b) 17 Cl (c) 49 In Electronic configuration Type of stability EXERCISE 4 19 LEWIS STRUCTURE Write the electron configuration of the outer shells of the following ions. State whether the above ions are stable or unstable and give your reason. (a) Zn2+ (b) N3(c) Al2+ (d) S2Ion Zn2+ N3Al2+ S2- Electronic configuration Stability Reason 20 LEWIS STRUCTURE FORMATION OF IONIC BOND Also known as ______________ The electrostatic forces between the positive ions and negative ions Involved the transfer of electrons from: Non-metal atom Metal atom (more electropositive) (more electronegative) 21 LEWIS STRUCTURE PROPERTIES OF IONIC BOND Solid at room temperature Soluble in water Properties of ionic compound High melting & boiling point Molten ionic compounds conduct electricity 22 LEWIS STRUCTURE LEWIS STRUCTURE OF IONIC BOND Formation of NaCl Formation of MgO Formation of CaBr2 23 LEWIS STRUCTURE EXERCISE 5 Draw Lewis structure to show the formation of the following compounds: (a) KF (b) BaO (c) Li2O (d) MgCl2 24 LEWIS STRUCTURE EXERCISE 6 The element X has one electron and the element Y has six electrons in their outermost shell respectively. (a) What is the formula of the compound formed between the elements X and Y? (b) Name the type of bond formed in (a) (c) Draw the Lewis structure to show the formation of compound in (a) 25 LEWIS STRUCTURE FORMATION OF COVALENT BOND Formed by ________ one or more pairs of valence electrons between the bonded atoms Bonding pair electron Lone pair electron 26 LEWIS STRUCTURE LEWIS STRUCTURE OF COVALENT BOND Single bond two atoms share one pairs of electrons Double Bond two atoms share two pairs of electrons Triple Bond two atoms share three pairs of electrons 27 LEWIS STRUCTURE BOND LENGTHS BETWEEN COVALENT BOND Is the distance between the nuclei of two bonded atoms Double Bond Triple Bond C-C C=C C C Bond Length (nm) 0.154 0.135 0.121 Bond Energy(kJmol-1) 346 611 837 Bond Type Bond strength increase Bond length increases Single bond Single bond < Double Bond < Triple Bond Triple bond < Double Bond < Single Bond 28 LEWIS STRUCTURE EXERCISE 7 Draw Lewis dot symbols for the following compound: (a) Cl2 (b) O2 (c) NH3 Electronegativity (pg287) 29 LEWIS STRUCTURE • An ionic bond joins an atom of a metallic element and an atom of a non-metallic element. • Covalent bonds involve atoms of non-metallic elements • Rule to follow: An ionic bond forms when the electronegativity difference between the two bonding atom is ≥ 2.0. 30 LEWIS STRUCTURE EXERCISE 8 X, Y and Z represent element with proton number of 9, 16 and 19. (a) Write the electronic configuration of X, Y and Z in terms of s and p orbitals. (b) Predict the type of bonding you would expect to form between: (i) X and Y (ii) X and Z (c) Show the Lewis structure for the formation of compound in (b)(i) 31 LEWIS STRUCTURE FORMATION OF DATIVE BOND Formed when one atom provides two electrons which are then shared with another atom Also known as ___________ covalent bond Is represented by an arrow from the donor atom to the acceptor atom LEWIS STRUCTURE FORMATION OF DATIVE BOND 32 Donor atom have a lone pair electrons Acceptor atom have an empty orbital to fill the two electrons. Same properties as the normal covalent bond 33 LEWIS STRUCTURE LEWIS STRUCTURE OF DATIVE BOND H3O+ NH4+ NH3 → BCl3 EXERCISE 9 34 LEWIS STRUCTURE Draw Lewis structure for the formation of the following compound: (a) NH4+ (b) NH3 → BF3 (c) Al2Cl6 35 EXERCISE 10 LEWIS STRUCTURE Boron hydride (BH3) reacts with ammonia in the molar ratio of 1:1 to form a product. (a) Draw the Lewis structures of boron hydride, ammonia and the product formed. (b) What type of bonding is formed between ammonia and boron hydride? 