We explain what the atom is and the history of its discovery. We also explain its main characteristics.
What is the atom?
The atom is the smallest particle into which matter can be divided.
It is important to clarify that the definition of atom often uses the term “indivisible particle” to refer to the smallest particle that still retains the properties of the chemical element to which it belongs, but the atom is composed of even smaller particles (protons, neutrons, electrons), but they do not have the properties of the chemical element.
The first notions of atoms emerged at the beginning of the 19th century.with the work of Dalton, who formulated the first atomic theory and described for the first time the existence of spherical, tiny, indivisible particles, which make up all matter and are identical to each other in each chemical element.
Throughout that century and at the beginning of the next, the concept was refined, by scientists such as Thomson and Rutherford, until reaching the formulation of the Böhr atomic model, proposed by Niels Böhr and according to which the electrons revolve around of the nucleus at well-defined energy levels.
See also: Dalton’s atomic model
Characteristics of the atom
- It is a very small particle. The atom is the smallest particle that maintains the properties of the chemical element to which it belongs. It is the smallest unit into which matter can be divided; In fact, in Greek the word atom means “not divisible”, although this term is not entirely correct, since the atom is composed of protons, neutrons and electrons.
- It is an infinitely light particle. The approximate mass of protons and neutrons is 1.6726 x 10-27 kg and 1.6749 x 10-27 kg respectively; that of the electrons is even smaller: 9.1 x 10-31 This makes the atoms extremely light.
- forms molecules. Atoms group together to form molecules. Each type of molecule is the combination of a certain number of atoms linked together in a specific way, and a molecule can contain atoms of different chemical elements or of the same element.
- It is unalterable. Each atom retains its structural characteristics, even if they are part of different molecules. During chemical reactions, atoms are neither created nor destroyed, but they are organized differently, creating bonds between one atom and another.
- It has a fixed number of protonsWhat distinguishes chemical elements from each other (among many other characteristics) is the number of protons their atoms have in their nucleus. The number of protons is represented by the letter Z and is called the “atomic number.” The number of protons matches the number of electrons in an electrically neutral atom. The atomic number is usually listed on the periodic table of elements, located above the chemical symbol, on the left.
- Tends to instabilityThe normal tendency of the vast majority of atoms is to join with other atoms (of the same or different types) to form stable groupings (i.e., chemical compounds) because doing so leads to a situation of minimum energy and maximum stability. When forming chemical bonds, they gain, lose, or share electrons. These bonds store energy that is eventually released as heat or light.
- Complies with the octet rule. What justifies the reactivity and formation of bonds is that the atoms comply with the Lewis octet rule, which indicates that the bonds respond to the need to acquire the electronic configuration that characterizes the noble or “inert” gases, with eight electrons located in their last energy level. For example: the formation of the water and acetylene molecules can be represented in the following diagram, where the electrons of carbon and oxygen are represented in red, while those of hydrogen are represented in black.
Structure of the atom
The atom is consisting of a central nucleus and a cloud of electrons around that nucleus. The nucleus contains positively charged particles called protons and also uncharged particles known as neutrons. The negatively charged electron cloud is attracted to the protons in the nucleus by an electromagnetic force. In turn, electrons are characterized by atomic orbitals, which are mathematical functions that represent the probability of finding an electron in a region of space around the nucleus.
You may be interested in: Carbon atom
Mass of the atom
The mass of an atom It is mainly given by the sum of the protons and neutrons in its nucleus (since the mass of electrons is infinitely small and therefore negligible). This parameter is called mass number and is represented by the letter A.
Although The number of protons is identical for all atoms of a given chemical element, the number of neutrons can vary in some of these elements. This happens, for example, with carbon or nitrogen, which are elements that have several isotopes, such as the so-called carbon -14 or nitrogen -15.
The mass numbers (sum of protons and neutrons) of these two isotopes are 14 and 15, respectively.. That is, carbon -14 has 6 protons and 8 neutrons, while nitrogen -15 has 7 protons and 8 neutrons.
chemical reactivity
Although protons and neutrons are important in terms of mass and nuclear reactions, it is the electrons (especially those in the last energy level of the electron cloud) that are responsible for the chemical reactivity of atoms.
It is the electrons that will ultimately allow infinite chemical compounds to be produced and decomposed all the time. That is, Electrons are the subatomic particles that form chemical bonds between atoms. to form the various chemical compounds.
It may help you: Intermolecular forces
References:
- The atom. Sokolovsky, Silvia. 2002
- Natural Sciences. Matter and environment: the matter of the universe. Francisco Soto, Alejandra Gallardo, Raúl Ladrón de Guevara and Judith Reyes. 2019
- Introductory nuclear physics. Kramer, Kenneth. ISBN 047180553X.
- Atom. Wikipedia