The periodic table is a seating chart where elements in the same column act like family — they react in similar ways. Knowing an element's seat lets a chemist predict how it behaves before ever touching it.
A map of the elements
The periodic table arranges elements by increasing atomic number (number of protons). Columns are called groups and share similar chemical behavior because they have the same number of outer (valence) electrons. Rows are called periods, across which properties change gradually.
Group 1 metals (like sodium) have one valence electron and react vigorously; the Group 18 noble gases have full shells and are nearly inert.
Sodium (Na) and potassium (K) sit in the same group, so both are soft, reactive metals that form +1 ions.
- Locate fluorine (F) and chlorine (Cl) in the same group.
- Recall that same-group elements behave alike.
- Predict whether chlorine, like fluorine, readily gains one electron.
What you should see: Both are halogens with seven valence electrons, so chlorine — like fluorine — readily gains one electron to form a −1 ion.