Question

Decrease in atomic number is observed during. (a) \(\alpha\) emission (b) \(\beta\) emission (c) positron emission (d) electron capture Select the correct answer. (a) \(1,2,3\) (b) \(2,3,4\) (c) \(1,3,4\) (d) \(1,2,3,4\)

Short answer

The correct answer is (c) 1, 3, 4.

Step-by-step solution

Understanding Alpha Emission

In alpha () emission, an  particle, which is a helium nucleus, is emitted. This particle contains 2 protons and 2 neutrons. Hence, the atomic number decreases by 2 units as two protons are lost.

Examining Beta Emission

During beta () emission, a neutron is converted into a proton while emitting an electron () and an antineutrino. This process increases the atomic number by 1 as a new proton is added.

Analyzing Positron Emission

In positron emission, a proton is converted into a neutron, releasing a positron (+) and a neutrino. This decreases the atomic number by 1 as one proton is changed to a neutron.

Understanding Electron Capture

Electron capture involves the absorption of an orbital electron by the nucleus, where it combines with a proton to form a neutron. This decreases the atomic number by one as a proton is transformed into a neutron.

Selecting the Correct Combination

Based on the analyses, the atomic number decreases during alpha emission, positron emission, and electron capture. Therefore, the correct combination that includes all these processes is option (c), which is: 1 (alpha emission), 3 (positron emission), 4 (electron capture).

Key concepts

Alpha Emission

Alpha emission is a type of radioactive decay where the nucleus of an atom releases an alpha particle. This alpha particle is essentially a helium nucleus, having 2 protons and 2 neutrons. Since protons determine the atomic number of an element, the loss of these 2 protons results in a decrease in the atomic number by 2.

• Alpha particles are generally not very penetrating due to their larger size.
• When an atom undergoes alpha emission, it transforms into a new element that is positioned two places left on the periodic table.

This type of emission is common in heavy elements like uranium and radium. For instance, when uranium-238 emits an alpha particle, it becomes thorium-234. This process changes both the atomic and the mass numbers of the original element.

Beta Emission

Beta emission, often referred to as beta decay, is a fascinating process involving the transformation of a neutron into a proton. During this decay, a beta particle, which is an electron, is emitted. Accompanying this release is an antineutrino.

• This emission results in an increase in the atomic number by 1 since the neutron is changed to a proton.
• The mass number remains the same as protons and neutrons have similar masses.

Beta emission allows elements to shift one position to the right on the periodic table, resulting in the formation of a new element. For example, carbon-14, when undergoing beta emission, is converted into nitrogen-14. It's a crucial process in radioactive dating methods.

Positron Emission

Positron emission is the radioactive decay process where a proton within a nucleus is converted into a neutron while releasing a positron and a neutrino. Positrons are essentially the antimatter counterparts of electrons.

• This results in a decrease in the atomic number by 1 since a proton is transformed into a neutron.
• The mass number remains constant because the overall number of nucleons (protons + neutrons) does not change.

Positron emission is often found in proton-rich nuclei and is a key process in medical imaging techniques such as PET scans. For instance, oxygen-15 undergoes positron emission to become nitrogen-15.

Electron Capture

Electron capture is a unique process where an atomic nucleus draws in an inner orbital electron. This electron combines with a proton to form a neutron, leading to a transformation within the nucleus.

• The process results in a decrease in the atomic number by 1 because a proton is turned into a neutron.
• The mass number again remains unchanged as the total number of nucleons doesn't vary.

Electron capture usually occurs in proton-rich atoms. For example, potassium-40 can undergo electron capture to become argon-40. This process is essential for achieving greater nuclear stability and can be observed in various isotopes across the periodic table.