1. An Introduction to Chemistry
PowerPoint Lectures to accompany Physical Science, 8e
Chapter 9
Chemical Bonds
An Introduction to Chemistry
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Core Concept
Electron structure will explain how and why atoms join together in certain numbers.

3. Compounds and Chemical Change
Atom - smallest elemental unit
Molecule
smallest particle still retaining the characteristic chemical properties of a substance
Examples:
oxygen, hydrogen gas - diatomic molecules
Ozone - triatomic oxygen molecule
Noble gases: helium, neon - “monatomic” molecules

4. Chemical Reactions
Formation and/or breaking of chemical bonds to form new molecules (products) from old ones (reactants)
Chemical energy - internal bonding potential energy
Chemical equation - symbolic summary of chemical reaction

5. Valence Electrons and Ions
Outer electrons determining the chemical properties of an atom
Octet rule
Atoms attempt to acquire an outer shell of eight electrons
Electrons can be gained/lost/shared in the process
Example: sodium (Na)

6. Chemical Bonds Covalent Three types: Metallic bonds Ionic
Attractive forces holding atoms together in compounds
Can be described in terms of molecular (delocalized) or atomic (localized) orbitals
Three types:
Ionic
Electrons transferred between atoms
Electrostatic force = binding force
Covalent
Octets achieved through sharing electrons
Typically between nonmetallic elements, r.h.s of periodic table
Metallic bonds
Outer electrons move freely throughout metal
“Electron gas” within rigid lattice of metal atoms
Conduct heat and electricity well

7. Ionic Bonds Chemical bond of electrostatic attraction
Form crystalline solids with orderly geometric structure
Example: NaCl
Na loses; Cl gains
No single NaCl molecule, per se

8. Energy and Electrons in Ionic Bonding
Reaction energy released = heat of formation
Divided conceptually into half-reactions
Electron transfer rules
Electrons lost/gained to form closed octets
Number gained = number lost

9. Ionic Compounds and Formulas
List elements in compound and their proportions
Proportions decided by electron gain/loss
Ionic compounds
Characterized by ionic bonds
White, crystalline solids soluble in water
Families IA and IIA lose electrons and form positive ions
Families VIA and VIIA gain electrons to form negative ions

10. Ionic compounds and formulas
List elements in compound and their proportions
Proportions decided by electron gain/loss
Ionic compounds
Characterized by ionic bonds
White, crystalline solids soluble in water
Families IA and IIA lose electrons and form positive ions
Families VIA and VIIA gain electrons to form negative ions

11. Covalent Bonds Chemical bonds formed by sharing pairs of electrons
Electrons shared to form octets, ideally
Overlap of shared electron clouds between nuclei yields net attraction
Atoms within covalent compounds are electrically neutral, or nearly so

12. Covalent Compounds and Formulas
Covalent compound - held together by covalent bonds
Electrons shared in covalent bonds
Electron dot representation
Bonding pairs shared
Lone (non-bonding) pairs not shared

13. Multiple Bonds Sharing of more than one electron pair Examples
Ethylene - double bond
Acetylene - triple bond

14. Bond Polarity Result of unequal sharing of electrons Electronegativity
Measure of an atom’s ability to attract electrons
Differences:
1.7 or greater - ionic
polar covalent
Less than covalent

15. Electronegativities

16. Composition of Compounds
Millions of different combinations of over 90 elements
Common names
Often related to historical usage (baking soda, washing soda,…)
Difficult to relate to actual molecular composition
Modern approach - systematic sets of rules
Different for ionic and covalent compounds
One common rule - “-ide” means compound contains only two different elements

17. Ionic Compound Names
Name of metal (positive) ion first; then nonmetal (negative) ion
Many elements have variable charges
Historical suffix usage
“-ic” for higher of two;
“-ous” for lower
Modern approach
English name of metal followed by Roman numeral indicating charge

18. Ionic Compound Formulas
Two rules
Write symbol for positive ion first followed by negative ion symbol
Assign subscripts to assure compound is electrically neutral
Example: Calcium chloride

19. Covalent Compound Names
Molecular - composed of two or more nonmetals
Same elements can combine to form a number of different compounds
Two rules
First element in formula named first with number indicated by Greek prefix
Stem name of second element next; Greek prefix for number; ending in “-ide” (for two elements)

20. Covalent Compound Formulas
Examples: carbon dioxide, carbon tetrachloride
Valence
Number of covalent bonds an atom can form
Hydrogen valence = 1
Oxygen = 2; single and double bonds
Nitrogen = 3; single, double and triple bonds
Carbon = 4 - single, double and triple bonds