Definition: A trend is a pattern observed within the periodic table.
Direction of Trends:
Groups: Top to bottom.
Periods: Left to right.
Properties Discussed:
Atomic Radius
Ionization Energy
Electronegativity
Atomic Radius
Definition: The size of an atom, measured as the distance from the nucleus to the outermost electron in the electron cloud.
Trends:
Top to Bottom in a Group: Atomic radius increases due to the addition of more electron shells.
Left to Right in a Period: Atomic radius decreases as additional protons and electrons cause a greater attraction, pulling electrons closer to the nucleus.
Snowman Analogy: Helps to remember that atomic radius increases going down a group.
Smallest and Largest Atoms:
Smallest: Helium
Largest: Francium
Ionization Energy
Definition: The energy required to remove an electron from an atom.
Trends:
Left to Right in a Period: Ionization energy increases since smaller atoms hold electrons more tightly.
Top to Bottom in a Group: Ionization energy decreases because larger atoms have electrons further from the nucleus and more shielding.
Effect of Shielding: Inner electrons reduce the effective nuclear charge felt by outer electrons, making it easier to remove electrons from larger atoms.
Electronegativity
Definition: A measure of how strongly an atom attracts electrons.
Scale: Ranges from 0 to 4, with 4 being the highest attraction for electrons.
Trends:
Left to Right in a Period: Electronegativity increases as atoms become smaller and more capable of attracting electrons.
Top to Bottom in a Group: Electronegativity decreases as atomic size increases, making it harder to attract electrons.
Comparison:
High Electronegativity: Fluorine (3.98)
Low Electronegativity: Lithium (0.98)
Conclusion
Understanding periodic table trends is essential for comprehending the behavior of elements.
Most trends are influenced by the size of atoms and the distance between the nucleus and valence electrons.