Encyclopedic Guide to the Periodic Table of Elements

Components of an Element Entry

Each entry in the periodic table provides four essential data points for an element:

• Atomic Number: Located at the top of the entry, representing the number of protons (e.g., $11$ for Sodium).

• Element Symbol: A one or two-letter abbreviation (e.g., $Na$ for Sodium).

• Element Name: The full name of the element (e.g., Sodium).

• Atomic Weight: Typically located at the bottom of the entry, representing the relative atomic mass (e.g., $22.990$ for Sodium).

Classification and Groups

The table is organized into vertical columns called groups (labeled $1A$ through $8A$ and $1B$ through $8B$) and horizontal rows called periods ($1$ through $7$). Elements are categorized into chemical series based on shared properties:

• Alkalai metals: Found in group $1A$ (excluding Hydrogen).

• Alkaline earth metals: Found in group $2A$.

• Transition metals: Found in the central block, groups $3B$ through $2B$.

• Post-transition metals: Located between transition metals and metalloids.

• Metalloids: Elements with properties intermediate between metals and nonmetals.

• Other nonmetals: Found to the right of the table.

• Halogens: Found in group $7A$.

• Noble gases: Found in group $8A$.

• Lanthanides: A subset of metals traditionally placed below the main table.

• Actinides: A subset of radioactive metals traditionally placed below the main table.

• Unknown properties: Elements whose chemical properties have not yet been fully characterized.

Period 1 Elements

• Hydrogen (H): Atomic number $1$, Atomic weight $1.0078$. Category: Other nonmetals.

• Helium (He): Atomic number $2$, Atomic weight $4.0026$. Category: Noble gases.

Period 2 Elements

• Lithium (Li): Atomic number $3$, Atomic weight $6.938$. Category: Alkalai metals.

• Beryllium (Be): Atomic number $4$, Atomic weight $9.0122$. Category: Alkaline earth metals.

• Boron (B): Atomic number $5$, Atomic weight $10.806$. Category: Metalloids.

• Carbon (C): Atomic number $6$, Atomic weight $12.009$. Category: Other nonmetals.

• Nitrogen (N): Atomic number $7$, Atomic weight $14.006$. Category: Other nonmetals.

• Oxygen (O): Atomic number $8$, Atomic weight $15.999$. Category: Other nonmetals.

• Fluorine (F): Atomic number $9$, Atomic weight $18.998$. Category: Halogens.

• Neon (Ne): Atomic number $10$, Atomic weight $20.180$. Category: Noble gases.

Period 3 Elements

• Sodium (Na): Atomic number $11$, Atomic weight $22.990$. Category: Alkalai metals.

• Magnesium (Mg): Atomic number $12$, Atomic weight $24.305$. Category: Alkaline earth metals.

• Aluminum (Al): Atomic number $13$, Atomic weight $26.982$. Category: Post-transition metals.

• Silicon (Si): Atomic number $14$, Atomic weight $28.084$. Category: Metalloids.

• Phosphorus (P): Atomic number $15$, Atomic weight $30.974$. Category: Other nonmetals.

• Sulfur (S): Atomic number $16$, Atomic weight $32.059$. Category: Other nonmetals.

• Chlorine (Cl): Atomic number $17$, Atomic weight $35.446$. Category: Halogens.

• Argon (Ar): Atomic number $18$, Atomic weight $39.948$. Category: Noble gases.

Period 4 Elements

• Potassium (K): Atomic number $19$, Atomic weight $39.098$. Category: Alkalai metals.

• Calcium (Ca): Atomic number $20$, Atomic weight $40.078$. Category: Alkaline earth metals.

• Scandium (Sc): Atomic number $21$, Atomic weight $44.956$. Category: Transition metals.

• Titanium (Ti): Atomic number $22$, Atomic weight $47.867$. Category: Transition metals.

• Vanadium (V): Atomic number $23$, Atomic weight $50.942$. Category: Transition metals.

• Chromium (Cr): Atomic number $24$, Atomic weight $51.996$. Category: Transition metals.

• Manganese (Mn): Atomic number $25$, Atomic weight $54.938$. Category: Transition metals.

• Iron (Fe): Atomic number $26$, Atomic weight $55.845$. Category: Transition metals.

• Cobalt (Co): Atomic number $27$, Atomic weight $58.933$. Category: Transition metals.

• Nickel (Ni): Atomic number $28$, Atomic weight $58.693$. Category: Transition metals.

