Transcript Unit: Chemical Bonding I. Compound - Pure substances

Unit: Chemical Bonding
I. Compound
• Pure substances - has 2 or more
elements chemically combined
– Water (H2O)
– Salt (NaCl)
– Oxygen (O2 )
– Sugar Sucrose (C12H22O11)
A. Different Combinations of
elements produce different
substances
• H2O  Water
• H2O2  Peroxide
• O2  Oxygen
• O3  Ozone
B. Compound has new set of
properties
• The individual elements that make up
the compound lose their own properties
•
•
•
H  gas, combustible
O  gas, supports combustion
H O  liquid, clear, extinguishes a
flame
2
2
2
B. Compound has new set of
properties
•
•
•
Na  Reactive, solid metal
Cl2  poisonous green gas
NaCl  table salt
C. Atoms form compounds when the
compound is
more stable than the
separate atoms.
• Noble gases 
Chemically stable
– 8 valence e-’s
• Elements w/out 8
valence electrons
more stable in
compounds
•Atoms can lose,
gain, or share
electrons to become
stable
•A chemical bond is
the force that hold
atoms together in a
compound
III. Chemical Formulas
• Shorthand way to represent
chemical compounds
• use chemical symbols combined to
make compound
• ex.
H2 O
Subscript
Subscripts
• The # represents the number of
atoms of the previous element that
are in one molecule of the
compound
• If there is NO subscript after the
element, then “ 1 ” is understood
to be there
– “1” is never written!!!!
How many atoms of each element
are in these ?
1. C6H12O6
2. CaCl2
3. Mg(OH)2
4. Ca(H2PO4)2
IV. Electron Dot Diagrams
(Lewis Dot diagrams)
Use element’s Valence electrons
electrons in outer shell
• Write elements chemical symbol
• Use a dot to represent valence e-’s
• Place valence e-’s around symbol
• **Hint: Like you would sit at the
dinner table
Electron Dot Diagrams
• Sulfur
Neon
Chlorine
V. Octet Rule
• Atoms are very stable
with 8 valence electrons
– ( 4 pairs)
• atoms wants to have a
full octet by either
gaining, losing, or
sharing electrons during
chemical combinations
VII. Oxidation Numbers
• Stands for  The # of electrons an
atom gains, loses, or shares to
become stable
– (also is its ion’s charge)
“ + ” #  means lose that # of
electrons
“ - ” #  means will gain/share that #
of electrons
VII. Oxidation Numbers
• Ex.
Sodium
Chlorine
+1
Na
-1
Cl
VIII. Writing Chemical Formulas
• Use oxidation numbers
• Use Criss-Cross Method
• When writing formulas, remember
compounds are Neutral
• ***Positive Oxidation number
written first (metal)
VIII. Writing Chemical Formulas
• Compound of Sulfur and Calcium?
Writing Chemical Formulas
• Compound of Sodium and Oxygen?
Writing Chemical Formulas
• Compound w/ Lithium and Carbonate
ion  CO3-2
Use Criss-Cross Method to write
chemical formula: Answers:
• 1. Mg and O
• MgO
• 2. O and Al
• Al2O3
• 3. I and K
• KI
• 4. Mg and OH -1 • Mg(OH)2
• 5. Ca and CO3 -2
• CaCO3
VIII. Type of Bonds
• A. Ionic Bonding:
– Electrons are transferred
– 1 atom loses and other atom gains
electrons
– Ion – charged atom, no longer neutral
• Can be positive (+) or negative (-)
• Na combining with Chlorine
• The sum of the charges on the ions is
zero!!
Lithium Fluoride
Ionic Bonds occur:
• Between Metals bonding with
Nonmetals
• Nonmetal 
Sumo wrestler
• Metal  Child
Ionic Compounds
• Two ions have
opposite electrical
charges therefore
attracted to each
other
– Holds Ionic
Bonds together
• Weak bond
between elements
• Ionic compounds form Crystal
Lattice structure
– regular repeating arrangement
due to “+” tend to be near “-“
Ionic Bond
•  weaker bonds
between elements than
covalent bonds
– Are easier to break
into ions
• But strong bonds b/w
molecules
– Substances tend to be
solids at Room Temp
– Have high melting
points
B. Covalent Bonding
• “Co” – to share
• “Valance” –
electrons
• electrons are shared,
not transferred
Covalent Bonding
• Happens when both
atoms attract electrons
• Nonmetal with Nonmetal
• Also Hydrogen with
Nonmetal
Covalent Bonding
• Attraction b/w nucleus and shared
electrons hold the atom together
Covalent Bonding
• Ex. Hydrogen with Carbon
Covalent Bonding
• - Covalent bonds often
occur b/w atoms of same
element
Diatomic molecules
Ex. O2, F2, Br2, I2, N2, H2
- When these are found in
nature, always 2 atoms
covalently bonded
Covalent Bonding
• F2
• Cl2
Covalent Bonding
• More than 2 electrons can be shared
b/w atoms
Ex. Carbon and Oxygen
Covalent Bonding
• If 3 pairs of electrons are shared called
a triple bond
Ex. N2
Covalent Bonds
• Strong bonds between elements
• But Weak bonds b/w molecules
– Triple bonds are strongest, then
double, then single
• Substances Tend to be liquids or
gases at room temp.
• Have Low boiling points
Covalent Bonding
• Molecule - smallest part of a
bonded substance, compound, that
has properties of that substance
- Are neutral, no overall charge
- Can be Polar or Nonpolar
1. Polar Covalent molecules
• one end is slightly negative and
one end is slightly positive, the
overall molecule is still neutral
• Ex. Water
2. Nonpolar Molecules
• – Electrons are
shared equally
– Ex. Oil, fuels,
fats
IX.
Polyatomic Ions
• Group of covalently bonded atoms that
act as a single atom when bonding with
other atoms
• As a group have a charge
• Form ionic bonds with other elements
Ex. Sodium and Hydroxide Ion
•
Calcium and Carbonate Ion
X. Predicting Types of Bonds
• Compound b/w Metal & Nonmetal
– Form Ionic Bond
• Compound b/w Nonmetal & Nonmetals
– Form Covalent Bond
– Like a Tug of war b/w 2 sumo wrestlers
• Compound b/w polyatomic ion &
element
– Form ionic bond
Predicting Types of Bonds
• Ex. F + Mg ?
– Ionic
• O + Cl ?
– Covalent
• Na + OH-1 ?
– Ionic
XI.
Naming compounds
• **Binary compounds – compounds
containing only two elements
• See Handout
• A. Binary Ionic
1. Write Positively Charged ion first
usually the METAL
2. Then add Name of Negative ion with
end changed to “-ide”
Usually the NONMETAL

