Trends on the

Important Trends Atomic radius – distance from the nucleus to the edge of the electron cloud. How do you think it changes as you go across a period? Decreases due to increase in size of nucleus. As the nucleus gets bigger, it is able to pull electrons closer as they are same distance (energy level) How about down a family (group)? Increase due to additional energy levels. Adding layers of electrons makes radius increase.

Important Trends Electron Affinity – ability of an atom to attract additional electrons while bonded to another atom. How do you think it changes as you go across a period? Increases due to increase in size of nucleus. As the nucleus gets bigger, it is able to pull electrons closer. Makes them harder to take away and easier to attract additional electrons. How about down a family (group)? Decrease due to further distance of the electrons from the nucleus. Adding layers of electrons makes radius increase which decreases the pull of the nucleus on the valence electrons.

Important Trends 3. Ionization Energy – amount of energy needed to remove the most loosely held electron in an atom How do you think it changes as you go across a period? Increases due to increase in size of nucleus. As the nucleus gets bigger, it is able to pull electrons closer. Makes them harder to take away. How about down a family (group)? Decrease due to further distance of the electrons from the nucleus. Adding layers of electrons makes radius increase which decreases the pull of the nucleus on the valence electrons. The bigger the atom the easier to take away electrons.

Important Trends 4. Electronegitivity – Energy needed to attract a pair of electrons while bonding. How do you think it changes as you go across a period? Increases due to increase in size of nucleus. As the nucleus gets bigger, it is able to pull electrons closer. Makes them harder to take away. How about down a family (group)? Decrease due to further distance of the electrons from the nucleus. Adding layers of electrons makes radius increase which decreases the pull of the nucleus on the valence electrons. The bigger the atom the easier to take away electrons.

What is the most important factor in determining these trends? Size of the atom. The larger the atom the harder to hold electrons and attract additional electrons. This is called the shielding effect.

Problems Which has a larger atomic radius Ca or Cl? Which has a greater ionization energy Mn or As? Which has a larger electronegitivity I or Li? Which element is the most reactive metal? Why? Which element is the most reactive nonmetal? Why?