Democritus and Atomic Structure
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Questions and Answers

What was the significance of Antoine L.Lavoisier's work in the field of chemical sciences?

  • He established the two important laws of chemical combination (correct)
  • He invented the ignition tube
  • He discovered the concept of atoms
  • He discovered the concept of elements and compounds

    • What is the reason for putting a cork on the mouth of the flask in the experiment?

  • To prevent the reaction from taking place
  • To allow the solutions to get mixed slowly
  • To prevent the solutions from getting mixed
  • To prevent the escape of gases (correct)

    • What can be concluded from the experiment shown in Fig. 3.1?

  • The solutions X and Y do not react with each other
  • The mass of the flask and its contents remains the same before and after the reaction (correct)
  • The flask and its contents lose weight after the reaction
  • A chemical reaction has not taken place

    • What was the occupation of John Dalton's father?

    <p>Weaver</p> Signup and view all the answers

    What is the significance of weighing the flask with its contents before and after the reaction?

    <p>To demonstrate the law of conservation of mass</p> Signup and view all the answers

    Who is credited with calling the indivisible particles 'atoms'?

    <p>Democritus</p> Signup and view all the answers

    What was the age of John Dalton when he became a teacher?

    <p>12 years</p> Signup and view all the answers

    What is the significance of tilting and swirling the flask in the experiment?

    <p>To mix the solutions X and Y</p> Signup and view all the answers

    What happened to John Dalton 7 years after he became a teacher?

    <p>He became a school principal</p> Signup and view all the answers

    What is the ratio of mass of elements in a chemical substance according to the law of constant proportions?

    <p>14:3</p> Signup and view all the answers

    Who is credited with providing the basic theory about the nature of matter?

    <p>John Dalton</p> Signup and view all the answers

    What is the smallest unit of matter according to Dalton's atomic theory?

    <p>Atoms</p> Signup and view all the answers

    What is the number of whole numbers in which atoms combine to form compounds?

    <p>Small whole numbers</p> Signup and view all the answers

    What is the characteristic of atoms of a given element according to Dalton's atomic theory?

    <p>Identical masses and chemical properties</p> Signup and view all the answers

    What is the difference between atoms of different elements according to Dalton's atomic theory?

    <p>Different masses and chemical properties</p> Signup and view all the answers

    What is the purpose of Dalton's atomic theory?

    <p>To explain the law of constant proportions</p> Signup and view all the answers

    What is the total mass of products formed in the reaction between sodium carbonate and acetic acid?

    <p>11.3 g</p> Signup and view all the answers

    What is the name of the law that states elements are always present in a definite ratio by mass?

    <p>Law of constant proportions</p> Signup and view all the answers

    What is the term used to describe the number of atoms constituting a molecule?

    <p>Atomicity</p> Signup and view all the answers

    What type of molecule has a simple structure with a very large and indefinite number of atoms bonded together?

    <p>Metal molecule</p> Signup and view all the answers

    What is the ratio of oxygen to nitrogen in a molecule of ammonia (NH3)?

    <p>1:3</p> Signup and view all the answers

    What is the molecular formula for ozone?

    <p>O3</p> Signup and view all the answers

    What is the term used to describe the ratio of atoms present in molecules?

    <p>Ratio by number</p> Signup and view all the answers

    What type of molecule consists of two atoms of oxygen?

    <p>Diatomic molecule</p> Signup and view all the answers

    What is the molecular formula for carbon dioxide?

    <p>CO2</p> Signup and view all the answers

    What type of elements do not have a simple structure but consist of a very large and indefinite number of atoms bonded together?

    <p>Metals</p> Signup and view all the answers

    What is the purpose of Table 3.2?

    <p>To show the atomic masses of elements</p> Signup and view all the answers

    What is the formula of sodium carbonate?

    <p>Na2CO3</p> Signup and view all the answers

    What is the formula of ammonium sulphate?

    <p>(NH4)2SO4</p> Signup and view all the answers

    What is the molecular mass of water (H2O)?

    <p>18 u</p> Signup and view all the answers

    What is the formula unit mass of a substance?

