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Chemical Bonding and Nomenclature
Chapter 5
What is a Molecule ?
Molecule
A collection of atoms bonded together
Elemental molecules
Atoms from same element
Diatomic: H2, N2, O2, F2, I2, Br2
What is a Molecule
Molecules of Compounds
Atoms of different elements
Simple vs. Complicated
Small vs. extremely large
Properties of Molecules
Molecules have different properties than their elemental component.
Element Properties
O Odorless, colorless very reactive toxic gas
H Odorless colorless gas reactive
Properties of Molecules
Molecule Properties
O2Colorless odorless gas moderately reactive not flammable
H2Colorless odorless gas moderately reactive flammable
H2OColorless odorless liquid, low reactivity
H2O2Colorless odorless liquid high reactivity
Why do molecules form?
To be like the noble gases
The noble gases are perfect hence they do not react with anything
They have 8 valence electrons in their outer most shell
Valence Electrons?
The outermost electrons. Determines the chemical properties of an element
The only electrons that bond
The roman numerals at the top of each group A element
Most elements prefer to have 8 electrons this is called the octet rule. Why?
The Octet Rule
Atoms tend to gain, lose, or share electrons until they have eight valence electrons.
Electron Dot diagrams
A way of keeping track of valence electrons.
How to write them Write the symbol. Put one dot for each valence
electron Don’t pair up until you have
too.
X
The Electron Dot diagram for Nitrogen
Nitrogen has 5 valence electrons.
First we write the symbol.
NThen add 1 electron at a time to each side.Until they are forced to pair up.
Write the electron dot diagram for
Na Mg C O F Al He
Electron Configurations for Cations
Metals lose electrons to attain noble gas configuration.
They make positive ions.
Electron Dots For Cations
Metals will have few valence electrons
Ca
Electron Dots For Cations Metals will have few valence electrons These will come off
Ca
Electron Dots For Cations
Metals will have few valence electrons These will come off Forming positive ions
Ca+2
Electron Configurations for Anions
Nonmetals gain electrons to attain noble gas configuration.
They make negative ions.
Electron Dots For Anions
Nonmetals will have many valence .electrons.
They will gain electrons to fill outer shell.
P P-3
Stable Electron Configurations
All atoms react to achieve noble gas configuration.
Noble gases 8 valence electrons . Also called the octet rule.
Ar
Covalent Bonding
How does H2 form?
The nuclei repel
++
How does H2 form?
++
The nuclei repel
But they are attracted to electrons
They share the electrons
Covalent bonds
Nonmetals hold onto their valence electrons.
They can’t give away electrons to bond. Still want noble gas configuration. Get it by sharing valence electrons with
each other. By sharing both atoms get to count the
electrons toward noble gas configuration.
Covalent bonding
Fluorine has seven valence electrons
F
Covalent bonding
Fluorine has seven valence electrons A second atom also has seven
F F
Covalent bonding
Fluorine has seven valence electrons A second atom also has seven By sharing electrons
F F
Single Covalent Bond
A sharing of two valence electrons.
Only nonmetals and Hydrogen.
How to show how they formed
It’s like a jigsaw puzzle.
I have to tell you what the final formula is.
You put the pieces together to end up with the right formula.
For example- show how water is formed with covalent bonds.
Water
H
O
Each hydrogen has 1 valence electron
Each hydrogen wants 1 more
The oxygen has 6 valence electrons
The oxygen wants 2 more
They share to make each other happy
Water Put the pieces together The first hydrogen is happy The oxygen still wants one more
H O
Water
The second hydrogen attaches Every atom has full energy levels
H OH
Multiple Bonds
Sometimes atoms share more than one pair of valence electrons.
A double bond is when atoms share two pair (4) of electrons.
A triple bond is when atoms share three pair (6) of electrons.
Carbon dioxide CO2 - Carbon is central atom
( I have to tell you) Carbon has 4 valence
electrons Wants 4 more Oxygen has 6 valence
electrons Wants 2 moreO
C
Carbon dioxide
Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short
OC
Carbon dioxide Attaching the second oxygen leaves
both oxygen 1 short and the carbon 2 short
OCO
Carbon dioxide
The only solution is to share more
OCO
Carbon dioxideCarbon dioxide The only solution is to share more
OCO
Carbon dioxideCarbon dioxide The only solution is to share more
OCO
Carbon dioxide The only solution is to share more
OCO
Carbon dioxideCarbon dioxide The only solution is to share more
OCO
Carbon dioxide The only solution is to share more
OCO
Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO
Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO8 valence electrons
Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO8 valence electrons
Carbon dioxideCarbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in
the bond
OCO
8 valence electrons
Hydrogen 2 valence e-
Groups 1,2,3 get 2,4,6 valence e-
Expanded octet more than 8 valence e- (e.g.
