Elements and the Periodic Table
The periodic table can look like a wall of boxes, but it is really one of the most organized charts ever made. Once you see how it is arranged, it turns from a memorization nightmare into a map that predicts how elements behave. That is why test questions reward students who understand its layout rather than those who just memorize squares.
This lesson explains what an element is, how the table is organized, and what its rows and columns tell you.
An element is a pure substance made of only one kind of atom. The periodic table arranges all known elements by increasing atomic number. Vertical columns are called groups and hold elements with similar properties; horizontal rows are called periods. The table’s position tells you a lot about how an element will react.
What is an element?
An element cannot be broken down into a simpler substance by ordinary chemical means, because it is made of a single type of atom. Gold, oxygen, and carbon are elements. Each has a one- or two-letter symbol, like O for oxygen and Na for sodium, which comes in handy when writing chemical formulas.
There are about 118 known elements, and they are the building blocks of every material you will ever meet, from the air you breathe to the metal in your phone.
How is the table organized?
Elements are listed in order of increasing atomic number, the number of protons. Reading left to right and top to bottom, each element has one more proton than the last. This simple ordering produces a repeating, or periodic, pattern in properties, which is where the table gets its name.
The groups are the vertical columns. Elements in the same group have similar chemical behavior because they have the same number of outer electrons. The periods are the horizontal rows, and as you move across a period, the elements shift gradually from metals on the left to nonmetals on the right.
| Feature | Direction | What it means |
|---|---|---|
| Group | Vertical column | Similar properties, same outer electrons |
| Period | Horizontal row | Metals to nonmetals across the row |
Metals, nonmetals, and metalloids
Most elements are metals, found on the left and center. They tend to be shiny, conduct electricity, and bend without breaking. Nonmetals, on the upper right, are often dull and poor conductors. Between them sits a narrow staircase of metalloids that share traits of both, like silicon, which is why silicon is so useful in electronics.
Two groups are worth knowing by name. The far-right column holds the noble gases, which barely react at all because their outer electron shells are full. The far-left column holds the very reactive alkali metals, which react strongly with water.
Watch: A Short Video Lesson
FuseSchool walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for periodic-table questions
- Recall that elements are ordered by atomic number (protons).
- For similar properties, look up and down a group (column).
- For the metal-to-nonmetal trend, look across a period (row).
- Place the element: left and center are metals, upper right are nonmetals.
- Remember noble gases (far right) are unreactive; alkali metals (far left) are very reactive.
Practice questions
- What property increases as you read the table from left to right and top to bottom?
- Elements in the same vertical column are called a what?
- Where on the table are most metals found?
- Why are noble gases so unreactive?
- What is the symbol for sodium?
- True or false: elements in the same period have very similar chemical properties.
Answers:
- The atomic number (number of protons).
- A group.
- On the left and center of the table.
- Their outer electron shells are already full, so they have little tendency to react.
- Na.
- False. Similar properties run down groups (columns), not across periods.
Where this fits
The table is organized by atomic number, so it follows directly from atomic number, isotopes, and ions and from atoms and their parts. An element’s group predicts how it will bond, which sets up the study of bonding and molecules. Explore all topics on the ASVAB General Science Learning Hub.
Recommended Prep Books
These study guides and practice books help you keep building momentum as you prepare:
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