Unit 3: Chemical BondingSection 1: Bond Types and Properties

● Chemical Bond – force that holds atoms or ions together to make a molecule or other chemical structure◦ Molecule - two or more atoms bonded together

● When bonding, atoms use their outermost electrons, called valence electrons

Chemical Bonds

● The goal of bonding is to have a full outer energy level◦ Some atoms GAIN electrons to reach 8 valence electrons◦ Some atoms LOSE electrons to empty their outermost level

(leaving a full one underneath!)

● Three main types of bonds:◦ Ionic Bonds◦ Covalent Bonds◦ Metallic Bonds

Chemical Bonds (cont.)

● Bonds that form by transferring electrons from one atom to another

● This changes their charges (makes them ions… get it IONic bonds?!) and now they attract one another!!

● Occurs when a positive cation (metal) combines with a negative anion (nonmetal)

● Metal + Nonmetal

Ionic Bonds

Properties of Ionic Compounds- Ionic Solids

- Solids at room temperature

- Form a rigid crystal lattice structure

- Caused by the attraction between the positive cations and negative anions

- This structure places ions close together = strong attractive force

Properties of Ionic Compounds- Conduct electricity when they are dissolved in water

(aqueous form) but not as solids. - Many are soluble in water (a polar molecule)- VERY High melting and boiling points

- Caused by the strong ionic bond- Strong Bonds = Strong Molecules = Hard, Brittle on the large

scale (not malleable)

Why do Ionic Compounds Dissolve in Water?

Water

Why are Ionic Compounds Conductive When Dissolved in Water?

- Electricity conducts because of free-flowing electrons.

- If electrons are not able to move, substances are not conductive (AKA insulators)- Conductive as aqueous and liquids because the ions

dissociate and are removed from crystal lattice structure (allows e- flow)

- NOT conductive as solids because crystal lattice is rigid and does not allow e- flow.

●Bonds that form by sharing a pair of electrons between atoms

●Forms between two nonmetals

Covalent Bonds

●Multiple Bonds – occur in covalent compounds when atoms share more than one pair of electronsDouble Bond – atoms share 2 pairs of electrons

Triple Bond – atoms share 3 pairs of electrons

Multiple Covalent Bonds

●The more bonds between 2 atoms, the stronger the bond●The more bonds between 2 atoms, the shorter the length of the bonds

Bond Strength

Single Bond < Double Bond < Triple Bond

Bond Length

Single Bond > Double Bond > Triple Bond

Bond Strength vs. Bond Length

Properties of Molecular Compounds (Covalent Bonds)- Solids, liquids, or gases at room temperature- Low melting and boiling points (weaker bond than ionic)- Poor electrical conductors in ALL phases (solid, liquid, gas,

aqueous)- No mobility of electrons to other molecules

- Some molecular compounds are polar, some are nonpolar- Polar molecular compounds dissolve in water- Nonpolar molecular compounds don’t - More info on polarity to come!

● When metal atoms come together, they can bond!● Metallic bond – bond formed between positive metal

cations and the “sea” of negatively charged delocalized electrons surrounding them◦ Delocalized electrons – electrons that move freely from one

cation to another in a metal structure

Metallic Bonds

● This free-flowing “sea” of electrons between metal ions helps to explain the ability of metals to conduct electricity and heat

Metallic Properties

Properties of Metallic Bonds- Solids at room temp (Hg is a liquid)- Malleable: able to be hammered or pressed out of shape without breaking

or cracking- Ductile: Able to be drawn out into a thin wire

- The malleability/ductility of metallic compounds is due to the sea of electrons (Different from ionic bonds because it is not a rigid bond)

- Melting/Boiling Point, Hardness, and Bond strength are variable- Generally weaker than a covalent bond, but not always