It is a big difference between the properties of reactants and products; an element is not a compound.
Elements.
This is called a compound.
The entire range of chemical compounds available in the universe
Compounds cannot be separated by physical means while elements are made up of only one kind of matter.
Non-metals and Metalloids
Diamond is a compound of carbon and does not combine, except minutely with other elements. Other elements can give diamond a subtle colour.
If elements did not combine then life would not exist. The would be no compounds or mixtures of any kind. Chemical and nuclear reactions would not take place. All bodies in the universe could consist of a single type of element.
If the elements (which were discovered by his time) were organized in the increasing order of their atomic weight, they will exhibit an apparent periodicity of properties. It also had the ability to predict physical and chemical properties of some undiscovered elements.
For example very rare radioactive chemical elements.
it is called a pure substance
because a group of elements in the periodic table behave in a single manner.they have a similar kind of physical properties,i can't surely tell about the chemical properties but in some exceptions these chemical properties are also same.
An element is a material that has only one kind of atom. For example- hydrogen is an element- it has only hydrogen atoms. Another element is oxygen- it has only oxygen atoms. But if we combine the two elements together, add a spark, we have a bang- and we now have a compound- water. Compounds are 2 or more elements that combine chemically.