Grade 11
  1. Basic concepts of chemistry  1.1. Importance of Chemistry  1.2. Nature and scope of chemistry  1.3. laws of chemical combination  1.3.1. Law of conservation of mass  1.3.2. Law of definite proportions  1.3.3. Law of multiple proportions  1.3.4. Law of gaseous volume  1.3.5. Avogadro's Law  1.4. Dalton's atomic theory  1.5. Mole concept and molar mass  1.6. Percent composition  1.7. Empirical and molecular formula  1.8. Stoichiometry and Stoichiometric Calculations  1.9. Limiting reagent concept
  2. Structure of the atom  2.1. Discovery of the electron, proton, and neutron  2.2. Atomic Model  2.2.1. Thomson's model  2.2.2. Rutherford's model  2.2.3. Bohr's model  2.3. Quantum mechanical model of the atom  2.4. Dual nature of matter and radiation  2.5. Heisenberg's uncertainty principle  2.6. Quantum numbers  2.7. Atomic orbitals and their shapes  2.8. Electronic configuration of elements  2.9. Aufbau principle  2.10. Pauli's exclusion principle  2.11. Hund's maximum multiplicity rule  2.12. de Broglie's hypothesis  2.13. Photoelectric effect
  3. Classification of elements and periodicity in properties  3.1. Historical development of the periodic table  3.2. Modern Periodic Law and Periodic Table  3.3. Periodic trends in properties  3.3.1. Atomic and Ionic Radius  3.3.2. Ionization enthalpy  3.3.3. Electron gain enthalpy  3.3.4. Electronegativity  3.3.5. Valency  3.3.6. Metallic and Non-Metallic Properties  3.3.7. Oxidation states  3.4. Unusual Properties of the First Elements
  4. Chemical Bonding and Molecular Structure  4.1. Kossel–Lewis approach to chemical bonding  4.2. Ionic or electrovalent bond  4.3. Covalent bond and its features  4.4. Bond parameters  4.5. VSEPR Theory  4.6. Valence bond theory  4.7. Hybridization and its types  4.8. Molecular orbital theory  4.8.1. Bond order and stability  4.9. Hydrogen bonding
  5. States of matter  5.1. Intermolecular forces  5.2. Gas Laws  5.2.1. Boyle's law  5.2.2. Charles's Law  5.2.3. Avogadro's Law  5.2.4. Dalton's law of partial pressure  5.2.5. Graham's law of spread  5.3. Ideal Gas Equation and Applications  5.4. Real gases and deviations from ideal behaviour  5.5. Kinetic molecular theory of gases  5.6. Liquefaction of gases  5.7. Properties of Liquids  5.8. Surface tension and viscosity
  6. Thermodynamics  6.1. System and environment  6.2. Types of systems in thermodynamics  6.3. Types of procedures  6.4. First law of thermodynamics  6.5. Internal energy and enthalpy  6.6. Heat capacity and specific heat  6.7. Hess's law of constant heat summation  6.8. Bond dissociation enthalpy  6.9. Enthalpy of formation and combustion  6.10. Enthalpy of solution and neutralization  6.11. Spontaneity and the second law of thermodynamics  6.12. Gibbs free energy and its applications
  7. Balance  7.1. The concept of balance  7.2. Equilibrium constant and its applications  7.3. Le Chatelier's principle  7.4. Ionic equilibrium in solutions  7.5. Acid and Base Theory  7.5.1. Arrhenius concept  7.5.2. Bronsted-Lowry concept  7.5.3. Lewis concept  7.6. pH Scale and pOH  7.7. Common ion effect  7.8. Hydrolysis of salts  7.9. Buffer solutions and their mechanism of action  7.10. Solubility equilibrium of sparingly soluble salts
  8. Redox reactions  8.1. Oxidation and reduction concepts  8.2. Oxidation number and its applications  8.3. Redox reactions in terms of electron transfer  8.4. Balancing redox reactions (oxidation number and ion-electron methods)  8.5. Types of redox reactions  8.6. Electrochemical Cells and Redox Reactions
  9. Hydrogen  9.1. Position of Hydrogen in the Periodic Table  9.2. Isotopes of hydrogen  9.3. Preparation of Hydrogen  9.4. Properties of Hydrogen  9.5. Hydrides and their classification  9.6. Water and heavy water  9.7. Hydrogen peroxide and its properties  9.8. Uses of Hydrogen and Its Compounds
  10. S-block elements (alkali and alkaline earth metals)  10.1. Group 1 Elements - Properties and Trends  10.2. Group 2 Elements - Properties and Trends  10.3. Unusual properties of lithium and beryllium  10.4. Important compounds of sodium and their uses  10.5. Important Compounds of Magnesium and Calcium
  11. Some p-block elements  11.1. General Introduction to p-Block Elements  11.2. Group 13 Elements  11.2.1. Boron and its compounds  11.3. Group 14 Elements  11.3.1. Carbon and its allotropes  11.3.2. Important Compounds of Carbon and Silicon
  12. Organic Chemistry - Some Basic Principles and Techniques  12.1. Classification and Nomenclature of Organic Compounds  12.2. Structural representation of organic compounds  12.3. Classification of organic reactions  12.4. Electronic Effects in Organic Chemistry  12.4.1. Inductive effect  12.4.2. Resonance effect  12.4.3. Hyperconjugation  12.5. Reaction mechanism and intermediate species  12.6. Purification and qualitative analysis of organic compounds
  13. Hydrocarbons  13.1. Hydrocarbons  13.1.1. Preparation and Properties of Alkenes  13.2. alkene  13.2.1. Preparation and Properties of Alkenes  13.2.2. Electrophilic addition reactions  13.3. Alkynes  13.3.1. Preparation and Properties of Alkynes  13.4. Aromatic hydrocarbons  13.4.1. Structure and properties of benzene  13.4.2. Electrophilic substitution reactions of benzene
  14. Environmental Chemistry  14.1. Environmental Pollution  14.2. Atmospheric pollution and the greenhouse effect  14.3. Water pollution and treatment methods  14.4. Soil pollution and its effects  14.5. Industrial waste and its treatment  14.6. Strategies for pollution control

Grade 11 → Classification of elements and periodicity in properties → Periodic 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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Valency

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