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Last updated: August 7, 2017
The 5 Most Important Acids To Know
Posted: 11 July 2015  

Formulas of the 5 acids

An atom of an element transfers electrons to become an ion, and then combines with other ions to make a chemical compound.

Some compounds, like acids, are not named by reading the elements in the formula of the compound. For example, the following compound

Nitric acid electrically neutral chemical compound.
Nitric Acid


looks like it might be pronounced hydrogen-something ... However the hydrogen in this compound indicates it is an acid, nitric acid, so the hydrogen is written in the chemical formula because acids by definition produce hydrogen protons when they react. The word acid signifies that the hydrogen is in the formula. Also the fact that there is no superscript indicating a positive or negative charge signifies that this is an electrically neutral chemical compound and not an ion. Some negative ions do have a hydrogen in the beginning of the formula and in those cases the hydrogen is pronounced. Nitric acid belongs to a very special class of 5 acids that we will show below which must be memorized because they are a key to understanding how to recognize other acids and anions.

Atoms of an element are neutral with no electrical charge until they gain or lose a certain number of negatively charged electrons and become an ion. Ions have either positive or negative charges depending on whether they lose or gain negatively charged electrons. Metals lose electrons to form positive ions and non-metals gain electrons to form negative ions. Positively charged ions are called cations and negatively charged ions are called anions.

Transition metals can make more than 1 type of positive ion. For example, Copper (Cu) a transition metal, can lose 1 electron to make a positive ion with a 1+ charge or it can lose 2 electrons to make a positive ion with a 2+ charge.

All chemical compounds made from 2 or more ions are electrically neutral. Chemical compounds are formed by an exchange of electrons from a positive ion to a negative ion. The chemical compound is electrically neutral because the value of the positive ion added to the value of the negative ion equals a net charge of zero.

In the formula for a chemical compound, a superscript indicating a positive or negative charge is not given because the net charge of a chemical compound is zero. The number of positive ions and negative ions in each chemical compound combine to equal zero. When compounds that have a net charge of zero are broken up into separate ions, the ions return to having either a positive or negative charge depending on whether they lose or gain electrons.

The subscript indicates how many atoms of the element are required to make the net charge of the chemical compound equal to zero.

A calcium atom loses 2 electrons making a 2+ positive ion. Calcium is in group 2 of the periodic table and all of the group 2 elements, metals, lose 2 electrons to make a 2+cation.

A chlorine atom gains an electron to have a negative charge of 1-. Like all elements in group 7, chlorine is a nonmetal that forms a 1- anion.

That is why it takes 2 chlorine atoms to make a net ionic charge of zero with calcium. The equation representing the charges on the calcium and chorine ions as they form a compound with a net charge of zero is:

+2 + (-1)2 = 0
(1 calcium ion) + (2 chlorine ions) = 0

In the formula of chemical compounds, the charge is invisible or not written because the net charge is zero. If you know what group one of the ions in the chemical compound belongs to, you can determine what the charge is on the other ion, because adding them together equals a net charge of zero.

Two cations, cannot make a binary ionic compound because they have positive charges, and adding 2 positive values together cannot equal zero. Positive charges multiplied by any number above zero will not equal zero. Metals are cations, so there are no chemical compounds made of 2 metals such as Lithium aluminum. Lithium has a positive charge of 2 (group 2) and aluminum has a positive charge of 3 (group 3). Negatively charged ions are required to make positive ions equal zero and thus only negative and positive ions together form chemical compounds.

Nonmetals can make a type of compound but they are still anions. The compound formed by 2 nonmetals does not have a net charge of zero.

To help grasp different types of chemical compounds, a introductory chemistry book may initially describe 3 types of chemical compounds, called binary ionic compounds before introducing the polyatomic ions. The 3 binary types compounds, made of 2 ions are:

Type 1: A metal and a nonmetal.

Type 2: A transition metal and a nonmetal. Roman numerals are used in the name of these compounds (not the formula) to indicate what charge the transition metal has, since it can form more than 1 kind of positively charged ion.

Type 3 binary compounds are made of 2 nonmetals. In addition to binary ionic compounds there are also polyatomic ions. Polyatomic ions can be cations or anions.

Acids are easy to identify because they are electrically neutral and their formula starts with a hydrogen ion, but Hydrogen is not in the name of the acid. Because the acids are chemical compounds, they have a net charge of zero.

The 5 most important acids to memorize are shown below. In the equation showing the breakdown from acid to anion and hydrogen proton, the acid compound does not have a charge because is electrically neutral but the ions do.

  1. Chloric acid
  2. Nitric acid
  3. Sulfuric acid
  4. Carbonic acid
  5. Phosphoric acid

positive ion
Chloric Acid
Chloric acid
Nitric Acid
Nitric acid with breakdown into nitrate anion.
Sulfuric Acid
Sulfuric acid showing breakdown into sulfate anion.
Carbonic Acid
Carbonic acid
Phosphoric Acid
Phosphoric acid with breakdown into phosphate anion.
*Notice that the acid compounds are electrically neutral and the ions are charged.

These 5 acids and their corresponding anions are important to memorize because the names of other elements in the same group follow the same pattern as them. The elements in the same group behave like each other in most cases.

The following ions can be identified as acid anions rather than acids because their formula (not shown here) shows that they have an electrical charge, they are not electrically neutral.

Hydrogen carbonate
Hydrogen sulfate,
Hydrogen sulfide
Hydrogen sulfite
Dihydrogen phosphate
Hydrogen phosphate

It is essential to do a lot of memorization when learning the nomenclature of chemistry. For an ability to name chemical formulas of acids It is required to memorize the 5 important acids, and the anion ions associated with each of them. Additionally, memorize the polyatomic ions of both cations and anions, and the periodic table.

It might be best to memorize the periodic table by groups, remembering the elements from top to bottom in the group, and starting with group 8 and working backwards to group 1. For example

Group 8

These are the noble gases. They do not lose or gain electrons. Group 7 and 8 show why it helps to memorize the periodic table by groups, because the elements in the groups tend to rhyme, indicating they have similar properties.

Group 7

Group 6

Group 5

Group 4

Skipping over the transition metals to the far left of the table, next it may be easiest to memorize groups 1 and 2 in that order.

Group 1

Group 2

Memorize the transition metals in whichever way you can. Perhaps learning them in the horizontal direction may be easiest, starting from the right going left, since the elements on the right have more familiar names to begin with such as

zinc, copper,nickel…
cadmium, silver, palladium…
mercury, gold, platinum…

by Andrea Boggs

Reference list

Cracolice & Peters. Introductory Chemistry. 5e. Cengage Learning. 2013.

  • “Chemical compounds are electrically neutral.” p.164


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