• Copper (Cu): Atomic number $29$, Atomic weight $63.546$. Category: Transition metals.

• Zinc (Zn): Atomic number $30$, Atomic weight $65.38$. Category: Transition metals.

• Gallium (Ga): Atomic number $31$, Atomic weight $69.723$. Category: Post-transition metals.

• Germanium (Ge): Atomic number $32$, Atomic weight $72.63$. Category: Metalloids.

• Arsenic (As): Atomic number $33$, Atomic weight $74.922$. Category: Metalloids.

• Selenium (Se): Atomic number $34$, Atomic weight $78.96$. Category: Other nonmetals.

• Bromine (Br): Atomic number $35$, Atomic weight $79.904$. Category: Halogens.

• Krypton (Kr): Atomic number $36$, Atomic weight $83.798$. Category: Noble gases.

Period 5 Elements

• Rubidium (Rb): Atomic number $37$, Atomic weight $85.468$. Category: Alkalai metals.

• Strontium (Sr): Atomic number $38$, Atomic weight $87.62$. Category: Alkaline earth metals.

• Yttrium (Y): Atomic number $39$, Atomic weight $88.906$. Category: Transition metals.

• Zirconium (Zr): Atomic number $40$, Atomic weight $91.224$. Category: Transition metals.

• Niobium (Nb): Atomic number $41$, Atomic weight $92.906$. Category: Transition metals.

• Molybdenum (Mo): Atomic number $42$, Atomic weight $95.96$. Category: Transition metals.

• Technetium (Tc): Atomic number $43$, Atomic weight $98.9062$. Category: Transition metals.

• Ruthenium (Ru): Atomic number $44$, Atomic weight $101.07$. Category: Transition metals.

• Rhodium (Rh): Atomic number $45$, Atomic weight $102.91$. Category: Transition metals.

• Palladium (Pd): Atomic number $46$, Atomic weight $106.42$. Category: Transition metals.

• Silver (Ag): Atomic number $47$, Atomic weight $107.87$. Category: Transition metals.

• Cadmium (Cd): Atomic number $48$, Atomic weight $112.41$. Category: Transition metals.

• Indium (In): Atomic number $49$, Atomic weight $114.82$. Category: Post-transition metals.

• Tin (Sn): Atomic number $50$, Atomic weight $118.71$. Category: Post-transition metals.

• Antimony (Sb): Atomic number $51$, Atomic weight $121.76$. Category: Metalloids.

• Tellurium (Te): Atomic number $52$, Atomic weight $127.60$. Category: Metalloids.

• Iodine (I): Atomic number $53$, Atomic weight $126.90$. Category: Halogens.

• Xenon (Xe): Atomic number $54$, Atomic weight $131.29$. Category: Noble gases.

Period 6 Elements

• Cesium (Cs): Atomic number $55$, Atomic weight $132.91$. Category: Alkalai metals.

• Barium (Ba): Atomic number $56$, Atomic weight $137.33$. Category: Alkaline earth metals.

• Hafnium (Hf): Atomic number $72$, Atomic weight $178.49$. Category: Transition metals. (Note: Elements 57-71 are the Lanthanides listed below).

• Tantalum (Ta): Atomic number $73$, Atomic weight $180.95$. Category: Transition metals.

• Tungsten (W): Atomic number $74$, Atomic weight $183.84$. Category: Transition metals.

• Rhenium (Re): Atomic number $75$, Atomic weight $186.21$. Category: Transition metals.

• Osmium (Os): Atomic number $76$, Atomic weight $190.23$. Category: Transition metals.

• Iridium (Ir): Atomic number $77$, Atomic weight $192.22$. Category: Transition metals.

• Platinum (Pt): Atomic number $78$, Atomic weight $195.08$. Category: Transition metals.

• Gold (Au): Atomic number $79$, Atomic weight $196.97$. Category: Transition metals.

• Mercury (Hg): Atomic number $80$, Atomic weight $200.59$. Category: Transition metals.

• Thallium (Tl): Atomic number $81$, Atomic weight $204.38$. Category: Post-transition metals.

• Lead (Pb): Atomic number $82$, Atomic weight $207.2$. Category: Post-transition metals.

• Bismuth (Bi): Atomic number $83$, Atomic weight $208.98$. Category: Post-transition metals.

• Polonium (Po): Atomic number $84$, Atomic weight $(209)$. Category: Metalloids.

• Astatine (At): Atomic number $85$, Atomic weight $(210)$. Category: Halogens.

