feb 1, 1897 - 1896 AD: Frederick Soddy, a radio-chemist who worked in nuclear chemistry studied the 1896 radioactivity phenomenon and he discovered after a chain of experiments that atoms could have the same chemical properties but can change those properties when it came to radioactivity. In 1913 Soddy claimed a new theory that atoms can have isotopes that change its weight.
Added to timeline:
Date:
feb 1, 1897
Now
~ 128 years ago