Chemistry Fundamentals: History, Matter, and States
History of Chemistry
The first experiences of humans as chemists involved the use of fire to transform matter. Obtaining iron from ore and glass from sand are clear examples. Gradually, humans realized that other substances also have this power of transformation. Great efforts were devoted to finding a substance that transforms a metal into gold, which led to the creation of alchemy. The accumulation of alchemical experiences played a vital role in the future establishment of chemistry. Chemistry is an empirical science, studying things through the scientific method, i.e., through observation, measurement, and especially experimentation. In its broadest sense, chemistry studies the various substances on our planet and the reactions that transform them into other substances. It also studies the structure of chemical substances at the molecular level, and, last but not least, their properties.
Field of Study
Matter is anything that occupies space and has mass. All material systems consist of atoms and molecules. Molecules are atoms joined together by chemical bonds. In turn, atoms are made up of particles considered indivisible: protons, neutrons, and electrons.
Atoms
Atoms consist of a central nucleus and electrons, negatively charged, rotating around it. The nucleus consists of protons, positively charged, and neutrons, which have no charge. The atom is neutral; therefore, the number of protons equals the number of electrons. In general, the mass of an atom is roughly the mass of the nucleus, as the electron mass is 1840 times smaller than the proton mass. The mass of the neutron is approximately equal to the mass of the proton.
Molecules
When two or more atoms of the same element or different elements join by chemical bonds, they produce a molecule of a chemical compound.
Simple Substances and Compounds
A material system is a body or set of bodies selected for observation according to certain purposes. Chemistry studies these material systems. They are classified as:
1. Homogeneous system: one that has the same values for all its intensive properties in different parts of the system. Examples: sugar dissolved in water, alcohol and water, steel.
2. Heterogeneous system: one that has different values for any of the intensive properties in part of the system, and these parts are separated from each other by well-defined discontinuity surfaces. Examples: oil and water, clouds, lather.
3. Inhomogeneous system: one in which the values of intensive properties are different in different parts of the system, but these parts are not separated from each other by well-defined discontinuity surfaces. Examples: air, water with the addition of a dye and without shaking.
Homogeneous systems can be:
a. Pure Substances: those that cannot be split without losing their intensive properties. Examples: water, sugar.
b. Solutions: those which are formed by more than one pure substance. Example: steel.
Simple substances are called chemical elements. Examples: iron, carbon, as part of steel.
II. Composite substances are chemical compounds. Example: water, sodium chloride.
STATES OF MATTER
There are three physical states of matter, also called aggregation states. They are: solid, liquid, and gas. There is now talk of a fourth state, plasma, but it is not discussed in this memo.
The phenomenon of vaporization can occur in two ways:
– Evaporation: only from the free surface of the liquid at any temperature.
– Boiling: from all the liquid at a given temperature, which depends on the fluid and external pressure.