Question

what happens to an atom when it emits an alpha particle?
the atomic number and the atomic mass remain constant.
the atomic number decreases by four and the atomic mass decreases by two.
the atomic number decreases by two and the atomic mass decreases by four.
the atomic number increases by one while the atomic mass remains constant.
the atomic number decreases by one and the atomic mass remains constant.

Explanation:

An alpha particle consists of 2 protons and 2 neutrons (so atomic number 2, mass number 4). When an atom emits an alpha particle, its atomic number (number of protons) decreases by 2, and atomic mass (sum of protons and neutrons) decreases by 4. Let's analyze each option:

• First option: Incorrect, as emission changes atomic number and mass.
• Second option: Atomic number decrease (2, not 4) and mass decrease (4, not 2) are wrong.
• Third option: Matches the alpha decay effect (atomic number -2, atomic mass -4).
• Fourth option: Describes beta - plus or electron capture? No, alpha decay doesn't do this.
• Fifth option: Describes beta - minus decay? No, not alpha decay.

Answer:

The atomic number decreases by two and the atomic mass decreases by four. (The option with this description, e.g., if it's the third option in the list, we can also write it as the option stating "The atomic number decreases by two and the atomic mass decreases by four.")