Pre-AP Chemistry
Periodic Trends
Essential Question
Describe the trends in properties of elements based on their position in
the periodic table.
Valence Electrons
●
●
●
The outermost electrons in an atom
Determine the Properties of an atom
Group matches the number of valence electrons
Ions
What charge of the atoms
when metals gain electrons?
●
●
●
Ions are formed when a neutral atoms gains or loses electrons
Metals LOSE valence electrons (cations)
- Positive charge
Non-metals GAIN electrons to achieve a full outer energy
level(anions)
-Negative charge
Trends in Atomic Size
●
●
What is ionization energy?
Atomic size is measure by atomic radius
-One half the distance the nuclei of 2 atom of the same element
In general, increases from top to bottom within a group and
decreases from left to right
Trends in Ionization Energy
What are the trends in
electronegativity?
●
Ionization Energy
-The energy required to remove an electron from an atom
● First ionization energy vs second vs third
●
Decrease from top to bottom
-More electrons “in the way” so the attractive force of the protons
in the nucleus os effectively smaller (shielding effect); not able to
hold onto the electrons as strongly
Increase left to right
-Greater pulling effect from the protons in the nucleus; holding
onto them tighter
●
Trends in Electronegativity
●
●
●
Summary
Electronegativity
-The ability of an atom of an atom of an element to attract
electrons when the atom is in a compound
-In general, EN values decrease from the top to bottom within a
group. Tend to increase from left to right across a period
Decrease from top to bottom
-More electrons in the way: harder to attract electrons
Increase from left to right
-More protons in the nucleus but the shielding effect remains the
same
The trends in atomic size increases from top to bottom and decreases
from left to right. The trends in ionization energy decrease from top to
bottom and increase from left to right. Finally the trends in
electronegativity is decreasing top to bottom and increasing from left to
right.