An atom is smallest particle in an element that has the properties of the element. It is not possible to breakdown the atom further retaining the properties of the element. Atoms are not visible to the naked eye and are the basic building blocks. For example the atoms of element gold cannot be broken down further and each atom has the properties of gold.
Molecules are formed by the combination of two or more atoms. Unlike atoms, molecules can be subdivided to individual atoms. The atoms are bonded together in a molecule. Molecules also are not visible to the naked eye, while can be seen through highly magnifying microscopes and other scientific devices. Water is comprised of numerous water molecules. Each water molecule is made up of one oxygen atom and two hydrogen atoms. So a water molecule can be further divided into oxygen and hydrogen atoms. But these atoms cannot be subdivided. In a molecule, atoms are bonded together by single, double, or triple bonds.
An atom has a nucleus surrounded by electrons. The electrons are negatively charged particles. The nucleus contains neutrons and positively charged protons. Depending on the majority of the particles, the atom can be positively or negatively charged. When these charged atoms bond together to form molecules, the bonds are formed by the electrons filling up the outer orbits of the atoms. Since atoms exist independently, there is no bonding in an atom.
When atoms combine in different numbers to form a molecule, the end result can vary. For example, when two atoms of oxygen combine to form a molecule, it becomes O2 which is the oxygen we breathe in. But when three oxygen atoms combine to form an O3 molecule, it becomes Ozone. So another difference between atoms and molecules is that when similar atoms combine together in varying numbers, molecules of different properties can be formed. But when similar molecules combine together in any numbers, a simple product is formed.
A molecule is usually stable to exist by itself but an atom is not stable by itself. This is owing to the presence of electrons in the atoms. Only when sufficient number of electrons are present in an atom, it becomes stable. The sufficient number of electrons are received in an atom, when two atoms bond together and share the electrons. Thus it becomes stable and forms a molecule. Not all atoms can bond together. The bonding depends on the charge and chemical properties of the atoms.
Atoms and molecules are present in all objects and living things. The composition and density levels vary the thickness and form of the objects. In gases, the molecules are very loosely packed so that the molecules can flow around easily without colliding. In liquids, the packing is a bit more compact and so the particles are always together. But in solids the packing is very compact and hardly any movement to the molecules is allowed, giving the object a firm shape....