Particles and Atomic Structure (States of matter (Solid (Solid to Liquid =…
Particles and Atomic Structure
Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties.
Rutherford designed an experiment to test the plum pudding model. It was carried out by his assistants Geiger and Marsden.
A beam of alpha particles was aimed at very thin gold foil and their passage through the foil detected. The scientists expected the alpha particles to pass straight through the foil but something else also happened.
Some of the alpha particles emerged from the foil at different angles and some even came straight back. The scientists realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom.
As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom.
States of matter
Solid to Liquid = Melting
Solid to Gas = Sublimation
Gas to Liquid = Condensing
Gas to Solid = Sublimation
Liquid to Gas = Boiling
Liquid to Solid = Freezing or Solidification
Arrangement of the Periodic Table by Mendeleev
Mendeleev arranged the elements known at the time in order of relative atomic mass, but he did some other things that made his table much more successful.
He realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
Sometimes this method of arranging elements meant there were gaps in his horizontal rows or 'periods'. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered.
He was also able to work out the atomic mass of the missing elements, and so predict their properties. And when they were discovered, Mendeleev turned out to be right.
For example, he predicted the properties of an undiscovered element that should fit below aluminum in his table. When this element, called gallium, was discovered in 1875, its properties were found to be close to Mendeleev's predictions. Two other predicted elements were later discovered, lending further credit to Mendeleev's table.