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 → Basic concepts of chemistry ↓


Empirical and molecular formula


The world of chemistry provides us with a systematic way to understand the composition and structure of substances. Two important concepts in this understanding are the empirical formula and the molecular formula. These formulas help us know the elements present in the compound and their proportions. Let us take a deeper look at each of these concepts to understand their importance in chemistry.

Understanding the empirical formula

The empirical formula of a compound gives the simplest whole number ratio of atoms of each element present in the compound. It does not show the actual number of atoms, but the simplest ratio of the elements.

For example, the molecular formula of the compound ethylene is C 2 H 4 The ratio of carbon atoms to hydrogen atoms is 1:2, so its empirical formula is CH 2.

To represent the empirical formula visually, imagine a simple square representing each atom, where the carbon atoms are black and the hydrogen atoms are white:

    CHH
    ,

Each black square is a carbon atom, and each white square is a hydrogen atom, representing their basic structure in its simplest form.

Steps to determine the empirical formula

Follow these steps to find the empirical formula of a compound:

  1. Determine the mass (in grams) of each element present in the compound.
  2. Convert these masses into moles using their atomic masses from the periodic table.
  3. Divide the mole value of each element by the smallest mole value obtained from your calculations.
  4. If necessary, multiply these numbers by integers to get whole numbers. This gives sub-numbers for each element in the empirical formula.

Example calculation

Suppose we have a compound that contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. Let's find its empirical formula:

  1. Let's say we have 100 grams of the compound. So, we have 40.0 grams of carbon, 6.7 grams of hydrogen, and 53.3 grams of oxygen.
  2. Convert these masses to moles:
    • Carbon: 40.0 div 12.01 approx 3.33 moles
    • Hydrogen: 6.7 div 1.008 approx 6.65 moles
    • Oxygen: 53.3 div 16.00 approx 3.33 mol
  3. Divide each mole value by the smallest number of moles, which is 3.33:
    • Carbon: 3.33 div 3.33 = 1
    • Hydrogen: 6.65 div 3.33 approx 2
    • Oxygen: 3.33 div 3.33 = 1
  4. Thus, the empirical formula is CH 2 O

Understanding the molecular formula

The molecular formula shows the actual number of each type of atom in the molecule. While the empirical formula gives the simplest ratio, the molecular formula displays the actual composition of the molecule, providing more detailed information about its structure.

A molecular formula is an integer multiple of its empirical formula. For example, the molecular formula of hydrogen peroxide is H 2 O 2, and its empirical formula is HO. This means that the molecular formula is an integer multiple of the empirical formula.

The molecular formula can also be seen with squares representing the atoms. In H 2 O 2, we have:

    huh

Steps to determine molecular formula

To find the molecular formula, you'll need two pieces of information: the compound's empirical formula and molar mass. Here are the steps:

  1. Calculate the mass by the empirical formula.
  2. Divide the molar mass of the compound by the mass of the empirical formula to get a whole number that is a multiple of the empirical formula.
  3. Multiply the sub-digits in the empirical formula by this factor to get the molecular formula.

Example calculation

Given that the empirical formula of a compound is CH and its molar mass is 78 g/mol, find the molecular formula:

  1. Calculate the mass of the empirical formula CH: 12.01 + 1.01 = 13.02 g/mol.
  2. Divide the molar mass of the compound by the empirical formula mass: 78 div 13.02 approx 6.
  3. Multiply the sub-numbers in the empirical formula by 6:
    • The molecular formula is C 6 H 6.

Visual examples of empirical vs. molecular formulas

Consider the compound glucose with the molecular formula C 6 H 12 O 6 The empirical formula of glucose is CH 2 O because it represents the simplest ratio of 1:2:1 for carbon, hydrogen, and oxygen.

Here's how the relationship between empirical and molecular formulas works visually:

    Molecular: CCCCCC
               ,
               hhhhhhh
               ,
               Ooooo

    Empirical: CHHO (repeated block)
               ,

Importance in chemistry

Both formulas are essential in the study and application of chemistry:

  • Empirical formula: This is used to determine the simplest structure, which is important in understanding how compounds react and interact at the most basic levels.
  • Molecular formula: Provides a complete picture for scientists wishing to synthesize chemicals or understand the function of a compound in biological systems.

Practice problems

1. A compound has a percentage composition of 85.7% carbon and 14.3% hydrogen. Determine its empirical formula.

2. A sample of an unknown compound has a molar mass of 180 g/mol and its empirical formula CH 2 O What is the molecular formula of the compound?

Conclusion

Understanding empirical and molecular formulas is a crucial step in the study of chemistry. By mastering these concepts, both students and professionals can understand the nature of compounds, leading to further discovery and innovation. Through both simple calculations and in-depth analysis, these formulas lay the groundwork for exploring the astonishing complexity of chemical interactions and their effects on the world.


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