Modern Periodic Table

Start with the Element Address

The modern periodic table is easiest to read as a seating chart. Each box is one element. The number that sets the seat order is called the atomic number, written as $Z$ , which is the number of protons in the atom's nucleus.

So, elements are not arranged by name or by the size of their symbols. They are arranged mainly by increasing $Z$ . Because the number of protons identifies the element, this order makes repeating chemical patterns visible.

Modern Periodic Table Pattern Model

Choose the part you want to read. Raised blocks show the main patterns: columns, rows, the middle region, lower series, metalloids, and noble gases.

In the main groups, elements in one column often have the same number of valence electrons. Hydrogen is in group $1$ because it has $1$ electron, but it does not behave exactly like the alkali metals.

MetalTransition metalMetalloidNonmetalNoble gasInner transition

Focus: A column with a similar outer pattern
Group: $1-18$
Period: $1-7$
Atomic number: $Z$

Two Directions to Read Fluently

A period is a horizontal row. Periods are read from left to right and numbered $1$ to $7$ . In the simple shell model, elements in the same period have the same number of main occupied shells.

A group is a vertical column. Groups are read from top to bottom and numbered $1$ to $18$ . In the main groups, the number of valence electrons is often the same, so chemical properties tend to be similar.

Elements in one group are not identical, but their outer features often follow a similar pattern. In chemistry, that outer feature is mainly the valence electrons.

Color Is a Clue, Not a Memorization Target

The periodic table also divides elements into regions.

Region	How to read it
Metals	Many are on the left and in the middle of the table. Many metals conduct electricity and tend to lose electrons when forming ions.
Nonmetals	Many are in the upper-right part of the table. Many nonmetals tend to gain or share electrons when bonding.
Metalloids	They sit at the boundary between metals and nonmetals. Their properties are in between, for example silicon can be used as a semiconductor.
Noble gases	They are in group $18$ . These elements are very unreactive because their outer electron arrangement is stable.

The metalloid boundary is not drawn exactly the same in every book because some elements sit in an overlapping property region. The important idea is the position: the transition area between metals and nonmetals.

Why Two Rows Sit Below

If the lanthanides and actinides were drawn in the middle of the main table, the periodic table would become very wide. They are usually moved below as a drawing choice that keeps the table readable, not because those elements are outside the periodic system.

Lanthanides are still part of period $6$ , while actinides are still part of period $7$ .

Check Patterns in the Periodic Table

Use the periodic-table model in the interactive card to check your own answers.

Question	Self-check
What group do $\mathrm{Mg}$ , $\mathrm{Ca}$ , and $\mathrm{Sr}$ share?	All three are in group $2$ .
Why are $\mathrm{Na}$ through $\mathrm{Ar}$ in period $3$ ?	In the simple shell model, their outer main shell is the $\mathrm{M}$ shell.
Why are $\mathrm{B}$ , $\mathrm{Si}$ , and $\mathrm{Ge}$ often discussed as metalloids?	They sit in the transition area between metals and nonmetals.
Why do main-group elements in one group often have similar chemical properties?	Their valence electrons are the same or follow a similar pattern, so their reactions are often similar too.

Modern element names and numbers can be checked in the iupac.org. A clear reference for periodic-table patterns is also available in openstax.org.