Role of Molecules, Ions and Atoms as Building Blocks of Matter:

Atoms of most elements are not able to exist independently. They form molecules and ions. These molecules or ions aggregate in large numbers to form the matter that we can see, feel or touch.

What is the significance of Molecules as the Building Blocks of Matter?

• Meaning: A molecule is in general a group of two or more atoms that are chemically bonded together, i.e, tightly held together by attractive forces. 
• Definition: A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance.
• Atoms of the same element or of different elements can join together to form molecules.

What role do Molecules play as the Building Blocks of Matter?

• Molecules of elements and their singular Atom Structure: The molecules of an element are constituted by the same type of atoms. 
  • Molecules of many elements, such as argon (Ar), helium (He) etc. are made up of only one atom of that element. 
• Diatomic Molecules  and the Unique Case of Ozone (O3): In the case of nonmetals such as a molecule of oxygen consists of two atoms of oxygen and hence it is known as a diatomic molecule, O2 . 
  • If 3 atoms of oxygen unite into a molecule, we get ozone, O3 . 
• Concept of Atomicity: The number of atoms constituting a molecule is known as its atomicity. 
• Complexity of Metal and Carbon Molecules: Metals and some other elements, like carbon, do not have a simple structure but consist of a very large and indefinite number of atoms bonded together.

What are the fundamental Building Blocks of matter in molecules?

Meaning: Atoms of different elements join together in definite proportions to form molecules of compounds.

How Atoms, Molecules, and Ions shape the essence of building blocks of matter?

• Meaning: Compounds composed of metals and nonmetals contain charged species known as ions.
  • Ions may consist of a single charged atom or a group of atoms that have a net charge on them. 
• Ionic Charges: Anions and Cations in Sodium Chloride: It can be negatively or positively charged. 
  • A negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’. 
  • Example: Sodium Chloride (NaCl) contains positively charged sodium ions (Na+) and negatively charged chloride ions (Cl–). 

• Polyatomic Ion: Groups of Atoms with Electric Charges: A group of atoms carrying a charge is known as a polyatomic ion.

Chemical Formulae: Valency and Composition in Building Blocks of Matter

• Representation: Significance of Chemical Formulas in Composition: The chemical formula of a compound is a symbolic representation of its composition. 
• Chemical Formulae: Valency, Composition, and Building Blocks of Matter: Valency or combining capacity can be used to find out how the atoms of an element will combine with the atom(s) of another element to form a chemical compound. 
• Balancing Valency, Metal-Nometal Compounds, and Polyatomic Ions: The rules that have to follow while writing a chemical formula are as follows: 
  • The valencies or charges on the ion must balance.
  • When a compound consists of a metal and a nonmetal, the name or symbol of the metal is written first. 
  • Example: Calcium oxide (CaO), sodium chloride (NaCl), iron sulphide (FeS), copper oxide (CuO) etc., where oxygen, chlorine, sulphur are nonmetals whereas calcium, sodium, iron and copper are metals. 
  • Polyatomic Ions: In compounds formed with polyatomic ions, the number of ions present in the compound is indicated by enclosing the formula of ions in a bracket and writing the number of ions outside the bracket. 
    • Example: Mg(OH)2. 

How are Binary Compound Formula constructed using the Building Blocks of Matter and Valency Crossovers?

• The simplest compounds, which are made up of two different elements, are called binary compounds. 
• While writing the chemical formulae for compounds, we write the constituent elements and their valencies. 
• Then we must cross over the valencies of the combining atoms.