National Chemistry Week 2026: theme, dates and Mole Day
National Chemistry Week 2026 runs from Sunday 18 to Saturday 24 October. This year's theme, set by the American Chemical Society (ACS), is "Chemistry Under Construction": the chemistry of concrete, steel, stone, glass and the other materials that buildings are made of (American Association of Chemistry Teachers).
Quick answers
- Dates: 18 to 24 October 2026. It is usually held in the third week of October.
- Theme: "Chemistry Under Construction". In Spanish, "La Química Bajo Construcción".
- Who runs it: the ACS, through its local sections, with schools, colleges, museums and libraries holding their own events. The official home is acs.org.
- Mole Day falls in the same week, on Friday 23 October.
What the theme covers
The idea is that chemistry decides how strong, safe and long-lasting a building is. The ACS livestream page puts it this way: discover how chemistry shapes the strength, safety and sustainability of materials like concrete and steel, and how chemists help create the structures we rely on every day. Topics that fit include:
- how cement sets and why concrete gets stronger over time
- rust and corrosion, and how metals are protected
- glass, insulation and new building materials
- why stone weathers and how sinkholes form
The AACT's resource list for the week includes classroom labs on corrosion, removing copper stains from masonry, chemical weathering and sinkholes.
The ACS livestream on 21 October
The ACS "Program-in-a-Box" livestream for the week is on Wednesday 21 October 2026 at 7:00 p.m. Eastern, with a pre-show from 6:45 p.m. Anyone can register to watch, ACS member or not, but the deadline is 16 October at 10:59 p.m. The physical boxes of giveaways go only to groups hosted by ACS members (registration page).
Local events
ACS local sections run free hands-on days during the week. One example: Kent State University at Ashtabula, Ohio, holds "Chemistry Under Construction" on Saturday 24 October from 9 a.m. to noon, with more than two dozen free demonstrations, including oil-spill containment and cement construction (Kent State). Check your nearest university chemistry department or science museum for its own event.
Mole Day, 23 October
Mole Day is celebrated every 23 October from 6:02 a.m. to 6:02 p.m., after Avogadro's number, 6.02 × 10²³, the number of particles in one mole of a substance. It was created to spark interest in chemistry, and schools mark it with mole-themed activities. The National Mole Day Foundation's theme for 2026 is "NMDF Molar Cup!" (moleday.org).
Ideas for a class or a family
- Mix a small batch of plaster or cement and time how long it takes to set.
- Leave a steel nail in salt water, in tap water and in oil for a week, and compare the rust.
- Walk around your school or street and list which materials each building uses.
- Watch the 21 October livestream together and try the activities it shows.
