LG: I can describe trends in the periodic table
and explain the reasons for these patterns
 Difficult to measure because outer edge of
atom is not strictly defined
 Determined by measuring the distance
between two nucleii and dividing by two
 Trends
 Increases from right  left
 Increases from top  bottom
 Every electron experiences a force of
attraction toward the nucleus, called the
effective nuclear charge.
 As you move down a group, we add energy
levels that are progressively further from the
nucleus
 Lower energy levels ‘shield’ outer electrons
from the pull of the nucleus
 Elements gain or lose electrons to form ions
 The ionic radius of an element is always
different than the atomic radius. In general:
 Metals lose electrons to
form smaller cations
 Nonmetals gain electrons to
form larger anions
 When an element loses electrons to obtain a
full valence shell the resulting ion is smaller
because:
 There are fewer electrons so each one experiences
a greater effective nuclear charge
 There is one less electron shell, so all electrons are
closer to nucleus
 When an element gains e-, there is a lower
effective nuclear charge
 I.E. is the energy required to remove a
valence e E.N. measures the tendency of an atom to
gain e I.E. and E.N. both increase from left  right
and from bottom  top
 I.E. and E.N. decrease from top  bottom
because valence e- are further from the
nucleus
 Electrons are easier to remove
 More difficult to attract e- from other atoms
 I.E. and E.N. increase from left  right
because there is a larger effective nuclear
charge
 Stronger hold on e Stronger pull on e- from other atoms
 Li, Na, K
 What happens when alkali metals are put in
water?
 Which one is the most reactive? Why?
 Video (Brainiac)
http://www.youtube.com/watch?v=m55kgyAp
YrY
 New Book: Pg. 41 #1 - 7, 10