SME
Grade 10 Science · Problem type
Ions: gaining and losing electrons
Use this to find an ion’s charge from its protons and electrons, or the electrons from its charge.
Diagram
Sulfur: 16 protons, so atomic number Z = 16.
18 electrons: charge 16 − 18 = −2, a negative ion (anion) S²⁻.
Shells: 2, 8, 8.
This is an example. Type your own values to start a new problem.
q
=
Z
−
e
Formulas
q
=
Z
−
e
−2 = 16 − 18
Assumptions
•
An ion has gained or lost electrons; its protons, and so its element, stay the same.
•
Nonmetals such as sulfur gain electrons to fill their outer shell: S²⁻ has two extra.
Step-by-step
WE KNOW
Z = 16, e = 18
FIND
charge (q)
Step 1 · Find charge (q)
Use q = Z − e
Each proton adds +1 and each electron −1.
q
=
16
−
18
q
=
−2
Check
Put the numbers back in. Both sides should match.
−2 = 16 − 18 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.