I was recently discussing with my fellow tutors on what we thought was the most important discovery in our given fields. The math tutor said the number system was the most important discovery in her field, the physics tutor said the discovery of gravity was in his opinion the most important discovery in physics.  As each one was discussing what they felt was the most important discovery I was thinking about the different discoveries in chemistry and what I felt was the most important discovery of them all.  Finally, when my turn came I said that the periodic table was the most important discovery in chemistry.  The discussion ended there but I kept considering my response and why I felt it was the most important discovery in Chemistry and decided to write down what I thought so here it goes.

As mentioned in a previous blog post. The difference between Atoms, Elements, Molecules, Compounds, and Mixtures all the matter in the universe is made of tiny particles called atoms.  There are 92 different kinds of atoms in nature. These 92 different atoms, combine with one another to form different kinds of matter that we see in nature.
It was found difficult to list all these 92 different elements and remember them. So, the scientists created a table, which gives a unique place to the elements based on their properties. This table is called the periodic table.
The Periodic table is one of the most outstanding pieces of work in chemistry. The beauty and simplicity of the periodic table have always fascinated the scientific community.

What is The Periodic Table?

The Periodic table is the tabular arrangement of elements based on the increasing order of the atomic number.

The table is made of 7 rows and 18 columns in which elements are placed in increasing order of their atomic number. Each element

  • * Has a specific place in the table
  • * Has its name mentioned
  • * Is represented by a symbol
  • * Its atomic number and atomic mass mentioned

The periodic table has more than 92 elements!
Recall that, there are only 92 elements which are present in nature. But, the periodic table has 118 elements altogether. So where did these extra elements come from?
Out of this 118 elements, 92 are naturally occurring and rest were created in labs by scientists.  Hence, are artificial or man-made elements.  The naturally occurring elements start from element 1, Hydrogen which is the lightest element in nature, and end with the heaviest, Uranium.
How are elements arranged in the periodic table?

Elements in the periodic table are arranged based on their increasing order of atomic numbers. When you observe carefully, you notice that the numbers are continuous.

Observe that, the table consists of rows and columns. There are totally 7 rows and 18 columns in a periodic table.

The first row consists of two elements, hydrogen, and helium, with atomic numbers 1 and 2.

The second row consists of  8 elements, starting with lithium which has atomic number 3 and ending with Neon which has atomic number 10.

The third row has 8 elements, the fourth and fifth rows have 18 each, sixth and seventh have 32 elements in each of them.

What do the last two hanging out rows represented in the periodic table?

The last two rows are not separate rows but, they are the part of sixth and seventh rows. One of the reasons to keep them separate is that the periodic table becomes too big with these elements in 6th and 7th rows.
Further, the elements of these two rows have special physical and chemical properties from the rest of the elements in the row and hence form a separate group of elements called inner transition elements.

The Significance of rows and columns

The rows in the periodic table are called Periods. The atomic number of the elements increases as one moves along the period.
The columns of the periodic table are called Groups. The elements of a particular group form a family as they share common physical and chemical properties.  For example, the first group, except hydrogen, are together called Alkali metals.  The second group elements are alkaline earth metals.  The group 17 elements are halogens and group 18 elements are Noble gases.
Observe the diagonally placed, stair-step line that consists of elements  B, Si, Ge,  As, Sb, Te, and Po. This forms a special group, Metalloids or semimetals. These elements have the properties in between that of metals and non-metals.
On the left-hand side of this diagonal are the transition metals and on the right-hand side of it,  are the nonmetals.

The 6th row of elements starting from Lanthanum with atomic number 57 and ending with Lutetium of atomic number 71 are called Lanthanides.
Lanthanides occur together in ores, difficult to separate during extraction and hence was believed to occur rarely. Due to this, they were also called rare earth elements.
The 7th-row elements, starting from Actinium with atomic number 89 and ending with Lawrencium with atomic number 103, are called actinides.
Actinides are radioactive, electropositive, dense metals most of which readily combine with non-metals.

Special Case of Hydrogen
Recall that, the alkali metals do not include Hydrogen, though hydrogen belongs to group 1.  Though hydrogen is to the left of the metalloids, it is not a metal. It’s a gas.  Wondering why hydrogen is placed in that position?
The interesting fact is that hydrogen is not considered to belong to any group and is considered a group by itself. Its because hydrogen has some of the unique properties from the rest of the elements in the periodic table.

Here are some of the interesting facts about hydrogen :

  • 1. It’s the lightest element with atomic number 1
  • 2. 75% of the elemental mass of the universe is of hydrogen
  • 3. Plays a great role in powering stars and giant galaxies through fusion reactions
  • 4. Hydrogen is a supporter of combustion
  • 5. 75% of the gas in Sun is hydrogen

There are many such interesting things which one comes across when studying the periodic table.
The Periodic table gives information about the atomic number, atomic mass, their physical properties such as boiling point, malleability, ductility, conductivity, chemical properties such as reactivity, oxidation and reduction potentials, electronegativity and others.

The proper understanding of the periodic table is very necessary to understand Chemistry itself.  Hence, can be called as the foundation for learning chemistry and that is why in my opinion it is the most significant discovery in the field of Chemistry.

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