Evolution of Atomic Models & Element Groups
The atom's structure was discovered gradually through several brilliant scientists. John Dalton first proposed atoms as solid spheres, then J.J. Thompson suggested the "plum pudding model" with electrons embedded in a positive charge. Rutherford's gold foil experiment revealed that atoms contain mostly empty space with a charged nucleus.
Niels Bohr refined this with his nuclear model showing electrons orbiting in fixed shells, and James Chadwick later discovered neutrons. Meanwhile, Dmitri Mendeleev created the periodic table in 1869, arranging elements by atomic weight but leaving gaps for undiscovered elements—a strategy that later proved correct!
Transition metals have unique properties: they can form multiple ions, act as excellent catalysts (like nickel and iron in the Haber process), and typically display vibrant colours. Group 1 elements (alkali metals) increase in reactivity as you move down the group because the outer electron becomes easier to lose. They form 1+ ions, create ionic compounds with non-metals, and react vigorously with water.
Did you know? During Rutherford's famous gold foil experiment, he was so shocked when some alpha particles bounced back that he said it was "as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you!"
