Grade 9
  1. Matter and its nature  1.1. Introduction to matter  1.2. Physical and chemical properties of matter  1.3. States of matter  1.3.1. Solid state  1.3.2. Fluid state  1.3.3. Gaseous state  1.3.4. Plasma and Bose–Einstein condensate  1.4. Changes in the states of matter  1.4.1. Melting and freezing  1.4.2. Evaporation and Condensation  1.4.3. Sublimation and deposition  1.5. Classification of matter  1.6. Elements, Compounds, and Mixtures  1.7. Pure substances and impurities  1.8. Separation Techniques  1.8.1. Filtration  1.8.2. Distillation  1.8.3. Crystallization  1.8.4. Chromatography  1.8.5. Centrifugation  1.8.6. Sublimation  1.8.7. Decantation and sedimentation
  2. Atomic Structure  2.1. Discovery of atoms  2.2. Dalton's atomic theory  2.3. Structure of the atom  2.4. Subatomic particles  2.5. Atomic number and mass number  2.6. Isotopes and Isobars  2.7. Electronic configuration  2.8. Bohr's atomic model  2.9. Modern Atomic Model (Quantum Mechanical Model - Introduction)  2.10. Valency and chemical bonding
  3. C hemical reactions and equations  3.1. Introduction to Chemical Reactions  3.2. Chemical Equation Formulation  3.3. Balancing Chemical Equations  3.4. Types of Chemical Reactions  3.4.1. Combination Reactions  3.4.2. Decomposition reactions  3.4.3. Displacement reactions  3.4.4. Double displacement reactions  3.4.5. Redox reactions  3.4.6. Endothermic and Exothermic Reactions  3.5. Effects of chemical reactions  3.6. Energy Changes in Chemical Reactions  3.7. Catalysts and their role in reactions
  4. Periodic table and periodicity  4.1. History of Periodic Classification  4.2. Mendeleev's periodic table  4.3. Modern Periodic Table  4.4. Periods and groups in the periodic table and periodicity  4.5. Trends in the Periodic Table  4.5.1. Atomic size  4.5.2. Ionization Energy  4.5.3. Electron affinity  4.5.4. Electronegativity  4.5.5. Metallic and Non-Metallic Properties  4.6. Noble gases and their properties
  5. Chemical bond  5.1. Introduction to Chemical Bonding  5.2. Types of chemical bonds  5.2.1. Ionic bond  5.2.2. Covalent bond  5.2.3. Metallic bond  5.2.4. Hydrogen bonding  5.2.5. Van der Waals force  5.3. Properties of Ionic and Covalent Compounds  5.4. Molecular Structure and Geometry (VSEPR Theory - Basics)
  6. Acids, Bases and Salts  6.1. Introduction to Acids and Bases  6.2. Properties of Acids  6.3. Properties of bases  6.4. pH scale and its importance  6.5. Indicators and their uses  6.6. Neutralization reactions  6.7. Strength of Acids and Bases (Strong vs. Weak)  6.8. Preparation of salts  6.9. Uses of acids, bases and salts in daily life
  7. Metals and Nonmetals  7.1. Physical Properties of Metals  7.2. Physical Properties of Nonmetals  7.3. Chemical properties of metals  7.4. Chemical Properties of Nonmetals  7.5. Reactivity Series of Metals  7.6. Extraction of metals  7.7. Corrosion and its prevention  7.8. uses of metals and nonmetals
  8. Carbon and its compounds  8.1. Introduction to Carbon  8.2. Allotropes of carbon (diamond, graphite, fullerene)  8.3. Hydrocarbons  8.3.1. Hydrocarbons  8.3.2. Alkene  8.3.3. Alkynes  8.4. Functional groups in organic chemistry  8.5. Isomerism in organic compounds  8.6. Alcohols and Carboxylic Acids  8.7. Soaps and detergents  8.8. Polymers (Introduction to Natural and Synthetic Polymers)
  9. Solutions and Mixtures  9.1. Types of mixtures  9.2. Homogeneous and Heterogeneous Mixtures  9.3. Concentration of solutions  9.4. Solubility and factors affecting solubility  9.5. Suspensions and Colloids  9.6. Saturated, unsaturated and supersaturated solutions
  10. Air and atmosphere  10.1. Composition of air  10.2. Role of gases in the atmosphere  10.4. Acid rain and its effects  10.5. Greenhouse effect and global warming  10.6. Ozone layer and its depletion  10.7. Air pollution control measures
  11. Water and its importance  11.1. Composition and properties of water  11.2. Hardness of water (temporary and permanent hardness)  11.3. Causes of water pollution  11.4. Effects of Water Pollution  11.5. Water purification methods (filtration, boiling, chlorination)
  12. Industrial Chemistry  12.1. Introduction to Industrial Chemistry  12.2. Important industrial chemicals (sulfuric acid, ammonia, sodium hydroxide)  12.3. Chemical processes in industry  12.4. Uses of Industrial Chemistry in Daily Life  12.5. Environmental impact of industrial chemical processes

Grade 9 → Atomic Structure ↓


Structure of the atom


The atom is the basic unit of matter and the defining structure of the elements. The concept of the atom originated in ancient Greece, where it was first proposed by the philosopher Democritus. He used the Greek word atomos, meaning "indivisible", to describe these tiny particles.