S, P, Xe)
Radicals odd # of valence e-
Exceptions:
A. Octet Rule
F B FFH O HN O
Very unstable!!
F F
F S F
F F
B. Drawing Lewis Diagrams Find total # of valence e-.
Arrange atoms - singular atom is usually in the middle.
Form bonds between atoms (2 e-).
Distribute remaining e- to give each atom an octet (recall exceptions).
If there aren’t enough e- to go around, form double or triple bonds.
B. Drawing Lewis Diagrams
CF4
1 C × 4e- = 4e-
4 F × 7e- = 28e-
32e- FF C F
F
- 8e-
24e-
B. Drawing Lewis DiagramsBeCl2
1 Be × 2e- = 2e-
2 Cl × 7e- = 14e-
16e-
Cl Be Cl - 4e-
12e-
B. Drawing Lewis DiagramsCO2
1 C × 4e- = 4e-
2 O × 6e- = 12e-
16e-
O C O - 4e-
12e-
C. Polyatomic Ions
To find total # of valence e-: Add 1e- for each negative charge. Subtract 1e- for each positive charge.
Place brackets around the ion and label the charge.
C. Polyatomic Ions
ClO4-
1 Cl × 7e- = 7e-
4 O × 6e- = 24e-
31e- OO Cl O
O
+ 1e-
32e-
- 8e-
24e-
NH4+
1 N × 5e- = 5e-
4 H × 1e- = 4e-
9e- HH N H
H
- 1e-
8e-
- 8e-
0e-
C. Polyatomic Ions
D. Resonance Structures
Molecules that can’t be correctly represented by a single Lewis diagram.
Actual structure is an average of all the possibilities.
Show possible structures separated by a double-headed arrow.
D. Resonance Structures
OO S O
OO S O
OO S O
SO3
Practice
Complete the worksheet
Nomenclature-Naming Chemical Compounds
Atoms and ions
Atoms are electrically neutral.
Same number of protons and electrons.
Ions are atoms, or groups of atoms, with a charge.
Atoms and Ions
Different numbers of protons and electrons.
Only electrons can move.
Gain or lose electrons.
Anion
A negative ion. Has gained electrons. Non metals can gain electrons. Charge is written as a super script on the
right.
F-1 Has gained one electron
O-2 Has gained two electrons
Cations
Positive ions. Formed by losing electrons. More protons than electrons. Metals form cations.
K+1 Has lost one electron
Ca+2 Has lost two electrons
Two Types of Compounds
Molecular compounds
Made of molecules.
Made by joining nonmetal atoms together into molecules.
Two Types of Compounds
Ionic Compounds
Made of cations and anions. Metals and nonmetals. The electrons lost by the cation are gained by
the anion. The cation and anions surround each other. Smallest piece is a FORMULA UNIT.
Formula Unit
The smallest whole number ratio of atoms in an ionic compound.
Ions surround each other so you can’t say which is hooked to which.
Two Types of Compounds
Smallest piece
Melting Point
State
Types of elements
Formula Unit Molecule
Metal and Nonmetal
Nonmetals
solidSolid, liquid or gas
High >300ºC Low <300ºC
Ionic Molecular
Chemical Formulas
Shows the kind and number of atoms in the smallest piece of a substance.
Molecular formula- number and kinds of atoms in a molecule.
CO2
Charges on ions
For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location.
Elements in the same group have similar properties.
Including the charge when they are ions.
+2
+1
+3 -3 -2 -1
Naming ions
We will use the systematic way.
Cation- if the charge is always the same (Group A) just write the name of the metal.
Transition metals can have more than one type of charge. Indicate the charge with roman numerals in
parenthesis.
Name these
Na+1
Ca+2
Al+3
Fe+3
Fe+2
Pb+2
Li+1
Write Formulas for these
Potassium ion Magnesium ion Copper (II) ion Chromium (VI) ion Barium ion Mercury (II) ion
Naming Anions
Anions are always the same.
