Atomic and Molecular Structure Quiz

Atomic and Molecular Structure

• Atoms are the fundamental building blocks of all matter, both living and non-living
• Greek philosopher Democritus proposed that matter is composed of indivisible particles called atoms
• John Dalton presented the first scientific atomic theory in the 1800s, with five key postulates:
  • Atoms are indivisible
  • All elements are composed of atoms
  • Atoms of the same element are identical
  • Atoms are neither created nor destroyed in a chemical reaction
  • Atoms combine in specific ratios to form compounds
• Atoms have internal structure containing electrons

Electrons

• J.J. Thomson discovered electrons using the cathode ray tube experiment, showing they are negatively charged
• Thomson used electric and magnetic fields to determine the charge-to-mass ratio of the electron
• Robert Millikan measured the charge of an electron, allowing the calculation of its mass
• Electrons are much lighter than the nucleus
• The plum pudding model of the atom depicts electrons as embedded within a positive sphere of charge

Protons and the Nucleus

• Ernest Rutherford's gold foil experiment demonstrated the atom's nucleus, a dense central core containing positive charge
• Rutherford's experiment determined that the atom's positive charge and most of its mass are located in a small nucleus
• The positive particles within the nucleus are called protons
• Protons have the same magnitude of charge as electrons but are positive
• Rutherford's model couldn't explain the entire mass of the atom because there wasn't a correct explanation of why some of the mass of the atom wasn't accounted for

Neutrons

• James Chadwick identified neutrons, neutral particles in the nucleus having nearly the same mass as protons
• Neutrons, along with protons, are responsible for the bulk of an atom's mass

Subatomic Particles

• Atomic number equals the number of protons
• Atomic mass number equals the sum of protons and neutrons

Structure of Atom

• The atom is composed of a central nucleus containing protons and neutrons
• The nucleus is surrounded by negatively charged electrons
• The arrangement of electrons around the nucleus determines many of an atom's properties and chemical behaviour
• Electrons can absorb or release energy, moving between different energy levels

Importance of Electrons

• Electrons, with their negative charge, balance the positive charges in the nucleus, stabilizing the atom.
• Electrons are involved in chemical bonding, as atoms interact through the exchange sharing or transfer of electrons.
• The electrons are related to the way matter bonds

Bohr's Model

• Bohr proposed that electrons orbit the nucleus in fixed energy levels or shells
• Specific orbits for the electron contain certain maximum numbers of electrons
• Electrons can move between orbits, absorbing or emitting energy in the form of light
• Bohr's model successfully explained the discrete lines in the hydrogen emission spectrum but had limitations in explaining more complex atoms

Wave-Particle Duality

• Light exhibits wave-like and particle-like nature
• Energy is quantized, meaning it comes in discrete packets called photons
• The energy of a photon is related to its frequency by Planck's constant
• All matter exhibits wave-like properties, described by the de Broglie wavelength

Heisenberg Uncertainty Principle

• It's impossible to precisely know both the position and momentum of a particle simultaneously
• The act of measuring one property inevitably affects the other
• The principle is important for understanding the behaviour of subatomic particles.