Grade 11

Grade 11Classification of elements and periodicity in propertiesPeriodic trends in properties


Valency


Valency is a fundamental concept in chemistry that describes how atoms of elements combine with each other. As we move through the periodic table, you will notice that elements have different abilities to form bonds. These abilities can be understood in terms of valency, which refers to the ability of an atom to form bonds with other atoms. Through this detailed document, we will uncover the nature of valency, how it is determined, and its periodic trends.

Understanding valency

Valency can be defined as the combining capacity of an element. It represents the number of electrons that an atom can lose, gain, or share to become stable. For many elements, especially in the main groups, valency corresponds to the number of electrons an atom needs to achieve a full outer shell.

For example, the noble gases have a complete outer shell, and thus their valency is zero, since they neither gain nor lose electrons.

Exploring valency with examples

Let's look at a simple example of how valency works. Consider hydrogen, which has one valence electron and needs one more electron to fill its outermost shell. Therefore, hydrogen has a valency of 1. Similarly, oxygen, which has six valence electrons, needs two additional electrons to complete its shell, making its valency 2.

Some common elements and their valencies are given below:

Element: Hydrogen (H)
         Valency: 1

Element: Oxygen (O)
         Valency: 2

Element: Nitrogen (N)
         Valency: 3

Element: Carbon (C)
         Valency: 4

Determining valency from the periodic table

The periodic table is a great tool for discovering the valency of elements. Elements in the same group often have the same valency. Generally, for elements in the main group:

  • Group 1: Valency 1
  • Group 2: Valency 2
  • Group 13: Valency 3
  • Group 14: Valency 4
  • Group 15: Valency 3
  • Group 16: Valency 2
  • Group 17: Valency 1
  • Group 18: Valency 0 (noble gases)

Let's take a closer look at how valency changes across the periodic table by considering the conceptual arrangement of the elements, using the basic table structure.

1 18 HO 2 3 4 3 4 Li B BCNOF Ne 11 12 13 14 15 16 17 18 Na Mg Al Si PS Cl Ar 19 20 31 32 33 34 35 36 K G G Ge As Se Br C

Valency and chemical bonding

Valency directly affects the ability of an atom to form chemical bonds. There are three primary types of bonds that elements can form, which depend largely on their valency:

  1. Ionic bonds: These are formed when one atom donates an electron to another. For example, in sodium chloride (NaCl), sodium (Na) gives up one electron to chlorine (Cl), allowing both atoms to achieve a stable electron configuration.
  2. Covalent bonds: These are formed when atoms share electrons. In the case of water (H2O), both the hydrogen and oxygen atoms share electrons to satisfy their respective valencies, forming a stable molecule.
  3. Metallic bonds: Found primarily in metals, these bonds involve a 'sea' of electrons that move freely around the structure, providing high electrical conductivity.

Periodic trends in valency

Valency shows different trends as you move along the periods in the periodic table. Generally, from groups 1 to 14, valency increases:

  • Group 1: Elements have a valency of +1 because they have one electron in their outer shell that can be easily lost.
  • Group 2: With two electrons in their outer shell, these elements have a valency of +2.
  • Group 13: Valency of elements is generally +3 (3 electrons in outer shell).

From group 15 onwards, the general valency decreases as these elements require less energy to gain electrons to achieve a complete outer shell:

  • Group 15: These elements generally show valency of 3 (-3 considering electron gain).
  • Group 16: Elements usually show valency of -2.
  • Group 17: Halogens generally have a valency of -1.
  • Group 18: Noble gases have complete electron shells and generally have valency of 0.

Discover trends with simple visual representation

See a visual representation of how valency is reflected as you move across a period on the periodic table. Each element is represented by its atomic configuration, which shows the change in valence electrons.

LiB BCNOF Valence Electron Configuration: .1. .2. .3. .4. .3. .2. .1. 0

Applications of valency

Understanding valency is important in predicting how elements will react. It helps chemists to:

  • Predict molecule formation and bonding patterns.
  • Understand the reactivity and stability of compounds.
  • Balance chemical equations accurately.

For example, valency helps us understand why carbon, with valency 4, can form different compounds, such as methane (CH4) and carbon dioxide (CO2).

Conclusion

Valency is an integral concept when examining the periodic table and understanding basic chemical reactions. Whether you are designing new compounds or simply trying to understand more about the elements, valency provides an important insight into the structure and behavior of materials. Using periodic trends, we gain a systematic understanding of how valency affects chemical properties in elements.


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