How Do You Change the Number of Mass?

You can change the number of mass of an element's sample by altering the number of atoms or by changing the isotopes involved; however, the mass of an individual atom can only be altered by nuclear changes.

Understanding Mass and Atomic Structure

It's important to distinguish between the mass of a single atom and the overall mass number of a sample.

• Individual Atom Mass: The mass of a single atom remains constant unless a nuclear change occurs. This is explained by the fact that an atom's mass is determined primarily by the number of protons and neutrons in its nucleus.
• Sample Mass Number: The mass number of a sample of an element, however, can change. According to the provided information, the mass number of a sample changes over time due to radioactive isotopes undergoing nuclear changes. This is important to understand, especially when dealing with radioactive elements that can decay.

How Mass Number Changes Over Time

Here's how a sample's mass number can change:

• Radioactive Decay: When radioactive isotopes decay, they release particles and energy. This leads to a change in the number of protons and neutrons, thus changing the mass number. The mass number changes as the sample converts from its original unstable isotopes to more stable forms. For example, if a heavy isotope undergoes decay, the sample mass number will decrease over time as the isotope transforms into lighter elements.
• Isotopic Composition: The average mass of an element remains essentially stable due to the presence of common isotopes. However, the abundance of these isotopes can fluctuate, resulting in subtle changes in the mass number over time, if different isotopes are introduced or removed from the sample.

Factors That Don’t Change Mass

It’s important to note that regular chemical reactions, which involve the exchange of electrons between atoms, do not change the number of protons and neutrons in an atom's nucleus. Thus, the mass of the individual atoms involved in typical chemical reactions does not change. Changes in the number of atoms due to a chemical reaction can change the overall mass, not the mass number.

Key Takeaways

• The mass of individual atoms changes only with nuclear changes.
• The mass number of an element's sample can change due to radioactive decay.
• Radioactive isotopes change mass numbers when they decay.
• The average mass of an element remains stable as an average of the common isotopes.