36 LEWIS STRUCTURE STEPS IN DRAWING LEWIS STRUCTURE 1 Drawing Lewis Structure 5 Form double or triple bond if octet rule is not satisfied Determine central atom & count valence e4 Place any remaining eat the central atom 2 Draw single bond and calculate the non-bonding e- 3 Complete the octet of the terminal atom DRAWING LEWIS STRUCTURE 37 LEWIS STRUCTURE CH4 1 Determine central atom & count valence e- Central atom : 2 Draw single bond & calculate the non-bonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining eat the central atom - 5 Form double or triple bond if octet rule is not satisfied - - DRAWING LEWIS STRUCTURE 38 LEWIS STRUCTURE NH3 1 Determine central atom & count valence e- Central atom : 2 Draw single bond & calculate the nonbonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining eat the central atom - 5 Form double or triple bond if octet rule is not satisfied - DRAWING LEWIS STRUCTURE 39 LEWIS STRUCTURE H2O 1 Determine central atom & count valence e- Central atom : 2 Draw single bond & calculate the nonbonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining eat the central atom - 5 Form double or triple bond if octet rule is not satisfied - DRAWING LEWIS STRUCTURE 40 LEWIS STRUCTURE NOCl 1 Determine central atom & count valence e- Central atom : 2 Draw single bond & calculate the nonbonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining e- at the central atom 5 Form double or triple 1 bond if octet rule is not satisfied 2 DRAWING LEWIS STRUCTURE 41 LEWIS STRUCTURE CO2 1 Determine central atom & count valence e- Central atom : C 2 Draw single bond & calculate the nonbonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining e- at the central atom 5 Form double or triple bond if octet rule is not satisfied 1 2 DRAWING LEWIS STRUCTURE 42 LEWIS STRUCTURE SCN - 1 Determine central atom & count valence e- Central atom : 2 Draw single bond & calculate the nonbonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining e- at the central atom 5 Form double or triple bond if octet rule is not satisfied 1 3 2 DRAWING LEWIS STRUCTURE 43 LEWIS STRUCTURE NO2 + 1 Determine central atom & count valence e- Central atom : 2 Draw single bond & calculate the nonbonding e- (NBe-) 3 Complete the octet of the terminal atom 4 Place any remaining e- at the central atom 5 Form double or triple bond if octet rule is not satisfied 1 2 EXERCISE 11 44 Draw the Lewis structure of: (a) O3 (b) SO3 (c) CO32(d) NO3- LEWIS STRUCTURE FORMAL CHARGE Negative FC -on more electronegative atom Positive FC -on more electropositive atom 45 LEWIS STRUCTURE Apparent charges on certain atom in a Lewis structure FORMAL CHARGE (FC) Is used to find the most stable Lewis structure The sum of the FC of the atoms must equal the charge on the molecule or ion FC should be as small as possible 46 EXAMPLE 1 LEWIS STRUCTURE Calculate the formal charge for each atom of the following compounds: (a)(b H (b) H – N – H I H–C–H I H (c) I H H–O–H (d) O O O - (e) (f) O S O O N O O ANSWER (a) (b) H1 I H3 – C – H2 I H4 H1 – N – H2 I H3 47 Formal charge of: Formal charge of: Formal charge of: (c) H1 – O – H 2 (d) Formal charge of: O2 O1 O3 48 ANSWER (e) S O1 (f) Formal charge of: O2 - O N O O Formal charge of: 49 EXAMPLE 2 LEWIS STRUCTURE Which of these Lewis structure is the most plausible structure of NO2+ ion? [O = N=O + A [ O – N O ]+ B 50 ANSWER (A) LEWIS STRUCTURE Formal charge of: [O 1 = N = O2 + (B) Formal charge of: [O 1 –N O ]+ 2 Structure A is _____stable because the positive charge is located on the more electropositive atom. ___ is more electropositive than _____. 