Change the element ending to – ide
F-1 Fluoride
Name these
Cl-1
N-3
Br-1
O-2
Write these
Sulfide ion
iodide ion
phosphide ion
Strontium ion
Polyatomic ions
Groups of atoms that stay together and have a charge. Acetate C2H3O2
-1
Nitrate NO3-1
Nitrite NO2-1
Hydroxide OH-1
Permanganate MnO4-1
Cyanide CN-1
Polyatomic ions
Sulfate SO4-2
Sulfite SO3-2
Carbonate CO3-2
Chromate CrO4-2
Dichromate Cr2O7-2
Phosphate PO4-3
Phosphite PO3-3
Ammonium NH4+1
Ions and Ionic Compounds
Naming Binary Ionic Compounds
Binary Compounds - 2 elements. Ionic - a cation and an anion. To write the names just name the two ions. Easy with Representative elements. Group A
NaCl = Na+ Cl- = sodium chloride
MgBr2 = Mg+2 Br- = magnesium bromide
Naming Binary Ionic Compounds
The problem comes with the transition metals.
Need to figure out their charges. The compound must be neutral. same number of + and – charges. Use the anion to determine the charge on
the positive ion.
Naming Binary Ionic Compounds
Write the name of CuO Need the charge of Cu O is -2 copper must be +2 Copper (II) chloride
Name CoCl3
Cl is -1 and there are three of them = -3 Co must be +3 Cobalt (III) chloride
Naming Binary Ionic Compounds
Write the name of Cu2S.
Since S is -2, the Cu2 must be +2, so each one is +1.
copper (I) sulfide Fe2O3 Each O is -2 Fe must be = + 3 iron (III) oxide
Naming Binary Ionic Compounds
Write the names of the following:
KCl
Na3N
CrN
Na2Se
Ternary Ionic Compounds
Will have polyatomic ions At least three elements name the ions
NaNO3
CaSO4
CuSO3
(NH4)2O
Ternary Ionic Compounds
LiCN
Fe(OH)3
(NH4)2CO3
NiPO4
Writing Formulas
The charges have to add up to zero. Get charges on pieces. Cations from name of table. Anions from table or polyatomic. Balance the charges. Put polyatomics in parenthesis.
Writing Formulas
Write the formula for calcium chloride.
Calcium is Ca+2
Chloride is Cl-1
Ca+2 Cl-1
CaCl2
Write the formulas for these Lithium sulfide tin (II) oxide tin (IV) oxide Magnesium fluoride Copper (II) sulfate Iron (III) phosphide Gallium (III) nitrate Iron (III) sulfide
Write the formulas for these
Ammonium chloride
ammonium sulfide
barium nitrate
Things to look for
If cations have (), the number is their charge.
If anions end in -ide they are probably off the periodic table (Monoatomic)
If anion ends in -ate or -ite it is polyatomic
Molecular Compounds
Molecular compounds
made of just nonmetals
smallest piece is a molecule
can’t be held together because of opposite charges
can’t use charges to figure out how many of each atom
Easier
Ionic compounds use charges to determine how many of each
Have to figure out charges
Have to figure out numbers
Molecular compounds name tells you the number of atoms
Uses prefixes to tell you the number
Prefixes
1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa-
Prefixes
9 nona-
10 deca-
One exception is we don’t write mono- if there is only one of the first element.
Name These
N2O
NO2
Cl2O7
CBr4
CO2
BaCl2
Write formulas for these
diphosphorus pentoxide tetraiodide nonoxide sulfur hexaflouride nitrogen trioxide Carbon tetrahydride phosphorus trifluoride aluminum chloride
Naming Acids
a little tricky so pay attention
Acids
Compounds that give off hydrogen ions when dissolved in water
Must have H in them (somewhere)
will always be some H next to an anion
The anion determines the name.
Naming acids
If the anion attached to hydrogen ends in -ide, put the prefix hydro- and change -ide to -ic acid
HCl - hydrogen ion and chloride ion
hydrochloric acid
H2S hydrogen ion and sulfide ion
hydrosulfuric acid
Naming Acids
If the anion has oxygen in it it ends in -ate or -ite change the suffix -ate to -ic acid
HNO3 Hydrogen and nitrate ions
Nitric acid change the suffix -ite to -ous acid
HNO2 Hydrogen and nitrite ions
Nitrous acid
Name these
HF
H3P
H2SO4
H2SO3
HCN
H2CrO4
Writing Formulas
Hydrogen will always be first
name will tell you the anion
make the charges cancel out.
Starts with hydro- no oxygen, -ide
no hydro, -ate comes from -ic, -ite comes from -ous
Write formulas for these
hydroiodic acid acetic acid carbonic acid phosphorous acid hydrobromic acid