CHEM 121 Chapter 4

Ionic v. Covalent Substances Ionic substances: Ionic bonds: Covalent substances: Covalent bonds: - +

Covalent Bonds Form when atoms share electrons to form molecules Usually between nonmetal and nonmetal Atoms with….

Covalent Bonding H + H H H F + F F F

More Covalent Compounds + H C + 4 H Carbon atom:

Another Covalent Compound + H N + 3 H Nitrogen atom:

One more Covalent Compound + H O + 2 H Oxygen atom:

Lewis Dot Structure Hints Draw only the ____________ electrons Carbon group elements want ____________ Nitrogen group elements want ___________ and… Oxygen group elements want ____________

Drawing Lewis Dot Structures Count the total number of valence electrons Arrange atoms so that at least one bond connects them How many electrons are left? These are lone pairs!

3-minute review Draw the Lewis Structures for each of the following covalent compounds: CH3Cl PH3 H2O2

Lewis Dot Structures for Ions Polyatomic ions are ________________ bonded When counting valence e-, include _____________ How many valence e- total in each of the following? NO3- SO42-

3-minute review How many valence electrons should be used to draw the Lewis Structure of acetate (C2H3O2-)?

Multiple Bonds O + C + O N + N

3-minute review Draw the Lewis Structures for each of the following covalent molecules: C2F6 C2F4 C2F2

Resonance Structures Molecules with more than one Lewis Structure O3 Usually involves swapping double bond e- with lone pair e- or other double bond e- True structure is a _______________ O3

3-minute review Draw 2 resonance structures for the nitrate ion: NO3-

Exceptions to the Octet Rule Hydrogen Group 3A Elements Third Row (and later) Elements

Examples: PCl3 and PCl5

Shapes of Molecules VSEPR: Minimize e- repulsion e- groups pushed as far apart as possible Electron groups: Note: double, triple bonds count as ONE group

Basic Molecular Shapes 2 electron groups 3 electron groups

Basic Molecular Shapes: 4 electron groups bent

Electronegativity Electronegativity: (EN)

Electronegativity & Bond Type ________________________ tells us whether a bond is more ionic or more covalent Ionic bond: Covalent bond: Some difference in electronegativity: No difference in electronegativity: Polar bonds create a

Polarity of Molecules O H H-H F-F H-F Polar bond: difference in electronegativities of bonded atoms H-H F-F H-F O H

Polarity of Molecules C H Add polar bonds (head to tail) Molecules with polar bonds may not be polar overall!

Covalent Compounds Combination of two different elements Rules for Naming ______________________ element first; ______________________ element is second. Second element: “root”-ide Add Greek numerical prefixes

Naming Covalent Compounds Example: CS2 Which element is less EN? Second element is root-ide Add prefix

Naming Covalent Compounds Example: N2O Which element is less EN? Second element is root-ide Add prefix

3-minute practice Write the name for the following compounds: CF4 P2O5 SCl6

Acetaminophen Draw in lone pairs. How many single bonds are in this molecule? How many double bonds? Are some bonds nonpolar? Are some bonds more polar? (Assume C and H have similar electronegativities.)