Periodic Trends What else could the periodic table possibly tell us???

Trends on the periodic table  There are already a few patterns that the periodic table has shown us that have been helpful so far: Families have number names that tell how many valence electrons they contain and help to figure out what ions they form Different sections of the periodic table represent the different orbitals Atomic number increases as you go from left to right and top to bottom

What else can the periodic table tell us???  There are a few more trends that we will now learn from looking at the periodic table: Atomic radius/atomic size Ionic radius/ionic size Ionization Energy Electronegativity/electron affinity

Atomic Radius  Atomic radius is the size of the atoms fuzzy cloud  Atomic size increases down a column because orbitals in higher principle energy levels have their electron clouds farther from the nucleus.  Atomic size decreases from left to right in the periodic table because the greater number of protons in the nucleus will exert a greater attraction on the electrons, pulling them closer to the nucleus.

Atomic Radius Picture

Atomic Radius

Atomic Radius Graph

Give it a try… WWhich of the following has the largest atomic radius? Ba or At C or Ge F or Fr

Ionic Size  Do atoms that form cations (positively charged ions) gain or lose electrons? They lose electrons…so who has more control, protons or electrons? The protons…that means that the remaining electrons are getting pulled towards the nucleus making the cation smaller than the atom!  Do atoms that form anions (negatively charged ions) gain or lose electrons? They gain electrons…so who has more control, protons or electrons? The electrons…that means that the remaining electrons are pulling outwards away from the nucleus making the anion larger than the atom!

Ionic Size

Give it a try!!! WWhich of the following is larger? Ca or Ca +2 I or I - Na + or Cl -

Shielding  As you add more and more electrons in more and more energy levels, the farther away those electrons get from the nucleus.  Those farthest electrons (the valence electrons) are getting blocked from the pull of the nucleus by all the other core electrons present.  Effectively, the core electrons are absorbing the “positiveness” of the nucleus so it doesn’t effect the valence electrons!

First Ionization Energy  First ionization energy is the amount of energy it takes to remove 1 electron from the outermost energy level (1 valence electron)  Second ionization energy is the amount of energy it takes to remove the 2 nd electron from the outermost energy level For example, lithium readily gives up it’s first valence electron (2s 1 ) to become like He so it has a low first I.E. Lithium holds on tight to it’s second electron (1s 2 ) though so it has a high second I.E.

What’s the Trend??  Ionization energy decreases down a group because the electrons in high quantum number orbitals are held less strongly by the nucleus than are electrons in low orbitals.  From left to right in a period, ionization energy increases the closer the element gets to a noble gas configuration.

Ionization Energy Picture

First ionization energy

First Ionization Graph

Give it a try!!! WWhich of the following has the largest first ionization energy? Cs or K B or C As or F DDoes calcium have a higher 1 st or 3 rd ionization energy?

Electronegativity  Electronegativity is the ability for atoms to draw electrons towards themselves. The higher the electronegativity the harder the atom pulls  It is also called electron affinity, or the desire for electrons

What’s the trend???  ELectronegativity decreases down a group because the larger the atomic size, the larger the fuzzy cloud, the farther away the nucleus is from the electrons it is trying to pull on  From left to right, electronegativity increases because the elements are closer and closer to behaving like noble gases. Also, the nucleus has more protons so it is able to pull on electrons harder.  Noble gases have NO electronegativity values

Electronegativity Picture

Electronegativity

Electronegativity Graph

Give it a try!!! WWhich of the following has the lowest electronegativity? Ne or Se Be or Ba Sr or Sn

Overall First Ionization Energy Atomic Radius Electronegativity