The Periodic Table Is a Prediction Machine — Not Just a List

The periodic table does far more than list elements alphabetically. It is organized so that position predicts behavior. Every element in Group 1 (the alkali metals) reacts violently with water. Every element in Group 18 (the noble gases) is almost completely unreactive. You do not need to memorize these facts separately — the table’s structure tells you.

Dmitri Mendeleev published the first recognizable periodic table in 1869. His key insight was to arrange elements by atomic mass and leave gaps for elements not yet discovered. He correctly predicted the properties of gallium, scandium, and germanium before they were found. That predictive power is exactly why chemists still use the same organizational logic today, now updated to use atomic number instead of atomic mass.

The modern table has 118 confirmed elements. Elements 1-92 occur naturally; elements 93-118 are synthetic, created in particle accelerators. For most chemistry courses, you need to know elements 1-36 well and recognize the symbols of common metals and nonmetals beyond that range.

How to Read an Element Box: A Step-by-Step Guide That Most Textbooks Skip

Reading one element’s box correctly unlocks every calculation that follows. Here is the standard layout and what each number means.

  +---------------------------+
  |           26              |  <-- Atomic Number (protons)
  |           Fe              |  <-- Chemical Symbol
  |          Iron             |  <-- Element Name
  |          55.85            |  <-- Atomic Mass (amu)
  +---------------------------+

  Protons    = 26      (= atomic number)
  Electrons  = 26      (neutral atom)
  Neutrons   = 56 - 26 = 30  (mass number - atomic number)
  Group      = 8       (transition metal)
  Period     = 4
    

The 5 Steps to Read Any Element Box

1. Top number = Atomic Number. Count of protons. This never changes for a given element. Iron always has 26 protons.
2. Center letters = Chemical Symbol. One or two letters. First letter is always uppercase. Second (if present) is always lowercase. Fe, not FE or fe.
3. Full name. Printed below the symbol. Use it to confirm you have the right element, especially for symbols derived from Latin (Fe = Ferrum, Na = Natrium).
4. Bottom decimal = Atomic Mass. The weighted average mass across all stable isotopes, in atomic mass units (amu). Round it to the nearest whole number to get the mass number of the most common isotope.
5. Position = Group and Period. Count the column (1-18) for the group. Count the row (1-7) for the period. Both reveal electron configuration and chemical behavior.

Groups and Periods Explain Chemical Behavior — Here Is the Proof

Groups and periods are not arbitrary labels. They encode the electron configuration of every element, and electron configuration determines how elements react.

Periodic Trends: What Changes as You Move Across or Down the Table

Three Worked Examples That Show Exactly How to Solve Worksheet Problems

These examples mirror the problems in the worksheet below. Work through each one before attempting the practice problems.

Common Mistakes Students Make on Periodic Table Worksheets — and the Correct Approach

These errors appear on nearly every graded worksheet I have reviewed. Avoiding them is straightforward once you know what to watch for.

On-Page Practice Worksheet: 10 Problems, Easy to Hard

Use a periodic table to answer each question. Work through the problems in order — they progress from basic identification to applying periodic trends. Check your answers with the key below.

How to use this worksheet: Print the PDF (button above or below), work through all 10 problems without looking at the answer key, then self-check. For any problem you got wrong, re-read the relevant worked example above before moving on.

1. What is the chemical symbol for Gold?
2. What is the atomic number of Carbon?
3. Which element has the symbol "Na" and what group does it belong to?
4. How many protons does an atom of Oxygen have?
5. Name the element in Period 3, Group 17.
6. What is the atomic mass of Iron (Fe), rounded to the nearest whole number?
7. Is Silicon (Si) a metal, nonmetal, or metalloid?
8. Which element has atomic number 79, and what category does it belong to?
9. As you move left to right across Period 2, does atomic radius increase or decrease? Name one element from Period 2 to support your answer.
10. Arrange the following elements in order of increasing electronegativity: Na, Cl, F, O. Explain your reasoning using periodic trends.

Frequently Asked Questions About the Periodic Table