Chemical Changes

1. Chemical Changes By Angel Mendez

2. Democritus • The Democritus Atomic Theory revolves around the atoms that are present in the atmosphere. These are about the atoms that are present in all the forms of existence; for instance, solid or liquid. The theory states that these atoms are all individually created and cannot be separated, no matter what scientific procedures are applied. The Democritus Atomic Theory is pretty much clear and the ideas are portrayed in manner that can be easily understood. The theory also claims that there is no specific size that can be attributed to the various atoms and that they can differ depending on the various factors influencing them. It can be arrived at that the atoms cannot be split no matter what their size. So, we see how the Democritus Atomic theory explains the existence of atoms and also its features.

3. John Dalton • He explained to the world that if two gasses were mixed together they behave as if they were totally independent of each other. The first gas does not attract or repel the second gas, it just behaves as if the second gas did not exist. The result of this "independence" was that the total pressure exerted by the mixture of gasses was the sum of the separate pressures exerted by each part in the mixture. • He was also able to show that the environment had a measurable affect on the pressure shown by his gasses, and that there was a mathematical relationship between the pressure of a vapor and its ambient temperature.

4. Ernest. Rutherford • publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.

5. Neil's Bohr • Applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit.

6. John. Thomson • Discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated the value of the charge itself.

7. Nucleus • The atomic nucleus is a tiny massive entity at the center of an atom The nucleus is composed of protons (charge = +1; mass = 1.007 atomic mass units ([μ]) and neutrons. The number of protons in the nucleus is called the atomic number Z and defines which chemical element the nucleus represents. The number of neutrons in the nucleus is called the neutron number N, whereas the total number of neutrons and protons in the nucleus is referred to as the mass number

8. Mass Number • An integer equal to the sum of the number of protons and neutrons of an atomic nucleus.

9. Molecules • A molecule refers to two or more atoms which have chemically combined to form a single species. Its mass 18.01528 u

10. Isotope • Atoms with the same number of protons, but differing numbers of neutrons. Isotopes are different forms of a single element.

11. Subatomic Particles • Any of various units of matter below the size of an atom, including the elementary particles and hadrons.

12. Spectrometry • A spectroscope equipped with scales for measuring wavelengths or indexes of refraction.

13. Periodic Table • There are 18 vertical columns, or groups, in the standard periodic table • The horizontal rows of the table are called periods. The elements of a period are characterized by the fact that they have the same number of electron shells; the number of electrons in these shells, which equals the element's atomic number, increases from left to right within each period. In each period the lighter metals appear on the left, the heavier metals in the center, and the nonmetals on the right. Elements on the borderline between metals and nonmetals are called metalloids. • Group 1 (with one valence electron) and Group 2 (with two valence electrons) are called the alkali metals and the alkaline-earth metals, respectively. Two series of elements branch off from Group 3, which contains the transition elements, or transition metals; elements 57 to 71 are called the lanthanide series, or rare earths, and elements 89 to 103 are called the actinide series, or radioactive rare earths; a third set, the super actinide series (elements 122–153), is predicted to fall outside the main body of the table, but none of these has yet been synthesized or isolated. The nonmetals in Group 17 (with seven valence electrons) are called the halogens. The elements grouped in the final column (Group 18) have no valence electrons and are called the inert gases, or noble gases, because they react chemically only with extreme difficulty.

14. Electron Shells • An electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the 1 shell also called K shellfollowed by the 2 shell or L shellthen the 3 shell or M shell and so on further and further from the nucleus the shell letters K L M are alphabetical

15. Neutral Atom • Atoms that bear no net electrical charge because their negative and positive charges