Question

Figure 2.3 How many neutrons do (K) potassium-39 and potassium- 40 have, respectively?

Short answer

Answer: Potassium-39 (K-39) has 20 neutrons, and potassium-40 (K-40) has 21 neutrons.

Step-by-step solution

Identify the atomic number of potassium (K)

The atomic number of potassium (K) is 19. This means every potassium atom has 19 protons.

Identify the mass numbers for the isotopes

The mass numbers for the potassium isotopes are given as 39 for potassium-39 (K-39) and 40 for potassium-40 (K-40). The mass number represents the sum of the number of protons and neutrons in the nucleus of an atom.

Calculate the number of neutrons in potassium-39 (K-39)

To find the number of neutrons in potassium-39 (K-39), we need to subtract the atomic number (number of protons) from the mass number. This can be done using the following formula: Number of neutrons = Mass number - Atomic number In the case of potassium-39 (K-39), Number of neutrons = 39 - 19 = 20 There are 20 neutrons in potassium-39 (K-39).

Calculate the number of neutrons in potassium-40 (K-40)

Similarly, we'll calculate the number of neutrons in potassium-40 (K-40) using the same formula: Number of neutrons = Mass number - Atomic number In the case of potassium-40 (K-40), Number of neutrons = 40 - 19 = 21 There are 21 neutrons in potassium-40 (K-40).

Conclusion

Potassium-39 (K-39) has 20 neutrons, and potassium-40 (K-40) has 21 neutrons, respectively.

Key concepts

Atomic Number

The atomic number is a fundamental property of an element. It tells us the number of protons present in the nucleus of an atom of that element. For potassium (K), the atomic number is 19, meaning every potassium atom has 19 protons. Knowing the atomic number is crucial because it defines the element and its position in the periodic table. Elements are arranged in increasing order of their atomic numbers. The atomic number also tells us the number of electrons in a neutral atom, which is essential for understanding chemical reactions and bonding.

Mass Number

The mass number of an atom is the total count of protons and neutrons in its nucleus. It helps in distinguishing isotopes of an element since isotopes have the same number of protons but differ in the number of neutrons. For example, for potassium, we have: - Potassium-39 (K-39) with a mass number of 39 - Potassium-40 (K-40) with a mass number of 40 Mass number is not displayed on the periodic table but is crucial in identifying different isotopes. It is calculated by adding the atomic number (number of protons) and the number of neutrons together.

Neutrons

Neutrons are subatomic particles found in the nucleus of an atom, alongside protons. They carry no charge, making them neutral, which is why they are called 'neutrons'. Neutrons play a key role in the stability of the nucleus by offsetting the repulsive forces among protons, which are positively charged.To calculate the number of neutrons in an atom, you can use the formula: \[ \text{Number of neutrons} = \text{Mass number} - \text{Atomic number} \]For potassium-39 (K-39):- Number of neutrons = 39 (mass number) - 19 (atomic number) = 20For potassium-40 (K-40):- Number of neutrons = 40 (mass number) - 19 (atomic number) = 21This method is applied to determine the neutron count for any isotope, hence aiding in understanding how different isotopes of an element may vary in their physical properties.