Template:Sequence of the Day for July 12

Intended for: July 12, 2012

Timetable

• First draft entered by Alonso del Arte on April 28, 2011 ✓
• Draft to be reviewed by May 12, 2012 preferably by someone who knows about chemistry.
• Draft approved by June 12, 2012

Yesterday's SOTD * Tomorrow's SOTD

The line below marks the end of the <noinclude> ... </noinclude> section.

---

A097478: Atomic numbers of halogens in the periodic table.

{ 9, 17, 35, 53, 85 }

This sequence demonstrates that there is a mathematical structure to physical matter. We can compute this sequence mathematically by taking the formula for magic numbers, which happen to be the atomic numbers of the noble gases and then subtracting 1. The outermost shell of a noble gas atom has as many electrons as it can possibly have. Halogen atoms, on the other hand, can admit precisely one more electron to their outer shell (specifically in their outer p subshell).

Note that as you go down the periodic table the elements tend to acquire more metallic properties, which happens to be the case of astatine (85), which has somewhat more metallic properties than iodine (53), although astatine is still considered a halogen.