Problem 85 - Chemistry Matter and Change

Question

Radioactive Emissions What change in mass number occurs when a radioactive atom emits an alpha particle? A beta particle? A gamma particle?

Step-by-Step Solution

Answer

Alpha emission decreases the mass number by 4; beta and gamma emissions cause no change.

Step 1: Understanding Alpha Particle Emission

When a radioactive atom emits an alpha particle, it releases a particle consisting of 2 protons and 2 neutrons. This means the mass number, which is the total number of protons and neutrons in the nucleus, decreases by 4. Therefore, if a radioactive atom emits an alpha particle, the mass number of that atom decreases by 4.

Step 2: Exploring Beta Particle Emission

A beta particle is essentially an electron or a positron. In beta-minus decay, a neutron is converted into a proton with the emission of a beta particle (electron). This change does not affect the mass number because the number of total nucleons (protons + neutrons) remains the same. Hence, when a radioactive atom emits a beta particle, there is no change in its mass number.

Step 3: Analyzing Gamma Radiation Emission

Gamma radiation involves the emission of gamma rays, which are high-energy photons. This type of radiation carries energy away from the nucleus but does not involve the loss or gain of any nucleons (protons or neutrons). Therefore, when a radioactive atom emits gamma radiation, there is no change in the mass number.

Key Concepts

Alpha Particle Emission

When we talk about alpha particle emission in radioactive decay, it's a process where an atom loses an alpha particle made up of 2 protons and 2 neutrons. This means, quite simply, that the atom's mass number decreases by four. The mass number is just the count of protons and neutrons in the nucleus. Imagine subtracting 4 candies from a jar; that's similar to what happens here, just with particles instead of candy!

• Mass of alpha particle: 4 (2 protons + 2 neutrons)
• Results in new element with lower atomic number by 2
• Mass number decreases by 4

Alpha particles are heavy compared to other emissions, and because of their mass, they don't travel far. However, they are powerful; they can cause significant damage if they interact with substances like our biological tissues.

Beta Particle Emission

Beta particle emission is another type of radioactive decay, but it's quite different from alpha emission. Here, a beta particle, which can be an electron or a positron, is expelled from the nucleus. In the most common type, a neutron is transformed into a proton, and the atom emits an electron, the beta particle. The heavy advantage? This doesn’t change the overall mass number of the atom.

• Beta-minus: Neutron turns into a proton; emits an electron
• Mass number stays the same; atomic number increases by 1
• Beta particles are lighter than alpha particles

Even though the mass number isn't affected, the atom changes its identity by gaining a new proton. This can turn one element into another! Beta particles can travel further than alpha particles but are less efficient at causing damage per particle. They have a knack for finding their way through almost anything, but not as far as gamma rays.

Gamma Radiation Emission

Gamma radiation is a little different. It doesn't involve particles like in alpha or beta emissions. Instead, it involves the release of gamma rays, which are essentially high-energy photons. These rays zip out of the atom carrying excess energy

• No actual particle emission occurs
• No change in mass number or atomic number
• Gamma rays possess high penetration power

Even though gamma rays do not change the mass or atomic numbers, they can rearrange the energy levels within the nucleus. This state change helps the atom reach a more stable configuration. Gamma rays are the most penetrating and can pass through many materials, requiring thick lead or concrete to block them.