Bonding Basics

I. Electronegativity and Bonding Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. No electronegativity difference (0) between two atoms leads to a pure non-polar covalent bond. A small electronegativity difference (0-2.0) leads to a polar covalent bond. A large electronegativity difference leads to (2.0 or more) an ionic bond.

I. Electronegativity and Bonding Which type of bond will be formed by Au and O?___________ Which type of bond will be formed by F and Cl? ____________

II. Intramolecular Intramolecular bonds: Intramolecular bonds are those within a molecule or compound. These bonds are relatively strong Methane Intramolecular bond

II. Intramolecular (Within a molecule – strong forces) Intramolecular bond

Ionic Bonds Between metal (cation) and nonmetal (anion) that transfer valence electrons in order to gain octets/be more stable Attraction between positive and negative ions results in the formation of crystalline structures with high melting points Picture:

Ionic Bonds Ionic solids break apart into positive and negative ions when in solution (known as electrolytes) - these solutions conduct electricity

Electrolytes and Batteries Many batteries contain two metals with different electronegativities and some sort of electrolyte solution. (This simple voltaic cell contains an acid as the electrolyte)

Covalent Bonds Between 2 or more nonmetals that share valence electrons to gain an octet Sharing of electrons results in the formation of molecular compounds with low melting points Molecules do not break apart in solution, so do not conduct electricity (nonelectrolytes) Picture:

Covalent Bonds Can be polar  uneven sharing of electrons leads to partial charges Or, nonpolar  even sharing of electrons leads to no partial charges Water: A polar covalent molecule

Polar (partially charged) Nonpolar (no charges)

Covalent Bond “Like dissolves like” – Polar substances will only dissolve in polar substances. Water is polar. Oil is nonpolar. They do not dissolve in one another!

By the way, Sometimes nonmetals form network solids For example, carbon atoms can arrange themselves into solids such as diamonds or graphite

Ionic and covalent bonding

Which solution contains a salt (ionic compound)? Which solution contains a nonpolar covalent compound?

Ionic, polar covalent, or non- polar covalent?

Metallic Bond Between metal ions (cations) that have loosely-held electrons called a “sea of electrons” Freely-flowing electrons create metallic solids that are malleable and conductive Picture:

Metallic bonding

Metallic Bond Most metals used in daily life are alloys - combinations of elements that contain one or more metal

III. Intermolecular Bonds Intermolecular forces are between separate molecules These bonds are relatively weak

Dipole-dipole forces: Between polar covalent molecules or any molecule with a permanent dipole (partial charge) Partial positive charges are attracted to partial negative charges - creates weak bond between molecules Picture:

Hydrogen Bonds (a type of dipole-dipole bond) Hydrogen Bond: A hydrogen bond is a special dipole-dipole interaction between molecules with a hydrogen atom bonded to another atom with a relatively high electronegativity like O, N, or F Hydrogen has a lower electronegativity, so it is partially positive (  +)

Hydrogen Bond Partially positive hydrogens are attracted to partially negative ends of other molecules – creates weak bond between water molecules that makes water “sticky”

Inter and Intramolecular Bonds

London Dispersion Forces Occurs due to random movement of electrons and occasional “pile-ups” of electrons on one side of atom Temporary dipoles (charged areas) can be created very briefly and cause atoms to be very weakly attracted to each other Picture:

London dispersion forces

Geckos use London dispersion forces to climb up surfaces

London Dispersion Forces Dispersion forces are greater for larger atoms Why?____________________________ ________________________________ larger atom = more electrons more electrons = more chance for “pile-ups”

GIST Use words to summarize the main points from these notes.

Active Listening Partner 2 tell partner 1 your gist Partner 1 repeat what your partner said back to them Both partners praise each other after talking (Good job. Thank you.)