Question

analyze: an isotope is an alternative form of an element. each isotope of an element has the same number of protons, but a different number of neutrons. the isotope is represented by the atomic symbol and mass number, such as he - 4. some isotopes are stable, while others are radioactive, which means the atoms decay over time and emit radiation.
a. what are the stable isotopes of carbon?
b. what are the stable isotopes of nitrogen?
c. list two radioactive isotopes of oxygen:
practice: use the gizmo to answer the following questions.
a. how many electrons are in a neutral atom of lithium?
b. how many neutrons are in an atom of mg - 25?
c. what is the mass number of an atom with 5 protons and 7 neutrons?
d. when an atom is charged, it is called an ion. how many electrons are in o²⁻?
e. how many electrons are in mg²⁺?

Explanation:

Step1: Recall carbon isotopes

Carbon - 12 and carbon - 13 are the stable isotopes of carbon.

Step2: Recall nitrogen isotopes

Nitrogen - 14 and nitrogen - 15 are the stable isotopes of nitrogen.

Step3: Recall oxygen radioactive isotopes

Oxygen - 13 and oxygen - 15 are two radioactive isotopes of oxygen.

Step4: Recall lithium electron number

Lithium has an atomic number of 3. In a neutral atom, the number of electrons equals the atomic number, so a neutral atom of lithium has 3 electrons.

Step5: Recall neutron number in Mg - 25

Magnesium (Mg) has an atomic number of 12. The mass number is 25. Number of neutrons = mass number - atomic number = 25 - 12 = 13.

Step6: Calculate mass number

Mass number = number of protons+number of neutrons. Given 5 protons and 7 neutrons, mass number = 5 + 7 = 12.

Step7: Recall electron number in O²⁻

Oxygen has an atomic number of 8. In O²⁻, it has gained 2 electrons, so the number of electrons is 8+2 = 10.

Step8: Recall electron number in Mg²⁺

Magnesium has an atomic number of 12. In Mg²⁺, it has lost 2 electrons, so the number of electrons is 12 - 2 = 10.

Answer:

A. Carbon - 12, Carbon - 13
B. Nitrogen - 14, Nitrogen - 15
C. Oxygen - 13, Oxygen - 15
D. 3
E. 13
F. 12
G. 10
H. 10