There are many tiny pieces in our world. Some pieces live in a row. Eight special pieces are in this row. They help make things like salt and sand. They help us every day. Can you find them?
Eight special pieces live in one row.
They are found in nature. Some are metals. Metals can be shiny and soft.
Other pieces are not metals. Some help make sand and glass. Some help make food for plants.
One piece is bright yellow. It is called sulfur. These pieces are all very useful. They help make our world work.
The periodic table is a map of all elements. It uses rows to show how elements act. The third row is called the third period. This row has eight elements in it.
First are sodium and magnesium. These are metals. Sodium is soft and silvery. It is found in rock salt. Magnesium is very common in the Earth. It is the fourth most common element in our planet.
Next are aluminium, silicon, phosphorus, sulfur, chlorine, and argon. Aluminium is a light metal. It is used to build planes. Silicon is a metalloid. This means it is between a metal and a nonmetal. It is used to make computer chips.
Phosphorus is a nonmetal. It is used in many fertilizers to help plants grow. Sulfur is a bright yellow solid. It is also used in fertilizers. Chlorine is a strong element. It is part of the salt we eat.
All eight elements are found in nature. They all have at least one stable isotope. An isotope is a version of an element. These elements help make our world work every day.
The periodic table is a map of all the building blocks in our world. It uses rows to show how different elements act. The third row is called the third period. This period contains eight specific elements. These elements follow a pattern as they grow. They belong to different groups called blocks. The first two elements are in the s-block. The other six elements belong to the p-block.
These elements work by filling up their electron shells. In science, we say they fill the third shell. They fill parts called the 3s and 3p subshells. This happens in a very specific order. This order follows a rule called the Aufbau principle. Because of this, these elements act like the elements in the second row. They follow the octet rule to stay stable. This rule helps them decide how to bond with others.
Many people discovered these elements over a long time. Humphry Davy first isolated sodium in the year 1807. He used a process called electrolysis. Silicon was first prepared in a pure form in 1824. Its name was changed in 1831 to match other elements. Phosphorus was first produced in 1669 as white phosphorus. It was named after a Greek word for a light-bearer. Carl Wilhelm Scheele studied chlorine gas in 1774.
Each element has its own special numbers and places. Sodium is found in many minerals like rock salt. Magnesium is the eighth most common element in the Earth's crust. It makes up about 13% of the planet's mass. Aluminium is the most abundant metal in the Earth's crust. It makes up about 8% of the Earth's solid surface. Silicon is the second most common element in the crust. It makes up about 28% of the crust by mass.
You can see these elements in your life every day. Sodium chloride is the salt you use on food. Magnesium is used to make strong, light metals for planes. Aluminium is used to build parts for the aerospace industry. Silicon is used to make the chips in computers. Phosphorus is used in many fertilizers to help plants. Sulfur is used in matches and even in some soaps. Chlorine is part of the salt we eat.
A period 3 element is a chemical element located in the third horizontal row of the periodic table. This row is officially called a period. The periodic table is organized into rows to show recurring trends in how elements behave. As the atomic number of an element increases, its chemical properties follow a predictable pattern. When these behaviors begin to repeat, a new row starts. This organization ensures that elements with similar characteristics fall into the same vertical columns. The third period contains exactly eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon.
To understand how these elements work, we must look at their atomic structure. In quantum mechanics, these elements correspond to the buildup of electrons in the third electron shell. Specifically, the electrons fill the 3s and 3p subshells. There is also a 3d subshell, but the Aufbau principle dictates that it is not filled until period 4. Because of this specific filling order, all eight elements act as analogs to the elements in period 2. They generally follow the octet rule, which describes how atoms seek a stable arrangement of eight electrons.
The elements in this period are categorized into different groups known as blocks. The first two elements, sodium and magnesium, belong to the s-block. The remaining six elements belong to the p-block. Sodium is a highly reactive, silvery-white metal and a member of the alkali metals. Magnesium is an alkaline earth metal. Aluminium is a p-block metal and a member of the boron group. Silicon is classified as a metalloid, meaning it has properties of both metals and nonmetals. Phosphorus and sulfur are nonmetals, while chlorine is a halogen. Argon is a noble gas.
History shows how humans gradually identified and isolated these substances. In 1807, Humphry Davy first isolated elemental sodium through the electrolysis of sodium hydroxide. Phosphorus was produced much earlier, in 1669, in the form of white phosphorus. Its name comes from a Greek word meaning "light-bearer." Silicon was prepared in pure form in 1824. While it was initially named silicium, its name was changed in 1831 to reflect its similarity to carbon and boron. In 1774, Carl Wilhelm Scheele characterized chlorine gas, though he initially thought it contained oxygen.
These elements are incredibly significant due to their massive presence in our world. Magnesium is the fourth most common element in the Earth as a whole, making up 13% of the planet's mass. Aluminium is the most abundant metal in the Earth's crust, accounting for about 8% of the solid surface by weight. Silicon is the second most abundant element in the crust, comprising about 28% of its mass. Even in space, silicon is the eighth most common element by mass. These numbers show how fundamental period 3 elements are to the structure of our planet and the universe.
Each element provides unique materials for modern life. Magnesium is used to create "magnalium," an alloy that is light and strong for transportation. Aluminium is vital to the aerospace industry because of its low density and resistance to corrosion through passivation. Silicon is the foundation of modern technology, as highly purified silicon is used in semiconductor electronics and integrated circuits. Phosphorus is used extensively in fertilizers to support plant growth. Sulfur is a key ingredient in making sulfuric acid and is used in matches and insecticides.
Finally, these elements connect to many different scientific and industrial systems. The study of these elements links chemistry to geology, as many are found in minerals like feldspars or bauxite. They also connect to biology, as sodium and magnesium ions are essential in Earth's waters and biological processes. The chemical behavior of sulfur and chlorine connects to industrial manufacturing and even the way we sense odors. From the massive scale of a supernova star creating magnesium to the tiny circuits in a computer, period 3 elements bridge the gap between the cosmos and everyday technology.
Where will your curiosity go next?
More to explore
✨ What else?
Related topics you might enjoy
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.