Question

which statement is true according to modern atomic theory?* isotopes, atoms of the same element, may have different mass numbers. atoms may be divided in ordinary chemical reactions. atoms can never combine with any other atoms. cathode rays are composed of protons.

Explanation:

• Isotopes: Isotopes are atoms of the same element (same number of protons) but different mass numbers (different numbers of neutrons). For example, carbon - 12 and carbon - 14 are isotopes of carbon. The mass number \(A = Z+N\) (where \(Z\) is the atomic number and \(N\) is the number of neutrons). Since isotopes have different \(N\) values, they can have different \(A\) values.
• Atoms in chemical reactions: In ordinary chemical reactions, atoms are rearranged, but they are not divided. Chemical reactions involve the breaking and forming of chemical bonds between atoms.
• Combining of atoms: Atoms combine with other atoms to form molecules (e.g., \(H_2O\) is formed by the combination of hydrogen and oxygen atoms) through chemical bonding (ionic, covalent, etc.).
• Cathode rays: Cathode rays are composed of electrons. J.J. Thomson's experiments with cathode ray tubes led to the discovery of electrons.

Answer:

Isotopes, atoms of the same element, may have different mass numbers.