1. How does one differentiate between formulas of ionic and molecular compounds?
ID: 898589 • Letter: 1
Question
1. How does one differentiate between formulas of ionic and molecular compounds? How is the naming system different for ionic and molecular compounds?
2.Hydrogen peroxide and water both contain the same 2 elements. Find the formulas for both compounds and give some properties of both. Discuss briefly why it is important to write correct chemical formulas?
3. When iron rusts it combines with the oxygen in the air. Predict the formula of this iron oxide using the highest oxidation number for iron.
4. How many atoms of O are in the compound Ca3(PO4)2?
5. Briefly describe the process for writing ionic compounds.
Explanation / Answer
question no 1
Formulas for Molecular Compounds
Molecules consist of two or more atoms bonded to one another through "covalent" bonds.
Empirical formula:
Consider the benzene molecule which has 6 carbon and 6 hydrogen atoms. Therefore the ratio of carbon to hydrogen atoms is 6 to 6 which we can simplify to 1 to 1 (i.e., 1:1). The empirical formula expresses this most simple ratio, i.e. C1H1 (or CH). The empirical formula expresses the most simple ratio of atoms in the molecule.
Examples: methane CH4 ,benzene CH, ethane CH3
Molecular formula:
Molecular formulas go one step beyond the empirical formula in that they express not only the correct ratio but the correct number of atoms in the molecule. In the case of benzene the molecular formula would be C6H6.
Examples: methane CH4, benzene C6H6
Structural formula:
The structural formula not only has the correct number of atoms but includes the bonding structure of the molecule (i.e., which atoms are bonded together).
Writing Formulas of Ionic Compounds
Remember the Prime Directive in writing formulas:
Ca(OH)2 ¹ CaOH2
Cation
Anion
Formula
Na+
Cl-
NaCl
Ca2+
Br-
CaBr2
Na+
S2-
Na2S
Mg2+
O2-
MgO
Nomenclature of Ionic and Covalent Compounds
A binary compound is a compound formed from two different elements. There may or may not be more than one of each element. A diatomic compound (or diatomic molecule) contains two atoms, which may or may not be the same.
Cl2
Not binary (only one type of atom), but diatomic (two atoms)
BrCl
Binary (two different elements), and diatomic (two atoms)
H2O
Binary (two different elements), but not diatomic (more than two atoms)
CH4
Binary (two different elements), but not diatomic (more than two atoms)
CHCl3
Neither binary nor diatomic
When naming binary ionic compounds, name the cation first (specifying the charge, if necessary), then the nonmetal anion (element stem + -ide).
Examples
NaCl
Sodium chloride
AlBr3
Aluminum bromide
Ca3P2
Calcium phosphide
Metals combine with polyatomic ions to give ionic compounds. Name the cation first (specifying the charge, if necessary).
Examples
NaOH
Sodium hydroxide
Ca(NO3)2
Calcium nitrate
K3PO4
Potassium phosphate
(NH4)2SO4
Ammonium sulfate
Acids are compounds in which the "cation" is H+. The word "hydrogen" is omitted, the word "acid" is added to the end; the suffix is changed as shown below:
Compound name
Acid name
-ate
-ic + acid
-ite
-ous + acid
-ide
hydro- -ic + acid
Examples
Example
Compound Name
Acid name
HClO3
hydrogen chlorate
chloric acid
H2SO4
hydrogen sulfate
sulfuric acid
HCl
hydrogen chloride
hydrochloric acid
Acid salts are ionic compounds that still contain an acidic hydrogen, such as NaHSO4. In naming these salts, specify the number of acidic hydrogens in the salt.
Examples
NaHSO4
sodium hydrogen sulfate
NaH2PO4
sodium dihydrogen phosphate
[Important exception: when the compound contains oxygen and a halogen, the halogen is placed first. If both elements are in the same group, the one with the higher period number is named first.]
1
mono-
2
di-
3
tri-
4
tetra-
5
penta-
6
hexa-
7
hepta-
8
octa-
9
nona-
10
deca-
Examples
SO2
sulfur dioxide
SO3
sulfur trioxide
N2O
dinitrogen monoxide
NO
nitrogen monoxide
NO2
nitrogen dioxide
N2O4
dinitrogen tetroxide
N2O5
dinitrogen pentoxide
question no 2
H2O2
Hydrogen peroxide is a strong oxidizing agent in either acid or alkaline solutions.
Hydrogen ion concentration (pH) and temperature are important controlling parameters in H2O2 reactions.
H2O2 has the distinct advantage of producing only water as a by-product.
Hydrogen peroxide has been used as an antiseptic.
H2O
Water has a high specific heat.
Water in a pure state has a neutral pH.
Water molecules exist in liquid form over an important range of temperature from 0 - 100° Celsius.
Water is a universal solvent. It is able to dissolve a large number of different chemical compounds.
Water has a high surface tension.
question no 3
The rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen.[3] The iron is the reducing agent (gives up electrons) while the oxygen is the oxidising agent (gains electrons).
The chemical formula for rust is Fe2O3.nH2O(s)
question no 4
In Ca3(PO4)2 there are 8 oxygen atoms are present
Question no 5
1. Identify the cation. Cation is written first in the name of the compound.
2. Write the correct formula and charge for the cation.
3. Identify the anion. Anion is written last in the name of the compound.
4. Write the correct formula and charge for the anion.
5. Combine the cation and anion to produce an electrically neutral compound.
6. If the charges on the cation and anion are equal in magnitude (i.e. +1/-1, +2/-2, +3/-3), combine the cation and anion in a 1:1 ratio.
7. If the charges on the cation and anion are not equal in magnitude, use the charge on the cation as the subscript for the anion. Use the charge on the anion (omitting the negative sign) as the subscript for the cation.
8. Place parentheses around a polyatomic ion if you need more than one of them in the final formula.
9. Do not show the charges of the ions when you write the final formula for the compound.
10. Make sure that the subscripts for the cation and anion are the smallest whole number ratio.
Formulas for Molecular Compounds
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