Ch 6 Chemical Names & Formulas
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Transcript Ch 6 Chemical Names & Formulas
Ch 6 Chemical Names &
Formulas
P132 Addison Wesley Chemistry
Contents
6.1 Introduction to Chemical Bonding
6.2 Representing Chemical Compounds
6.3 Ionic Charges
6.4 Ionic Compound
6.5 Molecular Compounds and Acids
6.6 Summary of Naming + Formula
Writing
6.1 Introduction to Chemical
Bonding
Molecules & Molecular Compounds
Contents
Monoatomic
Only noble gases exist as isolated atoms
Consist of single atoms
Ne, Ar, Ra
Diatomic
Molecules that exist in pairs naturally
O2, H2, N2
Triatomic
3 atoms of the same element
O3 - ozone
Molecule
Smallest electrically neutral unit of a
substance that still has the properties of the
substance and consisting of one or more
atoms bonded together
O + O O2
H + H + O H2O
Most atoms exist - in form of “molecule”
Compound
A substance formed from the combination
of two or more elements in a definite
proportion by weight.
A compound can be one or more
molecules.
Molecular compounds
Low melting pt.
Low boiling pt.
Many gas or liquid @ room temp.
Molecules composed of atoms of 2+
nonmetals
Ex carbon monoxide – CO- diatomic
Ex water – H2O – triatomic
Ions & Ionic Compounds
Ions- atoms or groups of atoms w/ ‘+’ or ‘-‘
charge
Form when loss or gain of electron from
atom
Na = 11 p+ + 11 eIf loose 1eNa + = 11p+ + 10e-
Cation
Any atoms w/ ‘+’ charge
Fewer e- than atom that formed it
Cation Naming
Metallic elements names
Name cation same as name of element
Sodium atom forms sodium cation
Do Not have same properties as atoms
Na atom explosive w/ H2O
Na very stable in H2O
Anion
Atoms of nonmetallic elements game
electrons
Have ‘-’ charge
Anion Naming
Nonmetallic elements name
Not same as name
End in “-ide”
Sulfide-S2 Bromide-Br
Ionic Compound
Compounds composed of cation and anions
Metal cation + nonmetal anion
Ex NaCl
Na+ + Cl Sodium Chloride – Table Salt
Ionic Compound Properties
Electrically neutral
‘+’ = ‘-‘ charge
usually solid crystals @ room temp.
melt @ high temp.
Table 6.1 Characteristics of
Molecular + Ionic Cmpds.
Characteristics
Molecular Cmpd
Ionic Cmpd
Representative Unit
Molecule
Formula unit
(balance of
oppositely charged
ion)
Types of Elements
Nonmetallic
Metallic combined
w/ nonmetallic
Physical State
Solid, Liquid, or Gas Solid
Melting Pt.
Low(usually below
300oC)
High(usually above
300oC)
6.2 Representing Chemical
Compounds
Contents
Chemical formulas
Shows kinds + numbers of atoms in the
smallest representative unit of the
substance
If the molecules of an element have more
than 1 atom a number is used as a subscript
Ex O2- Oxygen
H2, F2, O2, N2, Cl2, Br2, I2
O3- Ozone
Molecular Formulas
Shows kinds + numbers of atoms present in
a molecule of a compound
Ex H2O- Water
Ex CO2- Carbon dioxide
Ex C2H6- Ethane
Does not show arrangement
Structural Formula
ammonic gas (NH3)
H-N-H
H
Ball-and-stick molecular model
Methane – CH4
Penicillin
Formula Units
Representation of ionic compounds
(Na+) and (Cl-) form the solid NaCl (sodium
chloride)
Lowest whole number ratio of the ions
Charges not shown
Magnesium chloride – Mg2+ and Cl – for
MgCl2
*Remember there is no such thing as a molecule
of NaCl or MgCl2 – they exist as a repeating
positively and negatively charged ions in 3D
patterns.
Laws of Definite Proportions
In any sample of any chemical compound, the
masses of the elements are always in the same
proportion.
Means a sample of a chemical compound in our
lab is the same as a sample in someone else’s lab
by mass of elements in the compound.
Magnesium sulfide 100g =43.13g Mg + 56.87g S
Law of Multiple Proportions
Whenever 2 elements form more than one
compound, the different masses of 1
element that combine w/ the same mass of
the other element are in the ratio of small
whole numbers.
Example
A+B=C and 2A+B=D
Then A is a proportion of 1:2
Multiple Proportions
Example
H2O
H2O2
8gO
16gO
O is a proportion 8:16 or 1:2 by mass
Helps if have mass of 1 proportion allow
easy way to obtain mass of other
6.3 Ionic Charges
Contents
Monatomic Ions
ions consisting of only 1 atom
Metallic Elements
tend to lose electrons (became positive)
Group 1A => 1+ charge cation
Group 2A => 2+ charge cation
Group 3A => 3+ charge cation
Aluminum only common group 3A metal
Group A Nonmetals
tend to form anions
They tend to gain electrons (become negative)
Subtract the group # from 8 and make negative
Group 7A => 1- charge anion
Group 6A => 2- charge anion
Group 5A => 3- charge anion
3 nonmetals in this group
N3-, P3-, As3-
Group 4A
Group 4A and O generally don’t form ions
Transition metals + the Z metals in 4A
(Sn-tin + Pb-Lead)
Tend to form more than 1 cation
Transition metals
Transition metals + the Z metals in 4A
(Sn-tin + Pb-Lead)
Tend to form more than 1 cation
Table 6.3 p144
Formulas + Names of Common Metal Ions
w/ more than 1 Ionic Charge
Polyatomic Ions
Tightly bound groups of atoms that behave
as a unit and carry a charge.
