STEM Calculators

Lewis Structure of Group 7A Central Atoms

General Chemistry • Chemical Bonds

Written by STEM Calculators Team Published Updated
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Group 17 (7A) Central Atoms – Interhalogens & Hypervalent Halogens

Choose an interhalogen where a halogen is the central atom. This calculator counts valence electrons, highlights hypervalency, and shows how the Lewis structure connects to the final VSEPR shape.

The visualizations are interactive, the electron-count steps are shown clearly, and the optional compare field lets you paste supported formulas copied from a CSV or spreadsheet.

Direct paste is supported. The compare area accepts the supported formulas from copied CSV cells, spreadsheet rows, or simple comma-separated text.

Central halogens can exceed an octet in many interhalogens. In this set, ClF₃ and BrCl₃ are T-shaped (AX3E2), BrF₅ is square pyramidal (AX5E), and IF₇ is pentagonal bipyramidal (AX7).

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Frequently Asked Questions

What are interhalogens with a Group 17 central atom?

Interhalogens are molecules made only of halogens where one halogen (often Cl, Br, or I) is the central atom bonded to other halogens such as F or Cl. Examples include ClF3, BrF5, IF7, and BrCl3.

How do you count valence electrons for an interhalogen EXn?

Add 7 valence electrons for the central halogen E and 7 for each terminal halogen X. In plain form: N_valence = 7(E) + n x 7(X).

How does the calculator decide how many lone pairs are on the central halogen?

It accounts for n single bonds (bonding electrons = n x 2) and assigns the remaining electrons as nonbonding electrons. In plain form: N_nonbonding = N_valence - (n x 2), which corresponds to lone pairs after terminal octets are satisfied in the simplified model.

Why can Cl, Br, and I have expanded octets in molecules like ClF3 or BrF5?

Halogens in period 3 or below can accommodate more than 8 electrons around the central atom in some compounds, which is described as hypervalency. This is why structures like ClF3 (AX3E2) and BrF5 (AX5E) show more than four electron pairs around the central atom.

What shapes do these Group 17 central-atom examples have?

ClF3 and BrCl3 are T-shaped (AX3E2), BrF5 is square pyramidal (AX5E), and IF7 is pentagonal bipyramidal (AX7). The calculator reports the matching VSEPR type and geometry for the selected molecule.

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