Plus and minus in balance
Protons equal electrons in a neutral atom.
Balancing the charges
On a simple scale, a proton has a relative charge of +1 and an electron −1.
A helium atom has 2 protons. For the atom to be electrically neutral, how many electrons should it have?
What this lesson covers
The idea
All atoms are electrically neutral because the number of protons equals the number of electrons, so the total positive charge equals the total negative charge.
Balancing the charges
On a simple scale, a proton has a relative charge of +1 and an electron −1.
A helium atom has 2 protons. For the atom to be electrically neutral, how many electrons should it have?
- 2
- 1
- 4
Make the atom neutral
The nucleus shows its number of protons. Use + and − to change the number of electrons.
Plus equals minus
Each proton adds +1 and each electron adds −1. When the numbers are equal, the charges add up to zero.
All atoms are electrically neutral because the number of protons equals the number of electrons, so the total positive charge equals the total negative charge.
Notes
Atoms are neutral: the number of protons equals the number of electrons, so positive charge equals negative charge.
Check yourself
A neutral fluorine atom has 9 protons. How many electrons does it have?
Answer: 9
The number of electrons equals the number of protons: 9.
A neutral chlorine atom has 17 protons. How many electrons does it have?
Answer: 17
Protons and electrons are equal in a neutral atom: 17.
An atom has 3 protons and 3 electrons. What is its total charge on the scale where a proton is +1 and an electron is −1?
Why are atoms electrically neutral?
- +3. The 3 electrons add −3, which cancels the +3 from the protons.
- −3. The 3 protons add +3, which cancels the −3 from the electrons.
- 0 — correct. Yes!
- The total positive charge equals the total negative charge — correct. Yes!
- They have no protons. Atoms have protons in the nucleus.
- They have no electrons. Atoms have electrons around the nucleus.