The Nature of The Nature of Chemical Bonds Chemical Bonds Chapter 12 Chapter 12
Dec 21, 2015
Homework AssignmentHomework AssignmentChap 12Chap 12
Review Questions (p 262): 1 – 24Review Questions (p 262): 1 – 24
Multiple Choice Questions: 1 - 10Multiple Choice Questions: 1 - 10
Electron Shells and Chemical Bonding
Valence electrons
Group 1A Group 7A
Full capacity of a shell = 2n2
Fig 8.20 Electron dot notation for representative
elements1
5 6 7
8
3 42
Valence electronsValence electrons – outermost electrons in an atomOctet ruleOctet rule – atoms attempt to acquire 8 valence electrons
Closer look at the inert gases
• Inert gas atoms have filled valence shells
• Except for He, all have 8 valence electrons in4 nonbonding pairs
• Octet rule: An atom will gain. lose, or sharevalence electrons until it is surroundedby 8 valence electrons.
Three Types of Chemical BondsThree Types of Chemical Bonds(1) Ionic bonds
• Electrons are transferred from one atom to another
• Occur between a metal atom and a nonmetal atom
(2) Covalent bonds
• Electrons are shared between two atoms• Occur between two nonmetal atoms
(3) Metallic bonds
• Metal atoms share many electrons in a “sea” that is free to move throughout the metal
Na + Cl Na+ Cl -
The Ionic Bonds and Ionic Compounds
Na Na+ + e-
e- + Cl Cl -
NaCl• Opposite charges hold ions together
• Form between metals and nonmetals
Na 11 protons11 electrons Na+ 11 protons
10 electrons
Cl 17 protons17 electrons
Cl-17 protons18 electrons
Formation of an ionic bond
+ e−
Net reaction: Na + Cl → Na+Cl− + energy
This energy is called the heat of formation
Fig. 12.7(a) Model of the sodium chloride crystal
−+
No molecules in an ionic compound!No molecules in an ionic compound!
Na+ ionsCl− ions
Formula unit
• Ionic compounds consist of a combination of positive ions and negative ions
• Ions are formed as nonmetal atoms gain and metal atoms lose electrons to achieve stable noble gas structure
• The sum of the charges on the positive ions and negative ions in each formula unit must equal zero
• How do we determine the formula for an ionic compound?