Structure of matter
The States of Matter
Depending on temperature, pressure and a substance’s properties, a substance can take on
different physical forms. We call these physical forms States of Matter. There are three very
well known states of matter: Solids, Liquids, and Gases. Other states of matter also exist.
These include Plasma (a state of matter similar to a gas, but contains free -moving electrons
and ions - atoms that have lost electrons) and Bose-Einstein Condensates (BECs) (waves of
matter that can occur with some types of atoms at super cold temperatures).
Plasma State: Plasma is one of the four common states of matter - solid, liquid, gas, and
plasma. Plasma is an electrically charged gas. Because plasma particles have an electrical charge,
they are affected by electrical and magnetic fields. This is the main difference between a gas and
a plasma.
Bose Einstein Condensate:
A gas of atoms is trapped and cooled by lasers at -2730 C or 0 K. A magnetic trap then allows the
hottest atoms to escape, resulting in a gas so cold and so dense that it coalesces into a “superatom”
Classification of solids:
The atoms, molecules or ions in solid are attached to one another with strong attractive
forces. Solids are classified into two types:-
1. Crystalline solid and
2. Non-crystalline solid (amorphous)
Crystalline solid:
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or
ions) are arranged in a highly ordered microscopic structure. These atoms, ions, or molecules are
called lattice points and are typically visualized as round spheres. They are arranged in such a
way that their positions are exactly periodic in all dimensions. Examples: Diamond, table salt.
The crystalline solid are subdivided into two types
1. Single crystal
2. Polycrystal
Single crystal:
A crystal in which periodicity of atoms, molecules or ions extended throughout the whole crystal
is called single crystal. Some single crystals are of very small size. Those small size crystals are
known as mono-crystal. Examples: NaCl, diamond, quartz (SiO2)
Polycrystal:
Polycrystalline materials are solids that consist of many small crystals (the “grains”). The grains
are separated by grain boundaries and normally have random crystallographic orientations. The
size of the grains may vary from nanometers to millimeters. Examples: Most of the metals (Fe,
Cu, Al
Non-crystalline (amorphous):
Any noncrystalline solid in which the atoms and molecules are not organized in a definite lattice
pattern. Such solids include glass, plastic, and gel. amorphous solid.
Unit cell:
A unit cell is the smallest portion of a crystal lattice that shows the three- dimensional pattern of
the entire crystal. A crystal can be thought of as the same unit cell repeated over and over in three
dimensions.
Types of unit cells
The cubic crystal structure, for example, consists of three distinct unit cell types : (1)
plain cubic, (2) face-centered cubic, and (3) body-centered cubic.
Packing factor:
Packing factor, also known as packing fraction, is a measure of how efficiently atoms or ions are
packed within a crystal lattice. It is the ratio of the total volume occupied by the particles to the
volume of the unit cell.
Body centered Simple cubic structure Face centered
Different types of bonds in solid:
Three different types of primary or chemical bond are found in solids—ionic, covalent, and
metallic. For each type, the bonding necessarily involves the valence electrons; furthermore, the
nature of the bond depends on the electron structures of the constituent atoms. In general, each of
these three types of bonding arises from the tendency of the atoms to assume stable electron
structures, like those of the inert gases, by completely filling the outermost electron shell.
Secondary or physical forces and energies are also found in many solid materials; they are weaker
than the primary ones, but nonetheless influence the physical properties of some materials.
Strong bonds
• Ionic bond,
• Covalent bond,
• Metallic bond,
Weak bonds
• Hydrogen bond,
• Van der waals bond.
Ionic bond:
Ionic also called electrovalent bond, type of linkage formed from the electrostatic attraction
between oppositely charged ions in a chemical compound. Such a bond forms when the valence
(outermost) electrons of one atom are transferred permanently to another atom. The atom that loses
the electrons becomes a positively charged ion (cation), while the one that gains them becomes a
negatively charged ion.
Covalent bond
A covalent bond is formed by the equal sharing of electrons from both participating atoms.
The pair of electrons participating in this type of bonding is called a shared pair or bonding
pair. Covalent bonds are also called molecular bonds. Sharing of bonding pairs will ensure that
the atoms achieve stability in their outer shell, which is similar to the atoms of noble gases.
Metallic bond:
Metals are substances consisting of positively charged ions, fixed in crystal lattice with negatively
charged electrons moving freely through the crystal. Therefore free electrons act as the cohesive
force that hold the metal atoms together and form a metallic bond.
The bond produced due to the combination of electrostatic force of attraction between
electrons and positive nuclei of metal atoms is called metallic bond.
Van Der waals bond:
Van der Waals bond a weak attractive force between atoms or nonpolar molecules caused by a
temporary change in dipole moment arising from a brief shift of orbital electrons to one side of
one atom or molecule, creating a similar shift in adjacent atoms or molecules.
Hydrogen bond
A hydrogen bond is an attraction between two atoms that already participate in other chemical
bonds. One of the atoms is hydrogen, while the other may be any electronegative atom, such as
oxygen, chlorine, or fluorine. Hydrogen bonds may form between atoms within a molecule or
between two separate molecules
Inter-Atomic distance
Atomic spacing refers to the distance between the nuclei of atoms in a material. This space is
extremely large compared to the size of the atomic nucleus, and is related to the chemical
bonds which bind atoms together.[1] In solid materials, the atomic spacing is described by the bond
lengths of its atoms. In ordered solids, the atomic spacing between two bonded atoms is generally
around a few ångströms (Å), which is on the order of 10−10 meters. However, in very low density
gases (for example, in outer space) the average distance between atoms can be as large as a meter.
In this case, the atomic spacing isn't referring to bond length.
The atomic spacing of crystalline structures is usually determined by passing an electromagnetic
wave of known frequency through the material, and using the laws of diffraction to determine its
atomic spacing. The atomic spacing of amorphous materials (such as glass) varies substantially
between different pairs of atoms, therefore diffraction cannot be used to accurately determine
atomic spacing. In this case, the average bond length is a common way of expressing the distance
between its atoms.
