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Lecture 3

CHEM 217 Lecture Notes - Lecture 3: Phenyl Group, Organic Chemistry, Alkene

Course Code
CHEM 217

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Unit 3
3. 1
Compound properties generally very different from the properties of the elements
Law of definite proportions applies to compounds not mixtures
3. 2 BO N D S
Result of interactions between charged particles
Ionic bonds
oMetal lose (e-) to nonmetals
oElectrostatic forces make oppositely charged ions attracted to each other
oAs multiple ions pairs form, they can group together and th result is an ionic compound in the
solid phase composed of a lattice
Covalent bonds
oNonmetal & nonmetal
oNo transfer of electrons. Insteadm they share them
oShared electrons interact with both nuclei which loewers potential anergy of one system through
electrostatic interactions
oMolecular compound, composed of individually bound covalent molecules
oUnderstand stability of a covalent bond by considering the most stable/lowest potential energy
configuration of a negative charge interacting with two positive charges
oShowed that electrons hold the bonding atoms toether by attracting positively harged nuclei of
3. 3 R E P R E S EN T I NG CO M P O U N D S
Easiest way: chemical formula : indicates elements present in the compounds and the relative numbering
of atoms or ions of each
oUsually list the more metallic (or more positively charged ) elements first followed by less
metallic (or more negatively charged ones)
Types of formulas
oEmpirical formula
Gives relative # of atoms of each element in a compound
oMolecular formula
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Gives actual # of atoms of each element in a compound
Ex. hydrogen peroxide
oEmpirial – HO
oMolecular H2O2
Molecular always a whole-number multiple of the empirical and for some compounds they are the same
A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are
oAlso may be written to give asense of geometry
oStrucural can also depict types of bonds
Structural formula conveys the most information while empricial conveys the least
Elements can be atomic or molecular// compounds can be molecular, ionic
oAtomic elements – exist in nature with single atom basic units, most elements
oMolecular elements – exist as molecules – two or more atoms of the element bound together
oMolecular compounds are two or more covalently bound nonmetals. Basic units are molecules
composed of constituent atoms
oIonic compounds – made of cations (usualy one type of metal) and anions (1 or more nonmetals)
bound ionically
Basic unit is formula unit, the smallest, electrically neutral collection of ions and do not
exist as discrete entities but as a part of a large lattice
Many common ionic compounds contain ions that are composed of a group of
covalently bound atoms with an overall charge
3. 4 FO R MU L A & NA M ES
Common names – no info conveyed about composition
Systematic names – more info
Ionic compounds – occur through earth’s crust as minerals. Generally stable because of cation/anion
Writing formulas for ionic compounds
oSince they’re charge-neutral and since many elements ofrm only one type of ion with a
predictable charge, the formulas for many ionic compounds can be deduced from their
constituent elements
Always contain positive and negative ions
Sum of the charges must be equal to the sum of the negative ions and of the positive
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A formula reflects the smallest whole number ratio of ions
Procedure for writing ionic compounds
o1. Write the symbol for the metal cation and its charge, followed by the symbol for the non-
metal anion and its charge. Obtain charges from the elements group # in table
o2. Adjust subscript on each cation and anion to balance overall charge
o3. Check that the sum of the charges of the cations equals the sum of the charges of the anions
Naming ionic compounds
oFor metals that form cations with one possible charge, the name is just the metal
oFor metals that form cations with more than 1 possible charge, the name is metal followed by
the charge in roman numerals in brackets, this Fe2+ is Iron (II), etc.
oNames for nonatomic anions consist of base name of the element followed by suffix-ide
oIonic compounds with a polyatomic ion are named the same way but with the name of the
polyatomic ion
oIf the compound contains both a polyatomic cation and polyatomic anion, noth are named
Ex. NH4NO3
Most polyatomic ions are oxyanions – anions containing oxygen and another element
oWhen oxyanions contain different numbers of oxygen atoms, they are named systematically
according to # of O in the ion.
If there are only two ions in the series, the one with more oxygen atoms has ending
ate and the one with fewer has ending –ite.
Ex. NO3 - Nitrate
Ex. NO2 – Nitrite
If there are more than 2 ions in the series, the prefixes hypo- meaning less than and per-
meaning more than are used.
EX. ClO- is hypochlorite (less oxygenthan chlorite) and ClO4- is perchlorate (more
oxygen than chlorate)
Hydrated ionic compounds
oSome ionic compounds called hydrates have a specific # of water molecules associated with each
formula unit
oThe H2O molecules are waters of hydration – they can usually be removed by heating the
oHydrates are named just as other ionic compounds but they are given additional name “prefix
hydrate” where the prefix indicates the # of water molecules associated with each formula unit
Written as:
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