In the modern scientific world, the atom is considered the smallest unit that defines chemical elements and their isotopes. Although atoms are very small, typically about 100 picometers or less in diameter, they are made up of even smaller particles.

Basic components of an atom

An atom is made up of three main types of subatomic particles:

  • Proton: Positively charged particle found in the nucleus.
  • Neutrons: Neutral particles, which also reside in the nucleus.
  • Electrons: Negatively charged particles that orbit the nucleus.
Nucleus Proton (+) Neutrons (0) Electron (-)

The nucleus is the dense, central part of the atom and contains both protons and neutrons. This central part is very small compared to the overall size of the atom, but it contains almost all of the atom's mass.

Protons, neutrons and electrons

Proton

Protons are positively charged particles that reside in the nucleus of an atom. The number of protons in the nucleus of an atom is known as the atomic number and it determines the type of element. For example:

  • Hydrogen has one proton.
  • Helium has two protons.
  • Oxygen has eight protons.

Protons are represented as p^+ because of their positive charge.

Neutron

Neutrons are electrically neutral particles that are also located in the nucleus. They have no charge. The number of neutrons in an atom of the same element can vary, resulting in different isotopes. Isotopes are atoms of the same element that have different masses due to different numbers of neutrons.

For example, carbon has several isotopes, such as carbon-12 and carbon-14, which have the same number of protons but different numbers of neutrons.

Electrons

Electrons are negatively charged particles that orbit around the nucleus in regions called electron shells. They are represented by the symbol e^–. The mass of an electron is very small compared to that of a proton and a neutron.

  • Each electron shell can have different maximum number of electrons.
  • The arrangement of electrons in an atom is called electron configuration.

The behavior of electrons mainly determines the chemical properties of an element. The electrons present in the outermost shell, known as valence electrons, participate in chemical bonds.

Understanding isotopes

Isotopes are different forms of the same element that have different numbers of neutrons. They have the same number of protons but have different mass numbers due to the difference in neutrons.

For example, chlorine occurs naturally as two isotopes, chlorine-35 and chlorine-37, which have 18 and 20 neutrons, respectively:

Chlorine-35: 17 protons, 18 neutrons
Chlorine-37: 17 protons, 20 neutrons

The atomic mass of chlorine is an average of these isotopes, taking into account their abundance.

Bohr model of the atom

The Bohr model, formulated by Niels Bohr in 1913, describes the atom as a small, positively charged nucleus surrounded by electrons that move in circular orbits around the nucleus. The orbitals have quantized energy levels, which means that electrons can jump between them by absorbing or emitting energy:

Nucleus

In this model, if an electron absorbs energy, it can move to a higher orbit away from the nucleus. If it loses energy, it can fall back to a lower orbit, giving off the lost energy as light or other radiation. This model helps explain the emission spectrum of different elements.

Quantum model of the atom

The quantum model of the atom is the most modern approach. Unlike the Bohr model, it does not define exact orbits for the electrons, but rather highlights the probability of finding an electron at a particular location. The electrons exist in different regions or "clouds" that have different shapes:

  • s-orbitals: These are spherical in shape.
  • p-orbitals: These are shaped like dumbbells.
s orbital p orbital

This model more accurately represents the behavior of electrons, especially in larger atoms. It relies on complex mathematics to describe the electron distribution and led to the development of quantum mechanics.

Chemical bonding and the role of electrons

Atoms bond to achieve stability. Stability is often associated with having a full outer electron shell, similar to that of the noble gases. There are two primary types of chemical bonds:

Covalent bonds

Covalent bonding involves the sharing of electron pairs between atoms. This occurs in molecules such as water (H2O) and carbon dioxide (CO2). Each atom donates one electron to the shared pair, creating a stable equilibrium:

Water: H - O - H
Carbon Dioxide: O = C = O

Ionic bond

Ionic bonds form when electrons transfer from one atom to another, resulting in oppositely charged ions that attract each other. This is common in salts, such as sodium chloride (NaCl):

Na^+ + Cl^- -> NaCl

In NaCl, sodium loses an electron to form a positive ion, and chlorine gains an electron to form a negative ion, resulting in a stable ionic compound.

Conclusion

Understanding the structure of the atom is fundamental to chemistry. Atoms are the building blocks of matter, and their interactions shape everything we see around us. Their structure, with a central nucleus and orbiting electrons, defines the nature of chemical bonds and reactions.

The development from elementary models to advanced quantum models reveals the complexity and beauty of atomic structure. This provides the basis for understanding not only chemistry, but also the physics and biology of the universe.


Grade 9 → 2.3


U
username
0%
completed in Grade 9

← Prev (2.2)
Dalton's atomic theory
Next (2.4) →
Subatomic particles

Comments 



Structure of the atom

https://www.chemistryelite.com/g9/2.3?ceal=en