As you will remember, matter is everything that surrounds us, everything that has mass and occupies a place in space. Chemistry is the science that studies matter, its properties, its qualitative and quantitative constitution, the changes it undergoes, as well as the energy variations that accompany the transformations in which it is involved.
Since ancient times man has tried to describe the world around him through observations and experimentation. Air, water, earth and everything we know and use is made of matter. Matter is defined as everything that occupies a place in space and has measurable mass.
The Greek philosopher Democritus proposed the existence of a fundamental unit in matter, the atoms. He postulated, among other things, that these were indivisible and imperturbable and could neither be created nor destroyed. At that time the atom was conceived as the smallest portion of matter, but nothing was known about its conformation, composition and structure.
Therefore, Matter is everything that occupies space, has a property called mass and possesses inertia. Every human being is a material object. We all occupy space and we describe our mass by means of a property related to it, weight. All the objects we see around us are material objects.
Matter is made up of components. A sample of matter has certain components.
Properties of Matter
General or extrinsic properties
General properties are the properties common to all kinds of matter; that is, they do not give us information about the way a substance behaves and distinguishes itself from others. The most important general properties are:
- Mass, amount of matter that a body has.
- Volume, space occupied by a body.
- Weight, the result of the force of attraction or gravity exerted by the Earth on bodies.
- Inertia, tendency of a body to remain in a state of motion or at rest as long as there is no cause that modifies it and is related to the amount of matter that the body possesses.
- Impenetrability, characteristic by which a body cannot occupy the space occupied by another body at the same time.
- Porosity: the characteristic of matter that consists of having pores or empty spaces.
Specific or intrinsic properties
Matter also possesses properties and corresponds to the qualities and attributes that we can use to distinguish one sample of matter from another. The properties of matter are generally grouped into two categories: Physical Properties and Chemical Properties.
Specific properties are characteristic of each substance and allow us to differentiate one body from another. Specific properties are classified into physical properties and chemical properties.
Physical properties
Physical properties are those that can be determined without changing the nature of the bodies. Physical properties include:
- Organoleptic properties: are those that are determined through sensations perceived by the sense organs. For example, color, smell, taste, sound and texture.
- Physical state is the property of matter that originates from the degree of cohesion of molecules. The lesser or greater mobility of the molecules characterizes each state.
- Boiling point: the temperature at which a substance changes from a liquid to a gaseous state.
- Melting point: the temperature at which a substance changes from a solid to a liquid state.
- Solubility: the property of some substances to dissolve in a liquid at a given temperature.
- Density: the ratio of the mass of a substance to its volume. For example, a small piece of lead is denser than a large, light object such as cork.
- Hardness: is the resistance of substances to being scratched. It is measured on a scale called the Mohs scale, which ranges from one to ten. For example, within this scale, talc has a hardness of one (1), while diamond has a hardness of ten (10).
- Elasticity: the ability of bodies to deform when a force is applied to them and to recover their original shape when the applied force is removed.
- Ductility: measures the degree of ease with which certain materials can be converted into wires or threads.
- Malleability: measures the ability of certain materials to become sheets, such as copper or aluminum. In general, materials that are ductile are also malleable.
- Tenacity: the resistance of bodies to breaking or deforming when struck. One of the most tenacious materials is steel.
- Fragility: the tendency to break or fracture.
Chemical properties
Chemical properties are those that determine the behavior of substances when they come into contact with each other. When we determine a chemical property, substances change or alter their nature. For example, when we leave an iron nail outdoors for some time, we observe a change that is manifested by a thin layer of rust on the surface of the nail. We say then that the nail rusted and this constitutes a chemical property of both iron and air; the former for undergoing oxidation and the latter for producing it.
Some chemical properties are:
- Combustion: this is the quality that some substances have to react with oxygen, giving off, as a consequence, energy in the form of light or heat.
- Reactivity with water: some metals such as sodium and potassium react violently with water and form chemical substances called hydroxides or bases.
- Reactivity with acidic substances: this is the property of some substances to react with acids. For example, magnesium, which is a metal, reacts with hydrochloric acid to form hydrogen gas and a magnesium salt.
- Reactivity with bases: the property of certain substances to react with a group of chemical compounds called bases or hydroxides. Thus, for example, the formation of common salt or sodium chloride (NaCl) is due to the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH).
In summary, a Physical Property is a property that a sample of matter has as long as its composition does not change. A Chemical Property, on the other hand, is the ability of a sample of matter to undergo a change in its composition under certain conditions.
Transformations of matter
Physical transformations
These are those transformations or changes that do not affect the composition of matter. Physical changes do not involve the formation of new substances.
Physical changes occur when phenomena such as the following occur: the scent of a perfume spreads through the room when the bottle containing it is opened; when sugar is added to water, the sugar dissolves in the water. In these examples, the perfume evaporates and the sugar dissolves. Each of these transformations occurs without changing the identity of the substances; only some of their physical properties change, so a physical transformation is said to have occurred.
Changes of state are also physical changes, because the composition or nature of the substance is not altered. Changes of state depend on variations in the cohesive and repulsive forces between particles. When the pressure or temperature is changed, matter passes from one state to another. Let’s see.
- As the pressure increases, the particles of matter move closer together and the cohesive force between them increases. For example, a gas can be transformed into a liquid if it is subjected to high pressure.
