Structure Of An Atom

key notes :

Introduction to the Atom:

  • An atom is the smallest unit of an element that retains the chemical properties of that element.
  • Atoms are the basic building blocks of matter.

Subatomic Particles:

  • Protons: Positively charged particles located in the nucleus.
  • Neutrons: Neutral particles (no charge) also found in the nucleus.
  • Electrons: Negatively charged particles that revolve around the nucleus in orbitals.

Atomic Structure:

  • The nucleus, located at the center of the atom, contains protons and neutrons.
  • Electrons orbit the nucleus in energy levels or shells.
  • Atoms are mostly empty space, with the nucleus occupying only a tiny part of the atom’s volume.

Atomic Number (Z):

  • Represents the number of protons in the nucleus.
  • Determines the identity of an element (e.g., hydrogen has an atomic number of 1).

Mass Number (A):

  • The sum of the number of protons and neutrons in an atom’s nucleus.
  • Mass Number = Number of Protons + Number of Neutrons.

Isotopes:

  • Atoms of the same element with the same atomic number but different mass numbers (due to varying numbers of neutrons).
  • Example: Carbon has isotopes like Carbon-12, Carbon-13, and Carbon-14.

Atomic Models:

  • Thomson’s Model: Described the atom as a sphere of positive charge with embedded electrons (like a “plum pudding”).
  • Rutherford’s Model: Proposed that atoms have a small, dense nucleus with electrons orbiting around it.
  • Bohr’s Model: Suggested that electrons move in fixed orbits (shells) around the nucleus and can jump between energy levels.

Electron Configuration:

  • Electrons are arranged in shells around the nucleus according to their energy levels.
  • The maximum number of electrons in a shell is given by the formula 2n22n^22n2, where nnn is the shell number (e.g., 1st shell can hold 2 electrons, 2nd shell can hold 8 electrons, etc.).

Valence Electrons:

  • Electrons in the outermost shell of an atom.
  • Determine the chemical reactivity and bonding behavior of an element.

Octet Rule:

  • Atoms tend to gain, lose, or share electrons to achieve a stable configuration with 8 electrons in their outermost shell.

Ions:

  • Atoms that have gained or lost electrons.
  • Cations: Positively charged ions (loss of electrons).
  • Anions: Negatively charged ions (gain of electrons).

Atomic Theory Development:

  • The understanding of the atomic structure evolved over time with contributions from scientists like Dalton, Thomson, Rutherford, and Bohr.

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