Salt vs. Sugar. 1. Ionic Compounds. 2. Molecular Compounds (Cont.) 12/18/2014. What is this Compound You Speak Of? Sodium Chloride Dissolving in Water

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1 Salt vs. Sugar Unit 7: Chemical Compounds & Formulas Lesson#7.1: Types of Compounds What is this Compound You Speak Of? Compound: Any substance that is formed by the chemical bonding of atoms. We classify compounds by the types of bonds that hold the atoms together. 4 major types of compounds: 1. Ionic Compounds 2. Molecular Compounds 3. Network Solids 4. Metallic Solids Ionic Compounds eld together by ionic bonds. Ionic compounds only exist as solids, when you melt or dissolve them, the ions separate (but keep their charges) The strength of an ionic bond is very strong, so they have high boiling and melting points. As solids, they don t conduct electricity. As liquids and in solution, they do! Sodium Chloride Dissolving in Water Molecular Compounds eld together by covalent bonds (can be polar or non-polar). Individual particles = molecules Molecules can be polar or nonpolar, based on type of bond and molecular shape. Molecules are held together by intermolecular attractions forces = IMAF. 2. Molecular Compounds (Cont.) IMAF aren t as strong as ionic attractions, so.. molecular substance can be in all states at room temperature. covalent substances have lower melting and boiling points and they evaporate easily. they are pretty soft as solids. When you dissolve molecules in water, the molecules move apart and the covalent bonds remain intact. There are no ions to carry electrical currents so they are nonelectrolytes. - Acids are the only exception. 5 1

2 IMAF s in Water 7 3. Network Solids Chemical compounds where the atoms are bonded covalently in a continuous network. In a network solid there are no individual molecules and the entire crystal is the molecule. Very high melting and boiling points. Very hard. Very brittle. Do not conduct electricity. Examples of network solids include diamond and silicon dioxide or quartz with a continuous three dimensional network of SiO 2 units. Graphite a consist of continuous two dimensional layers covalently bonded within the layer with other bond types holding the layers together. The structure of Quartz (SiO 2 ), a network solid Diamond Graphite Metallic Solids Put a bunch of metals together and they all loose their electrons. The electrons become a moving glue that holds the positive metal ions together. Some people talk about a sea of electrons with ions floating about. This is called metallic bonding It makes metals: Malleable (bendy) Great conductors of electricity in all phases. In Summation

3 Why are Molecular Substances in all States at STP? Because of: Intermolecular Attractive Forces (aka van der Waals ) They are what make solid and liquid molecular compounds possible. They are the weakest among all attraction forces (Intra-molecular and intermolecular) and are called van der Waal s forces - there are two kinds: Nonpolar And. Polar Nonpolar IMAF s London Dispersion Forces (LDF) weakest of all, caused by motion of e - come from the temporary attractions between induced dipoles in a non-polar molecule. These are polar regions of the molecules that are formed as the electrons are moving around the molecule. 14 Nonpolar IMAF s See? The bigger the nonpolar molecule, the stronger the LDF s are. Small non-polar molecules are gasses at room temperature (ex. Methane: C 4 ). Medium-sized non-polar molecules are liquids at room temperature (ex. Octane: C 8 18 ). Big non-polar molecules are solid at room temperature (ex. Paradichlorobenzene: C 6 4 Cl 2 ). The closer the molecules are, the stronger the LDF s are #2. Dipole interactions Occurs when polar molecules are attracted to each other. 2. Dipole interaction happens in water positive region of one molecule attracts the negative region of another molecule. #2. Dipole interactions Occur when polar molecules are attracted to each other. Slightly stronger than dispersion forces. Opposites attract, but not completely hooked like in ionic solids. F F 3

4 #2. Dipole Interactions #3. ydrogen bonding is the attractive force caused by hydrogen bonded to N, O, F, or Cl N, O, F, and Cl are very electronegative, so this is a very strong dipole. And, the hydrogen shares with the lone pair in the molecule next to it. This is the strongest of the intermolecular forces. #3. ydrogen bonding defined: When a hydrogen atom is: a) covalently bonded to a highly electronegative atom, AND b) is also weakly bonded to an unshared electron pair of a nearby highly electronegative atom. The hydrogen is left very electron deficient (it only had 1 to start with!) thus it shares with something nearby ydrogen is also the ONLY element with no shielding for its nucleus when involved in a covalent bond! ydrogen Bonding (Shown in water) O d + This hydrogen is bonded covalently to: 1) the highly negative oxygen, and 2) a nearby unshared pair. ydrogen bonding allows 2 O to be a liquid at room conditions. ydrogen Bonding in Water O 24 4

5 Order of Intermolecular attraction strengths 1) Dispersion forces are the weakest 2) A little stronger are the dipole interactions 3) The strongest is the hydrogen bonding 4) All of these are weaker than ionic bonds A andy Chart For You 26 Another andy Chart Can You Do These Things? 1. Identify whether a compound is molecular, ionic, metallic or a network solid based on its properties. 2. Draw dot diagrams of simple molecules. 3. Draw structural formulas of simple molecules. 4. Determine the shape of simple molecules. 5. Determine if simple molecules are polar or nonpolar. 6. Draw the dipole moment of polar molecules and ID charged ends. 7. Determine the type of IMAF that attracts specific simple molecules to each other Any Questions? What now? 29 5