×

Warning

Please Login to Read More...

From Darkness to Light From darkness to light Black holes, which abound in the universe, convert matter into geometry − the larger the amount of matter that disappears, the larger they grow. In the process, a great deal of extremely hot gas is generated, and that gas emits hard X−rays. Now NASA’s NuSTAR (Nuclear Spectroscopic Telescope ARray) space telescope can find black holes by forming high − resolution images of the cosmos in hard X−rays. The Production of X−rays is related to the structure and energy levels of atom, which is discussed in this topic.

Learning objectives

After completing the topic, the student will be able to:

  • Understand the early model of atom and the theories involved in building the structure of Atom.
  • Analyze how Rutherford developed his theory based on his experimental observations and the limitations of his model.
  • Explore Bohr′s atomic model and its relevance when applied to hydrogen atom.
  • Estimate the radius of the orbit, velocity of the electron and the energy levels of the electron in various orbits of hydrogen atom using the Bohr's atomic model.
  • Discover the disadvantages of the Bohr′s model and analyze the importance and success of shell model.
Structure of Atom Diagram of the structure of the atom An atom consists of one or more electrons that whirl about the tiny, central nucleus. The nucleus consists of protons (red) & neutrons (blue). The number of electrically positive protons balance the number of electrically negative electrons to make the atom neutral overall.
Early model of atom

The great Caltech Physicist Richard Feynman, in a series of lectures given for Caltech undergraduates observed that if scientific history had to be reduced to one important statement it would be "All things are made of atoms" –– little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.

Richard P. Feynman also shared some of his thoughts he had standing at the seashore. "There are the rushing waves... Mountains of molecules, each stupidly minding its own business, trillions apart, yet forming white surf in unison. Deep in the sea, all molecules repeat the pattern of one another till complex new ones are formed. They make others like themselves and a new dance starts. Growing in size and complexity – living things, masses of atoms, DNA, protein – dancing a pattern ever more intricate.

Out of the cradle onto dry land here it is standing: atoms with consciousness; matter with curiosity. Stands at the sea, wonders at wondering: I a universe of atoms an atom in the universe."

Avogadro Number of Atoms Avogadro number of atoms One mole of carbon(12.01 grams) is 6.022 × 1023 atoms of carbon (Avogadro's number).The mass of a single carbon atom is 1.994 × 10–23 g, as we divide mass of a mole of atoms by Avogadro Number.
Avogadro number of atoms

It is interesting to get a perspective of numbers concerning atoms. Number of molecules of oxygen in 32 grams (molecular weight of oxygen) is about 6 × 1023. In the whole universe there are about few hundred billion galaxies and each galaxy contains a few hundred billion stars. So there may be about 1023 stars in the universe which means there are a few times more molecules of oxygen in 32 grams of oxygen than there are stars in the whole universe.

So to put it in human perspective, if you take a deep breath, you have more molecules of air in your lungs than there are stars in the universe. One cubic centimeter of air contains about 45 billion billion molecules and hence many more atoms. The number of atoms in the universe is almost inconceivable!

Atoms are so tiny that it would take ten million times, side by side to stretch across the edge of a postage stamp. The ratio of size of one atom to the width of a millimeter line is like comparing the thickness of a sheet of paper with the height of Empire State Building!

So in short, atoms are tiny and atoms are abundant. They are so durable and long lived that they pass through several stars and millions of organisms before being part of you. Each one of us contains so many atoms that it is quite possible that you are carrying atoms which are once part of Buddha or Jesus Christ.