Transcription of Chapter 9 Bonding - 1 - Professional Home
1 Chapter 9 Bonding -1Dr. SapnaGuptaLewis Dot Symbol Lewis dot symbols is a notation where valence electrons are shown as dots. Draw the electrons symmetrically around the sides (top, bottom, left and right)Dr. Sapna Gupta/Bonding2 Why Bonding ? And Types? Bonding occurs to make elements more stable. Noble gases are stable, non reactive it must be the electronic configuration. All elements try to have the noble gas configuration OCTET RULE: have 8 e-in the valence of electrons-Between metals and non metals-Cationsand Anions-High melting pointsCovalent-Sharing of electrons-Between non metals only-No ions-Low melting pointsDr.
2 Sapna Gupta/Bonding3 Ionic Bond Made from transfer of electrons Metals lose electrons and become cations(metals have low ionization energy so lose electrons easily) Non metals gain electrons and become anions (non metals have high electron affinity so they gain electrons) Metals give electrons to non metals (Writing Lewis dot structures of ions) Below is a representation of transfer of electrons.+Ca2+CaO+O2 ][Dr. Sapna Gupta/Bonding4 Lewis Structure Ionic Compounds Sodium and ChlorineNa needs to give one electron becomes Na+Cl needs to gain one electrons becomes Cl-Na + |Cl Na+[ |Cl| ]- Calcium and FluorineCa needs to give two electron becomes Ca2+F needs to gain one electrons becomes F-Ca: + |F + |F Ca2+2[ | F | ]- Aluminum and Oxygen Al + | O 2Al3+3 [ | O |] 2- Dr.
3 Sapna Gupta/Bonding5 covalent Compounds Lewis Structures Atoms share electrons to form covalent bonds. HH + HHH HorCl +Cl Cl Cl Dr. Sapna Gupta/Bonding6 covalent BondsA single bondis a covalent bond in which one pair of electrons is shared by two double bondis a covalent bond in which two pairs of electrons are shared by two triple bondis a covalent bond in which three pairs of electrons are shared by two atoms. Double bonds form primarily with C, N, and O. Triple bonds form primarily with C and Cl Cl Cl O C O O O =C= N NN NBond strength and bond lengthbond strengthsingle < double < triplebond lengthsingle > double > tripleN NN=NN NBond Strength163 kJ/mol418 kJ/mol941 kJ/molBond Dr.
4 Sapna Gupta/Bonding7 Writing Lewis the skeleton structure of the molecule or ion by placing the lowest electronegative element in the the total number of valence electrons. Subtract electron(s) if is a cationand add electron(s) if one pair of electrons between each atom, and subtract those from the total number of electrons to the atoms surrounding the central atom or atoms to satisfy the octet the remaining electrons as pairs to the central atom or multiple bonds if atoms don t have the : H and halogens have single bonds (unless halogen is in the center)O and S has two bonds (two single or one double)N and P has three bonds (three single, one double one single or triple)C has four bonds (different combination)Dr.
5 Sapna Gupta/Bonding8 Steps for Writing Lewis StructureDr. Sapna Gupta/Bonding9 Exceptions to the Octet Rule Exceptions to the octet rule fall into three categories: Molecules with an incomplete octet Molecules with an expanded octet Molecules with an odd number of electronsDr. Sapna Gupta/Bonding10 Incomplete OctetsExample: BF3 (boron trifluoride)BF3 (1 3) + (3 7) = 24 val. e :F::F B = F: ::::+1-1 Common with Be, B and Al compounds, but they often dimerizeor :ClClClBe BeBeBeClClCl:F::F B F: :::::no octetDr.
6 Sapna Gupta/Bonding11 Expanded OctetElements of the 3rd period and beyond have d-orbitals that allow more than 8 valence :F Xe F::::::(Xehas 10 valence electrons)22 valence e (S has 12 valence electrons)FFSFF:F: :F:SF6 =48 valence e Dr. Sapna Gupta/Bonding12 Odd Numbers of ElectronsExample: NO (nitrogen monoxide or nitric oxide)NO (1 5) + (1 6) = 11 valence e Example: NO2(nitrogen dioxide)NO2 (1 5) + (2 6) = 17 val. e :N=O:.:N=O:.Are these both equally good? :O=N O:.:O N=O:.:O=N O:.:O N=O.
7 Are these all equally good? better00 1+10000000+1 1 1+10bestDr. Sapna Gupta/Bonding13 Key Points Lewis dot symbols Ionic Bonding covalent Bonding Octet rule Lewis structures Exceptions to the Octet Rule Incomplete octets Expanded octets Odd numbers of electronsDr. Sapna Gupta/Bonding14
