Molecular properties of Materials, Physics tutorial


A molecule is the smallest particle in the chemical element or compound which has chemical properties of that element or compound. Molecules are composed of atoms which are held together by chemical bonds. These bonds form due to sharing or exchange of electron s among atoms.

Atoms of certain elements voluntarily bond with other atoms to produce molecules. Examples of such elements are oxygen and chlorine. Atoms of some elements don't simply bond with other atoms. Examples are neon and argon


Atoms are fundamental building blocks of ordinary matter. Atoms can unite together to produce molecules, that in turn form most of the objects around us.

Atoms are made up of particles known as protons, electrons and neutrons. Protons carry the positive electrical charge, electrons carry the negative electrical charge and neutrons carry no electrical charge at all. Protons and neutrons group together in central part of atom, known as nucleus, and electrons orbit the nucleus. The particular atom will have same number of protons and electrons and the majority of atoms have at least as many neutrons as protons.

Molecular Motion:

All molecules are in constant motion. Molecules of the liquid have more freedom of movement than those in the solid. Molecules in the gas possess the greatest degree of motion.

Heat, temperature and motion of molecules are all connected. Temperature is the measure of average kinetic energy of molecules in the material. Heat is energy transferred between materials which have different temperatures.

Gas Molecule Motion:

At the low temperature a gas molecule travels, on te average, at the slower speed than it would at a high temperature. So, at the low temperature molecules have, on average, less kinetic energy than they do at the high temperature. Lower speeds, lower kinetic energies.

Though, for any temperature there is average kinetic energy and the corresponding average speed for motion of the molecules. This animation visualizes molecules to be traveling at average speed.

Moving Molecules in a Solid:

In the solid, atoms are very attracted to one another. Atoms vibrate but stay in fixed positions due to strong attractions for one another. Heating the solid increases the motion of atoms. Increase in motion of the atoms fights with attraction between atoms and causes them to move the little further apart. Cooling the solid decreases the motion of atoms. The decrease in motion of atoms permits attractions between atoms to bring them little close together.

Liquid Molecule Motion:

Liquids have more energy than solids. For instance; water exists as the solid (ice) at very low temperatures, but goes through the phase transition to liquid state when heat energy is added. Energy in the liquid exceeds attractive forces between molecules, permitting molecules to move freely. Molecules in the liquid slide past and bump into each other but stay close together. As molecules remain close together, they can't easily be compressed. Strong attractive forces develop surface tension, so liquids form droplets; energy of liquid is not adequate to cause individual molecules to break free. Molecules in the liquid flow freely, assuming the shape of the container or channel.

Molecular Mass:

Molecular mass of the substance is relative mass of the molecule as compared with mass of the 12C atom taken as 12-units. It points at number of times; one molecule of substance is heavier than

1/12 of a 12C

Molecular volume:

The volume occupied by the molecule is molecular volume. It is another property of matter. Form Avogadro's hypothesis, we can explain volume occupied by the mole of gas - therefore we have molar volume. Molar volume of gases at standard temperature and pressure (S.T.P.) is 22.4 liters. The mole of gas has 6.0 x 1023 molecules. Therefore we can figure out volume of one molecule to be contribution methods such as McGowan volume approximation.

Molecular Density:

The density of the substance is mass of that substance per unit volume. Therefore molecular density states density of the molecule that is mass of molecule in kg per 1m3 volumes. It states how heavy or light the molecule is. Hydrogen molecule has been found to be lightest gas on earth. Therefore its molecular density is smallest in value.

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