Periodic+Trends

= = Periodic Tables are used to find specific information about different elements . Such information could be easily obtained such as the symbol, the name or the atomic mass number of a certain element. Since elements that are placed next to each other in the periodic table share similar chemical and physical properties, certain periodic trends were observed such as : ·  __Definition:__ The net positive charge experienced by an electron in a many electron atom; this charge is not the full nuclear charge because the nucleus by the other electrons in the atom. ·  __How it is found:__ The effective Nuclear Charge, Z eff,   is found from a simple relationship. Zeff = Z - S   Where Z is the number of protons in the nucleus and S is the number of core electrons, or is the number of all the electrons but the valence electrons.  v  For Example: Sodium (Na) Zeff = Z - S        Sodium has 11 protons inside the nucleus. It has 11 electrons but only 10 are core electrons (the other electron is a valence electron) Therefore Z eff = 11 – 10. This makes the Z eff equals to +1.  §  __Trend:__ 1) Since the core electrons increase going across a period, the nuclear pull increases as we more left to right across the period.  2) Since the core electrons increase going down a group, the nuclear pull decreases as we go down a group.  §  __Definition:__ The size of an atom.  §  __Trends:__ 1) Since nuclear pull increases across a period, atomic radius decreases as we move from left to right across a period. With more nuclear pull, the nucleus pulls the electrons towards it more, causing the atomic radius to decrease.     2) Since the nuclear pull decreases as we go down, the atomic radius increases down the group. Since there are more core electrons, there is barely and effect from the nuclear pull on the outer shells, causing the atomic radius to increase.  §  __Definition:__ The minimum energy required to remove an electron from a gaseous atom in its ground state.  §  __Trends:__ 1) across a period, Ionization energy increases going from left to right.    2) Within a group, Ionization energy decreases going from up to down. 4 . Electron Affinity:  §  __Definition:__ The negative of the energy charge that occurs when an electron is accepted by an atom to form an anion.  §  __Trends:__ 1) Across a period, electron affinity increases going from left to right.    2) Within a group, Electron Affinity decreases going from up to down. 5. Electronegativity:  §  __Definition:__ A measure of the ability of an atom that is bonded to another atom to attract electrons to itself.  §  __Trends:__ 1) Across a period, electronegativity increases going from left to right.    2) Within a group, electronegativity decreases going from up to down. 
 *  1.    **  The Effective Nuclear charge ( Zeff ) :
 *  2.    **  Atomic Radius:
 *  3.    **  Ionization Energy:
 * i.  The first ionization energy is the amount of energy needed to remove the first electron from an atom.  **
 * ii.  The second ionization energy is the amount of energy needed to remove the second electron from an atom.  **
 * iii.  The greater the ionization energy, the harder it is to remove an electron.  **