Question

you can become more familiar with the atomic structure of some common substances by completing the chart below. for each substance, you have been given enough information to fill in all the blanks.
substance | symbol | atomic number | mass number | number of protons | number of neutrons | number of electrons
helium | he | 2 | 4 | | |
magnesium | mg | 12 | | | 12 |
zinc | zn | 30 | 65 | | |
bromine | br | | 80 | | | 35
aluminum | al | | | 13 | 14 |

Explanation:

Step1: Recall atomic rules

Key relationships:

1. Atomic Number = Number of Protons = Number of Electrons (neutral atom)
2. Mass Number = Protons + Neutrons
3. Valence electrons: Group number (main group elements)

Step2: Fill Helium row

Protons = Atomic Number = $2$
Neutrons = $4-2=2$
Electrons = Protons = $2$
Valence electrons = $2$ (full outer shell)

Step3: Fill Magnesium row

Protons = Atomic Number = $12$
Mass Number = $12+12=24$
Electrons = Protons = $12$
Valence electrons = $2$ (Group 2)

Step4: Fill Zinc row

Protons = Atomic Number = $30$
Neutrons = $65-30=35$
Electrons = Protons = $30$
Valence electrons = $2$ (Group 12)

Step5: Fill Bromine row

Atomic Number = Electrons = $35$
Protons = Atomic Number = $35$
Neutrons = $80-35=45$
Valence electrons = $7$ (Group 17)

Step6: Fill Aluminum row

Atomic Number = Protons = $13$
Mass Number = $13+14=27$
Electrons = Protons = $13$
Valence electrons = $3$ (Group 13)

Answer:

Valence Electrons	Substance	Symbol	Atomic Number	Mass Number	Number of Protons	Number of Neutrons	Number of Electrons
2	Magnesium	Mg	12	24	12	12	12
2	Zinc	Zn	30	65	30	35	30
7	Bromine	Br	35	80	35	45	35
3	Aluminum	Al	13	27	13	14	13