    <p>The sum of the atomic masses of all atoms in a formula unit</p> Signup and view all the answers

    What is the molecular mass of HNO3?

    <p>63 u</p> Signup and view all the answers

    How is the formula unit mass of a substance calculated?

    <p>By summing the atomic masses of all atoms in a formula unit</p> Signup and view all the answers

    What is the purpose of calculating the formula unit mass of a substance?

    <p>To determine the molecular mass of a compound</p> Signup and view all the answers

    What is the formula of sodium oxide?

    <p>Na2O</p> Signup and view all the answers

    What is the formula of aluminium chloride?

    <p>AlCl3</p> Signup and view all the answers

    What is the atomicity of oxygen?

    <p>Diatomic</p> Signup and view all the answers

    What is the ratio by number of atoms for water?

    <p>H:O = 2:1</p> Signup and view all the answers

    What is the atomic mass of helium?

    <p>1 u</p> Signup and view all the answers

    What is an ion?

    <p>A group of atoms with a net charge</p> Signup and view all the answers

    What is the atomicity of phosphorus?

    <p>Tetra-atomic</p> Signup and view all the answers

    What is the atomic mass of oxygen?

    <p>16 u</p> Signup and view all the answers

    What is the atomicity of chlorine?

    <p>Diatomic</p> Signup and view all the answers

    What is the characteristic of compounds composed of metals and non-metals?

    <p>They contain charged species</p> Signup and view all the answers

    What is the atomicity of hydrogen?

    <p>Diatomic</p> Signup and view all the answers

    Study Notes

    Democritus and the Concept of Atoms

    • Democritus introduced the idea of indivisible particles called atoms.
    • He believed that atoms are the building blocks of matter and cannot be divided further.

    Laws of Chemical Combination

    • By the end of the 18th century, scientists recognized the difference between elements and compounds.
    • Antoine Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.
    • A chemical reaction occurs when solutions X and Y are mixed in a conical flask.
    • The mass of the flask and its contents remains the same before and after the reaction, illustrating the law of conservation of mass.
    • John Dalton's law of definite proportions states that elements in a chemical substance are always present in definite proportions by mass, regardless of the method or source.

    Dalton's Atomic Theory

    • John Dalton introduced the concept of atoms as the smallest particles of matter.
    • He said that atoms are indivisible and cannot be created or destroyed in a chemical reaction.
    • Dalton's atomic theory explains the law of constant proportions.
    • Atoms of a given element are identical in mass and chemical properties.
    • Atoms of different elements have different masses and chemical properties.
    • Atoms combine in the ratio of small whole numbers to form compounds.

    Atomicity of Elements

    • Atomicity refers to the number of atoms constituting a molecule.
    • Metals and some non-metals, such as carbon, do not have a simple structure but consist of a large and indefinite number of atoms bonded together.
    • Examples of atomicity include:
      • Diatomic molecules: oxygen (O2), hydrogen (H2), chlorine (Cl2)
      • Monoatomic elements: argon, helium
      • Tetra-atomic element: phosphorus
      • Poly-atomic element: sulphur

    Ions and Compounds

    • Ions are charged species that can consist of a single charged atom or a group of atoms with a net charge.
    • Ions can be negatively or positively charged.
    • Compounds composed of metals and non-metals contain ions.

    Formulae and Molecular Mass

    • Formulae represent the composition of a compound in terms of its constituent elements.
    • Examples of formulae include:
      • Sodium carbonate: Na2CO3
      • Ammonium sulphate: (NH4)2SO4
    • Molecular mass is calculated by summing the atomic masses of all atoms in a molecule.
    • Formula unit mass is calculated in the same manner as molecular mass.

    Chapter Activities and Questions

    • Activity 3.2 involves finding the ratio by number of atoms of elements in molecules.
    • Questions include:
      • Writing formulae for compounds represented by their names.
      • Calculating molecular mass and formula unit mass.

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    Description

    This quiz is about Democritus' concept of atomic structure and an experiment involving solutions X and Y.

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