Question

objectives:

• use the atomic number and mass number to calculate the number of protons, neutrons,

and electrons.

• define an isotope and calculate average atomic mass.
• determine atomic mass, mass number and amount of each subatomic particle of an

element.
a. isotope

1. what is an isotope?
2. what does the number next to isotopes signify?
3. how can you tell isotopes apart?

b. for each of the following isotopes, fill in the missing information. assume all
atoms are neutral

Explanation:

1. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
2. The number next to isotopes (e.g., Chromium - 58, Chromium - 63) signifies the mass number. The mass number is the sum of the number of protons and neutrons in an atom.
3. Isotopes can be told apart by their mass numbers (since they have different numbers of neutrons, which affects the mass number while the atomic number/proton number remains the same for the same element).

For part B:

• Chromium has an atomic number of 24. For neutral atoms, the number of protons = number of electrons.
• For Chromium - 58:
• Number of protons = 24 (from atomic number of Chromium)
• Number of neutrons = mass number - number of protons = 58 - 24 = 34
• Number of electrons = 24 (since atom is neutral)
• For Chromium - 63:
• Number of protons = 24 (from atomic number of Chromium)
• Number of neutrons = mass number - number of protons = 63 - 24 = 39
• Number of electrons = 24 (since atom is neutral)

Answer:

1. Atoms of the same element with same proton number but different neutron numbers.
2. The mass number (sum of protons and neutrons).
3. By their mass numbers (due to different neutron counts).

For the table:

	Chromium - 58	Chromium - 63
# of neutrons	34	39
# of electrons	24	24