Atomic Radius - Properties of the Elements

Introduction - Look for patterns in the following three graphs with respect to atomic number and family in light of information in the periodic table. Record your observations in the quickwrite.

Deduction is the process of drawing a conclusion from available information While inductive reasoning allows you to learn something new about the world; deductive reasoning allows you to apply what you have learned.

Example of a deductive argument:

All noble gasses are stable.

Neon is a noble gas.

Therefore, neon is stable.

      • The first premise (all noble gasses are stable) is the result of inductive reasoning.
      • The second premise (neon is a noble gas ) identifies a specific member of that group (neon).
      • The conclusion then applies the knowledge about the quality that the group shares to the individual member (or instance) identified.
      • Considering the information given in the the premises, the conclusion is valid. No other conclusion can be drawn based on the premises given (lines 1 and 2).

Sample Deductive Reasoning Activity

Task: Plot Atomic Radius vs. Atomic Number using deductive reasoning


(1) the radius is dependent upon outermost electrons

(2) the nucleus is positive

(3) electrons are negative

(4) opposites attract

(5) electrons can occupy only specific energy levels

Based upon this, we can assume that atomic radius increases within a family and deacreases within a period.

Deductive task

Plot the relative first ionization energy as a function of atomic number for the first 3-5 periods on graph paper.


Get free graph paper

Additional activity: Find the missing elements