THE 1st STATE OF MATTER – SOLID

The Periodic Table of Elements currently contains 118 elements we have knowledge about, yet the element 118 is definitelly not the last one. The same I can say about the states of matter. Before anything else let’s recall the definition of matter.

MATTER is referred to as anything that has mass and occupies space.

So far we are mostly familiar with 4 states of matter which naturally occur on Earth namely: solids, liquids, gases and plasmas. But as new elements are continuously added in the periodic table, new states of matter are also investigated. In addition to the main 4 , from what is currently known and largelly acknowledged by scientific comunity the matter can also take 3 other states, therefore making the list of 7 different states the matter can take. These are the following:

1. Solid
2. Liquid
3. Gas
4. Plasma
5. Quark-Gluon Plasma
6. Bose-Einstein Condensate and
7. Degenerate Matter.

All these 7 states of matter are caracterized by their unique properties which are of 2 categories namely either physical or chemical properties.

1. Physical properties can change the physical appearance of a substance, but allow the chemical composition to stay the same.
2. Chemical properties can change the chemical composition of a substance. These are usually seen during chemical reactions.

Physical properties can be further broken down into another 2 categories:

1. Intensive properties – properties that are independent of the size or amount of substance.
2. Extensive properties – properties that are dependent on the size or amount of substance present.

This article I’ll be briefly talking about the 1st State of Matter: SOLID

WHAT IS A SOLID?

A SOLID is: the most ordered state of matter. Under constant conditions all the constituent particles (atoms, ion or molecules) in the structure of a solid are connected together to form an object with a fixed shape and a fixed volume (although the shape can be altered by applying force).

Almost all elements found in nature are solids. Solids can hold their shape, and it is because of their unique properties that we can drink coffee in our favorite mug, without the mug changing its shape, or sleep on the bed without the bed turning into a liquid or disappearing into a gas!

In solids, the particles are held together very closely in a regular pattern. The attractive intermolecular forces between individual atoms or molecules in solids are greater than the energy causing them to move apart, hence the atoms cannot move freely within the substance and cannot be compressed into a smaller volume. The molecular motion of particles in a solid is confined only to very small vibrations of the atoms back and forth around their fixed positions. As result, solids have the lowest kinetic energy of all the states of matter. This makes the solids to maintain a certain shape and volume, no matter their container, in opposite like liquids and gases do. Some solids, like sponges, can be squashed but that is because air is squeezed out of pockets in the material – the solid itself does not change size. We can preciselly measure solids 3-dimensionaly and we can weight them exaclty.

The size of a solid can be know, either in the base dimensional unit a.k.a. meter (m) or in its submultiples (such as centimeter (cm), millimeter (mm), micrometer (µm) etc…) or multiples (such as hectometer (hm), kilometer (km) etc…

The mass of a solid can be preciselly measured in the base unit known as gram (g) or with its submultiples (such as centigram (cg) milligram (mg), microgram (µg) respectivelly multiples such as hectogram (hg), kilogram (kg), megagram or tonne (t) etc…

However, solids encompass a diverse group of materials, and other properties can vary greatly, depending on the exact solid involved. Solids, of course, are not necessarily permanent. Solids are sometimes formed when liquids or gases are cooled; ice is an example of a cooled liquid which has become solid. Also extremely high temperatures can be used to melt solid iron so it can be shaped into a skillet, for example. Once that skillet is formed and cools back to room temperature, though, its shape and size will not change on its own, as opposed to molten metal, which can be made to drip and change shape by gravity and molds. The same is true for ice cubes that are kept in the freezer: Once they are formed, their size and shape doesn’t change.

In their structure, the solids occur in 2 types:

1. crystalline solids
2. non-crystalline (amorphous) solids.

Crystalline solids are particles with a well-organized pattern and shape, such as a 3D structure in which all bonds between particles have equal strength. Therefore the resulted solid has a distinct melting point.

Amorphous solids are particles that have random arrangements, so they lack an organized shape and/or pattern and melt over a range of temperatures.

Solids are placed into their corresponding category based on differences in the type of particle (ion, atom, or molecules) and the type of attractive force present.

