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Chapter 5: Chemical Names and Formulas
Random Music to Lighten Your Day
Mike Stanfill, Private Hand - Flash Animation - The Elements, by Tom Lehrer
Elements to Memorize (Name and Symbol) – 32 Total Hydrogen Lithium Sodium Potassium Magnesium Calcium Iron Chromium Manganese Cobalt Nitrogen Phosphorus Chlorine Bromine Neon Argon
Nickel Copper Silver Gold Zinc Mercury Boron Carbon Aluminum Silicon Oxygen Sulfur Fluorine Iodine Helium Krypton
I HIGHLY recommend flash cards for these. Practice nightly.
Common Polyatomic Ions (-1) C2H3O2
-
HSO3-
HSO4-
HCO3-
NO2-
NO3-
CN-
OH-
MnO4-
ClO-
ClO2-
ClO3-
ClO4-
Acetate Hydrogen sulfite Hydrogen sulfate Hydrogen carbonate Nitrite Nitrate Cyanide Hydroxide Permanganate Hypochlorite Chlorite Chlorate Perchlorate
Common Polyatomic Ions (-2)
C2O42-
SO32-
SO42-
CO32-
CrO42-
SiO32-
Oxalate Sulfite Sulfate Carbonate Chromate Silicate
Common Polyatomic Ions (Other)
PO43- Phosphate
PO33- Phosphite
NH4+ Ammonium
5.1 The Periodic Table
Arranges elements according to similarities in their properties.
Each column is known as a group. Groups 1-2, and 13-18 are known as the
representative elements. These exhibit the entire range of chemical
properties. Made up of three basic groups
Metals Metalloids Nonmetals
Metals
On the left side of the periodic table. High electrical conductivity and luster, ductile
and malleable. With one exception, all are solid at room
temperature. Groups 3 through 12 are transition metals,
and groups at bottom are called inner transition metals or the rare earth metals.
Nonmetals
Upper right of periodic table Nonlusterous, generally poor conductors of
electricity. Hydrogen is actually a nonmetal
Metalloids
The elements that act as the “border” between metals and nonmetals.
Has the properties of both metals and nonmetals.
Overall Periodic Table
We’ll get back to this topic later in the year. Pg. 108 has a good break-down of
metals/non-metals and metalloids. On to naming!
5.2 – Atoms and Ions
Normally, an atom is neutral. Why? Sodium for example. Has 11 protons. How
many electrons? 11
When forming a compound, Na will lose an electron. Now no longer has same # of protons as
electrons. Now the sodium ion is positively charged.
Ions
Ions are atoms or groups of atoms that have a positive or negative charge. To have a positive or negative charge, what must
have happened? Must have gained or lost an electron
Positive? Negative?
Metals tend to lose electrons during bonding. An ion with a positive charge is called a
cation. So a sodium cation would be represented
symbolically as Na+
Na1+ also acceptable Magnesium (Mg) forms Mg2+.
How many electrons did magnesium gain? Just kidding. How many did it lose?
Ion Naming
For metals The name of the cation is exactly the same as the
name of the element Sodium atoms (Na) form sodium cations (Na+) Potassium atoms (K) form potassium cations (K+)
Even though the name is the same, they react differently. Sodium metal explodes when exposed to water Sodium cations are in salt-water, harmless
Nonmetals
Atoms of nonmetallic elements tend to gain electrons.
They form anions, which are atoms or groups of atoms with a negative charge.
Name of anion is NOT the same as the element. The name of the anion ends in –ide.
Sulfur atom (S) forms sulfide anion (S2-) Bromine atom (B) forms bromide anion (B-)
5.3 Compounds
From before, atoms of different elements may come together to form compounds.
In many compounds, atoms are bound together to form a molecule. A molecule is an electrically neutral group of
atoms that act as one unit. Compounds can be molecules
Compounds made from molecules are called molecular compounds. Tends to have relatively low melting and boiling
points. Many exist as gases at room temperature. Usually made from two or more nonmetallic
elements. Not all compounds are made from molecules
however.
Ions can join together to form ionic compounds NaCl (table salt) is an example Ionic compounds are always formed from
combining cations with anions. Although composed of ions, are ionic compounds
are electrically neutral. Why? Almost always formed from metallic and
nonmetallic elements.
