Periodic Trends in Chemistry

Study Notes

Periodic Trends

Dmitri Mendeleev organized the periodic table by increasing atomic mass.
Henry Mosely organized the periodic table by increasing atomic number.
Periodic Law: Elements arranged in order of increasing atomic number show a periodic recurrence of their properties.
Groups (columns) on the periodic table represent families of elements with similar properties.
Periods (rows) on the periodic table show elements with varying properties as you move across the row.
Alkali Metals (Group 1) are the most reactive.
Noble Gases (Group 18) are the least reactive.
Metals are located on the left side of the periodic table.
Metalloids are located along the staircase line.
Nonmetals are located on the right side of the periodic table.
Representative Elements are located in the s and p blocks.
Sub-levels have specific shapes:
- s: Sphere
- p: Dumbbell
- d: Clover
- f: Double Clover
Malleable means a substance can be hammered into shapes.
Ductile means a substance can be drawn into wires.
Brittle means a substance is hard but can break or shatter easily.
Coulomb's Law:
- Charge directly affects the force of attraction: Greater charge, greater force.
- Distance inversely affects the force of attraction: Greater distance, weaker force.
Electron Configuration describes the arrangement of electrons in an atom's sublevels.
- Nitrogen (N): 1s² 2s² 2p³
- Sodium (Na): 1s² 2s² 2p⁶ 3s¹
- Cobalt (Co): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷
- Sulfur (S): 1s² 2s² 2p⁶ 3s² 3p⁴
Atomic Radius is half the distance between the nuclei of two identical atoms.
Electronegativity measures an element’s tendency to attract electrons when chemically bonded.
Ionization Energy is the energy needed to remove an electron from a gaseous atom.
Removing a Second Electron: Requires more energy than removing the first.
Cations are positively charged ions.
Anions are negatively charged ions.

Periodic Trends in the Periodic Table

Atomic Radius: Increases down a group and decreases across a period (towards the right).
Ionization Energy: Decreases down a group and increases across a period (towards the right).
Electronegativity: Decreases down a group and increases across a period (towards the right).

Identifying Trends

Larger Atomic Radius:
- Ca (Calcium) is larger than Mg (Magnesium)
- Si (Silicon) is larger than N (Nitrogen)
- Br (Bromine) is larger than Ga (Gallium)
- P (Phosphorus) is larger than Rb (Rubidium)
Larger 1st Ionization Energy:
- S (Sulfur) is larger than O (Oxygen)
- F (Fluorine) is larger than K (Potassium)
- Cl (Chlorine) is larger than Al (Aluminum)
- Fe (Iron) is larger than Al (Aluminum)
Larger Electronegativity:
- In (Indium) is larger than B (Boron)
- Ga (Gallium) is larger than P (Phosphorus)
- Li (Lithium) is larger than K (Potassium)
- Al (Aluminum) is larger than N (Nitrogen)
Larger Atom/Ion:
- F^-1 (Fluoride ion) is larger than F (Fluorine atom)
- Mg (Magnesium atom) is larger than Mg⁺² (Magnesium ion)
- Cr⁺³ (Chromium(III) ion) is larger than Cr⁺² (Chromium(II) ion)
- P^-3 (Phosphide ion) is larger than P (Phosphorus atom)