Usually, when conditions are steady (such as slow and gradual cooling/heating), the particles have a chance to align uniformly becoming crystalline such as for instance sugar. However, when there are extreme and rapid temperature changes, an indefinitely shaped solid will most likely be the result and the solid is an amorphous one such as glass. In an other case when solids are formed by a long chain of molecules they become polymeric solids such as rubber or plastics which often have mixed areas in their structure including both amorphous and crystalline phases. For examples, candle waxes are amorphous solids composed of large hydrocarbon molecules. Some substances, such as silicon dioxide, can form either crystalline (as quatz or sand) or amorphous solids (as glass or fused silica) too (as shown in Figure 3), depending on the conditions under which it is produced. Also, amorphous solids may undergo a transition to the crystalline state under appropriate conditions. There is no solid which is 100% crystalline or 100% amorphous. In their structure solids always contain more or less both of these types of structures.

Let’s now have a closer look at the 2 main categories of solids: CRYSTALLINE SOLIDS and AMORPHOUS SOLIDS.

CRYSTALLINE SOLIDS

Crystalline solids, or crystals, are regarded as “true solids.” In crystalline solids, the atoms, ions or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal. The smallest repeating structure of a solid is called a unit cell, which is like a brick in a wall. In turn, the unit cells combine to form a 3D network called a crystal lattice. Most minerals are crystalline solids. Common table salt (NaCl) is one example of this kind of solid as well. Some substances, such as diamond (a crystalline pattern form of carbon), form one large crystal. However, most are made up of lots of smaller crystals.

There are 14 different basic types of such structural arrangements in crystalls also known as Bravais lattices, but this is a topic which I’ll explain later in another article. For now let’s just review what crystalline solids are.

The blue and red dots seen in the lattice corners represents a lattice point and consists of a specific atom, molecule, or ion.

Aside from the regular arrangement of particles, crystalline solids have several other characteristic properties. They are generally incompressible, meaning they cannot be compressed into smaller shapes. Because of the repeating geometric structure of the crystal, all the bonds between the particles have equal strength. This means that a crystalline solid will have a distinct melting point, because by applying heat, it will break all the bonds at the same time.

Most crystalline solids exhibit anisotropy. This means that properties such as refractive index (how much light bends when passing through the substance), conductivity (how well it conducts electricity) and tensile strength (the force required to break it apart) will vary depending on the direction from which a force is applied. Crystalline solids also exhibit cleavage; when broken apart, the pieces will have planed surfaces, or straight edges.

Generally this type of solids (n. : crystalline) are classified according the nature of the forces that hold the particles together. These forces are primarily responsible for the physical properties exhibited by the bulk solids. Crystal structure determines a lot more about a solid than simply how it breaks. Structure is directly related to a number of important properties, including, for example, conductivity and density, among others. Without getting to much in details to explain these relationships, I first need to introduce the 4 main types of crystalline solids, namely:

1. COVALENT NETWORK SOLIDS;
2. IONIC SOLIDS;
3. MOLECULAR SOLIDS;
4. METALLIC SOLIDS;

NOTE: These 4 subtypes of solids are typically the cases for crystalline versions, yet under certain conditions these categories also occur as amorphous versions.

Later on I will write an individual post for each of these, but for now just to have an ideea their definitions are as follows next.

COVALENT NETWORK SOLIDS

A Covalent Network Solid is = a crystal (ordered) or amorphous (non-ordered) solid in which the atoms are held together by covalent bonds in a continuous network.

A covalent bond is = a type of chemical bond where 2 atoms equally share one or more pairs of valence electrons within the bond. This happens because the atoms are trying to fill their outermost energy level, or valence shell, with a full complement of electrons. The more equally they are shared, the more covalent character the bond has.

When the atoms share electrons in this way, they become more stable and less likely to react with other substances. Because of this, there are no individual molecules, so the entire solid can be considered a macromolecule (fancy word for “big molecule”). If you think of a covalent network solid like a quilt, the unit cells are the patches that repeat across the pattern. These usually occur between 2 non-metals or a non-metal and a metalloid.

Diamond, graphite, quartz, amethysts, rubies and many other minerals have networks of covalent bonds in their structure.

Covalent network solids have similar properties to ionic solids. They are very hard, somewhat brittle solids with extremely high melting points (higher than 1,000°C). Unlike ionic compounds, they do not dissolve in water and in other solitions generally all covalent network solids are insoluble, nor do they conduct electricity and heat (except of diamond which is a good heat conductor, and graphite which has soft texture and is a good conductor of electricity.)

IONIC SOLIDS

A ION is a particle, an atom or a molecule with an imbalance of electrical charge. Therefore ions are charged and contain different numbers of protons and electrons. Ions form when atoms move into a more stable electron configuration. Ions are identified by a superscript that shows the sign and size of the electric charge – for example Ca⁺² (Calcium ion). There are 2 types of ions: cations and anions.