Most end in ‘-ite’ or ‘-ate’
3 exceptions
ammonium – (NH4+)
cyanide – (CN-)
hydroxide- (OH-)
‘ite’ vs. ‘ate’ ending
‘ite’ signifies 1 less oxygen than ‘ate’ ion
does not tell # of O atoms
Hydrogen at Beginning
It is H+ cation combined w/ polyatomic
anion
It is algebraic sum of ionic charges
H++ CO32- →HCO3- hydrogen carbonate
H++ PO43- → HPO42- hydrogen phosphate
H++ HPO42-→H2PO- dihydrogen phosphate
6.4 Ionic Compound
Contents
Writing Formulas for Binary
Ionic Compounds
Binary compounds
Compounds composed of 2 elements
KCL – potassium chloride (K+) + (Cl-)
Anion charge = cation charge
In writing formulas
The positive charge cation must balance the
negative charge anion
The net ionic charge is zero
Cation (+) is written first
Anion (-) is written second
Binary Compound Examples
Calcium bromide
Ca2+ +Br- => CaBr2
2-2=0
took 2 Br to equal zero
1:2
rust-Iron (III) oxide
Fe3+
+
O2=>Fe2O3
Make sure it is lowest whole # ratio
2:3 ratio
Naming Binary Ionic
Compounds
CuO
Metallic cation- copper
Nonmetallic anion- oxide
1:1 ratio
Oxide anion always 2- so copper cation must
balance it w/2Copper(П) oxide= CuO
Transition metals may have 2 common ions
Cu- 1++2+ - copper
Sn- 2++4+ - tin
Prefixes & Suffixes p 152
Binary Compounds
All end in ‘ide’
Contain only 2 elements
One type-“molecular compound”
Prefixes represent # of atoms
Carbon monoxide
Carbon dioxide
Polyatomic Ions
End in ‘ite’ or ‘ate’
Most consist of 3 or more atoms
‘ite’ or ‘ate’ relate to the # of O atoms
‘ite’ is 1 less O than ‘ate’
Nitrite ion-NO2- or nitrate ion NO3Neither ending represents a specific #
Ternary Ionic Compounds
A compound containing atoms of 3
different elements
Usually contain a polyatomic ion
Ternary Ionic Compound
Formula
1st write formula (symbol+ charge) for each
ion
then balance charges
‘ate’ or ‘ite’ endings indicate a polyatomic
anion that includes O
‘ide’ only 2 common polyatomic ions end
in this
hydroxide-(OH-)
cyanide-(CN-)
NH4+- Ammonium
Calcium nitrate
(Ca2+) + (NO3-)
Ca2+ + NO3- Ca(NO3)2
Parenthesis tell that more than 1 of the
polyatomic ion are needed – they keep it
together as a unit
Parenthesis not needed if only 1 polyatomic
ion
Lithium carbonate
Li+ - lithium cations
CO32- - carbonate anions
Li+ + CO32- Li2CO3
Naming
1st recognize polyatomic ion
Name cation in 1st positon
Follow it w/ name of anion
K2Cr2O7 – potassium dichromate
K2 – cation potassium
Cr2O7 – anion dichromate
6.5 Molecular Compounds and
Acids p 158
Contents
Binary Molecular Compounds
Composed of 2 nonmetallic elements
Because composed of molecules ionic
charges are not used to assign formulas or
names
When 2 nonmetallic elements often
combine in more than 1 way
CO – carbon monoxide
CO2 – carbon dioxide
Prefixes help distinguish different
compounds
Tell how many atoms
Mono- 1, di- 2, tri-3…p159
All end in ‘ide’ same as binary ionic
compounds
Sometimes the vowel @ end of prefix is
dropped as in monoxide
Writing Formulas (given names)
Use prefixes to tell subscript of each
element
Write correct symbols for the 2 elements
Tetraiodine nonoxide – I4O9
Naming Common Acid
Acids are compounds that produce H+ ions
in H2O
Consider them a combination of anions
connected to as many H+ ions needed to
make electrically neutral
Common Acids
Hydrochloric acid –HCl
Sulfuric acid – H2SO4
Nitric acid – HNO3
Acetic acid – H3PO4
Phosphoric acid – H2Co3
6.6 Summary of Naming +
Formula Writing
p 161 Figure 6.21 – naming flowchart
Contents
Acids
If 1st compound is an H it is an acid
HNO3 – Nitric acid
2 Elements (Not an Acid)
2 elements
binary compound – ends in ‘ide’
1st part is a metal and Group A element then just
name the ions (BaS – barium sulfide)
1st part is a metal and not a Group A element then
name the ions and use Roman numerals w/ the cation
(FeCl2 – iron (II) chloride
1st part is not a metal then it is a binary molecule so
use prefixes in the name (N2O3 – dinitrogen trioxide)
More Than 2 Elements (Not an
Acid)
compound contains a polyatomic ion
name generally ends in ‘ite’ or ‘ate’
1st part is a Group A element then name the
ions(LiCO3 – lithium carbonate)
1st part is not a Group A then name the ions
+ use a Roman numeral w/ the cation
(CuSO4 – copper (II) sulfate)
Chemical Formula Rules
In an ionic compound, the net ionic charge = 0
An ‘ide’ ending generally is a binary compound
An ‘ite’ or ‘ate’ ending means there is a
polyatomic ion that includes O in the formula
Prefixes in a name generally indicate that the
compound is molecular
Prefixes show the # of each kind of atom in the
molecule
A Roman numeral after a cation shows the ionic
charge of the cation
p 162 Figure 6.23 Chemical formula
flowchart
Contents
6.1 Introduction to Chemical Bonding
6.2 Representing Chemical Compounds
6.3 Ionic Charges
6.4 Ionic Compound
6.5 Molecular Compounds and Acids
6.6 Summary of Naming + Formula
Writing