• Radon (Rn): Atomic number $86$, Atomic weight $(222)$. Category: Noble gases.

Period 7 Elements

• Francium (Fr): Atomic number $87$, Atomic weight $(223)$. Category: Alkalai metals.

• Radium (Ra): Atomic number $88$, Atomic weight $(226)$. Category: Alkaline earth metals.

• Rutherfordium (Rf): Atomic number $104$, Atomic weight $(261)$. Category: Transition metals. (Note: Elements 89-103 are the Actinides listed below).

• Dubnium (Db): Atomic number $105$, Atomic weight $(262)$. Category: Transition metals.

• Seaborgium (Sg): Atomic number $106$, Atomic weight $(266)$. Category: Transition metals.

• Bohrium (Bh): Atomic number $107$, Atomic weight $(264)$. Category: Transition metals.

• Hassium (Hs): Atomic number $108$, Atomic weight $(269)$. Category: Transition metals.

• Meitnerium (Mt): Atomic number $109$, Atomic weight $(268)$. Category: Unknown properties.

• Damstadtium (Ds): Atomic number $110$, Atomic weight $(268)$. Category: Unknown properties.

• Roentgenium (Rg): Atomic number $111$, Atomic weight $(268)$. Category: Unknown properties.

• Copernicium (Cn): Atomic number $112$, Atomic weight $(268)$. Category: Unknown properties.

• Ununtrium (Uut): Atomic number $113$, Atomic weight $(268)$. Category: Unknown properties.

• Flerovium (Fl): Atomic number $114$, Atomic weight $(268)$. Category: Unknown properties.

• Ununpentium (Uup): Atomic number $115$, Atomic weight $(268)$. Category: Unknown properties.

• Livermorium (Lv): Atomic number $116$, Atomic weight $(268)$. Category: Unknown properties.

• Ununseptium (Uus): Atomic number $117$, Atomic weight $(268)$. Category: Unknown properties.

• Ununoctium (Uuo): Atomic number $118$, Atomic weight $(268)$. Category: Unknown properties.

Lanthanide Series

• Lanthanum (La): Atomic number $57$, Atomic weight $138.91$.

• Cerium (Ce): Atomic number $58$, Atomic weight $140.12$.

• Praseodymium (Pr): Atomic number $59$, Atomic weight $140.91$.

• Neodymium (Nd): Atomic number $60$, Atomic weight $144.24$.

• Promethium (Pm): Atomic number $61$, Atomic weight $(145)$.

• Samarium (Sm): Atomic number $62$, Atomic weight $150.36$.

• Europium (Eu): Atomic number $63$, Atomic weight $151.96$.

• Gadolinium (Gd): Atomic number $64$, Atomic weight $157.25$.

• Terbium (Tb): Atomic number $65$, Atomic weight $158.93$.

• Dysprosium (Dy): Atomic number $66$, Atomic weight $162.50$.

• Holmium (Ho): Atomic number $67$, Atomic weight $164.93$.

• Erbium (Er): Atomic number $68$, Atomic weight $167.26$.

• Thulium (Tm): Atomic number $69$, Atomic weight $168.93$.

• Ytterbium (Yb): Atomic number $70$, Atomic weight $173.04$.

• Lutetium (Lu): Atomic number $71$, Atomic weight $174.97$.

Actinide Series

• Actinium (Ac): Atomic number $89$, Atomic weight $(227)$.

• Thorium (Th): Atomic number $90$, Atomic weight $232.04$.

• Protactinium (Pa): Atomic number $91$, Atomic weight $231.04$.

• Uranium (U): Atomic number $92$, Atomic weight $238.03$.

• Neptunium (Np): Atomic number $93$, Atomic weight $(237)$.

• Plutonium (Pu): Atomic number $94$, Atomic weight $(244)$.

• Americium (Am): Atomic number $95$, Atomic weight $(243)$.

• Curium (Cm): Atomic number $96$, Atomic weight $(247)$.

• Berkelium (Bk): Atomic number $97$, Atomic weight $(247)$.

• Californium (Cf): Atomic number $98$, Atomic weight $(251)$.

• Einsteinium (Es): Atomic number $99$, Atomic weight $(252)$.

• Fermium (Fm): Atomic number $100$, Atomic weight $(257)$.

• Mendelevium (Md): Atomic number $101$, Atomic weight $(258)$.

• Nobelium (No): Atomic number $102$, Atomic weight $(259)$.

• Lawrencium (Lr): Atomic number $103$, Atomic weight $(262)$.