Example of Ionic Compound
5.4 Chemical Formulas
Over 10 million compounds have been identified. Some ionic, some molecular.
No two have identical properties Composition can be represented by a
chemical formula Shows the kind and numbers of atoms in the
smallest representative unit of the substance
The molecular formula shows the number and kinds of atoms in a molecule or compound. Water has two hydrogens bound to an oxygen
Molecular formula of H2O
Number of atoms of each element is given by the subscript written next to each element symbol
Formula for ethane is C2H6. What is the composition of ethane?
Some elements exist naturally as molecules Hydrogen, fluorine, oxygen, nitrogen, chlorine,
bromine and iodine all are found in a molecular form in nature
H2, F2, O2, N2, Cl2, Br2 and I2
These are called diatomic molecules Means they contain two of the same element
Formulas tell nothing about structure, only what’s it made from
Formulas can also be written for ionic compounds, though formula doesn’t represent a molecule Represents a formula unit
The lowest whole-number ratio of ions in an ionic compound
NaCl Shows lowest ratio is 1 Na+ to 1 Cl-
Combine Mg2+ with Cl-
MgCl2
Example of Ionic Compound
5.5 Laws of Definite and Multiple Proportions
Simply put, in any sample of a chemical compound the masses of the elements are always in the same proportions.
Also, the number of atoms in a given compound are always in the same proportions.
Skipping the math in this section.
5.6 Ionic Charges of the Elements
This section is super-important! To write formulas for ionic compounds, need
to know what kind of ions atoms tend to form. Luckily, the periodic table will help with this! Here are the rules:
Ionic Rules
Ionic Charges of Representative Elements
1A 2A 3A 4A 5A 6A 7A 8A
Li+
Na+
K+
Rb+
Cs+
Be2+
Mg2+
Ca2+
Sr2+
Ba2+
Al3+
Does not form ions
N3-
P3-
O2-
S2-
Se2-
F-
Cl-
Br-
I-
Does not form ions
•Nonmetals in 4A tend to be found in molecular compounds, not ionic compounds
•Elements in 8A do not tend to form compounds at all
Transition Metals and Ionic Charge
Unlike the cations of 1A, 2A and 3A, most transition metals have more than one common ionic charge.
This is also characteristic of tin and lead (4A) For example, iron commonly forms Fe2+ and Fe3+.
List of these common ions on pg. 120 (do not need to memorize)
Basic rule (called the Stock system) Cu+ written as Copper(I) ion Sn2+ written as Tin(II) ion Mn3+ written as Manganese(III) ion
Exception for Transition Metals
Silver cations always have 1+ charge Cadmium and zinc cations always have 2+
charge.
5.7 Polyatomic Ions
All of the ions we’ve discussed so far are formed from single atoms. Called monatomic ions
Unlike those, there are other ions formed from groups of atoms so tightly bound together, they act as a single unit and carry a charge. Called polyatomic ions These are the compounds you need to memorize
Besides being composed of multiple atoms, act the same way as a normal ion If an anion, will bond to a cation (or more than
one) to balance out charges NO3
- (nitrate anion) will readily bond with Na+ cation to form compound with formula NaNO3
Similarly, CO32- will bond with Na+ to form
compound with formula Na2CO3
5.8 Common and Systematic Names
In early days of chemistry, compounds often named after person who discovered them
Or for the name to describe some property or source of the compound K2CO3 (Potassium carbonate) commonly called potash. Named this way because the compound was separated by
boiling wood ashes in iron pots.
Laughing gas (N2O), baking soda, quicksilver, all common names.
Needed a common naming scheme. Going to learn this soon.
5.9 Writing Formulas for Binary Ionic Compounds
Binary Ionic Compounds are composed of TWO elements.
Happens when two monatomic ions bond Remember, ionic compounds are electrically
neutral So positive charge must equal negative charge Easy with K+ and Cl-. Charges exist in 1:1 ratio,
so compound would be KCl
A little harder… Ca2+ and Br-.
Charges exist in 2:1 ratio, so ions must combine in 1:2 ratio.
Why is this? So formula should be CaBr2
Even harder…remember, look at ratio of charges! Iron (III) ion and oxide anion.
Iron (III) ion = Fe3+
Oxide anion = O2-
Ratio of charges is 3:2…not a simple thing to do Need to find least common multiple of the
charges What would it be? 6!
