Atoms
John Dalton, an English scientist, proposed the most significant of all chemical theories in 1805. He suggested the idea of matter being made up of atoms. His revolutionary yet basic theory was that all matter, regardless of its form (liquid, gas, or solid), is made up of units he termed atoms.
For almost a century, Dalton's conception of atoms as solid, indivisible objects was widely accepted. We now know that atoms may be broken down into even smaller subatomic particles, some of which reside in a "cloud" around a dense central core known as the nucleus. Over 100 million atoms of even highly thick and heavy things if lined up would measure barely an inch and would contain largely of empty space! As a consequence of continuing study, we are learning more about the quantity and nature of subatomic particles, as well as the core nucleus around which they flow.
Structure of the atom
Atoms include a variety of smaller or subatomic particles, which can be located in the core nucleus or in the electron cloud or field around it. Figure 2-1, A is an atomic model of carbon that depicts the most significant subatomic particles:
- Protons (p)
- Neutrons (n")
- Electrons (e)
Figure 2-1 shows a carbon atom with a central core-like nucleus. It is made up of six positively charged protons (+ or p) and six uncharged neutrons and is found deep within the atom (n). There's also a "cloud" or "field" of six negatively charged electrons around the nucleus (or e). The nucleus of an atom has a positive electrical charge equal to the amount of protons present since protons are positively charged and neutrons are neutral. Electrons travel about the nucleus of an atom in what is known as an electron "cloud" or field (Figure 2-1, B).
The amount of positively charged protons in an atom's nucleus is equal to the number of negatively charged electrons flowing around the nucleus. As a result of the opposite charges cancelling or neutralising each other, atoms are electrically neutral particles.
Atomic weight and atomic number
Because of variations in the number of protons in their atomic nuclei, elements have different chemical and physical characteristics. The atomic number, or the number of protons in an atom's nucleus, is crucial since it determines what sort of element it is. Examine the components mentioned in Table 2-1 that are vital to living creatures once again. The symbol and atomic number of each element are used to identify it. The atomic number of hydrogen, for example, is 1, which indicates that all hydrogen atoms—and only hydrogen atoms—have one proton in their nucleus. The atomic number 6 is assigned to all carbon atoms, and only carbon atoms, which contain six protons. With eight protons and an atomic number of 8, all oxygen atoms, and only oxygen atoms, have an atomic number of 8. In a nutshell, each element is distinguished by its own unique number of protons, or atomic number. Two atoms with differing numbers of protons have distinct atomic numbers and are thus separate elements.
On Earth, there are 92 elements that occur naturally. Because each element is defined by the number of protons in its atoms (atomic number), atoms with 1 to 92 protons exist.
The mass of a single atom is referred to as atomic weight. It is equal to the number of protons plus neutrons in the nucleus of an atom. Electrons have a weight that is almost insignificant. Because protons and neutrons weigh almost the same, the following calculation may be used to calculate atomic weight:
Atomic Weight (p + n)
Uranium is the biggest naturally occurring atom. It contains a nucleus with 92 protons and 146 neutrons and has an atomic weight of 238. Hydrogen, on the other hand, has an atomic weight of one since its nucleus contains just one proton and no neutrons.
PHOTO 2-1 Atomic models are mathematical representations of the atom. The nucleus, which consists of protons (+) and neutrons, is at the centre. Electrons live in what are known as electron shells (A) or "clouds" in the outer regions (B). This is a carbon atom, whose identity is defined by the number of protons in its nucleus. There are six protons in every carbon atom (and only carbon atoms). (In this example, not all of the protons in the nucleus are visible.)
Shells of electrons
The number of protons in an atom's nucleus equals the total number of electrons in the atom (Figure 2-1). These electrons are thought to reside in a cloudlike envelope around the nucleus of the atom. The "cloud" implies that no one electron can be precisely found at a certain instant in time. Earlier theories indicated that electrons travelled about the nucleus in predictable patterns, similar to how planets in our solar system revolve around the sun. The so-called "Bohr model" (Figure 2-1. A) is arguably the most effective tool for viewing atom structure as it enters chemical processes. It was named after Niels Bohr, a Danish scientist who made significant contributions to our knowledge of atomic structure.
The electrons in this model are shown as shells or concentric rings, indicating their relative distances from the nucleus. The electrons that surround the nucleus of an atom are shown in the Bohr model as simple two-dimensional concentric rings. Each ring or shell represents a distinct energy level, and each shell has a limit amount of electrons it can carry. The quantity and configuration of electrons in an atom's energy shells influence whether or not the atom is chemically active.
The electrons in the outermost shell contribute in the creation of chemical bonds in atom-to-atom chemical processes. Electrons tend to congregate in pairs in each shell. If an atom's outermost shell possesses four pairs, or eight electrons, it can be classified as chemically inert and incapable of reacting with another atom. The electron configuration of such an atom is considered to be stable. The importance of electron pairing cannot be overstated. The atom will be chemically active if the outer shell includes solitary, unpaired electrons. Atoms in the outer shell with less or more than eight electrons will try to lose, acquire, or share electrons with other atoms in order to attain stability. The octet rule is the name for this trend. Except for atoms with a single shell that can only store a maximum of two electrons, this rule applies. Hydrogen, for example, contains only one electron in its solitary shell.
As a result, it possesses an unpaired electron and an imperfect shell. As a result, hydrogen has a high reactivity and is involved in a variety of emical processes. In its single shell, helium, on the other hand, contains two electrons. Because this is the shell's maximum number, no chemical activity is conceivable, thus no naturally occurring helium compound exists.
Figure 2-2 depicts many of the most essential facts about electron shells using atoms. Positive and negative charges balance even in the most fundamental structure of the hydrogen atom. However, because the hydrogen nucleus only has one proton, its solitary energy shell only has one electron. Hydrogen is chemically active due to the unpaired electron. The helium atom, on the other hand, has a complete outer shell and, like neon, is inactive or inert. Carbon and oxygen have just four and six electrons in their outer shells, respectively, and will react chemically because they do not meet the octet rule.
ELECTRONIC SHELLS OF FIVE COMMON ELEMENTS (FIGURE 2-2). Positive and negative charges are evenly distributed among all atoms. Two electrons are necessary for stability in atoms with a single shell; hydrogen with a single electron is reactive, but helium with a full shell is not. Eight electrons in the outermost shell are required for stability in atoms having more than one shell. Because neon's outer shell has eight electrons, it is stable. Chemically active are oxygen and carbon, which have six and four electrons in their outer shells, respectively.
QUICK INSPECTION
1. Make a list of the three most essential types of subatomic particles and define them.
2. Explain how an atom's atomic number and atomic weight are determined!
3. What is the definition of an electron shell?
4. Explain what the "octet rule" means.
~1.webp)
