physical science

• What is PHYSICAL SCIENCE?
• ELEMENTS IN THE PERIODIC TABLE
• ATOMIC NUMBER AND ATOMIC MASS
• Atomic mass


  Number of protons + number of neutrons
• Atomic mass


  Atomic number + number of neutrons
• The discovery of the subatomic particles prompted other scientists to study the variations in the characteristics of elements
• Atomic number


  The number of protons in the nucleus of each atom of an element
• In a neutral atom

  The number of protons is equal to the number of electrons
• The atomic number indicates the number of electrons in a neutral atom
• Atomic number of Carbon

  • 6 protons, 6 electrons
• Atomic mass


  The total number of neutrons and protons present in the nucleus of an atom of an element
• Hydrogen has one proton and no neutron
• Mendeleev arranged the elements according to their atomic weights in 1869, paving the way to the construction of the periodic table
• Moseley confirmed in 1913 that the basis for the arrangement in the periodic table should be the atomic number
• The periodic table is still arranged in terms of the atomic number
• Isotopes


  Atoms that have the same atomic number (Z), but different atomic masses (A)
• During a chemical reaction, the number of protons remain the same in the atomic nucleus, but the electrons may be lost by an atom and gained by another
• Ions


  Charged atoms formed by the loss or gain of one or more electrons, with a net positive charge (cation) or negative charge (anion)
• Nuclear Reactions
• Types of Nuclear Reactions

  • Alpha decay - loss of an alpha particle
  • Beta decay - loss of a beta particle
  • Gamma radiation - emission of a gamma particle
  • Positron emission - conversion of a proton in a nucleus into a neutron, releasing a positron
  • Electron capture - drawing of an electron
  • Bombardment of alpha particle - addition of alpha particle
• The big bang theory was first expressed in the early 1900s, when Edwin Hubble offered an explanation that the universe is expanding
• Hubble observed that many stars and galaxies shine with light shifted toward the red end of the visible spectrum (redshift)
• Hubble Law suggests that the size of the redshift is proportional to the distance and speed of the star moving away from the Earth
• Big Bang theory postulates that approximately 14 billion years ago, a sphere about one-centimeter diameter experienced a huge explosion, spreading its products as a fast-moving cloud of gas
• The event was accompanied by an emission of huge amount of light. Within the first second after explosion, subatomic particles such as protons, neutrons, and electrons were formed
• As the expanding universe cooled, the protons and neutrons started to fuse (combine) to form heavier nuclei of deuterium (an isotope of hydrogen with one neutron and one proton) and some into helium
• Isotopes


  Atoms that have the same number of protons but different numbers of neutrons
• Subsequent nuclear fusion reactions resulted in the production of other light elements and their isotopes
• Astronomers believe that a few minutes after the Big Bang, the universe was composed of approximately 75% (by mass) hydrogen, 25% helium, and trace amounts of lithium
• The process through which these light elements formed are called the big bang nucleosynthesis