2. Atomic Structure

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Atomic structure is one of the main foundations of chemistry and is therefore a crucial topic for any student preparing for the ENEM exam. Understanding atomic structure is essential to understanding how elements interact with each other to form compounds and how these compounds react with each other.

The atom is the smallest unit of an element that retains the properties of that element. Atoms are made up of three main subatomic particles: protons, neutrons, and electrons.

Protons

Protons are subatomic particles with a positive charge located in the nucleus of an atom. The number of protons in an atom determines the element's atomic number and therefore the element's identity. For example, an atom with a single proton is a hydrogen atom, while an atom with two protons is a helium atom.

Neutrons

Neutrons are uncharged subatomic particles located in the nucleus of an atom. The number of neutrons in an atom does not affect the identity of the element, but it does affect the mass of the atom and therefore the isotope of the element. For example, hydrogen-1 (protium) has zero neutrons, while hydrogen-2 (deuterium) has one neutron.

Electrons

Electrons are negatively charged subatomic particles that orbit the nucleus of the atom in regions called orbitals. The distribution of electrons around the nucleus of the atom determines the element's reactivity and its ability to form chemical bonds with other elements.

Atomic Models

Throughout history, various atomic models have been proposed to explain the structure of the atom. Dalton's model, proposed in 1803, was the first to suggest that atoms are indivisible particles. However, subsequent experiments revealed that atoms are composed of subatomic particles.

Thomson's model, proposed in 1897, suggested that atoms are a "soup" of positive charge with electrons embedded in it. This model was later refuted by Rutherford's experiment, which showed that most of the atom's mass and all of its positive charge are concentrated in the nucleus of the atom.

Bohr's model, proposed in 1913, described the atom as a nucleus with electrons orbiting in specific shells, or energy levels. While this model has been useful in explaining many aspects of chemistry, it has failed to explain the behavior of electrons in atoms with more than one electron.

The quantum model of the atom, which is the currently accepted model, describes electrons as existing in a probability cloud surrounding the nucleus. This model is based on quantum mechanics and provides an accurate description of the behavior of electrons in atoms of all sizes.

Understanding atomic structure is crucial to understanding chemistry. Each element in the periodic table has a unique number of protons, neutrons, and electrons, and it is the configuration of these subatomic particles that determines the element's properties. Understanding how these particles interact with each other and with the particles of other atoms is the key to understanding chemistry.

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32.1. Atomic Structure: Atomic Models