NaCl

Li2O

CaO
• B. Naming Compounds with Transition
Metals
remember transition metals may have
more than one Oxidation Number
-
form positive ions
Ex. Copper 
Iron
• 1. Write name of Transition Metal first
2. In Parenthesis ( ) write a Roman Numeral
to indicate the ox # of the Transition metal in
this compound
3. Write name of nonmetal and Change end
to “-ide”
Ex.
Cu+1 and Cl
Cu+2 and Cl
• Write the name for the following:
1. PbO
2. TiCl4
3. HgCl4
Write the Chemical formula:
1.
Tin (IV) Flouride
2.
Lead (I) Sulfide
3.
Cobalt (III) Chloride
• C. Naming Binary Molecular
(covalently bonded) Compounds
1. Write element that is Least
Electronegative first
a. Use your table for this
• 2. On the most electronegative element give
a prefix for # of atoms of that element in the
compound
Prefix
mono
di
tri
tetra
penta
hexa
hepta
octa
# of atoms
4
6
8
1
2
3
5
7
• Name the following:
1. SO2
3. SF6
2. SiO2
• X. Molar Mass of a Compound
A. Mole – the unit of measurement used to
count numbers of
atoms, molecules or formula units
Abbreviated “mol”
The number of things in one mole is
6.02 X 1023
-
Avogadro’s number
1 mole = 6.02 X 1023
• B. Using this we can count the number of
atoms in one mole of a substance
Ex. 1 mole of Carbon is 6.02 X 1023 at
atoms of
Carbon
sodium
1 mole of Na is 6.02 X 1023 atoms of
• Molar Mass – the mass of one mole of a
substance
Ex. The mass of one Carbon-12 atom is
exactly 12 amu
The mass of one mole of C-12 is 12
grams
• ** Molar mass is the mass in grams of
the average atomic mass of the
substance**
ex. Molar mass of Iron?
- 55.847 grams
• Try these! Find the molar mass of each
substance.
1. Oxygen
2. Uranium
3.
Copper
• C.Finding the molar Mass of a Compound:
-find the molar mass of each element in the
compound
-multiple it times the number atoms of that
element in the compound
- the Sum of the molar masses = the
Molecular Mass (or gram formula weight) of
the compound
ex. Ethanol – C2 H6 O
• Try These:
1. Ca Cl2
2. C6H5Br
3. (NH4)3PO4
• Which Has the largest Mass?
3 Mol of Magnesium or 1 mol
of sucrose
or 10 mol of helium