5 mistakes learners make with atomic structure, each one named and explained.
Protons decide which element it is, neutrons change the mass, electrons do the chemistry.
A proton is given a charge of zero or plus two.
Three particles and three charges is a small set, but nothing about it is memorable on its own.
Question. The relative charge of a proton
A common answer. 0
The answer. +1
Why. Zero is the neutron, which is exactly what the name says.
Two of the three name themselves. Learn the proton and the rest follow.
A neutral atom is given a different number of electrons from its protons.
Electrons are learned as the particles that move, so their number feels flexible.
Question. A neutral sodium atom with 11 protons
A common answer. 12 electrons
The answer. 11 electrons
Why. Neutral means the positive and negative charges cancel exactly.
Unless the question says ion, the two numbers are the same.
Isotopes are described as having the same neutrons and different protons, or different atomic numbers.
Both numbers change between isotopes on the page, so which one is fixed is easy to invert.
Question. What isotopes of one element share
A common answer. the same number of neutrons
The answer. the same number of protons
Why. Changing the protons would change which element it is altogether.
Protons define the element, so protons can never be what varies between isotopes.
Sodium, mass number 23, is given 23 neutrons.
The mass number is the bigger number and neutrons are the particles that add mass.
Question. Sodium, atomic number 11, mass number 23
A common answer. 23 neutrons
The answer. 12 neutrons
Why. Mass number counts protons and neutrons together, so the protons have to be taken off.
Neutrons are always a subtraction, never a number you read straight off.
The proton is given a charge of minus one.
The two are learned as an opposite pair, and which one is positive is an arbitrary fact.
Question. The relative charge of a proton
A common answer. -1
The answer. +1
Why. Protons are positive, electrons negative, neutrons neutral.
Pro sounds like positive. That mnemonic settles it permanently.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.