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 atomic - electron relationship

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

Step2: Calculate neutrons in Mg - 25

The mass number of Mg - 25 is 25, and the atomic number of magnesium (Mg) is 12. Neutrons = Mass number - Atomic number. So, neutrons = 25 - 12 = 13.

Step3: Calculate mass number

The mass number of an atom is the sum of protons and neutrons. Given 5 protons and 7 neutrons, mass number = 5 + 7 = 12.

Step4: Determine electrons in O²⁻

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

Step5: Determine electrons in Mg²⁺

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

Answer:

A. 3
B. 13
C. 12
D. 10
E. 10