- As the temperature increases, the particles of matter move faster and, therefore, the repulsive force between them increases. For example, if a liquid is heated, it changes to a gaseous state.
Changes of state include melting, solidification, vaporization, condensation and sublimation.
- Melting: the change from the solid state to the liquid state.
- Solidification: the reverse of fusion, i.e., the change from the liquid to the solid state.
- Vaporization: the change from liquid to gas by the action of heat.
- Condensation: the reverse of evaporation, i.e. the change from gas to liquid.
- Progressive sublimation: the change from the solid state to the gaseous state without passing through the liquid state.
- Regressive sublimation: the reverse of progressive sublimation. From the gaseous state it passes to the solid state by lowering the temperature.
Chemical transformations
These are transformations or changes that affect the composition of matter. In chemical changes, new substances are formed. For example, when phenomena such as the following occur: a paper burns in the presence of air (combustion) and a metal oxidizes in the presence of air or water (corrosion), we can say that the type of substance changed, becoming a different one: this is why it is said that a chemical transformation took place.
In chemical transformations, chemical reactions occur. A chemical reaction occurs when two or more substances come into contact with each other to form different substances. It is possible to detect when a chemical reaction is taking place because we observe changes in temperature, release of gases, etc.
In short. In a physical transformation, some of the physical properties of the sample of matter may change but its composition remains unchanged, whereas in a chemical transformation, one or more samples of matter become new samples with different compositions. Therefore, the key to identifying a chemical transformation is to observe a change in composition.
Classes of matter
Matter can occur as a pure substance or as a mixture.
Pure substances
A pure substance is one that is composed of a single type of matter, has a fixed composition and can be characterized by a number of specific properties.
Pure substances cannot be separated into their components by physical methods. According to the chemical composition, pure substances are classified into: simple substances or chemical elements, and compound substances or chemical compounds.
Chemical element
A chemical element is a pure substance that cannot be broken down into simpler substances. Iron, gold and oxygen are examples of chemical elements, since they cannot be decomposed into substances other than themselves.
Chemical elements are represented by symbols. Symbols always begin with a capital letter. In some cases the symbol corresponds to the initial letter of the element’s name, for example, carbon (C) and oxygen (O). In other cases, it is symbolized by the initial letter of the element in upper case, followed by a second letter of the name which is always lower case, e.g. cesium (Cs) and magnesium (Mg).
There are some elements whose Latin or Greek names do not coincide with the Spanish ones and hence there are symbols that have no relation with the Spanish name of the element, for example, iron (Fe), from the Latin ferrum.
The chemical elements are classified into two main groups: metals and nonmetals.
Chemical compound
A chemical compound is a pure substance formed by the chemical combination of two or more elements in defined proportions. For example, 1 g of sodium chloride always contains 0.3934 g of sodium and 0.6066 g of chlorine, chemically combined. Compounds are represented by formulas. A chemical formula shows the symbols of the elements that make up the compound, and the proportion that exists between them, i.e., they indicate its chemical composition. For example, the formula for water is H2O, which indicates that this substance is made up of hydrogen and oxygen in a 2:1 ratio.
A chemical element is a substance made up of only one type of atom. Chemical compounds are substances in which atoms of different chemical elements are combined with each other. Millions of different chemical compounds have now been identified.
Compounds can be classified into two main groups:
Organic compounds: are those that have carbon as the main element combined with elements such as hydrogen, oxygen and nitrogen. Carbohydrates, lipids and proteins are examples of organic compounds.
Inorganic compounds are those that do not have carbon as the main element. Water (H2O) and sodium chloride (NaCl) are examples of inorganic compounds.
Mixtures
Mixtures are physical unions of substances in which the structure of each substance does not change, so their chemical properties remain constant and the proportions can vary. In addition, it is possible to separate them by physical processes. For example, the union of water with soil is a mixture.
In a mixture, the substance that is in greater proportion is called the dispersing phase or medium, and the substance that is in smaller proportion is called the dispersed phase. According to the strength of cohesion between the substances, the particle size of the dispersed phase and the uniformity in the distribution of these particles, mixtures can be homogeneous or heterogeneous.
- Homogeneous mixtures are those mixtures that have the maximum cohesive force between the combined substances; the particles of the dispersed phase are smaller, and these particles are uniformly distributed. Thus, their components are not identifiable to the naked eye, i.e. they are perceived as a single phase. They are also called solutions or dissolutions.
- Heterogeneous mixtures: these are mixtures in which the cohesive force between substances is lower; the particles of the dispersed phase are larger than in solutions and these particles are not uniformly distributed. Thus, their components can be distinguished with the naked eye. For example, sand and stones together form a heterogeneous mixture.
- Heterogeneous mixtures can be suspensions or colloids.
- Suspensions: these are the mixtures in which phase separation is most clearly visible. They usually consist of a solid dispersed phase insoluble in the liquid dispersing phase, so they have an opaque appearance and, if left to stand, the particles of the dispersed phase settle out. The particle size of the dispersed phase is larger than in solutions and colloids. For example, water with sand is a suspension.
- Colloids: are heterogeneous mixtures in which the particles of the dispersed phase are intermediate in size between solutions and suspensions, and do not settle. Colloidal particles are recognized because they can reflect and scatter light. For example, egg white and soapy water are colloids.
