Electron configuration + Ions

• Electron distribution is the distribution of electrons of an atom, in their subsequent energy levels or electron shells
• Electrons in different shells have different energies, depending on their distance from the nucleus, and the shell they occupy
• A maximum of 2 electrons can fit in the first shell, 8 in the second, 8 (actually 18) in the third, and then any leftovers in the fourth shell. This pattern only works for the first 20 elements, after that it gets quantum mechanical
• An ion is a charged atom or molecule. It is charged because the number of electrons do not equal the number of protons in the atom or molecule.
• If an atom or molecule loses an electron, it gains a positive charge (cation)
• If an atom or molecule gains an electron, it gains a negative charge (anion)
• Valence electrons require the least amount of energy to be removed from the atom and are usually involved in chemical reactions and bonding
• What is the octet rule?


  Is the tendency of an atom to gain, lose, or share electrons in order to achieve eight electrons in their valence shell
• The octet rule: atoms with 3 or less electrons in their outer shell tend to lose electrons
• The octet rule: atoms with 5 or more electrons in their outer shell tend to gain electrons
• The octet rule: atoms with 4 electrons in their outer shell tend to share electrons
• In the periodic table, elements are arranged in order of increasing atomic number
• Main group elements are 1, 2, and 13 - 18
• For main group elements, the group number can be used to determine the number of valence electrons
• In groups 1 and 2, the number of valence electrons are equal to the group number
• In groups 13-18, the number of valence electrons is equal to the group number minus 10
• Elements in the same group, have the same number of valence electrons and thus have similar chemical properties
• The period number is equal to the number of occupied electron shells in an atom
• Atomic radius is the measure used for the size of atoms
• Atomic radius is affected by two factors, number of protons in the nucleus providing positive charge and the number of inner shell electrons "shielding" the valence electrons from the full attraction of the nucleus
• As we go down a group atomic radius increases, as we go across a period more protons are added causing atomic radius to decrease
• If given sufficient energy, electrostatic attraction between nucleus and valence electrons can overcome and valence electrons can be completely removed. This is called ionisation
• Valence electrons are removed first because they're the furthest electrons from the nucleus and more weakly held
• The magnitude of first ionisation energy reflects how strongly the valence electron is attracted to the nucleus, the stronger the attraction, the more energy required to remove it
• First ionisation energy increases left to right across a period