Atomic model

• What are the key points of John Dalton's atomic theory?

  1. Atoms are indivisible. 2) Atoms of the same element are identical. 3) Atoms of different elements differ. 4) Atoms combine in fixed ratios to form compounds.
• Describe J.J. Thomson's plum pudding model of the atom.

  The atom is a sphere of positive charge with negatively charged electrons embedded in it, like "plums" in a pudding
• What experiment led Rutherford to propose the nuclear model?

  The gold foil experiment, where alpha particles were fired at gold foil. Most passed through, but some were deflected, showing the presence of a dense nucleus.
• How did Niels Bohr improve Rutherford's model of the atom?


  Bohr suggested that electrons orbit the nucleus in fixed energy levels or shells.
• How did Niels Bohr improve Rutherford's model of the atom?

  Bohr suggested that electrons orbit the nucleus in fixed energy levels or shells.
• What is the difference between an atom and an ion?

  An atom is neutral (equal protons and electrons), while an ion is charged (due to gaining or losing electrons).
• What is the atomic number, mass number, and element of an atom with 11 protons, 12 neutrons, and 11 electrons?

  Atomic number = 11, Mass number = 23, Element = Sodium (Na).
• Why was the discovery of neutrons important for understanding isotopes?

  It explained why isotopes of an element have the same chemical properties but different mass numbers due to varying neutron numbers.
• Compare the plum pudding model with the nuclear model of the atom.

  Plum pudding: Positive sphere with electrons inside. Nuclear model: Dense nucleus with protons and neutrons, electrons orbit in shells.
• Why do atoms have no overall charge?

  Protons (+) and electrons (-) cancel each other out. Neutrons are neutral and don’t affect charge.
• What was the significance of Rutherford’s gold foil experiment?

  It showed atoms have a dense, positively charged nucleus and are mostly empty space, disproving the plum pudding model.
• What happens when sodium reacts with chlorine?

  Sodium loses 1 electron to form , and chlorine gains it to form .