1 Periodic Trends

2 Early Design Changes developed by Dmitri Mendeleev in the mid- 1800s –Organized elements by mass into rows and columns –Found elements in the same column had similar properties Columns called –Groups or Families

3 Electron Configurations Horizontal rows called periods Elements now arranged by atomic number (not mass) Elements in the same group have similar electron configurations –1 st family all end in s 1 –2 nd group all end in s 2 Etc.

4 Atomic Radius TrendsAtoms on the left of a period are bigger than atoms on the right. Why? –Electrons in same energy level –Elements gain a proton each step to the right More protons = more positive charge = closer electrons

5 Atoms at the bottom of the table are bigger than atoms at the top. Why? –Outermost electron level increases Electrons further away from nucleus An up/down move in the periodic table is a much more important change in atomic size than a left/right move.

6 Ionic Radius Ionic Radius Trends Ionic Radius Truths Distance from the nucleus to the outermost electron orbital Same periodic trends as neutral atoms Positive ions are always smaller than neutral atoms –Why? Less electrons than protons = greater pull toward nucleus

7 negative ions are always bigger than neutral atoms –Why? More electrons than protons = less pull toward nucleus

8 Ionization Energy Ionization Energy Trends The amount of energy required to remove an electron from an atom to make a positive ion. I.E. increases from left to right –Why? More protons = greater pull on the electrons I.E. Increases from bottom to top –Why? Electrons closer to the nucleus

9 Electronegativity Electronegativity Trends The tendency for atoms of an element to attract electrons when they are chemically bonded to atoms of another element. “How strongly they attract electrons” The same as Ionization energy