A Ionic Solid is = a chemical compound which consist of ions joined together in electrostatic interaction by ionic bonds, a type of chemical bond that occurs between an cation (a positively charged ion) and a anion (a negatively charged ion).

These solids usually occur between a metal (as cation) and an non-metal (as anion) but there are exceptions. Ionic solids have lattice energy, which is the energy that gets released when ions join together to form ionic solids. Lattice energy also tells how strong the attractive force between the ions is. The greater the lattice energy, the stronger the ionic bond. Some crystals are also isotropic – that is, their physical properties are the same in whichever direction they are measured, while others are anisotropic – their properties are different in different directions.

Solids in this category are brittle, hard, and have high melting and boiling points. Ionic solids can only conduct electricity in a water solution or molten state, they are poor conductors of heat as well and in general have varying solubility in water. Sodium chloride (table salt) (NaCl) is also a type of ionic solid. The sodium ion (Na⁺) has a charge of +1, and the chlorine ion (Cl^–) has a charge of -1. The melting point of NaCl is 801 °C, which is very high!.Potassium chloride (KCl) is another example of Ionic solid.

MOLECULAR SOLIDS

A Molecular solid is = composed of a weak crystalline lattice made of atoms or molecules covalently bonded attracted to each other by weak electrostatic forces (called van der Waals forces). Electrostatic, meaning that they are caused by the attraction/repulsion of electrical charges.

Because covalent bonding involves sharing electrons rather than outright transfer of those particles, the shared electrons may spend more time in the electron cloud of the larger atom, causing weak or shifting polarity. This electrostatic attraction between the two poles (dipoles) is much weaker than ionic or covalent bonding, so molecular solids tend to be softer than ionic crystals and have lower melting points (many will melt at less then 100°C).

The attractive forces holding the molecules together depend on their polarity. They ca be:

• Polar molecular solids have dipole-dipole and London dispersion forces present.
• Nonpolar molecular solids only possess London dispersion forces.

London dispersion forces are the electrostatic forces between a non-polar species with an instantaneous dipole and a non-polar species with an induced dipole. Induced dipoles are considered temporary since they will disappear when moved away from a molecule with a dipole.

Most molecular solids are nonpolar. These nonpolar molecular solids will not dissolve in water, but will dissolve in a nonpolar solvent, such as benzene and octane.Solids in this group have soft textures because the intermolecular forces holding the molecules together are weak compared to the chemical bonds found in other types of solids. Their melting point (MP) varies but generally is low. Nonpolar molecular solids generally have low melting points, while polar molecular solids tend to have slightly higher melting points and unable to conduct electricity.

Dry ice (solid CO₂) is considered a non-polar molecular solid, whereas ice (H₂O) is a polar molecular solid. Some other examples of molecular solids also include table sugar (sucrose, C₁₂H₂₂O₁₁), iodine, halogens like solid chlorine (Cl₂), and compounds consisting of a halogen and hydrogen such as hydrogen chloride (HCl).

Polymers, which are large molecules, are also molecular solids. These polymers are composed of small, repeating units called monomers. Polyethylene terephthalate (PET) is a type of polymer that is used to make plastic bottles.

METALLIC SOLIDS

A Metallic solid is = a substance in which the particles are linked through  a lattice of metallic bonds composed of positive ions (cations) that are attracted to each other in a cloud of  delocalized electrons. Within this cloud the electrons can move freely between atoms.

Metalic bonds are nondirectional, meaning that metal atoms can remain bonded while they roll against each other as long as some parts of their surfaces are in contact. These unique properties of metallic bonds are largely responsible for some of the valuable behavior of metals, including their conductivity and malleability.

A metal may be simply described as a lattice of positive cations within a “sea” of negative electrons and due to the electron’s ability to move, these solids are great conductors of electricity and heat. Metallic solids have very diverse melting points which usually are high, though notable exceptions are mercury (Hg), which has a melting point of -38.8°C, and phosphorous (P), with a melting point of 44° C while Tungsten has a melting point at 3400°C. The hardness of metallic solids also varies. These solids also have unique characteristics such as being opaque, malleable, ductile, shiny and insoluble in water.

Alloys are solid mixtures of between 2 or more metals or between a metallic element with another non-metalic substance. An alloy will usually have properties that are very different from those of the constituent metals.While pure metals can be overly malleable and heavy, alloys are more workable. Bronze is an alloy of copper and tin, while steel is an alloy of iron, carbon and other additives.

