The nature of matter has challenged science since the beginning of time. In 450 BCE, the philosopher Democritus considered a question that has yet to be answered. To what extent can we define what exists? To what extent can we take the Universe apart? From this philosophy came the word atom from the Greek word atomos, meaning indivisible. Although we now know that the atom can be divided further, the name remains. The atom is the smallest unit of an element. For example, the smallest quantity of iron that can be obtained is a single atom of iron. If the atom were divided further, it would no longer be iron. The study of the atom and its characteristics is the focus of the entire science of chemistry.
More specifically, chemistry deals with the electronic configuration of the atom and the electronic interactions between them. The force that causes these interactions is known as the weak force. The weak force causes electrons to be attracted to the nucleus of the atom. This force extends beyond the atom itself, however, and attracts electrons from other atoms. When the atom’s weak force is occupied with a certain number of electrons (determined by the element), the atom is said to be at a low level of energy. Atoms that are not at this optimal level of energy tend to interact in order to allow the most stable electronic configuration. These interactions are chemical reactions.
When atoms interact to achieve lower energy states, they tend to interact in two fundamentally different ways. The first of these means of interaction is through the formation of ions. Ions form when atoms gain or loose ownership of electrons. The increased or reduced number of electrons induces a charge on the atom. The atom can either be positively charged (caused by a decrease in the quantity of electrons), or negatively charged (caused by an increase in the number of electrons.) These charged atoms attract to atoms of opposite charge to form ionic compounds. This form of interaction forms extremely resilient bonds, causing ionic compounds to have massive melting points.
Atoms can also interact through covalent bonding. This occurs when the atoms do not differ as much in the nature of their electron configurations (more specifically, differing electronegativity.) Therefore, electrons are not transferred permanently from one atom to another, but instead alternate between atoms. The bonded electrons are attracted most strongly to the most electronegative atom in the compound, causing the electrons to be shared unequally.
Atoms differ not onlty in electronic configuration, but also in nuclear configuration. The nucleus of the atom determines the total mass of the atom (electron mass is negligible), and the lowest energy electronic configuration. The nucleus defines the element of the atom; more specifically, it is defined by the number of protons in the nucleus (determining electron structure.) The sum of the proton count of the nucleus is equivalent to the nuclear charge of the atom. The sum of the electron count is equivalent to the electronic charge of the atom, and is negative. The sum of the proton count and the electron count is the total charge of the atom, which can either be positive or negative. The atom is commonly modelled in its 0 charge form.
The quantum model of the atom describes the electrons as occupying a cloud, where darker regions are more frequently occupied by an electron. The area in which an electron can be found is known as an orbital. The shape and arrangement of the orbitals in three dimensions determines numerous chemical properties, such as bond angle, bonding type, and possible bonding configurations. It is the most accurate method to date used to describe the mysterious atom, in particular the transition metals.
It is important to remember, however, that the properties described are associated only with theory. Although current models accurately describe chemical behaviour, in the future the models may change. The quantum model, although currently sufficient, may not be the true nature of the atom. Our image of matter is not set in stone. Until the Universe is described in full, we cannot know the full nature of matter and existence.
