Atomic Structure and Radioactivity

Greek philosopher Democritus proposed that all matter, “ the stuff” that makes us the world around us, is actually composed of tiny, invisible particles.

2 Important Principles of Chemical Behavior

The atom is mostly empty space. Its mass is concentrated in the nucleus. (Nuclear Model)The protons and neutrons are particles inside the nucleus.He proposed the atomic model which is called nuclear atom.The nucleus is tiny and densely packed compared with the atom as a whole.

a Danish physicist who developed the Bohr model of the atom and the principles of correspondence and  complementarity. He and Werner Heisenberg developed the “Copenhagen interpretation” of quantum theory.

Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. He discovered that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

The chemical element bohrium (Bh), No. 107 on the Periodic Table of the Elements, is named for him. The atom is like a solar system. Its mass is concentrated in the nucleus in circular orbits.Each electron carries discrete amount of energy and does lose any energy as long as it stays in its given orbit.

Electron that has received enough energy can jump to a higher energy orbit. Upon return to a lower energy orbit, energy is emitted in the form of light. The energy of the light emitted is equal to the energy of the two orbits involved in the transition.

Wilhelm Roentgen

materials used as anodes in vacuum tubes gave off highly penetrating radiations, which is like light in some properties are what we know as x-rays.X-rays pass through paper, wood, light metals like aluminum and even human flesh.X-rays can be completely stopped by a thin layer of metals such as platinum, gold, or lead and by any human bones.

At the end of 1895, Wilhelm Röntgen discovered X rays. Becquerel learned that the X rays issued from the area of a glass vacuum tube made fluorescent when struck by a beam of cathode rays.He undertook to investigate whether there was some fundamental connection between this invisible radiation and visible light such that all luminescent materials, however stimulated, would also yield X rays.

To test this hypothesis, he placed phosphorescent crystals upon a photographic plate that had been wrapped in opaque paper so that only a penetrating radiation could reach the emulsion. He exposed his experimental arrangement to sunlight for several hours, thereby exciting the crystals in the customary manner. Upon development, the photographic plate revealed silhouettes of the mineral samples, and, in subsequent experiments, the image of a coin or metal cutout interposed between the crystal and paper wrapping.

Marie and Pierre Curie

Marie described the behaviour of uranium and thorium as radioactivity.Also, she was the first to study radioactivity/

Marie Curie discovered two new elements: radium and polonium. We now know these are inevitable by products of uranium.Science tells us, for example, that all material things are made up of tiny atoms. The atoms found in most substances are remarkably stable, but in the case of radioactive materials, the atoms are unstable.