Download Trends on the Periodic Table

Trends on the Periodic Table
Trend 1: Atomic Radius
Group Trend: Moving down the group, the radius of the atom __________________. More shells
are added, so the outer shells are not pulled in so tightly.
Periodic Trend: moving from left to right across the periods, the radius ____________________.
Electrons are being added to the same shell and protons are being added to the nucleus. The
electrons get pulled in closer, therefore the radius decreases.
Trend 2: Ionization Energy
Ionization Energy: The energy that is required to overcome the attraction of nuclear charge and
remove an electron from a gaseous atom.
Ex. Na  Na+ + eGroup Trend: the first ionization energy ________________________ as we move down the
table. Size is increasing, so electrons are farther from the protons in the nucleus  easier to
remove the electrons, so lower ionization energy.
Periodic trend: I.E. _______________________ as we move left to right (more energy is
needed). The nuclear charge is increasing, therefore greater attraction to the nucleus by the
electrons, so the valence electrons are harder to pull off.
Trend Three: Electron Affinity
Electron Affinity: the energy that accompanies the addition of an electron to a gaseous atom; a
numerical value which dictates the relative ease in which an element gains an electron.
***most elements release (lose) energy when they gain an electron, so most EA are negative
ex.
F(g) + e-  F-(g) + 328 kJ
Be (g)  e- + 240 kJ  Be- (g)
EA = -328 kJ/mol
EA = +240 kJ/mol
Periodic Trend: EA ______________ as we move left to right (# gets more negative)  atom gets
smaller with a larger (+) nuclear charge
Group trend: EA __________________ as we move down the table (# gets more positive) 
shell is farther from nucleus
Trend 4: Electronegativity
Electronegativity: the tendency for an atom to attract electrons to itself when it is chemically
combined to another element. Measured arbitrarily on the Pauling electronegativity scale ***not
as regular in transition metals
Cs / Fr – least electronegative (0.7)
F – most electronegative – really attracts electrons to become negative (4.0)
Periodic trend - _______________ left to right
Group trend - _________________top to bottom
Practice Problems
3. Explain why fluorine has a smaller atomic radius than both oxygen and chlorine.
4. In general, would you expect nonmetals to have larger electron affinities than metals? Why or
why not?
5. Which of these elements has a larger ionization energy?
a) sodium or potassium b) magnesium or phosphorous
7. What criterion did Mendeleev use in arranging his periodic table? What criterion was used in
constructing the modern periodic table?
8. What is the periodic law?
9. How do the terms group and period relate to the periodic table?
10. What are the representative elements, the transition elements and the inner transition
elements?
11. Which of the following are representative elements? Na, Mg, Fe, Ni, Cl
16. Arrange these elements in order of increasing atomic size: Sulfur, chlorine, aluminum, and
sodium. Does you arrangement demonstrate a periodic or group trend?
17. In general, would you expect metals or nonmetals to have higher ionization energies? Why?
18. Arrange the following in order of increasing ionization energy:
a) Be, Mg, Sr
b) Bi, Cs, Ba
c) Na, Al, S
19. Would you expect the noble gas neon to have a negative electron affinity? Explain your
answer.
20. In each pair, which element is more electronegative?
a) chlorine, fluorine
b) carbon, nitrogen c) magnesium, neon
d) arsenic, calcium