Matter is defined as anything that occupies space. Matter has to display the properties of volume and mass. Almost all matter in the world exists in only three forms. These forms are liquid, solid and gas. There is a fourth state of matter that is very rare on earth but can be found in the sun and sometimes can be found as lightning. The states of matter can also be referred to phases of matter. The composition of matter is tiny particles which are called molecules or atoms. The particles attract in each other to make up various forms of matter. The greater the attraction is in molecules, the closer the atoms get together. These molecules and atoms are always in a constant motion which is dependent on temperature. The higher the temperature the faster the molecules will move (Grigg, 1).
Matter has chemical and physical properties. Physical properties can be measured and observed and are used to describe matter. Chemical properties describe the potential of matter to undergo chemical reactions or changes because of its composition. Physical changes are divided into two properties which are intensive and extensive. Intensive properties include color, conductivity, malleability, luster and density. Extensive properties include mass, length and volume. Chemical properties are dependent on the electrons, type of bonding and elements present in the matter (Chemistry LibreTexts, Physical and Chemical Properties of Matter).
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Solids have fixed volumes and shapes because their particles occupy specific positions. They have very strong cohesive forces that keep the particles in place. Solids also have very low thermal expansions and compressibility. They have high densities that vary with temperature. Liquids have cohesive forces that are slightly stronger compared to solids. Particles in liquids are loosely stacked enabling them to have some degree of freedom. This property is what makes liquids fluid. They also have very low thermal expansion and low compressibility. Densities of liquids vary faintly with temperature. Gases have kinetic energy and its particles have freedom of motion. The distances between the particles are larger and its kinetic energy increases with temperature. They occupy large volumes and are greatly compressible with very low densities that are dependent on pressure and temperature (Berkeley City College, 1-2).
The altering of a state of matter is a change that is physical. This change is highly dependent on the surrounding pressure or temperature of a substance. These changes are divided into two states which are endothermic and exothermic. Endothermic phases require heat to take place and they include melting, vaporization, evaporation and sublimation. Exothermic process which do not require heat include freezing, condensation, and deposition. Melting is defined as the change of matter from a solid state to a state that is liquid. The melting point of an ice block is 0 o Celsius or 32 o Fahrenheit. Heating of solids will cause the atoms and molecules to move faster leading to melting. Freezing is defined as the change of state of matter from liquid to solid. This is the reverse process of melting. If the temperature of a liquid such as water is lowered, then it will begin to freeze. The freezing point of water is 0 o Celsius or 32 o Fahrenheit. These values are described as the freezing or the melting point of water (Grigg, 2).
Grigg (2) states that vaporization is defined as the altering of the state of a substance from a state that is liquid to a gaseous form. This is achieved when matter is heated to a boiling point. Particles in the liquid begin to move faster during heating and when the boiling point is achieved it becomes vapor which is gaseous in nature. The boiling point of water is 212 o Fahrenheit or 100 o Celsius. Evaporation is defined as vaporization that takes place on the surface of a liquid matter and can take place at temperatures that are below the boiling point of a liquid. Condensation is the altering of a substance is gaseous state to a state that is liquid. This is achieved through the cooling process as it is the reverse process of vaporization. The condensation point of water is equivalent to its boiling point.
Sublimation is the process where a solid substance will change directly to a gaseous state without going through the liquid state. Dry ice is one of the substances that sublimates. This process happens when the temperature of matter is below the freezing point. Deposition is the reverse process of sublimation. Here, matter goes from a gaseous state directly to a solid state and in carbon dioxide gas it is achieved by freezing. Chemistry LibreTexts (Phase Changes) states that this method can be achieve by the formula ; CO 2 ( s ) CO 2 ( g ) and it takes at − 78.5 ∘ C. To determine the total heat being transferred from solidification or melting, the formula used is heat = n × ΔH fus where the n is the number of molecules present in the matter and ΔH fus is expressed in energy or mole . In condensation or boiling; the formula used is; heat= n × ΔH vap.
There are forces that are found within molecules. These forces are called intramolecular forces and are responsible for keeping the molecules together. An example of such a force is the bond between atoms in a substance (OpenStax College, 528). Intermolecular forces are forces that cause attraction between molecules. Forces that attract atoms together (intramolecular) are stronger compared to intermolecular forces. The attractive forces that are found between molecules and neutral atoms are referred to as van der Waals forces. Van der Waal forces include the dispersion forces, dipole-dipole attraction and hydrogen bonding (OpenStax College, 537).
