CHAPTER 2: Atomic Structure and Interatomic Bonding 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba1

What promotes bonding? What types of bonds are there? What properties are inferred from bonding? ISSUES TO ADDRESS... 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 2

Nucleus: Z = # protons = 1 for hydrogen to 94 for plutonium N = # neutrons Atomic mass A ≈ Z + N BOHR ATOM 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 3

have discrete energy states tend to occupy lowest available energy state. Electrons... ELECTRON ENERGY STATES 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 4

have complete s and p subshells tend to be unreactive. Stable electron configurations... STABLE ELECTRON CONFIGURATIONS 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 5

Most elements: Electron configuration not stable. SURVEY OF ELEMENTS 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 6

Columns: Similar Valence Structure Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions. THE PERIODIC TABLE 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 7

Ranges from 0.7 to 4.0, Smaller electronegativity Larger electronegativity Large values: tendency to acquire electrons. ELECTRONEGATIVITY 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 8

Occurs between + and - ions. Requires electron transfer. Large difference in electronegativity required. Example: NaCl IONIC BONDING 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 9

Give up electronsAcquire electrons EXAMPLES: IONIC BONDING 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 10

Requires shared electrons Example: CH 4 C: has 4 valence e, needs 4 more H: has 1 valence e, needs 1 more Electronegativities are comparable. COVALENT BONDING 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 11

Molecules with nonmetals Molecules with metals and nonmetals Elemental solids (RHS of Periodic Table) Compound solids (about column IVA) EXAMPLES: COVALENT BONDING 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 12

Arises from a sea of donated valence electrons (1, 2, or 3 from each atom). Primary bond for metals and their alloys METALLIC BONDING 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 13

Type Ionic Covalent Metallic Bond Energy Large! Variable large-Diamond small-Bismuth Variable large-Tungsten small-Mercury Comments Nondirectional (ceramics) Directional semiconductors, ceramics polymer chains) Nondirectional (metals) SUMMARY: BONDING 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 14

Bond length, r Bond energy, E o Melting Temperature, T m T m is larger if E o is larger. PROPERTIES FROM BONDING: T M 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 15

Elastic modulus, E E ~ curvature at r o E is larger if E o is larger. PROPERTIES FROM BONDING: E 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 16

Coefficient of thermal expansion,   ~ symmetry at r o  is larger if E o is smaller. PROPERTIES FROM BONDING:  10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 17

Ceramics (Ionic & covalent bonding): Metals (Metallic bonding): Polymers (Covalent & Secondary): Large bond energy large T m large E small  Variable bond energy moderate T m moderate E moderate  Directional Properties Secondary bonding dominates small T small E large  SUMMARY: PRIMARY BONDS 10/28/2015 9:56 AM Dr. Mohammad Abuhaiba 18