Chemical Bonding. Chapter 12 GCC CHM 130. 12.1 Chemical Bonding. Atoms want to be like noble gases (stable and happy) Goal = 8 outer valence electrons =Octet Rule (except H, He) Metals lose electrons and become (+) cations Nonmetals gain electrons and become (-) anions
12.1 Chemical Bonding
Why is the formula CaBr2? Why one Ca per two Br? Any ideas?
Because Ca ion is +2 and Br ion is -1. So need two Br -1 ions to balance with one Ca +2 ion. +2-1-1=0 (Br-1Ca2+Br-1)
The answer is NOT because Br is diatomic
Note, Br is diatomic BY ITSELF (Br2) but when in a compound the Br ‘s break apart to bond with other atoms! The diatomic elements are NOT diatomic anymore once bonded with others.
Answer: The ones with a metal and a nonmetal.
KBr and MgCl2
12.2 Ionic Bonding
Electrons are completelytransferred from metal to nonmetal.
Draw electron dot structures for Mg and S atoms then Mg2+ and S2- ions in MgS. How many protons and electrons in Mg2+ and S2- ions?
Notice that Mg2+ and S2- are “like” noble gases. They are isoelectronic with Ne and Ar, and that is what makes them happy and stable. While the number of electrons changed, the number of protons did NOT. # Protons never change in chemical reactions.
True or False regarding an ionic bond
between aluminum and iodine?
12.3 Covalent Bonding
…is when nonmetals share electrons.
Single = 2, double = 4, triple = 6 e- shared
Note the bond length is less than r1+r2 due to orbital overlap
HCl (g) + heat H (g) + Cl (g)
H (g) + Cl (g) HCl (g) + heat
True or False regarding H2S?
12.4 Electron Dot Structures
bonding e-= shared e-
lone pairs = unshared e-
If single bonds don’t work, try double, then triple.
Total = 8e-
Examples to put on board:
The central atom is in bold.
12.5 Electron Dots of Polyatomic Ions
+1 charge means one less e-
5 + 4(1) – 1 = 8 e-
Examples for the board:
The central atom is in bold.
12.10 Valence Shell Electron Pair Repulsion Theory
A = Central Atom B = Outer AtomE = Lone Pair on central atom
Linear – AB and AB2
Examples: H2, HCl, CO2
Bond Angle is 180
Trigonal Planar – AB3
Example: Formaldehyde, CH2O
Tetrahedral – AB4
Example: CH4, CF4, CH2F2
Bent – AB2E
Trigonal Pyramidal – AB3E
Example: ammonia, NH3
Bent – AB2E2
Example: water, H2O
Get used to the Table of Shapes online – you will get it on the exam over this chapter!!!
Practice: PH3 and ozone O3
12.6&7 Polar and Nonpolar Covalent Bonds
Symbols used to indicate polarity:
d+ = Partially positive atom
d- = Partially negative atom
points toward more EN atom
Electronegativity (EN) is the ability of a BONDED atom to attract electrons.
Well noble gases don’t BOND! So they can’t pull bonded electrons close. So what is the atom with the highest EN???
Yep, F. F pulls electrons closer than anything! F is an electron hog. Nothing holds electrons tighter than F.
Nonpolar covalent bonds
H2, N2, F2, O2, I2, Cl2 , Br2
C-H bond in CH4
Polar covalent bonds
Examples of polar bonds:
C-O, H-F, S-F, C-N
Ionic, polar covalent, or nonpolar covalent???
Polar Bonds BUT Nonpolar Molecule
Polar bonds cancel out = nonpolar molecule.
Draw the electron dot structure, determine shape, bond angle, determine if bonds are polar and if molecule is polar.
Yes, we skipped sections 8 and 9