Question

directions: for each of the following isotopes, write the isotope name and the number of protons, neutrons, and electrons.

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

sodium - 23
sodium - 28
nitrogen - 15
nitrogen - 20
chromium - 58
chromium - 63
selenium - 79
selenium - 83
sulfur - 32
sulfur - 40
carbon - 12
carbon - 16

Explanation:

Step1: Recall atomic number concept

The number of protons in an atom is equal to its atomic number. For a neutral atom, the number of electrons is equal to the number of protons. The number of neutrons is calculated as the mass - number minus the number of protons.

Step2: Sodium - 23

Sodium (Na) has an atomic number of 11. So, number of protons = 11, number of electrons = 11, number of neutrons = 23 - 11=12.

Step3: Sodium - 28

Number of protons = 11 (since it's still sodium), number of electrons = 11, number of neutrons = 28 - 11 = 17.

Step4: Nitrogen - 15

Nitrogen (N) has an atomic number of 7. So, number of protons = 7, number of electrons = 7, number of neutrons = 15 - 7 = 8.

Step5: Nitrogen - 20

Number of protons = 7, number of electrons = 7, number of neutrons = 20 - 7 = 13.

Step6: Chromium - 58

Chromium (Cr) has an atomic number of 24. So, number of protons = 24, number of electrons = 24, number of neutrons = 58 - 24 = 34.

Step7: Chromium - 63

Number of protons = 24, number of electrons = 24, number of neutrons = 63 - 24 = 39.

Step8: Selenium - 79

Selenium (Se) has an atomic number of 34. So, number of protons = 34, number of electrons = 34, number of neutrons = 79 - 34 = 45.

Step9: Selenium - 83

Number of protons = 34, number of electrons = 34, number of neutrons = 83 - 34 = 49.

Step10: Sulfur - 32

Sulfur (S) has an atomic number of 16. So, number of protons = 16, number of electrons = 16, number of neutrons = 32 - 16 = 16.

Step11: Sulfur - 40

Number of protons = 16, number of electrons = 16, number of neutrons = 40 - 16 = 24.

Step12: Carbon - 12

Carbon (C) has an atomic number of 6. So, number of protons = 6, number of electrons = 6, number of neutrons = 12 - 6 = 6.

Step13: Carbon - 16

Number of protons = 6, number of electrons = 6, number of neutrons = 16 - 6 = 10.

Step14: Answer to "How can you tell isotopes apart?"

Isotopes of an element have the same number of protons but different numbers of neutrons. We can tell them apart by their mass - numbers (sum of protons and neutrons) or by the number of neutrons.

Step15: Answer to "What does the number next to the isotope signify?"

The number next to the isotope (e.g., in carbon - 12) is the mass number, which is the sum of the number of protons and neutrons in the nucleus of the atom.

Answer:

Isotope	# of Protons	# of Neutrons	# of Electrons
Sodium - 28	11	17	11
Nitrogen - 15	7	8	7
Nitrogen - 20	7	13	7
Chromium - 58	24	34	24
Chromium - 63	24	39	24
Selenium - 79	34	45	34
Selenium - 83	34	49	34
Sulfur - 32	16	16	16
Sulfur - 40	16	24	16
Carbon - 12	6	6	6
Carbon - 16	6	10	6

How can you tell isotopes apart? Isotopes of an element have the same number of protons but different numbers of neutrons. We can tell them apart by their mass - numbers or by the number of neutrons.

What does the number next to the isotope signify? The number next to the isotope is the mass number, which is the sum of the number of protons and neutrons in the nucleus of the atom.