Question

atomic structure - practice problems
instructions: for each element below, identify the amount of each subatomic particle.
12 mg magnesium 24.31
protons: 12
neutrons:
electrons: 12
3 li lithium 6.94
protons: 3
neutrons:
electrons:
8 o oxygen 15.99
protons:
neutrons:
electrons:
18 ar argon 39.95
protons: 18
neutrons:
electrons:
14 si silicon 28.09
protons: 14
neutrons:
electrons:
78 pt platinum 195.08
protons: 78
neutrons:
electrons:

Explanation:

Step1: Recall atomic number rule

The number of protons is equal to the atomic number. For an atom in a neutral state, the number of electrons is equal to the number of protons. The number of neutrons is approximately the mass - number (rounded) minus the number of protons.

Step2: For Oxygen (O)

The atomic number of oxygen is 8, so the number of protons is 8. In a neutral atom, the number of electrons is also 8. The mass - number is approximately 16 (rounded from 15.99), so the number of neutrons is $16 - 8=8$.

Step3: For Argon (Ar)

The atomic number of argon is 18, so the number of protons is 18, the number of electrons is 18. The mass - number is approximately 40 (rounded from 39.95), so the number of neutrons is $40 - 18 = 22$.

Step4: For Silicon (Si)

The atomic number of silicon is 14, so the number of protons is 14, the number of electrons is 14. The mass - number is approximately 28 (rounded from 28.09), so the number of neutrons is $28 - 14=14$.

Step5: For Platinum (Pt)

The atomic number of platinum is 78, so the number of protons is 78, the number of electrons is 78. The mass - number is 195.08, approximately 195, so the number of neutrons is $195 - 78 = 117$.

Answer:

Element	Protons	Neutrons	Electrons
Ar	18	22	18
Si	14	14	14
Pt	78	117	78