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ATOMS AND MOLECULES

 ATOMS AND MOLECULES

 Three Laws of Chemical Combinations

1.     Law of Conservation of Mass:

  • 3In a chemical action, the law of conservation of mass stipulates that mass cannot be created or destroyed.
  • According to this law, the overall mass of the products remains equal to the total mass of the reactants after any physical or chemical change.

2. Law of Constant proportion:

  • This law was expressed by another French chemist, Joseph Proust, as follows: A chemical compound always comprises the same elements mixed in the same proportion by mass.

3. Law of Multiple Proportions:

  • As established by John Dalton, when two elements combine to form two or more compounds, the mass of the element that combines with the fixed mass of the other bears a simple whole-number ratio (1803).

Dalton’s Atomic Theory: According to Dalton's atomic theory, all matter, whether an element, a compound, or a mixture, is made up of microscopic particles called atoms.

This theory's postulates are as follows:

  1. All matter is made up of atoms, which are very small tiny particles that engage in chemical reactions.
  2. In a chemical reaction, atoms are indivisible particles that cannot be formed or destroyed.
  3. A given element's atoms have the same mass and chemical characteristics.
  4. The masses and chemical characteristics of atoms of various elements differ.
  5. Compounds are formed when atoms join in a ratio of tiny whole numbers.
  6. In a given compound, the number and types of atoms remain constant.

Atom:

  • An atom is an element's defining structure that can't be broken chemically.
  • The electron, proton, and neutron are the three particles that make up an atom.
  • An atom's nucleus holds the entire mass of the atom.
  • An atom's electrons are grouped in shells/orbitals.
  • The atomic symbol is made up of three parts: A, Z, AND X
  • The radius of an atom is measured in nanometres.

 

 Atomic Mass:

  • The atomic mass was proposed by Dalton as an atomic hypothesis.
  • The average mass of an atom, or a set of atoms, is the sum of the masses of the electrons, neutrons, and protons.
  • The atomic mass is the mass of an atomic particle.
  • This is often stated in terms of a unified atomic mass unit, as per the international agreement (AMU).
  • The average mass of one atom of an element, as compared to 1/12th the mass of one carbon- 12 atom, is called atomic mass.

 Valency:

  • The electrons in the atom's outermost orbit are referred to as valence electrons.
  • The valency of an atom is determined by its ability to lose, gain, or share valence electrons in order to complete its octet.

Molecule:

  • The total masses of the elements present in a molecule is the molecule's molecular mass.
  • The atomic mass of an element is multiplied by the number of atoms in the molecule, and the masses of all the elements in the molecule are added to get the molecule's mass.
  • The number of atoms in a single molecule of an element is known as its atomicity.
  • For example, each of the molecules of hydrogen, nitrogen, oxygen, chlorine, iodine, and bromine has two atoms, and hence they all have two atomicity each.

Compound: When two or more elements join chemically in a defined mass ratio, the result is known as a compound.

  • Compounds are substances made up of two or more different types of atoms in a specific ratio.

Ions: An ion is an atom or molecule with a net positive or negative charge due to the gain or loss of one or more of its valence electrons.

  • A negatively charged particle is an anion, and a positively charged particle is a cation.
  • Ionic compounds are chemical compounds in which ions are held together by ionic bonds, which are a type of specialised bond.
  • The positive and negative charges in an ionic substance are always in equal amounts.

Molecular Mass:

  • The total masses of the elements present in a molecule is known as the molecule's molecular mass.
  • The atomic mass of an element is multiplied by the number of atoms in the molecule, and then the masses of all the elements in the molecule are added.

Examples:

 Mole and Avogadro Number:

  • A mole is the number of entities existing in a substance, such as atoms, molecules, and ions.
  • A mole is 6.022 × 1023 molecules of any substance.

 

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