Smith (4) states examples of bonds as such as ionic bonds which holds the ions of metals or nonmetals together. Polar covalent bonds are shared unequally between non-metals while non-polar covalent binds are shared equally between nonmetals. Examples of intermolecular forces are London dispersion which is found between nonpolar molecules and dipole-dipole force that is found between polar molecules. Ion-dipole force is found in a polar molecule and a fully charged ion. Hydrogen bridging is found when hydrogen is bonded to nitrogen, oxygen or fluorine within the molecule.
Molecules are constantly moving and as such a molecule or atom whose electrons are dispersed asymmetrically, can develop an instantaneous dipole which is temporary in nature. The dipole can interfere with the electrons of an adjoining molecule or atom and in turn produce an induced pole. These temporary dipoles therefore result in a weak electrostatic magnetism between the two molecules or atoms which is referred to as dispersion force. Since the forces are relatively weak they become significant only when the molecules are close to each other. The heavier and larger molecules will display stronger attractions compared to the lighter and smaller ones. An example of such a force can be found in Fluorine (F 2 ) and Chlorine (Cl 2 ) gases which have weaker attractive forces. However, Iodine (I 2) as a solid and bromine (Br 2 ) as a liquid have stronger attractive forces.
The strengths of these forces can be determined by melting and freezing. When melting is increased, then the forces weaken as molecules and atoms are widely dispersed. However, when freezing takes place molecules or atoms are closely brought together resulting in strong dispersion forces (OpenStax College, 530). The valence electrons in larger atoms are far away from nuclei as compared to the smaller atoms and it is because of this that they are more likely to form temporary dipoles creating dispersion forces. Polarizability is the measure of how an atom with temporary dipoles is likely distort the distribution charge of another atom. Molecules are able to have permanent dipole interactions as well. Due to the presence of asymmetrical distribution of charges in a molecule, there exists a negative charge on one side of the molecule and a positive charge on the opposite side. The attraction between these sides of the molecules and other neighboring molecules is referred to as permanent dipole-permanent-dipole attraction.
Dipole-Dipole attraction is created when there are two molecules with opposite charges. An example of such a molecule is hydrogen chloride. It is a polar molecule because there are partial negative charges on the Chloride electronegative atom and partial positive charges on the hydrogen atom. An attraction between the two atoms results in a dipole-dipole attraction where the opposite ends attract (OpenStax College, 532). When determining the strength of the forces, boiling and freezing points are used. At 150 Kelvin, hydrogen chloride forms a liquid while fluorine remains a gas. This shows that hydrogen chloride molecules have a stronger dipole-dipole forces (OpenStax College, 534). Hydrogen bonding is a specific strong form of dipole-dipole magnetism and are attractive forces within the molecules. Molecules withFluorine-Hydrogen (F-H), Oxygen-Hydrogen (O-H) or Nitrogen-Hydrogen (N-H) moieties are very strongly magnetized to identical moieties in adjacent molecules. The huge difference in electronegativity between the H atom (2.1) and the atom that it is attached to (4.0 for an F atom, 3.5 for an O atom, or 3.0 for a N atom), merged with the minuscule magnitude of a H atom and the fairly miniature sizes of F, O, or N atoms, leads to exceedingly concentrated partial charges with these atoms. In spite of the hydrogen bonds being weaker compared to covalent bonds, they are still stronger than any other dipole-dipole and dispersion attraction forces (OpenStax College, 535).
References
Berkeley City College. Chapter 6 – The States of Matter. Retrieved from http://www.berkeleycitycollege.edu
Chemistry LibreTexts. Phase Changes, (2016). Updated on Feb 28, 2016 and retrieved from https://chem.libretexts.org
Chemistry LibreTexts. Physical and Chemical Properties of Matter, (2016). Updated on May 24, 2016 and retrieved from https://chem.libretexts.org
Grigg Cindy. Changing States of Matter, (2012). edHelper. Retrieved from https://www.mrsd.org
OpenStax College. Chemistry OpenStax College, 11 March 2015. Rice University. Retrieved from http://cnx.org
Smith Clark. Intermolecular Forces: Types of Intermolecular Forces. (2018) Retrieved from https://web.gccaz.edu
