Common Valencies of Important Elements

Valency is one of the basic ideas in chemistry that helps us understand how atoms combine with one another. When elements form compounds, their atoms interact by losing, gaining, or sharing electrons. The combining capacity of an atom is commonly described by its valency. Knowing the common valencies of important elements makes it much easier to understand chemical formulas, write compounds correctly, and study chemical reactions.

Different elements have different valencies. Some elements usually show one common valency, while others can show two or more valencies depending on the compound they form. For example, sodium commonly has a valency of 1, while magnesium has a valency of 2. Iron can commonly show valencies of 2 and 3, which is why compounds such as FeCl₂ and FeCl₃ exist.

Learning the common valencies of important elements provides a useful foundation for studying inorganic chemistry. It also helps when naming compounds, balancing chemical equations, understanding ions, and predicting how elements may combine.

What Is Valency?

Valency is the combining capacity of an atom with other atoms. It is related to the number of electrons an atom loses, gains, or shares while forming a chemical bond.

For example, sodium has one electron in its outermost shell. It can lose this electron to form a sodium ion, Na⁺. Therefore, the common valency of sodium is 1.

Magnesium has two electrons in its outermost shell and commonly loses both to form Mg²⁺. Its common valency is therefore 2.

Chlorine has seven valence electrons. It commonly gains one electron to complete its outer shell and forms Cl⁻. Thus, chlorine has a common valency of 1.

Valency is often written as a positive number without the charge sign. Therefore, the valency of Na⁺ is 1, Mg²⁺ is 2, and Cl⁻ is 1.

Why Are Common Valencies Important?

Knowing valencies is useful because chemical formulas depend on the combining capacities of the elements involved.

Suppose we want to form a compound between magnesium and chlorine. Magnesium has valency 2, while chlorine has valency 1. One magnesium atom combines with two chlorine atoms, giving the formula MgCl₂.

Similarly, aluminium has valency 3 and oxygen has valency 2. Their valencies are balanced by using two aluminium atoms and three oxygen atoms, producing Al₂O₃.

Common valencies are especially useful for:

• Writing chemical formulas

• Understanding ionic compounds

• Naming chemical compounds

• Predicting combinations of elements

• Studying chemical reactions

• Understanding ions

• Learning oxidation states

• Solving basic chemistry problems

Common Valencies of Important Elements

The following table contains many commonly encountered elements and their usual valencies.

These are common valencies encountered in basic and intermediate chemistry. Some elements can exhibit additional valencies or oxidation states in particular compounds.

Valencies of the First Twenty Elements

The first twenty elements are especially important when learning the fundamentals of chemistry.

The noble gases helium, neon, and argon generally have valency 0 because their outer electron shells are stable. They usually do not need to gain, lose, or share electrons to achieve a stable electronic configuration.

Elements With Valency 1

Several important elements commonly have valency 1.

Hydrogen has a common valency of 1. Sodium, potassium, lithium, and other alkali metals also commonly show valency 1 because they tend to lose one outer electron.

Some metals can also show valency 1. Copper can have valency 1 or 2, while silver commonly has valency 1.

Examples include:

• Hydrogen — 1

• Lithium — 1

• Sodium — 1

• Potassium — 1

• Silver — 1

• Copper — 1

• Gold — 1

• Chlorine — 1

• Bromine — 1

• Iodine — 1

For example, sodium and chlorine combine to form NaCl. Sodium has valency 1 and chlorine has valency 1, so their ratio is 1:1.

Elements With Valency 2

Valency 2 is common among several elements, particularly alkaline earth metals.

Important examples include:

• Beryllium — 2

• Magnesium — 2

• Calcium — 2

• Strontium — 2

• Barium — 2

• Oxygen — 2

• Zinc — 2

• Copper — 2

• Iron — 2

• Mercury — 2

• Lead — 2

For example, magnesium combines with oxygen to form MgO. Both magnesium and oxygen have valency 2, so one atom of each is sufficient to form the compound.

Calcium chloride provides another example. Calcium has valency 2, while chlorine has valency 1. Therefore, the formula is CaCl₂.

Elements With Valency 3

Several important elements commonly show valency 3.

Examples include:

• Boron — 3

• Aluminium — 3

• Scandium — 3

• Iron — 3

• Chromium — 3

• Gallium — 3

• Cobalt — 3

• Nitrogen — 3

Aluminium oxide is a useful example. Aluminium has valency 3 and oxygen has valency 2. Balancing these valencies gives Al₂O₃.

Iron can also have valency 3. Iron(III) chloride has the formula FeCl₃ because one Fe³⁺ ion combines with three Cl⁻ ions.

Elements With Valency 4

Some elements commonly show valency 4.

Important examples include:

• Carbon — 4

• Silicon — 4

• Titanium — 4

• Tin — 4

• Lead — 4

• Germanium — 4

Carbon is particularly important because its valency of 4 allows it to form a huge variety of compounds. Methane, CH₄, is a simple example. Carbon has valency 4, while each hydrogen atom has valency 1. Therefore, four hydrogen atoms combine with one carbon atom.

Silicon also commonly shows valency 4 and forms many important compounds in minerals and materials.

Elements With More Than One Valency

Not every element has only one common valency. Many elements, particularly transition metals, can show more than one valency.

Iron is a well-known example. It commonly shows valencies 2 and 3.

