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Understanding the Periodic Table
Groups (Columns)
Elements in the same group share similar chemical properties and have the same number of valence electrons. Groups are numbered 1-18.
- Group 1: Alkali Metals (highly reactive)
- Group 2: Alkaline Earth Metals
- Groups 3-12: Transition Metals
- Group 17: Halogens (very reactive nonmetals)
- Group 18: Noble Gases (inert)
Periods (Rows)
Elements in the same period have the same number of electron shells. Period number = number of electron shells.
Blocks (s, p, d, f)
Blocks indicate which orbital is being filled with electrons:
- s-block: Groups 1-2 (valence electrons in s orbital)
- p-block: Groups 13-18 (filling p orbitals)
- d-block: Groups 3-12 (transition metals, filling d orbitals)
- f-block: Lanthanides & Actinides (filling f orbitals)
Electron Configuration
Shows how electrons are distributed in atomic orbitals. Format: [Noble Gas] orbitalelectrons
- Example: Carbon = [He] 2s² 2p² (2 electrons in 2s, 2 in 2p)
- Aufbau Principle: Electrons fill lowest energy orbitals first
- Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
- Orbital Capacity: s=2, p=6, d=10, f=14 electrons
- Valence Electrons: Outermost shell electrons determine chemical properties
Oxidation States
The charge an atom would have if all bonds were ionic. Indicates electron loss/gain in compounds.
- Positive (+): Metals lose electrons (e.g., Na⁺, Ca²⁺, Fe³⁺)
- Negative (−): Nonmetals gain electrons (e.g., Cl⁻, O²⁻, N³⁻)
- Multiple States: Transition metals can have several (e.g., Fe: +2, +3)
- Group Patterns: Group 1=+1, Group 2=+2, Group 17=−1, Group 18=0
- Variable States: Allow formation of different compounds (FeCl₂ vs FeCl₃)
Periodic Trends
Electronegativity
Ability of an atom to attract electrons in a chemical bond (Pauling scale: 0.7-4.0).
- Increases →: Left to right across periods (more protons attract electrons)
- Decreases ↓: Top to bottom down groups (electrons farther from nucleus)
- Highest: Fluorine (3.98) - most electronegative element
- Lowest: Francium (0.7) - least electronegative
- Predicts Bonding: Large difference = ionic, small = covalent
Ionization Energy
Energy required to remove an electron from a gaseous atom (measured in kJ/mol).
- Increases →: Left to right across periods (stronger nuclear attraction)
- Decreases ↓: Top to bottom down groups (electrons farther, easier to remove)
- Highest: Helium (2372 kJ/mol) - hardest to ionize
- Lowest: Francium (380 kJ/mol) - easiest to ionize
- Noble Gases: Highest in each period (stable electron configuration)
Atomic Radius
Distance from nucleus to outermost electron shell (measured in picometers, pm).
- Decreases →: Left to right across periods (more protons pull electrons closer)
- Increases ↓: Top to bottom down groups (more electron shells added)
- Largest: Francium/Cesium (~298 pm) - most electron shells
- Smallest: Helium (31 pm) - only one electron shell
- Cations: Smaller than parent atom (lost electrons)
- Anions: Larger than parent atom (gained electrons)
Walter Russell's Spiral Periodic Table (1926-1953)
This revolutionary design shows elements arranged in 9 octaves following musical wave patterns, with noble gases at amplitude peaks and elements spiraling from hydrogen at the center outward.