The Periodic Table

01 Why It Works

Elements are arranged by atomic number (number of protons). Elements in the same column (group) share similar chemical properties because they have the same number of electrons in their outermost shell. Mendeleev predicted undiscovered elements by leaving gaps - and he was proved right.

02 Periods and Groups

Rows are called periods. Moving left to right across a period, atoms get more protons and electrons. Columns are groups. Group 1 (alkali metals) all react violently with water. Group 18 (noble gases) are all inert. Group 17 (halogens) are all reactive non-metals.

03 Trends

Atomic radius decreases left to right (more protons pull electrons closer). Ionisation energy increases left to right and up to down. Electronegativity peaks at fluorine. These trends explain almost every chemical reaction.

04 Key Facts

→The periodic table has predicted 9 elements before they were discovered.

→Element 43 (Technetium) was the first artificially produced element.

→The longest element name is "Ununennium" (predicted element 119).

🔗 Nuclear Connection

Chemistry and nuclear physics are deeply intertwined. Explore the nuclear side of ChemHub's parent site:

☢️ Nuclear Elements 🏥 Radiation & Health 🔋 Fuel Cycle