Wilhelm Conrad Roentgen was a German scientist who discovered x-rays through the use of Crookes tube, a tube he used in studying cathode rays that emitted new kinds of invisible ray that was capable of penetrating through a black paper.
After hearing such discovery, Henri Becquerel, a French scientist had also took interest in the connection between the phosphoresence he had already been investigating and the newly discovered rays. He thought that the phosphoresence uranium salts he had been observing and studying might absorb sunlight and emit it as x-rays.
To test such idea which was disproved later on, Becquerel wrapped photographic plates in black paper so that sunlight could not reach them. He then placed the crystals of uranium on top of the wrapped plates and put the whole set up outside, exposed under the sun.
When he developed the plates, he saw an outline of the uranium crystals. He also placed other objects such as coins or cut out metals between the crystals and the photographic film/plate. It also turned out that he could also produced outlines of those shapes.
Answer:
Explanation:
First write all numerators above the common denominator
4/5 - 1/2 - 1/2=
- 1/2
Subtract the numbers
- 1/2 =
- 
Write all numerators above the least common denominator 10
- =
Subtract the numbers and you got your answer :)
Physical chemistry.
organic chemistry.
inorganic chemistry.
analytical chemistry.
biochemistry.
Periods are rows horizontally along the periodic table whereas groups are vertical columns down the periodic table.
Elements in the same group react similarly. E.g. the group 1 metals (found in the first column of the periodic table) react readily with air and water (this is the similarity) but these reactions become more vigorous / explosive as you go down the group (this is why they are similar but not the same). This is because elements in the same group have the same number of electrons in their outermost energy level (and electrons are responsible for how an element reacts)
Elements in the same period of the periodic table have the same number of inner most (also known as 'main') energy levels so have the same amount of electron shielding.
