Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Atomic Structure ↓


Atomic number and mass number


Atoms are the basic building blocks of matter. To truly understand the nature of atoms, it is necessary to know about two fundamental concepts: atomic number and mass number. These concepts help us describe the properties of an atom and distinguish one type of atom from another.

What is an atom?

Before diving into atomic number and mass number, let's briefly discuss what an atom is. An atom is the smallest unit of ordinary matter that makes up a chemical element. Every solid, liquid, gas, and plasma is made up of atoms. At the center of an atom, there is a nucleus made up of protons and neutrons. Electrons orbit around this nucleus in regions called electron shells.

Visual example of an atom:

         ,
         |N|N = neutron
         ,
           |P| P = proton
          ,
     |e|  / |e|  
     ,   
      ,  
       E = electron

Atomic number

The atomic number of an atom is an important concept in chemistry. It is represented by the letter Z and tells us the number of protons in the nucleus of an atom. Since each element has a specific number of protons, the atomic number uniquely identifies an element.

For example, if we consider the element hydrogen, its atomic number is 1, which means it has 1 proton. Helium's atomic number is 2, which means it has 2 protons.

Examples of atomic number:

  • Hydrogen: Z = 1 (1 proton)
  • Helium: Z = 2 (2 protons)
  • Lithium: Z = 3 (3 protons)
  • Carbon: Z = 6 (6 protons)

Visual representation of atomic number:

    Atomic number (Z) = number of protons

    Element | Atomic Number (Z) | Protons
    ,
    Hydrogen| 1 | 1
    Helium | 2 | 2 
    Lithium | 3 | 3
    Carbon | 6 | 6

Mass number

Mass number is another important concept. It is represented by the letter A and is the sum of the number of protons and neutrons in the nucleus. The mass number gives us an idea of the mass of an atom because most of the mass of an atom is concentrated in its nucleus.

For example, consider carbon, which has 6 protons and usually 6 neutrons. Therefore, its mass number would be:

    Carbon: A = 6 (protons) + 6 (neutrons) = 12

Examples of mass numbers:

  • Hydrogen: A = 1 + 0 = 1
  • Helium: A = 2 + 2 = 4
  • Carbon: A = 6 + 6 = 12
  • Oxygen: A = 8 + 8 = 16

Visual representation of mass numbers:

    Mass number (A) = Number of protons + Number of neutrons

    element Proton Neutron mass number (A)
    ,
    Hydrogen | 1 | 0 | 1
    helium | 2 | 2 | 4
    carbon | 6 | 6 | 12
    Oxygen | 8 | 8 | 16

Difference between atomic number and mass number

To better understand these concepts, let's clarify the differences and similarities between atomic number and mass number:

  • Atomic number (Z): It refers to the number of protons in the nucleus of an atom. The atomic number determines the identity of an element and its position in the periodic table.
  • Mass number (A): It is the sum of protons and neutrons in the nucleus. Mass number helps to estimate the mass of the atom.
  • Calculation:
    • There is no need to calculate the atomic number as it is simply the number of protons.
    • The mass number is calculated from the sum of the protons and neutrons in the nucleus:
      •                 A = Number of protons (Z) + Number of neutrons

Isotopes

Understanding isotopes is an essential part of atomic number and mass number. Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different number of neutrons.

For example, carbon has two stable isotopes:

  • Carbon-12: It has 6 protons and 6 neutrons, so the mass number is 12.
  • Carbon-13: Has 6 protons but 7 neutrons, so the mass number is 13.
                 Isotopes of Carbon

            Proton: | Neutron: | Mass Number (A):
            ,
            carbon-12| 6 | 6 12
            carbon-13| 6| 7 13

Isotopes have almost similar chemical properties because they have the same number of protons and electrons.

Closing thoughts

Understanding the concepts of atomic number and mass number is fundamental to understanding chemistry and atomic structure. The atomic number gives information about the identity of an element, while the mass number can tell us about its mass and isotopic nature.

As you progress in chemistry, these concepts will be important in exploring the behavior of atoms during chemical reactions and interactions. They also form the basis for understanding the rich variety of elements in the periodic table.


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Atomic number and mass number

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