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ATOM, REFERENCES, MODELS, STRUCTURE, DEVELOPMENTS - Coggle Diagram

- - - - Through a series of experiments from 1909 to 911, Rutherford established that atoms have nuclei. His discovery came by accident and as a total surprise. His experiment consisted of firing alpha particles at a very thin sheet of gold foil. Alpha particles consisted of two protons and two neutrons.
        
        The idea of the experiment was to measure how much the alpha particles deflected from their original course when they passed through the gold foil. Because alpha particles are positively charged and electrons are negatively charged, the electrons were expected to slightly alter the trajectory of the alpha particles.
        
        Rutherford expected the beam of alpha particles pass through the gold foil in a manner that would indicate how. However, to his surprise, most of the alpha particles was hardly deflected and passed through the gold foil as if it was just an empty space and some evern deflected at 180 degrees, right back in the direction they came from.
        
        The unexpected result shows that the mass of an atom is not as evenly distributed as Thomson and others had formerly assumed. It was then established by Rutherford that the mass of an atom is concentrated on its nucleus, which is made up of tightly bonded positively and neutrally charged subatomic particles.
  - - - Danish physicist and a student of Rutherford, Bohr developed a new model of the atom that somehow resembled the Solar System. He was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit defines the properties of an element.
        
        The Bohr model is summarized below:
        
        Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher orbit to a lower one.
        
        Each orbit has an energy associated with it. The orbit nearest the nucleus
        has an energy of E1, the next orbit is E2, and so on.
        
        Electrons occupy only certain orbits around the nucleus. Those orbits are
        stable and are called “stationary orbits”.
        
        The energy and frequency of light emitted or absorbed can be calculated by using the difference between the two orbital energies.
  - - - In 1897, Thomson discovered the electron which he first called corpuscles, by experimenting with cathode ray tubes. He demonstrated the cathode rays were negatively charged. In addition, he also studied positively charged particles in neon gas. This led to the discovery that atoms are not the smallest things that exist, and that they can still be further divided.
        
        Thomson proposed the plum pudding model where he stated that electrons are small negative charges attached to a positively charged medium.
        
        Further, Thomson added that the negatively charged electrons would "balance out" the positively charged medium so that all atoms will become neutrally charged.
  - - - In 1932, neutrons were found to have the same mass as protons which accounted for more of the mass of the atom.
        
        The common understanding of an atom was now a nucleus containing positively charged protons and neutral neutrons with the rest of the atom being space in which negatively charged electrons.
        
        James Chadwick played a vital role in the atomic theory, as he discovered the neutron in atoms. Neutrons are located in the center of an atom, in the nucleus among with the protons. They have neither a positive nor negative charge, but contribute the atomic weight with the same effect as a proton. Chadwick discovered this subatomic particle by using a neutron chamber in his experiments.
  - - - Dalton was able to build on Democritus' idea of atoms as the fundamental building blocks of matter and go further to say that there were many kinds of atoms. He performed a number of experiments that eventually led to the acceptance of the idea of the atoms in the early 1800's.
        
        He proposed the atomic theory which stated the following:
        
        Atoms of different elements are different;
        
        Compounds are formed when atoms of different elements combine in fixed proportions and;
        
        Atoms of the same elements are exactly alike;
        
        A chemical reaction involves rearrangement of atoms, not a change in the atoms themselves.
        
        All elements are composed of atoms which are indivisible and indestructible;
- - - - Electrons are the negatively charged particles of atom. Together, all of the electrons of an atom create a negative charge that balances the positive charge of the protons in the atomic nucleus.
        
        Why is atomic structure important to life?
        
        Atoms are extremely important structures that make up all of the materials on earth.
        
        Atoms are in our bodies and they bond together to form molecules, which make up matter.
    - - An uncharged elementary particle that has a mass nearly equal to that of the proton and is present in all known atomic nuclei except the hydrogen nucleus.
    - - An elementary particle that is identical with the nucleus of the hydrogen atom, that along with the neutron is a constituent of all other atomic nuclei, that carries a positive charge numerically equal to the charge of an electron, and that has a mass of 1.673 × 10−27 kilogram.
        
        This is how atoms work
        
        Most atoms have three different subatomic particles inside them: protons, neutrons, and electrons. The protons and neutrons are packed together into the center of the atom (which is called the nucleus) and the electrons, which are very much smaller, whizz around the outside. Most of an atom is empty space.
        
        PIcture of protons, electrons, and neutrons.
        
        Electrons
        
        Neutrons
        
        Protons
- - - - Leucippus and Democritus
        
        The ancient atomic theory was proposed in the 5th century bc by the Greek philosophers Leucippus and Democritus and was revived in the 1st century bc by the Roman philosopher and poet Lucretius.
        
        Atom first theorized
        
        Around 450 B.C., the Greek philosopher Democritus introduced the idea of the atom. However, the idea was essentially forgotten for more than 2000 years. In 1800, John Dalton re-introduced the atom. He provided evidence for atoms and developed atomic theory.
        
        Atomic Theory
        
        Atomic theory is the scientific theory that matter is composed of particles called atoms.
        
        An atom is now defined as the basic particle that composes a chemical element.
        
        Atomic theory traces its origins to an ancient philosophical tradition known as atomism.