Why can the O7+ ion be consider hydrogen-like

[Limesy]

Homework Statement

Explain, in two or three sentences, why the O7+
ion can be considered to be a
hydrogen-like ion. State what subatomic particles it is composed of and how
many there are of each

Homework Equations

The Attempt at a Solution

I know the correct answer to this, I just don't understand why it's correct. O7+ only has one bound electron. Why then is it called an O7+ion? should it not be an O1+ion as the other 7 electrons have been released?

 

[Redbelly98]

Welcome to Physics Forums.

The convention is to designate ions by their net charge, not by how many electrons it has.

When you remove 7 electrons from a neutral O atom, the result is an ion with a charge of 7+. Thus, O⁷⁺

 

[Tian WJ]

Dear Limesy:

1. Neutral O is the 8th element and has 8 protons and 8 electrons. O7+ acts like the hydrogen atom because it has only one electron.

(Further comments: Indeed we need to know the kinetics and dynamics of the bounded electrons, so we run into Quantum Mechanics. However, due to mathematical difficulties, for multi-electron atoms, even like the simplest Helium, we haven't got the rigorous solution to draw an exact picture for the electrons, though we could in principle. The atom of hydrogen is the only one that could be analyzed rigorously, so people developed the quantum theory and use H-atom for testing. On this point, the most significant property of the simplification of H-atom is that H-atom has only one bounded electron. Hence, we use not only H-atoms, but other severely ionized one-electron ion to test quantum theory. So, the significance of H-like atoms is only remarkable for advanced physics and chemistry.)


2. A O7+ atom is composed of one electron, eight proton, and eight neutron for O_16(Oxide nucleus with mass number 16).

3. If external energy is properly introduced, a neutral atom will be ionized. Given a neutral atom with mass number A, proton number = positive charge units = atomic number in the periodical table = Z, bounded electron number = Z, neutron number = A-Z. Z protons carry Z units of positive charge, and Z electrons carry Z negative charge. As the whole atom is neutral to particles in the distance. However, if the atom is ionized, or it loses electrons, the number of protons will exceed that of electrons, the positive charge will exceed the negative, and the atom (ion) will appear to be electrically positive. For the atom losing $m$ electrons, only Z-m electrons remains bounded, and the bulk of the total charge will be $m$. That is to say, for an atom losing m electrons, it will carry m positive charge units when interacts with external particles.

Hence, Oxide losing 7 electrons carries 7 units of positive charge, and is denoted O7+.