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

More on this later

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