To reach a charge of 6 for each, need 2 Fe3+ and 3 O2-
Gives us formula of Fe2O3
Let’s try something a little different… Sn3N4
What version of tin is this? To determine, need to figure out charge contributions N exists as N3-
N contributes 12- charge So Sn must contribute 12+ charge Look at number of atoms in tin How many times does that number go into 12? 4 times! That is the positive charge on tin! So this ion is a Tin (IV) cation
5.10 Naming Binary Ionic Compounds
Very3 important section When dealing with NOT a transition metal:
Is the name of the cation followed by the name of the non-metallic anion. MgCl2
Would be magnesium chloride
K3N Would be potassium nitride
However, when dealing with the transition metals that can form more than one ion…things become a little more difficult In name, must include the Stock notation to identify cation
formed by the transition metal CuO
Copper oxide would be incorrect, because Stock notation not used
First must determine which ion of copper is formed This is a Cu2+ ion. How do I know? So name would be Copper (II) oxide
Let’s try that again… SnO2
Again, Tin oxide would be incorrect Need to determine charge on tin What would be charge on tin have to be? Sn4+
How do I know? Each O provides 2- charges, so oxygen provides a
total of 4- charges Therefore, this is named tin (IV) oxide
5.11 Ternary Ionic Compounds
Ternary ionic compounds contain atoms of 3 different elements Hint: We’re going to use those polyatomic ions
we talked about These are handled exactly the same way as
a binary ionic compound, except that instead of 2 ions, we are using (usually) 1 ion and 1 polyatomic ion.
Example Sodium cation and nitrate anion. Na+ and NO3
-
Charges exist in 1:1 ratio, so ions combine in 1:1 ratio
So would be NaNO3
Another example, a little harder Calcium cation and nitrate anion Ca2+ and NO3
-
Charges exist in 2:1 ratio, so we need 2 nitrates for every calcium
Ca(NO3)2
What does the () mean? Means there are 2 of the NO3 polyatomic ions How many oxygens in this?
Naming Named just like binary ionic compounds So previous example would be calcium nitrate
5.12 Naming Binary Molecular Compounds
This is for MOLECULAR COMPOUNDS, not ionic compounds, rules are slightly different
How can we tell a molecular compound from an ionic compound?
Molecular compound made from nonmetals. Ionic charges NOT used to assign formulas or
names to these Two nonmetallic elements can also combine in more
than one way Carbon and oxygen can form CO and CO2, also form two
polyatomic ions, CO32- and C2O4
2-.
For the previous carbon and oxygen compounds, the desire to call them carbon oxide can be strong. Resist this temptation Each of those compounds is very different
We use prefixes to name everything
Table 5.5, page 131
Prefixes Used in Naming Binary Molecular CompoundsPrefix Number
mono- 1
di- 2
tri- 3
tetra- 4
penta- 5
hexa- 6
hepta- 7
octa- 8
nona- 9
Deca- 10
How to Use Chart
If I had CO molecule Would use prefix mono- for the single oxygen Finally, ALL binary molecular compounds end in –ide.
So this would be carbon monoxide. If first atom has only 1 of it, then we don’t use
prefix on it. Which is why isn’t monocarbon monoxide.
If CO2 Use di- prefix for oxygen Carbon dioxide
H2O 2 hydrogens so di-prefix 1 oxygen so mono-prefix Dihydrogen monoxide Also known as:
Water Hehe….
Final rule: The vowel at the end of the prefix is dropped when the name of the element begins with a vowel. Which is why the above is monoxide, not monooxide.
Let’s try a few more I4O9
Tetriodine nonoxide.
SF6
Sulfur hexafluoride
N5Cl10
Pentanitrogen decachloride
Br7S8
Heptabromine octasulfide
5.13 Naming Acids
Don’t worry about this section for now, we’ll cover acids later
5.14 Summary for Naming
Ionic compounds Always neutral Positive charge = negative charge Metals always positive, nonmetals always
negative When using a transition metal that forms more
than one ion, must indicate which ion was formed by using Stock system.
Should always end in –ide Polyatomic ions treated as a unit. They travel
together
Molecular Compounds Must indicate how many of each element by prefix
system If only 1 of the first element, does not need a
prefix If element names starts with a vowel, and prefix
ends with a vowel, drop the vowel on the prefix
Homework
22-26, 28-30
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