Question

In terms of the numbers of protons, neutrons and electrons: a) Why does the notation \({ }^{13} \mathrm{C}^{-}\) have a negative sign in the upper right hand corner? b) What feature distinguishes a neutral atom from an ion? c) Provide an expression for calculating the charge on an ion.

Short answer

(a) The negative sign indicates that the atom has one more electron than it has protons, giving it a negative charge. (b) A neutral atom has equal protons and electrons, while an ion has a net electric charge due to an imbalance between protons and electrons. (c) Charge on an ion = Number of protons - Number of electrons.

Step-by-step solution

Understanding Atomic Notation

The atomic notation shown as \({ }^{13} \mathrm{C}^{-}\) is used to present information about an isotope of an element. The number '13' in the upper left corner represents the sum of the protons and the neutrons in the nucleus that comprises the atomic mass number. The 'C' in the middle represents for carbon, the element in question. The negative sign in the upper right corner represents the charge of the atom. In this case, the negative charge indicates that there is one more electron than there are protons. For the atom to be balanced, there will need to be equal protons and electrons - a negative implies an excess electron.

Defining Neutral Atom and Ion

A neutral atom has an equal number of protons and electrons, leading to a net charge of zero. An ion, on the other hand, is an atom that has either gained (negative ion) or lost (positive ion) electrons. Therefore, ions carry a net electric charge, while neutral atoms do not.

Calculating Ion Charge

The charge on an ion can be calculated by subtracting the number of electrons from the number of protons. If there are more electrons than protons, the ion is negatively charged. If there are more protons than electrons, the ion is positively charged. The equation could be expressed as: Charge on ion = Number of protons - Number of electrons