Ions and Molecules

Naming Ions and Molecules

by Patrick Antes

​Molecules

•When atoms of nonmetals share electrons, they form an electrically neutral aggregate called a molecule.

​

•Nonmetallic elements exist in nature as diatomic molecules, consisting of two atoms of the same element. They are more stable this way rather that as individual atoms.

 

  Ex: N₂, O₂, H₂, F₂, Cl₂, Br₂, and I₂​

Multiple Choice

Which of the following statements is not true about an atom?

• Atoms are always neutral in nature

• Atoms are not able to exist independently

• Atoms are the basic units from which molecules and ions are formed

• Atoms aggregate in large numbers to form the matter that we can see, feel or touch

Multiple Choice

What is an element?

• Two or more atoms joined together.

• One of over 100 types of atoms

• Two or more different elements joined together.

• A particle with no charge found in the nucleus of an atom.

Multiple Choice

What is a compound?

• Two different elements bonded together.

• Two of the same elements bonded together.

• A mixture of different substances.

• Two substances stuck together with glue.

​Four types of chemical formula​

​Four types of chemical formula:

​•Molecular Formula - gives the composition of the molecule, in terms of the actual number of atoms present.

  Example: C₆H₁₂O₆, Na₂C₂O₄

​

•Empirical Formula - gives the composition of the molecule, in terms of the smallest ratio of the number of atoms present.   Example: CH₂O, NaCO₂

Multiple Choice

A formula with the lowest whole # ratio of elements in a compound is called

• Molecular Formula
• Chemical Formula
• Empirical Formula 
• Distance Formula

Multiple Choice

What is the empirical formula for C₄H₆?

• CH

• CH₃

• C₂H₃

• C₄H₆

Multiple Choice

What is the empirical formula for N₂S₃?

• NS

• N₃S₂

• N₂S₃

• N₁S_1.5

Multiple Choice

Si₂F₆

Choose the correct empirical formula...

• SiF

• Si₂F₆

• SiF₃

• Si₆F₂

Multiple Choice

What is the best definition for subscript?
 

• The big number that tells you the number of molecules.
• The atomic number
• The little number that tells the number of atoms for each element.

Multiple Choice

What is the best definition for coefficient?
 

• The big number that tells you the number of molecules.
• The little number that tells the number of atoms for each element.
• The atomic number

Multiple Choice

A chemical formula that shows the actual # and kinds of atoms present in one molecule of a compound is called_________

• ionic formula
• covalent formula
• empirical formula
• molecular formula

Multiple Choice

C₂H₆O

Which is the correct empirical formula

• CHO

• C₂H₆O

• C₄H₁₄O₂

• None

​Structural formula – shows the bond pattern and connectivity of atoms in compounds. An atom is represented by its element symbol, while lines depict the type of chemical bond between the atoms.

​

Multiple Choice

What is the molecular formula for structure showed?

• C₈H₁₈

• C₃H₃

• C₈H₃

• C₃H₂(CH₃)₃

Multiple Choice

According to the Octet Rule, Nitrogen (N) has ____ valence electrons and forms ___ bonds

• 2, 6

• 3, 5

• 4, 4

• 5, 3

​Condensed structural formula – simplifies the structural formula, in which the bonding patterns and connectivity are less obvious but are still apparent.

​

  Ethanol- CH₃CH₂OH 

​

Propane- CH₃CH₂CH₃

​Key points!

​•Most cations and anions can combine to form neutral compounds (typically solids under normal conditions) that are usually referred to as salts.

​

•The net charge of an ionic compound must be zero. Therefore, the number of cations and anions in an ionic compound must be balanced to make an electrically neutral molecule.

​

​•When naming ionic compounds, the cation retains the same name as the element. The anion’s name is similar to the elemental name, but the ending of the name has been removed and replaced with “-ide.”

​

•If a metallic element has cations of different charges, which cation is used has to be indicated by its suffix (an older method) or by Roman numerals in parentheses after its name in writing (the Stock system ).

Multiple Choice

When naming ionic compounds you always write the name of the positive element  _______ .

• first
• second
• with "ide"
• with a prefix

Multiple Choice

When naming a compound, what must the last part be?

• the element with "ide" at the end

• the element with the ending "ite"

• the name of the element

• the element with "ide" at the end, unless its a polyatomic ion

Representative elements have predictable charges.

Stock System

• Most transition metals and large p block metals have variable charge

• Roman numeral used to indicate the charge of the cation

• Exceptions to stock system (do not use the roman numeral): Groups 1 & 2, Ag⁺¹, Zn⁺², Cd⁺², Al⁺³

Multiple Choice

What is the name of the compound Na₂(SO₄)?

• Sodium sulfate

• Sodium sulfide

• Sodium sulfite

• Sodium sulfuroxide

Multiple Choice

Which of the following combinations would need roman numerals in the name?

• potassium + fluorine

• beryllium + oxygen

• boron + iodine

• gold + oxygen

Multiple Choice

What is the formula for Lead (IV) Oxide?

Hint: Think about the charges for lead and oxygen. You can reduce!

• Pb₂O₄

• PbO₂

Representative elements have predictable charges.

Stock System

• Most transition metals and large p block metals have variable charge

• Roman numeral used to indicate the charge of the cation

• Exceptions to stock system (do not use the roman numeral): Groups 1 & 2, Ag⁺¹, Zn⁺², Cd⁺², Al⁺³

Cation charge from chemical formula

• Anions: get the charge from periodic table or charge of polyatomic anion.

• Get total (-) charge by multiplying subscript by charge.

• Total (-) charge = Total (+) charge

• Divide (+) charge by cation subscript

• Roman numeral is the charge of ONE cation.

Multiple Choice

What is the name of the compound Na₂(SO₄)?

• Sodium sulfate

• Sodium sulfide

• Sodium sulfite

• Sodium sulfuroxide

Multiple Choice

Which of the following combinations would need roman numerals in the name?

• potassium + fluorine

• beryllium + oxygen

• boron + iodine

• gold + oxygen