Answer: Number of valence electrons.
- A Number of valence electrons
- B Atomic mass in most textbook accounts
- C Number of neutrons during normal conditions
- D Atomic radius as generally observed
Correct answer: A. Number of valence electrons
Explanation: Elements in the same group have the same number of valence electrons, giving them similar chemical properties.
The complete modern periodic table (118 elements). Image: Cepheus et al., Public Domain, via Wikimedia Commons.
Concept context
The periodic table organises all 118 elements by atomic number and similar properties. Study periodic trends like atomic radius, ionization energy, and electronegativity, and learn how an element's position predicts its behaviour.
Read the full Classification of Elements and Periodicity in Properties notes →