51 EXAMPLE 3 LEWIS STRUCTURE Which of these Lewis structure is the most plausible structure of SCN- ion? [ S–C N ]A [ S C N ]B [ S=C=N C 52 ANSWER LEWIS STRUCTURE Formal charge of: (A) [ S–C N ]Formal charge of: (B) [ S C N ]Formal charge of: (C) [ S=C=N - 53 EXERCISE 12 LEWIS STRUCTURE Two Lewis structures for the sulphate ion, SO42are shown below. 2- O O S O O 2- O O S O O I II Which of these Lewis structure is the stable structure for sulphate ion? ANSWER 12 O1 O2 S 54 LEWIS STRUCTURE 2- Formal charge of structure I: 2- Formal charge of structure II: O 4 3 O O 1 O2 S 4 O 3 O Structure II is ______stable because _______________________________________ 55 LEWIS STRUCTURE EXCEPTION TO OCTET RULE Incomplete octet Expanded octet Exception to octet rule Odd No. Electron 56 LEWIS STRUCTURE EXCEPTION TO OCTET RULE Incomplete Octet occur when central atom has less than 8 electron in its valence shell Beryllium, boron and aluminium – electron deficient species 57 LEWIS STRUCTURE EXCEPTION TO OCTET RULE BF3 Incomplete Octet AlCl3 BeH2 Surrounded by 6 eValence electronic configuration of B: Surrounded by 4 eValence electronic configuration of Be: Surrounded by 6 eValence electronic configuration of Al: 58 LEWIS STRUCTURE EXCEPTION TO OCTET RULE Expanded Octet occur when central atom has more than 8 electron in its valence shell Involves nonmetal atom of the third period onward (due to the existence of the empty d orbitals) 59 LEWIS STRUCTURE EXCEPTION TO OCTET RULE PCl5 P atom is surrounded by 10 eValence electronic configuration of P: Expanded Octet S atom is surrounded by 12 eValence electronic configuration of S: SF6 60 LEWIS STRUCTURE EXCEPTION TO OCTET RULE Odd Number electron occur when central atom has odd no. of electrons in its valence shell Involves atom from an odd numbered group such as N (group 15) and Cl (group 17) 61 LEWIS STRUCTURE EXCEPTION TO OCTET RULE Odd Number electron NO2 ClO2 62 LEWIS STRUCTURE EXERCISE 13 Draw the Lewis structure of the following molecules and state the special features at the central atoms. (a) NO (b) TeCl4 (c) AlBr3 (d) XeF2 63 EXERCISE 14 LEWIS STRUCTURE (a) Elements phosphorus and nitrogen are in the group 15 of the Periodic Table. Draw the Lewis structures for PCl5 and NCl3 molecules. (b) but Nitrogen and phosphorus are Group 15 element in the periodic table. Explain why phosphorus can form PCl3 and PCl5 nitrogen can only form NCl3 64 LEWIS STRUCTURE CONCEPT OF RESONANCE RESONANCE STRUCTURE Two or more Lewis structures for a single molecule that cannot be represented accurately by only one Lewis structure Are shown by using double headed arrow (↔) Have same bond length and bond energy Involved the sharing of the same no. of electron pairs 65 LEWIS STRUCTURE CONCEPT OF RESONANCE RESONANCE HYBRID Two or more plausible Lewis structure can be written for certain molecule but cannot neither one could accurately represent the molecules Are shown by using dotted line to show the delocalised of electron over the entire molecule Also known as equivalent resonance structure 66 LEWIS STRUCTURE CONCEPT OF RESONANCE Resonance Structure of O3 Resonance Structure of SO2 Resonance Hybrid of O3 Resonance Hybrid of SO2 67 LEWIS STRUCTURE CONCEPT OF RESONANCE Resonance Structure of CO32- Resonance Hybrid of CO32- 68 LEWIS STRUCTURE CONCEPT OF RESONANCE Resonance Structure of NO3- Resonance Hybrid of NO3- EXERCISE 15 69 LEWIS STRUCTURE Write three resonance structures for NCO- ion. Designate formal charge on each atom, if any. Which structure is more stable? Explain. 70 EXERCISE 18 LEWIS STRUCTURE Based on the skeletal structure of peroxynitrite ion, OONO-, draw all the possible Lewis structures. Assign formal charge to each atom in the structure. Determine the most stable Lewis structure for the ion and explain your answer. ...
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