This document summarizes periodic trends among elements. It describes how nuclear charge shielding increases down groups but is constant across periods. Atomic radius decreases across periods as more protons attract electrons closer, but increases down groups as electrons are farther from the nucleus. Ionization energy increases across periods as more protons hold onto electrons, but decreases down groups as outer electrons are easier to remove. Electronegativity generally increases across periods as additional protons pull electrons closer, but decreases down groups due to increased shielding blocking the proton pull.

1. Section 3:Periodic Trends

2.  Describe trends among elements for
shielding of nuclear charge;
 Describe trends among elements for atomic
size;
 Explain how ions form;
 Define ionization energy;
 Describe trends among elements for
ionization energy and ionic radius;
 Define electronegativity; and
 Describe trends among elements for
electronegativity

3.  Electrons (e-) are attracted to protons (p+)
 Trends relate to how those added protons
and electrons interact
 As you add 2nd p+ and e-, not much between
them
 Adding e- to 2nd energy level, have inner e-
shielding charge of added p+
 As you move across the table, added e-
experience same level of shielding

4. Nuclear
Charge
Shielding
Increases (adding protons)
Constant ( e- get same view of nucleus)
Increases(addingprotons
Increases(morelevels)

5.  Atomic radius: half of distance between
nuclei of two atoms of the same element
when the atoms are joined
 General trend:
 Increases down a group
 Decreases across a period

7. Atomic
Radius
Decreases (shielding constant, so p+suck in e-)
Increases(levelswin)

8.  Ion: atom or group of atoms that has a
charge
 Cation: Ion with a positive charge

9.  Ion: atom or group of atoms that has a
charge
 Cation: Ion with a positive charge
 Anion: ion with a negative charge

10.  Cations always smaller than
neutral atom
◦ Lose one e-
◦ More protons, suck in remaining
electrons
 Anions always bigger than
neutral atom
◦ One extra e-
◦ Not as much positive charge to go
around

11.  Ionization energy: energy required to
remove an electron from an atom in its
gaseous state
 Generally increases across periods
◦ Shielding constant
◦ Increased nuclear charge holds onto electrons
◦ As get closer to nonmetals, rather gain than lose
 Generally decreases down groups
◦ Valence electrons further from nucleus
◦ Easier to pull off

13. Ionization
Energy
Increases (shielding constant, p+hold onto e-)
Decreases(further
away,easiertolose)

14.  Electronegativity: ability of an atom to attract
electrons when in a compound
 Cs least electronegative element
◦ Lowest ionization energy
◦ Loses electrons easily, doesn’t attract them
 •F most electronegative element

15. Electro-
negativity
Increases (extra protons pull on electrons)
Decreases(Shielding
blockspull)

16. Electronegativity
Ionization Energy
Increases
Increases
Decrease
Increases
Constant
Decreases
Decreases
increases
Increases
Increases
Atomic Radius
Nuclear Charge
Shielding

17.  Describe trends among elements for
shielding of nuclear charge?
 Describe trends among elements for atomic
size;
 Explain how ions form?
 Define ionization energy?
 Describe trends among elements for
ionization energy and ionic radius?
 Define electronegativity?
 Describe trends among elements for
electronegativity?