About three quarters of the known elements are metals. In the periodic table Group I metals are known as the alkali metals (Li, Na, K, Rb, Cs, Fr).Group II metals are called the alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra).Groups 3-12 contain many transition metals such as Fe, Cu, Ag, and Au. Group 13-16 also have some metals called post-transition metals or poor metals (Al, Ga, In, Tl, Pb, Sn, Bi, and Po).

AMORPHOUS SOLIDS

In amorphous solids, the smallest unit can be an ion, atoms, molecules, or even polymers yet unlike in crystailline solids, the atoms or molecules that make up amorphous solids are not arranged in a regular pattern.Instead they are arranged more like those in a liquid, although they are unable to move around.

In amorphous solids (literally “solids without form”), the electrostatic forces present in amorphous solids can vary. That’s why they are also called “pseudo solids.” Amorphous solids are often formed when atoms and molecules are frozen in place before they have a chance to reach the crystalline arrangement, which would otherwise be the preferred structure because it is energetically favored. One important consequence of the irregular structure of amorphous solids is that they don’t always behave consistently or uniformly. For example, they may melt over a wide range of temperatures, in contrast to a crystalline solid’s very precise melting point. An amorphous solid melts gradually over a range of temperatures, because the bonds do not break all at once. This means an amorphous solid will melt into a soft, malleable state (think candle wax or molten glass) before turning completely into a liquid.  In addition, amorphous solids have no characteristic symmetry so they break unpredictably and produce fragments with irregular, often curved surfaces, while crystalline solids break along specific planes and at specific angles defined by the crystal’s geometry.

Amorphous solids are isotropic because properties such as refractive index, conductivity and tensile strength are equal regardless of the direction in which a force is applied, glass, plastic and soot are such examples. An amorphous material has the density of a solid but the internal structure of a liquid, although one with an enormously great viscosity. They are considered to be super-cooled liquids in which the molecules are arranged in a random manner similar to that of the liquid state.

Examples of amorphous solids include glass, rubber, gels and most plastics.

PROPERTIES OF SOLIDS

Due to their different force interactions, solids can have different physical and chemical properties. For example they may be strong or weak, hard or relativelly soft, and may return to their original shape after been having subjected to force or may be permanently deformed. A solid material’s properties depend on the atoms or molecules that make it up, whether the solid is crystalline or amorphous, and whether or not there are defects in the material.

Some crystalline solids have defects in the definite repeating pattern of their particles.These defects (which include vacancies, atoms or ions not in the regular positions, and impurities) can change the material’s physical properties such as electrical conductivity, which is exploited in the silicon crystals used to manufacture computer chips. Some other properties include elasticity, conductivity, light transmittance, plasticity, just to name few of them.

Based to their physical properties solid materials can be mainly categorized based on their behavior under loading into 3 types: ductile, brittle or malleable materials.

DUCTILE = Ductile materials change shape when streched so they can be drawn out into long wires. They exibit some permanent deformation before they fracture under loading. This type of deformation, in which a material changes shape permanently is known as plastic deformation. Many metals are ductile becasue the bonds between the atoms allow the atoms to slide over each other. Simply put ductility measures how much a material can be stretched or deformed without breaking. This property is essential in many engineering applications, such as construction, where materials like steel are often used because of their high ductility and ability to withstand external loads and stresses. In this case the relationship between ductility and metallic bonding is a direct one. Metallic bonding is exactly the type of chemical bonding that holds the atoms of metallic elements together, and it is responsible for the unique properties of metals, such as ductility, electrical conductivity, and thermal conductivity.

BRITTLE = When under stress, brittle solids such as ceramics snap without changing shape much. These materials tend to fracture with little to no permanent deforamtion under loading. Cracks pass easily through these materials, becasue the atoms cannot move to absorb the stress. If the material can deform, it will be less brittle but also less hard. Brittleness is the opposite of ductility, namely that the brittle materials are characterized by their inability to be stretched or deformed without breaking. This property is often associated with materials like ceramics, which are highly resistant to compression but can be very brittle and prone to cracking or fracturing when subjected to tensile stresses. Note: there is no well-defined point that classifies brittleness, but typically a material that fractures at a strain of less than 5% is considered a brittle material.

MALLEABLE = Malleable solids can deform plastically when compressed. As a result, they can be flattened, into sheets by rolling or hamering. Many malleable materials are also ductile, although the two properties do not occur together; for example lead is highly malleable but has low ductility.