Periodic TrendsLG: I can describe trends in the

periodic table and explain the reasons for these patterns

Atomic RadiusDifficult to measure because outer

edge of atom is not strictly defined

Determined by measuring the distance between two nucleii and dividing by two

TrendsIncreases from right leftIncreases from top bottom

Explaining Trends in Atomic RadiusEvery 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

Ionic RadiusElements 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

Explaining Trends in Ionic RadiusWhen 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

Ionization Energy & ElectronegativityI.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

Explaining Trends in I.E. and E.N.I.E. and E.N. decrease from top bottom

because valence e- are further from the nucleus Electrons are easier to removeMore difficult to attract e- from other atoms

I.E. and E.N. increase from left right because there is a larger effective nuclear chargeStronger hold on e-Stronger pull on e- from other atoms

Demo: Alkali MetalsLi, 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=m55kgyApYrY

Homework

New Book: Pg. 41 #1 - 7, 10