Unit 3: Chemical Bonding. Section 1: Bond Types and Properties

Transcription

1 Unit 3: Chemical Bonding Section 1: Bond Types and Properties

2 Chemical Bonds 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

3 Chemical Bonds (cont.) 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

4 Ionic Bonds 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

5 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

6 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)

7 Why do Ionic Compounds Dissolve in Water? Water

8 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.

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10 Covalent Bonds Bonds that form by sharing a pair of electrons between atoms Forms between two nonmetals

11 Multiple Covalent Bonds Multiple Bonds occur in covalent compounds when atoms share more than one pair of electrons Double Bond atoms share 2 pairs of electrons Triple Bond atoms share 3 pairs of electrons

12 Bond Strength vs. Bond Length 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

13 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!

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15 Metallic Bonds 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

16 Metallic Properties This free-flowing sea of electrons between metal ions helps to explain the ability of metals to conduct electricity and heat

17 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