• Fe²⁺ → valency 2

• Fe³⁺ → valency 3

This gives rise to compounds such as:

• FeCl₂ — iron(II) chloride

• FeCl₃ — iron(III) chloride

Copper also commonly shows two valencies:

• Cu⁺ → valency 1

• Cu²⁺ → valency 2

Therefore, copper can form compounds such as CuCl and CuCl₂.

Tin commonly shows valencies 2 and 4, while lead commonly shows 2 and 4 as well.

Common Variable-Valency Elements

Some elements that frequently show more than one valency include:

These values should be treated as common valencies rather than a complete list of every possible oxidation state.

How Valency Helps in Writing Chemical Formulas

Valency can be used to determine the ratio in which elements combine.

Consider aluminium and oxygen.

Aluminium has valency 3.

Oxygen has valency 2.

To balance the combining capacities, we need two aluminium atoms and three oxygen atoms.

Therefore:

Al₂O₃

Now consider calcium and chlorine.

Calcium has valency 2.

Chlorine has valency 1.

One calcium atom needs two chlorine atoms.

Therefore:

CaCl₂

Another example is aluminium chloride. Aluminium has valency 3 and chlorine has valency 1, so the formula is:

AlCl₃

This method is commonly taught using the criss-cross method, although understanding why the subscripts balance the combining capacities is more useful than simply memorizing the procedure.

Valency and Ions

Valency is closely related to the formation of ions.

When an atom loses electrons, it usually forms a positively charged ion called a cation. When an atom gains electrons, it usually forms a negatively charged ion called an anion.

For example:

Na → Na⁺ + e⁻

Sodium loses one electron and forms Na⁺. Its common valency is 1.

Similarly:

Mg → Mg²⁺ + 2e⁻

Magnesium loses two electrons and forms Mg²⁺. Its common valency is 2.

Chlorine gains one electron:

Cl + e⁻ → Cl⁻

Therefore, chlorine commonly has valency 1.

The charge of an ion can help indicate its combining capacity, although valency and oxidation state are not identical concepts in all chemical situations.

Valency of Noble Gases

Noble gases generally have valency 0 in basic chemistry because their outer electron shells are already stable.

Important noble gases include:

• Helium — 0

• Neon — 0

• Argon — 0

• Krypton — 0

• Xenon — 0

Helium has two electrons in its only electron shell, while the other common noble gases have stable outer shells. As a result, they generally do not readily form compounds under ordinary conditions.

Some heavier noble gases, particularly xenon, can form certain compounds under specific conditions. Therefore, valency 0 is best understood as their usual behavior in elementary chemistry.

A Simple Way to Remember Common Valencies

Instead of trying to memorize the entire periodic table at once, it is easier to learn elements in groups.

Many elements in Group 1 commonly have valency 1:

• Li

• Na

• K

• Rb

• Cs

Many elements in Group 2 commonly have valency 2:

• Be

• Mg

• Ca

• Sr

• Ba

Some main-group elements show predictable patterns, while transition metals often have variable valencies.

It is also useful to learn common elements through familiar compounds. For example:

• NaCl shows Na valency 1 and Cl valency 1.

• MgO shows Mg valency 2 and O valency 2.

• CaCl₂ shows Ca valency 2 and Cl valency 1.

• Al₂O₃ shows Al valency 3 and O valency 2.

• FeCl₂ and FeCl₃ demonstrate the variable valencies of iron.

This approach connects memorization with actual chemical formulas.

Valency and Oxidation State

Valency and oxidation state are related but should not always be treated as exactly the same concept.

Valency generally describes the combining capacity of an element in a compound. Oxidation state describes the hypothetical charge assigned to an atom according to specific rules for assigning bonding electrons.

For simple ionic compounds, the two ideas may appear very similar. For example, sodium commonly has valency 1 and an oxidation state of +1 in NaCl.

However, oxidation states can take positive, negative, or zero values and can vary significantly in covalent compounds. Therefore, when studying more advanced chemistry, it is important to distinguish between valency and oxidation state.

Common Valencies at a Glance

A useful quick-reference list is:

Valency 1: H, Li, Na, K, Ag, Cu, Au, F, Cl, Br, I

Valency 2: Be, Mg, Ca, Sr, Ba, O, Zn, Fe, Cu, Hg, Pb

Valency 3: B, Al, N, Fe, Cr, Sc, Ga

Valency 4: C, Si, Ti, Sn, Pb, Ge

Variable valencies: N, P, S, Cl, Fe, Cu, Cr, Mn, Sn, Pb, Hg, Au

Usually valency 0: He, Ne, Ar, Kr, Xe

This list is useful for quickly checking the common combining capacities of many important elements.

Conclusion

Common valencies provide a simple way to understand how elements combine to form compounds. They help explain why sodium and chlorine form NaCl, why magnesium and oxygen form MgO, and why aluminium and oxygen form Al₂O₃. While many elements have a familiar common valency, some elements can show more than one valency depending on the compound and chemical environment.

Learning the common valencies of important elements is therefore more than memorizing a table. It creates a foundation for writing chemical formulas, understanding ions, studying chemical bonding, and exploring chemical reactions. As chemistry becomes more advanced, concepts such as oxidation states and electronic structure provide a deeper explanation of why elements exhibit particular combining behaviors.