Question

refer to the atomic models of helium and lithium to complete the table.

	helium model	lithium model
number of neutrons	(blank)	4
number of electrons	2	(blank)
mass of the atom (amu)	(blank)	7

Explanation:

Step1: Find neutrons in helium

Helium: protons = 2, mass (amu) ≈ protons + neutrons. For helium, common mass is 4 amu. So neutrons = 4 - 2 = 2.

Step2: Find electrons in lithium

Lithium: protons = 3 (neutral atom, electrons = protons), so electrons = 3.

Step3: Find mass of helium

Mass = protons + neutrons = 2 + 2 = 4 amu.

Answer:

• Number of neutrons (helium): 2
• Number of electrons (lithium): 3
• Mass of the atom (helium, amu): 4