Molecules and Atomicty

The atoms of certain elements readily bond with other atoms to form molecules. Examples of such elements are oxygen and chlorine. The atoms of some elements do not easily bond with other atoms. Examples are neon and argon.

Molecules can vary greatly in size and complexity. The element helium is a one-atom molecule. Some molecules consist of two atoms of the same element. For example, O ₂ is the oxygen molecule most commonly found in the earth’s atmosphere; it has two atoms of oxygen. However, under certain circumstances, oxygen atoms bond into triplets (O ₃ ), forming a molecule known as ozone. Other familiar molecules include water, consisting of two hydrogen atoms and one oxygen atom (H ₂ O), carbon dioxide, consisting of one carbon atom bonded to two oxygen atoms (CO ₂ ), and sulfuric acid, consisting of two hydrogen atoms, one sulfur atom, and four oxygen atoms (H ₂ SO ₄ ).

ATOMICITY OF ELEMENTS

1.MONOATOMIC ELEMETS:these are elements with only one atom e.gthe noble gases(neon,argon,helium),sodium magnesium, in short all metals are monoatomic.

2.DIATOMIC ELEMENTS:these elements contains two atoms .most non metals fall under this category.e.g N₂.F₂.Cl₂,O₂,Br₂.I₂.H_2.

3.POLYATOMIC ELEMENTS: are those elements with more than two atoms.e.g phosphorus 5,sulphur 8

Foundations of Dalton’s atomic theory

1. All matter consists of tiny particles. The existence of atoms was first suggested more that 2000 years before Dalton’s birth. Atoms remained pure speculation through most of this time, although Newton used arguments based on atoms to explain the gas laws in 1687. (Newton’s speculations about atoms in the Principia were carefully copied by hand into Dalton’s notebooks.)
2. Atoms are indestructible and unchangeable. Atoms of an element cannot be created, destroyed, broken into smaller parts or transformed into atoms of another element. Dalton based this hypothesis on the law of conservation of mass and on centuries of experimental evidence.

With the discovery of subatomic particles after Dalton’s time, it became apparent that atoms could be broken into smaller parts. The discovery of nuclear processes showed that it was even possible to transform atoms from one element into atoms of another. But we don’t consider processes that affect the nucleus to be chemical processes. The postulate is still useful in explaining the law of conservation of mass in chemistry. A slightly more restrictive wording is “Atoms cannot be created, destroyed, or transformed into other atoms in a chemical change”.