Chlorine Bohr model overview
The chlorine Bohr model represents a neutral chlorine atom by placing its electrons into concentric shells around the nucleus. For chlorine, atomic number \(Z = 17\) fixes the proton count at 17 and the electron count at 17 for a neutral atom, giving the shell distribution 2–8–7.
Atomic number, mass number, and isotopes
Chlorine always contains 17 protons because \(Z = 17\). Neutron count depends on the isotope, using the relationship \[ A = Z + N \] where \(A\) is mass number and \(N\) is neutrons. The most common naturally occurring isotopes are chlorine-35 and chlorine-37.
| Isotope notation | Protons \(Z\) | Neutrons \(N\) | Electrons (neutral) |
|---|---|---|---|
| \(^{35}_{17}\mathrm{Cl}\) | 17 | \(35 - 17 = 18\) | 17 |
| \(^{37}_{17}\mathrm{Cl}\) | 17 | \(37 - 17 = 20\) | 17 |
Shell occupancy in the Bohr picture
The Bohr model assigns electrons to shells labeled by the principal quantum number \(n = 1, 2, 3, \dots\). A useful capacity rule for shell \(n\) is \[ \text{maximum electrons in shell } n = 2n^2 \] which gives capacities of 2 (first shell), 8 (second shell), 18 (third shell), and so on. Chlorine’s 17 electrons fill lower shells first, producing 2–8–7.
| Shell \(n\) | Common name | Maximum \(2n^2\) | Electrons in chlorine (neutral) |
|---|---|---|---|
| \(n = 1\) | K shell | \(2 \cdot 1^2 = 2\) | 2 |
| \(n = 2\) | L shell | \(2 \cdot 2^2 = 8\) | 8 |
| \(n = 3\) | M shell | \(2 \cdot 3^2 = 18\) | 7 |
Valence electrons and typical bonding behavior
Valence electron count
The outer-shell (valence) electrons in the chlorine Bohr model are the 7 electrons in the third shell. A valence count of 7 aligns with halogen chemistry and a strong tendency to gain one electron to complete an octet.
The octet picture corresponds to an outer shell reaching 8 electrons for many main-group atoms in simple ions and covalent bonding patterns.
Neutral atom versus chloride ion
A neutral chlorine atom has 17 electrons (2–8–7). The chloride ion \(\mathrm{Cl^-}\) has one additional electron (18 total), giving 2–8–8. The added electron occupies the third shell.
Charge bookkeeping follows electron count: \(\mathrm{Cl^-}\) has 17 protons and 18 electrons, producing a net \(-1\) charge.
Connection to electron configuration
The Bohr shell distribution compresses a more detailed quantum description. For chlorine, the electron configuration is \[ 1s^2\,2s^2\,2p^6\,3s^2\,3p^5 \] which totals \(2 + 2 + 6 + 2 + 5 = 17\) electrons. Grouping by principal shell gives 2 electrons in \(n=1\), 8 electrons in \(n=2\), and 7 electrons in \(n=3\), matching the chlorine Bohr model.
Visualization of the chlorine Bohr model
Model scope and limitations
The chlorine Bohr model captures shell counts and valence electrons, but it does not represent subshell structure (s, p, d), orbital shapes, or electron probability distributions. Modern descriptions treat electrons as occupying orbitals rather than fixed circular paths, while the Bohr picture remains a compact bookkeeping model for introductory atomic structure.
A neutral chlorine atom is assumed unless an ionic charge is specified. Isotope choice affects neutron count and mass, while electron-shell occupancy for a neutral atom remains set by \(Z = 17\).