|Atomic Structure : Periodic Trends|
1) As you move down a group, atomic radius increases.
||WHY? - The number of energy levels increases as you move down a group as the number of electrons increases. Each subsequent energy level is further from the nucleus than the last. Therefore, the atomic radius increases as the group and energy levels increase.|
2) As you move across a period, atomic radius decreases.
1) Anions (negative ions) are larger than their respective atoms.
WHY?2) Cations (positive ions) are smaller than their respective atoms.
Electron-electron repulsion forces them to spread further apart.
Electrons outnumber protons; the protons cannot pull the extra electrons as tightly toward the nucleus.
WHY?First Ionization Energy
There is less electron-electron repulsion, so they can come closer together.
Protons outnumber electrons; the protons can pull the fewer electrons toward the nucleus more tightly.
If the electron that is lost is the only valence electron so that the electron configuration of the cation is like that of a noble gas, then an entire energy level is lost. In this case, the radius of the cation is much smaller than its respective atom.Definition: The energy required to remove the outermost (highest energy) electron from a neutral atom in its ground state.1) As you move down a group, first ionization energy decreases.
WHY?2) As you move across a period, first ionization energy increases.
Electrons are further from the nucleus and thus easier to remove the outermost one.
"SHIELDING" - Inner electrons at lower energy levels essentially block the protons' force of attraction toward the nucleus. It therefore becomes easier to remove the outer electronWHY? - As you move across a period, the atomic radius decreases, that is, the atom is smaller. The outer electrons are closer to the nucleus and more strongly attracted to the center. Therefore, it becomes more difficult to remove the outermost electron.Exceptions to First Ionization Energy Trends
||1) Xs2 > Xp1 e.g. 4Be
(See Hund's Rule)
Veiw a periodic table with first ionization energies.
Second and Higher Ionization EnergiesDefinition: Second Ionization Energy is the energy required to remove a second outermost electron from a ground state atom.
Subsequent ionization energies increase greatly once an ion has reached the state like that of a noble gas. In other words, it becomes extremely difficult to remove an electron from an atom once it loses enough electrons to lose an entire energy level so that its valence shell is filled.
2) As you move across a period, electron affinity increases.
Xp6 < 0: Stable atom with filled valence (outermost) shell.
Coulomb's Law - The force of attraction between oppositely charged particles is directly proportional to the product of the charges of the particles (q1 and q2) and inversely proportional to the square of the distance between the particles.
1) As you move down a group, lattice energy decreases.
with Halides (kJ/mol)
of OH- and O2- with Cations
of varying charge (kJ/mol)
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