Chemistry - What is a neutral atom?
Solution 1:
Electrons and protons are charged particles. The electrons have negative charge, while protons have positive charge. A neutral atom is an atom where the charges of the electrons and the protons balance. Luckily, one electron has the same charge (with opposite sign) as a proton.
Example: Carbon has 6 protons. The neutral Carbon atom has 6 electrons. The atomic number is 6 since there are 6 protons.
Solution 2:
Here, a "neutral atom" is simply an atom that has no charge.
See, an atom consists of protons, neutrons, and electrons. Protons are positively charged, electrons are negatively charged (with the same magnitude of charge per particle as a proton). Neutrons have no charge.
Now, in a "neutral atom", the number of protons must be equal to the number of electrons, otherwise it would not be neutral.
Basically, the definition is saying that "in a neutral atom, the atomic number is equal to both the number of protons , and the number of electrons, because, well, they both are the same."
Compare this with an ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge
Here, the atomic number cannot be equal to both--because they are unequal. In this case, a better definition would be:
The number of protons present in an atom is it's atomic number. It is represented by $Z$.
Solution 3:
I totally agree with George that "neutral atom" is close to nonsense. Indeed, IUPAC recommends the following definition for atom:
atom
Smallest particle still characterizing a chemical element. It consists of a nucleus of a positive charge ($Z$ is the proton number and $e$ the elementary charge) carrying almost all its mass (more than 99.9%) and $Z$ electrons determining its size.
As one can see, for an atom the proton number, also known as atomic number, which is the number of protons in the atomic nucleus, is the same as the number of electrons. Consequently, any atom is (electrically) neutral by definition, as George mentioned in his comment.
Solution 4:
Because sometimes scientists use the term "atom" when it is not neutral.
This is most often in the phrase "hydrogen like atoms":
A hydrogen like atom consists of one nucleus of charge Ze and a single electron of charge -e.
See also:
Correlation in Helium-Like Atoms (2-electron atoms regardless of charge)
The Spectra of some Lithium-like and Sodium-like Atoms (3 and 11-electron atoms)
Quadruply excited beryllium-like atoms – a semiclassical model (4-electron atoms)
Fine-structure studies of the ground state of boron-like atoms (5-electron atoms)
Relativistic corrections to the ground state energies of the carbon-like atoms (6-electron atoms)
etc.