Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Atomic Structure ↓


Excitation and emission spectra


Understanding the concept of excitation and emission spectra is an important part of studying atomic structures in chemistry. Atoms are the fundamental building blocks of matter, and they contain electrons that revolve around a central nucleus in specific energy levels or shells. These movements and their associated energy changes can produce visible light and other forms of electromagnetic radiation.

Atoms and their energy levels

At the center of every atom is a nucleus, which contains protons and neutrons. Surrounding the nucleus are electrons, which orbit in specific levels or shells. Each shell corresponds to a certain energy level. The electrons in an atom can be at any of these levels, but they naturally reside at the lowest possible energy level, also called the ground state.

Ground State: Lowest energy level that an electron can occupy.

What is excitement?

Excitation occurs when an electron absorbs energy and moves from a lower energy level to a higher energy level. This energy can come from a variety of sources such as heat, light, or electrical energy. When the electron absorbs the exact amount of energy needed to make the jump to the higher energy level, it is said to be "excited."

Excitation: Process where an electron absorbs energy and jumps to a higher energy level.

Visual example of stimulation

Imagine a ladder. Each rung of the ladder represents an energy level that an electron can occupy. In the ground state, the electron is on the lowest rung. When the electron absorbs energy, it moves to a higher rung.

In this diagram, the red circle represents an electron in its ground state (the bottom of the ladder). After excitation, this electron can move to a higher rung.

What is emission?

The electron does not stay in the excited state forever. Eventually, it will lose energy and fall back to its original lower energy level or ground state. As it falls back, the energy it absorbed is released in the form of light or electromagnetic radiation. This release of energy is known as "emission."

Emission: Process where an excited electron releases energy as it returns to a lower energy level.

Visual example of emissions

Continuing our ladder example, when the electron loses the energy it gained, it falls back to a lower level.

In this picture, the electron starts at a higher level (the excited state, the top of the ladder), then falls to a lower level (the ground state), emitting light energy in the process.

Excitation and emission spectra

Each element has a unique arrangement of electrons, and thus a unique set of energy levels. As a result, the light emitted by an element forms a characteristic spectrum, known as an emission spectrum. The light absorbed during the excitation process forms an absorption spectrum. These spectra can be used to learn about the structure of the atom and to identify the elements.

Spectrum: The range of colors or wavelengths of light emitted or absorbed by an atom.

Example of spectra

Imagine looking at the colors emitted by hot hydrogen gas through a prism. You will see distinct lines of color corresponding to specific wavelengths of light. Each line on this spectrum corresponds to an energy difference in the electron energy levels of hydrogen.

Here's a simplified illustration of what an emission spectrum might look like:

The colored lines indicate different energies of light emitted by electrons returning to lower energy levels.

Real life applications of excitation and emission spectra

Studying emission spectra helps scientists identify the composition of stars and galaxies. By analyzing the light coming from these celestial objects, scientists can determine which elements are present based on their unique spectral lines. This offers a fascinating look at what stars are made of, even trillions of miles away.

Its second application lies in chemical analysis using a method called spectroscopy. Different chemicals emit or absorb different wavelengths of light. By examining these wavelengths, chemists can identify the substances present in a sample without touching it.

Summary of key points

Now that we've explored excitation and emission spectra, the key ideas to remember are:

  • Atoms are made up of electrons orbiting the nucleus at different energy levels.
  • Excitation occurs when an electron absorbs energy and moves to a higher energy level.
  • Emission occurs when an electron moves back to a lower energy level, releasing energy.
  • The spectra are unique for each element and can be used to identify them.
  • Spectroscopy, a real-life application, helps identify elements in various substances in stars and on Earth.

Understanding how atoms absorb and emit light energy helps us unravel many mysteries about the physical world.


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Excitation and emission spectra

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