Chemical Bonding I www.chem.hawaii.edu/Bil301/welcome.html CHEMISTRY 161 Chapter 9 Chemical Bonding I www.chem.hawaii.edu/Bil301/welcome.html

THE OCTET RULE ns2np6 atoms combine to form compounds in an attempt to obtain a stable noble gas electron configuration ns2np6

IONIC BONDING COVALENT BONDING

THE OCTET RULE COVALENT BONDING sharing electrons (electron pair) F electronic configuration of F is 1s22s22p5 F F

F F + F F non-bonding, or lone pair of electrons bonding pair of electrons

H2 is the simplest covalent molecule + H H H H + the bond length of H2 is the distance where the total energy of the molecule is minimum

EXAMPLES H2O NH3 CH4 HX single bonds O2 CO2 C2H4 double bonds C2H2 N2 HCN triple bonds transition metal compounds w/ halides quadruple bonds

EXAMPLES H2O NH3 CH4 HX O2 CO2 C2H4 C2H2 N2 HCN

few thousands kJ/mol

IONIC OR COVALENT electronegativity difference between the two atoms involved in the bond

energies of the atomic orbital with the unpaired electron ELECTRONEGATIVITY is the tendency of an atom in a bond to attract shared electrons to itself F > O > N, Cl > Br > I, C, S …….. Na, Ba, Ra > K, Rb > Cs, Fr Electronegativity increases F Cl I O N C S Na K Rb Cs Fr Ra Ba Li Br energies of the atomic orbital with the unpaired electron

ELECTRONEGATIVITY F is the most electronegative F > O > N, Cl > Br > I, C, S …….. Na, Ba, Ra > K, Rb > Cs, Fr Electronegativity increases Li Br P I N O Cl F C S Na K Rb Cs Fr Ra Ba Se F is the most electronegative H has an electronegativity about the same a P

IONIC VERSUS COVALENT BONDS bonds are neither completely ionic nor covalent (only in homonuclear molecules)

IONIC VERSUS COVALENT BONDS compounds composed of elements with large difference in ELECTRONEGATIVITY significant ionic character in their bonding B has greater electronegativity A B

IONIC VERSUS COVALENT BONDS B has a greater share A B

Fluorine is more electronegative than hydrogen. HYDROGEN FLUORIDE Fluorine is more electronegative than hydrogen. + F F H H +

Fluorine is more electronegative than hydrogen. HYDROGEN FLUORIDE Fluorine is more electronegative than hydrogen. + F F H H + d+ d– This is a polar covalent bond. The bond has a partly ionic and partly covalent nature.

Variation of ionic character with electronegativity.

H2O2 OF2 NF3 CO32- NO3- HCOOH H2CO CH3COOH

SUMMARY IONIC BONDING COVALENT BONDING

Homework Chapter 9 pages 338-346, problem sets