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 ↓


Structure of the atom: protons, neutrons and electrons


Atoms are the basic units of matter and the defining structure of elements. The word "atom" is derived from the Greek word "atomos," meaning indivisible. Atoms are the building blocks of everything around us, from the smallest particles of sand to giant mountains. Each atom consists of three fundamental particles: protons, neutrons, and electrons. Understanding these components helps us understand how matter is structured and how it behaves.

Basic structure of the atom

An atom consists of a central nucleus and an outer shell of electrons. The nucleus contains positively charged particles called protons and neutral particles called neutrons. Negatively charged electrons orbit around the nucleus in different energy levels or shells. Here is a simplified representation of an atom:

Nucleus Electron

The nucleus is represented by the central circle, while the smaller outer circles represent the electrons. The electrons are shown orbiting the nucleus on paths called orbitals.

Proton

Protons are positively charged particles found within the atomic nucleus. They have a relative mass of about 1 atomic mass unit (amu) and a charge of +1. The number of protons in the nucleus of an atom determines the identity of the element and is called the atomic number (Z).

For example, hydrogen has one proton, so its atomic number is 1. Carbon has six protons, so its atomic number is 6. The atomic number is unique to each element and serves as a defining characteristic.

Neutron

Neutrons are neutral particles, meaning they carry no charge and are found with protons in the nucleus. Like protons, neutrons also have a mass of about 1 amu. The presence of a neutron contributes to the mass of an atom but does not affect its charge.

By combining the number of neutrons with the number of protons we get the atomic mass or mass number (A) of an atom. The formula can be represented as:

A = Z + N

where A is the atomic mass, Z is the atomic number, and N is the number of neutrons.

Electrons

Electrons are negatively charged particles found in electron clouds orbiting the nucleus. They are much smaller than protons and neutrons, with a relative mass of about 1/1836 amu, and have a charge of -1. Electrons are responsible for the chemical properties of atoms and their interactions with other atoms.

Electrons occupy energy levels or shells around the nucleus, and these shells can hold a certain number of electrons. The arrangement of electrons in these shells determines how atoms bond with each other.

Visualization of atomic structure

The following is a simplified visual illustration showing the oxygen atom, which has 8 protons, 8 neutrons, and usually 8 electrons:

8p, 8n Electron

Isotopes

Isotopes are different forms of a particular chemical element that have the same number of protons but different numbers of neutrons. This difference in neutron number gives isotopes different atomic masses.

For example, carbon, which has an atomic number of 6, has the isotopes carbon-12 and carbon-14. Carbon-12 has 6 neutrons, while carbon-14 has 8 neutrons. The carbon-14 isotope is radioactive and can be used for dating objects (radiocarbon dating).

Isotopes can be represented as follows, where A is the mass number, Z is the atomic number, and X is the chemical symbol:

^A_ZX

Example:

^12_6C and ^14_6C

Anions

An ion is an atom that has gained or lost one or more electrons, giving it a net charge. If an atom loses an electron, it becomes positively charged and is known as a cation. If it gains an electron, it becomes negatively charged and is known as an anion.

Example:

Na^+ - Sodium cation (lost one electron)
Cl^- - Chloride anion (gained one electron)

Conclusion and summary

Atoms are composed of protons, neutrons, and electrons. Understanding these components and their arrangement helps us predict how atoms will interact in chemical reactions, which forms the basis of all chemical science. Protons define the element, neutrons contribute mass and stabilize the nucleus, and electrons determine the chemical behavior of the atom. The study of isotopes and ions further enhances our understanding of chemical reactions and interactions.


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Dalton's atomic theory
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Structure of the atom: protons, neutrons and electrons

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