Periodic table patterns
Use atomic number to order elements. Periods are rows; groups are columns. This subset supports pattern-finding, not a complete periodic table.
How many protons does chlorine have?
Atomic number counts protons. For a neutral atom, electrons equal protons. Isotopes differ in neutron number; do not calculate neutron counts from this table because mass numbers are not supplied.
📝 Investigate
Find two elements in group 1: lithium and sodium. Find two noble gases in group 18: neon and argon. Elements in the same group often share chemical behavior because of outer-electron patterns, but this table alone does not establish reaction rates.
Compare sodium and neon: consecutive atomic numbers do not mean the same group. Crossing to a new period changes the row.
✅ Check your understanding
Which pair shares a group?
Can you infer an isotope’s neutron number from this table?
📝 Use the table to challenge a claim
A learner says argon has 18 neutrons because its atomic number is 18. Correct the claim. Then identify the group-1 element in period 3 and the number of electrons in its neutral atom.
🔑 Worked answer
18 is argon’s proton count; neutron count needs a mass number. The group-1 period-3 element is sodium: its atomic number is 11, so a neutral atom has 11 electrons.