Chem 240 Notes for Week 3
Chem 240 Notes for Week 3 Chem 240
Edinboro University of Pennsylvania
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This 4 page Class Notes was uploaded by Cassandra Notetaker on Friday February 12, 2016. The Class Notes belongs to Chem 240 at Edinboro University of Pennsylvania taught by Dr. Tracy Olin in Spring 2016. Since its upload, it has received 18 views. For similar materials see Principles of Chemistry 1 in Chemistry at Edinboro University of Pennsylvania.
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Date Created: 02/12/16
Olin CHEM 240 Lecture Ionic Compounds 2/1/16 Metal ions are more likely to lose electrons and form cations; less electronegative. Nonmetal ions are more likely to gain electrons and form anions; more electronegative. Ex. Calcium ion Ca , so it has 20 protons and 18 electrons. **Common Polyatomic Ion Chart is a mustknow!** Recognizing an Ionic Compound: An ionic compound is composed of a metal cation and a nonmetal anion or contains a polyatomic ion with a cation or anion. Compounds that don’t meet either requirement are molecular compounds. Examples: Al 2 3– ionic compound (metal – nonmetal) H 2 – molecular compound (nonmetal – nonmetal) CaF 2– ionic compound (metal – nonmetal) NaOH – ionic compound (metal – polyatomic anion) NH C4 – ionic compound (polyatomic cation – nonmetal) P4 10– molecular compound (nonmetal – nonmetal) NaHCO – 3onic compound (metal – polyatomic anion) Writing Formulas: Olin CHEM 240 Lecture Chemical Formula shorthand notation for composition of compounds. Subscript indicates relative proportions of atoms in a compound. **All compounds are electrically neutral because the charges have to balance each other out** When writing a formula, take the charge of the first element and make it the subscript on the second element, and vice versa. Ex. A B means that A B Y X Molecular Formula the actual number of atoms in a given formula. Empirical Formula the relative ratios for each atom in a compound. Formula Unit smallest wholenumber ratio (simplest) of number of cations to anions in a compound. (Ionic compounds don’t exist as individual molecules, they usually form crystals. Therefore, we use formula units to describe their composition.) Ex. Give the empirical and molecular formulas for a compound having 12 carbon atoms, 14 hydrogen atoms, and 6 oxygen atoms. Empirical Formula C H O6 7 3 Molecular Formula C H O12 14 6 Naming Ionic Compounds: Atom on the left has its original name (if not in dblock on periodic table) 2+ 4+ 2+ 4+ o Exceptions: Pb or Pb and Sn or Sn Transition cations get roman numerals 2+ o Example: Fe is written as Iron (II) Olin CHEM 240 Lecture Replace the end of the anion name with –ide (–ite or –ate depending on number) Continuation of Compounds – 2/3/16 Atoms form bonds so they can “feel” like noble gases. Ionic Bonds bonds between a metal and nonmetal due to electrostatic forces. Covalent Bonds bonds between two nonmetals; there are both polar and nonpolar variations. Metallic Bonds bonds between two metals. **nonmetals are much more electronegative than metals** Electrostatic forces hold bonds together; crystal lattices sometimes form (based on electrostatic force) Coulomb’s Law attraction between oppositely charged ions increase with charge and decreases 2 2 with distance . F = K (Q1Q 2/ d ) Ionic Compounds: Distinctive crystalline shapes Easily cleaved High melting point (to break ions out of crystalline structure) Don’t conduct electricity as a solid, but can as a molten or dissolved substance. Molecular Compounds: Low melting point Brittle and weak or soft and waxy Poor conductors of heat and electricity Exist as solids, liquids, or gases Olin CHEM 240 Lecture Covalent Bonds have a partial positive on one of the elements and a partial negative on the other, indicating unequal sharing. Naming Molecular Compounds: Left Atom: regular name (with a prefix if there is more than one) Examples include mono (not written), di, tri, tetra, penta, hexa, hepta, octa, nona, deca, undeca, dodeca. Right Atom: depending on number, add appropriate prefix; add suffix –ide. Ex. H 2 – dihydrogen monoxide, H O – 2i2ydrogen dioxide Hydrocarbons Alkanes type of hydrocarbon that has the max number of hydrogens that can be held by one carbon. Isomers 2 or more compounds with the same formula but different properties.
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