Periodic Table and Its Concept

Key Concepts

• Elements
• Periodic Table
• Groups
• Periods

The Periodic Table 

What is an element? 

An element is a pure substance that is made up of only one kind of atom and it is a pure substance that cannot be broken down or separated into simpler substances because each element is made of only one kind of atom.  

Elements can be found in the objects we use, like our pencils, coins, and portable music players. The magnets that help to convert the electric signal to sound are made of three different elements: iron, boron, and neodymium.  

The Periodic Table: 

When chemists began looking for a way to organize the elements, they started to think of some questions like: 

• The element which have similar properties can be grouped together?  
• What sort of properties could be used?  

In 1867, a Russian chemist and teacher, Dmitri Mendeleev, wrote down properties he thought were important, such as density, color, melting point, and boiling point. Then he sorted and re-sorted the cards into rows and columns until he found a pattern. 

Many scientists were trying to organize the elements into a table, but Mendeleev’s special insight was that there needed to be holes in the table—places left for elements that had yet to be discovered. From the placement of the holes and the properties of the surrounding elements, Mendeleev was able to predict the properties of elements that were later discovered.  

We use Mendeleev’s table today, but we call it the periodic table. The periodic table is a chart that organizes the elements according to their physical and chemical properties. There are many versions of the periodic table, each of which includes different sets of information. Most versions include each element’s name, symbol, atomic number, and atomic mass. 

• The atomic number equals the number of protons in the nucleus of each atom of an element. It is always a whole number. The atomic number also represents the mass of the protons measured in atomic mass units (amu). 
• The atomic number for any atom also equals the number of electrons surrounding the nucleus of each atom of an element. All atoms are neutral in charge, so the number of positive charges (protons) equals the number of negative charges (electrons). 
• Atomic numbers increase one by one through the periodic table.  

• Atomic mass is the average mass of the atoms of an element. It is written as a decimal number and is also measured in amu. 
• The mass number is the number of protons and neutrons in an atom of an element.  The number of neutrons in an atom can be calculated from the mass number and the atomic number: 

number of neutrons = mass number – atomic number 

• Atomic mass and mass number tend to increase along with the atomic number. There are some exceptions, such as between cobalt and nickel. 

The Periodic table contains tiles like the ones shown above. The tile contains the atomic number on the top right corner. Atomic mass on the top left corner. The chemical name and the chemical symbol on the middle of the tile. The rows of the periodic table are called the periods, and the columns are called the groups. 

In the periodic table, elements belonging to the same period have the same number of shells for electrons. Elements belonging to the same group have the same number of electrons in their outermost orbit. The properties of the elements present in the same group are mostly similar and some other properties of elements in the same period are similar as well. 

Summary

• The element is the combination of the one and only one atom.
• The arrangement of the elements based on their properties is called the periodic table.
• The modern periodic table contains the elements based on the atomic number.