Physical Science

• DEMOCRITUS- Democritus considered the question, “What happens if you keep dividing a body into smaller and smaller parts?
• He hypothesized that there was a limit to this process; that is you reached a point in which the parts were very small and could not be cut into parts, i.e. “atomos” (indivisible)
• THOMSON’S PLUM PUDDING ATOMIC MODEL- Plum pudding is an English dessert similar toablueberry muffin. I
• In Thomson's plum pudding model of the atom, the electrons were embedded in a uniform sphere of positive charge, like blueberries stuck into a muffin.
• During his experiment, he discovered electrons using a cathode ray tube and it is one of themost important discoveries in the history of physics.
• He was even awarded a Nobel Prize in physics for this discovery.
• RUTHERFORD’S GOLD FOIL EXPERIMENT- Through this experiment, it was concluded that anatom is mostly empty space with a dense, positively charged nucleus
• An atom consists of a central nucleus that is surrounded by one or more negatively charged electrons. T
• The nucleus is positively charged and contains one or more relatively heavyparticles known as protons and neutrons.
• Each period corresponds to the number of orbitals of each element
• Orbitals are rings that surround an element.
• The Roman numeral group number pertains to the number of valence electrons
• Valence electrons are electrons found in the outer shell/ last orbital of anelement.
• The last group of elements are noble gases.
• The 0 on the top portion means these elements cannot share/donate electrons, they also don’t need any electrons because they are stable
• The valence which is a maximum electrons of noble gas elements are 8 which is the maximum number.
• This is called “octet rule”. Octet means 8 (the number of valence electrons neededtoattain stability.
• Another way to present the valence electrons is through the Lewis dot diagram.
• The dots represent the number of valence electrons of an element.
• Atomic number= no. of protons and electrons
• Neutrons= atomic mass – atomic number (always round off the atomic mass into a whole number)
• Ionic- transfer of electrons
• Covalent- sharing of electrons
• Electronegativity is the key factor in determining the polar or nonpolar covalent.
• Electronegativity - is the property of an element to attract electrons to itself
• The most electronegative element is Fluorine.
• Electronegativity = first element EN - second element EN
• Polar - greater than or equal to 0.5
• Non polar - less than 0.5