At North Sydney Girls High School, one in two students sat the HSC chemistry exam on Friday. By comparison, only 14 per cent of students across the state took on the science subject this year.

The figure at North Sydney Girls is all the more striking because they are women sitting the exam at a time when female participation in science continues to sink to new lows.

Three times as many females are studying no maths and science at all compared to 2001, research from the University of Sydney has found.

Of the physics students who sit their exam on Tuesday, 75 per cent will be male, according to statistics from the Board of Studies.

The figures are no hurdle for North Sydney chemistry students Shannon Gao and Deborah Gu, who will be back in the exam room next week to take on physics.

"I was in the zone," said 17-year-old Shannon, as she emerged triumphant on Friday, after nailing questions on chlorofluorocarbon compounds.

"Some parts were challenging but most were expected."

Her classmate Deborah wasn't quite so confident. "I managed to finish just as the time came up, I was just over-thinking the questions," she said.

The head of science at the school, Andrew McGlynn, said the exam was more conservative than previous years. "It was challenging but fair," he said.

The grand dame of chemistry, Marie Curie, might have been looking down kindly on the North Sydney pair as the timing of the exam could not have been better.

Friday was International Mole Day – that's "mole" as in molecule, the International Day of Chemistry.

The teenage girls were surprised to learn that outside of their school lab, fewer and fewer women in Australia were celebrating the day at all.

Research published in October by University of Sydney academics Rachel Wilson and John Mack said that due to an "illogical decline in science ... Australians can no longer think of themselves as belonging to the clever country".

Outside of biology, female participation had been in a slow decline, the study found.

It is part of the reason why the Board of Studies is seeking to overhaul the curriculum this year with its release of draft papers including proposals for 3-unit chemistry and physics.

Deborah and Shannon are all for the changes, unable to fathom a life without chemistry.

"When I learn chemistry I'm a more informed citizen of the environment around me," said Deborah.

"By understanding the fundamentals, the logic of sequencing, you understand the basic building blocks of life," agreed Shannon.

"Once I understand that knowledge I can use it for everything I encounter."

The two hope their next sequences will involve degrees in dentistry and medicine respectively.