A chemical reaction expressed by writing the full names of reactants and products is called a word equation. For example:

Hydrogen + oxygen -----------> Water

Four factors that bring about a chemical change are:

> Heat                               > Catalyst
> Light                               > Solution
> Pressure                        > Electricity

In the modern periodic table, the physical & chemical properties of the elements are changed to the periodic function of their atomic numbers instead of atomic weight which solves the problem with isotopes. All isotopes of some element represented by the same atomic number. All the gaps of Mendeleev's periodic table are filled by discovering new elements. The column for inert gases was developed and all groups have sub-groups. In this way, the modern periodic table removes all the demerits of Mendeleev's periodic table.

The atomic weight of an element expressed in grams is called gram atomic weight.

The molecular weight of a substance expressed in grams is called molecular weight.

We know, the properties of f-block elements are similar to the transition metals of d-block, However, their last electron enters count f-orbital. So, f-block elements are kept separately below d-block elements or transitional elements. Hence, these elements are called inner transitional elements.

The 14 elements from cerium te lawrencium after lutetium are called lanthanides.
The elements from thorium to lawrencium after actinium are called actinides.

These elements are placed at the bottom of the periodic table because of their similar properties. Lanthanides are rare metals whereas actinides are artificial radioactive metals. They show similar properties to the transitional elements. So, they are placed separately below the transitional elements in blocks of the modem periodic table.