Quiz - The Atomic Theory - 3 | The Atomic Theory

The existence of isotopes, which are atoms of the same element with different masses due to varying numbers of neutrons, contradicts the postulate that all atoms of a given element are identical. This postulate was revised as science advanced to account for isotopes.

Carbon is not commonly found in nature as a diatomic molecule. Diatomic molecules are pairs of atoms from the same element bound together, such as H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂.

Protons are positively charged subatomic particles found in the nucleus of an atom, and they contribute to the atom's identity and atomic number.

Electrons are located outside the nucleus of an atom and orbit around it in various energy levels or orbitals.

Rutherford's experiment showed that most alpha particles passed through the gold foil, indicating that atoms are mostly empty space. However, some alpha particles were deflected, suggesting the presence of a dense, positively charged nucleus.

The mass number (A) in nuclear notation represents the total number of nucleons in the nucleus, which includes both protons and neutrons.

The number of neutrons is calculated by subtracting the atomic number (20) from the mass number (40), resulting in 20 neutrons.

The number of protons is equal to the atomic number Z

Chlorine ${}_{17}{}^{35}{\mathrm{Cl}}^{-}$ has 17 protons and 18 neutrons. Since it has gained one electron to become an anion, the total number of electrons is 17 + 1 = 18.

Sodium () has 11 protons and 12 neutrons. Since it is a neutral atom, the number of protons and electrons are equal, giving 11 electrons.