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Lecture 3

CHEM 101 Lecture Notes - Lecture 3: Nonmetal, Roman Numerals, Ionic Compound


Department
Chemistry
Course Code
CHEM 101
Professor
Dr.Emil F.Khisamutdinov
Lecture
3

Page:
of 3
Compounds and Molecules:
Matter
oPure substances
Element and compound
Element
Monatomic
Diatomic
Compound
Ionic
Covalent
A compound is composed of 2 or more different atoms in a definite whole-
number proportion
Ionic compounds
Composed of metals and non-metals that attract each other
Form lattice structure
Naming
oMetal then non-metal
Chemical Bond
Ionic bond
oConnects metals and non-metals
Electronegativity
A measure of tendency of an atom to attract a bonding pair of electrons
How badly an atom wants electrons
Polyatomic Ions
Monoatomic cation
oFormed when a metal loses one or more valence electrons
Monoatomic anion
oFromed when a nonmetal gains one or more valence electrons
Polyatomic ion
oAn ion form when a molecule, rather than a single atom, gains or
loses one, two, or three electrons
Formula Unit
Ionic compound is identified by ration of cations and anions
Forming Steps
1. Determine the charge on the cation
2. Determine the charge on the anion
3. Determine the subscripts
Naming
1. Write the name of the cation followed by the name of the anion
If cation is a transition metal, write its name followed by
roman numeral in parentheses
Ionic bond
Connects metals and non-metals
Covalent compounds (molecular compounds)
Between atoms consist of shared valence electrons
molecule
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oA set of atoms joined by covalent bonds
Most substances are covalent compounds
Each one consists of a pair of shared electrons
Diatomic Molecules
Each contains two atoms
Sharing electrons
Shared electrons are part of the valence shell
With ionic compounds, sharing seeks to achieve a filled octet
Single
oOne pair of shared electrons
Double
o2 pairs of shared electrons
Triple
o3 pairs of shared electrons
oShortest
Properties of covalent compounds
Properties of covelent compounds differ from ionic compounds due to the
different character of their bonds
Ionic compounds Covalent Compunds
Metals/nonmetals Non-metals/non-metals
High boiling point Low boiling point
High melting point Low melting point
Solutions conduct electricity Soultions do not conduct electricity
Usually solids May be solids, liquids, or gasses
Naming covalent molecules
For the first element start with the element name
For the second element, start with the -ide name
Use prefixes to show how many atom of each type there are
Do not use "mono-" on the first element
If you have "ao" or "oo", turn it into "o"
Polarity of molecules
Molecular polarity
oA characteristic of molecules that determines how they interact with
other molecules
Electronegativity
oA measure of an atom's ability to draw electrons toward itself in a
covalent bond
Dipole Forces
polar covalent
oA polar covalent bond exists between 2 atoms with a significant
difference in electronegativity
oBond dipole is separation of opposite charge
Nonpolar covalent
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oExists between 2 atoms with similar electronegativity
oBonding electroms are evenly distributed between both atoms
Polar and nonpolar molecules
Depends on molecular shape
Polar molecule
oHas a separation of charge a positive end and a negative end of
the molecule
oMolecules with 1+ bond dipoles and a trigonal pyramidal or bent
molecular shape are polar because the bond dipoles cant cancel
Nonpolar molecule
oHas an even distribution of electrons throughout the molecule
oHydrocarbons
Contain only C-C and C-H nods, both nonpolar bonds
oBond dipoles cancel when there are 3 (trigonal planar molecular
shape), 4 identical bond dipoles (tetrahedral molecular shape)
A molecule with 2+ polar covalent bonds need to look at the shape of the
molecule
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