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
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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
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.
between aluminum and iodine?
…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
bonding e-= shared e-
lone pairs = unshared e-
If single bonds don’t work, try double, then triple.
Total = 8e-
The central atom is in bold.
+1 charge means one less e-
5 + 4(1) – 1 = 8 e-
The central atom is in bold.
A = Central Atom B = Outer AtomE = Lone Pair on central atom
Linear – AB and AB2
Examples: H2, HCl, CO2
Bond Angle is 180
Example: Formaldehyde, CH2O
Example: CH4, CF4, CH2F2
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
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.
H2, N2, F2, O2, I2, Cl2 , Br2
C-H bond in CH4
Examples of polar bonds:
C-O, H-F, S-F, C-N
Ionic, polar covalent, or nonpolar covalent???
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