Skip to main content Skip to table of contents. Advertisement Hide. Editors view affiliations D. Michael P. Front Matter Pages i-viii.
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Structure and Bonding: The Early Days. Pages Single-Molecule Magnets and Related Phenomena. Evans, Xue Duan. The Renaissance of Fullerene Superconductivity. Synthetic Bioinorganic Chemistry: Scorpionates Turn Back Matter Pages About this book Introduction Chemical structure and bonding. The scope of the series spans the entire Periodic Table and addresses structure and bonding issues associated with all of the elements. Energy is the capacity to do work. Matter has mass and occupies space. All matter is composed of basic elements that cannot be broken down to substances with different chemical or physical properties.
Elements are substances consisting of one type of atom , for example Carbon atoms make up diamond, and also graphite. Pure 24K gold is composed of only one type of atom, gold atoms. Atoms are the smallest particle into which an element can be divided. The ancient Greek philosophers developed the concept of the atom, although they considered it the fundamental particle that could not be broken down. Since the work of Enrico Fermi and his colleagues, we now know that the atom is divisible, often releasing tremendous energies as in nuclear explosions or in a controlled fashion in thermonuclear power plants.
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Subatomic particles were discovered during the s. For our purposes we will concentrate only on three of them, summarized in Table 1. The proton is located in the center or nucleus of an atom, each atom has at least one proton. Elements differ from each other in the number of protons they have, e. Hydrogen has 1 proton; Helium has 2. The neutron also is located in the atomic nucleus except in Hydrogen.
The neutron has no charge, and a mass of slightly over 1 amu. Some scientists propose the neutron is made up of a proton and electron-like particle. The electron is a very small particle located outside the nucleus. Because they move at speeds near the speed of light the precise location of electrons is hard to pin down. Electrons occupy orbitals, or areas where they have a high statistical probability of occurring. The charge on an electron is Its mass is negligible approximately electrons are needed to equal the mass of one proton. Name Charge Location Mass Proton.
The atomic number is the number of protons an atom has. It is characteristic and unique for each element. The atomic mass also referred to as the atomic weight is the number of protons and neutrons in an atom. Atoms of an element that have differing numbers of neutrons but a constant atomic number are termed isotopes. Isotopes, shown in Figure 1 and Figure 2, can be used to determine the diet of ancient peoples by determining proportions of isotopes in mummified or fossilized human tissues. Biochemical pathways can be deciphered by using isotopic tracers.
The age of fossils and artifacts can be determined by using radioactive isotopes, either directly on the fossil if it is young enough or on the rocks that surround the fossil for older fossils like dinosaurs.
Isotopes are also the source of radiation used in medical diagnostic and treatment procedures. Figure 1. Note that each of these isotopes of hydrogen has only one proton. Isotopes differ from each other in the number of neutrons, not in the number of protons. Image from Purves et al. Some isotopes are radioisotopes, which spontaneously decay, releasing radioactivity. Other isotopes are stable.
Examples of radioisotopes are Carbon symbol 14 C , and deuterium also known as Hydrogen-2; 2 H. Stable isotopes are 12 C and 1 H.
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Figure 2. Carbon has three isotopes, of which carbon and carbon are the most well known. The Periodic Table of the Elements, a version of which is shown in Figure 3, provides a great deal of information about various elements.
An on-line Periodic Table is available by clicking here ,. Figure 3. The Periodic Table of the Elements. Each Roman numeraled column on the label at least the ones ending in A tells us how many electrons are in the outer shell of the atom. Each numbered row on the table tells us how many electron shells an atom has. Thus, Hydrogen, in column IA, row 1 has one electron in one shell.
Phosphorous in column VA, row 3 has 5 electrons in its outer shell, and has three shells in total. Image from James K. Hardy's chemistry site at the University of Akron. Electrons, because they move so fast approximately at the speed of light , seem to straddle the fence separating energy from matter. Because of his and others work, we think of electrons both as particles of matter having mass is a property of matter and as units or quanta of energy. When subjected to energy, electrons will acquire some of that energy, as shown in Figure 4. Figure 4. Excitation of an electron by energy, causing the electron to "jump" to another electron energy level known as the excited state.
Orbitals have a variety of shapes. Each orbital has a characteristic energy state and a characteristic shape. The s orbital is spherical. Since each orbital can hold a maximum of two electrons, atomic numbers above 2 must fill the other orbitals. The p x , p y , and p z orbitals are dumbbell shaped, along the x, y, and z axes respectively.
These orbital shapes are shown in Figure 5. Energy levels also referred to as electron shells are located a certain "distance" from the nucleus. The major energy levels into which electrons fit, are from the nucleus outward K, L, M, and N.
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Sometimes these are numbered, with electron configurations being: 1 s 2 2 s 2 2 p 1 , where the first shell K is indicated with the number 1, the second shell L with the number 2, etc. This nomenclature tells us that for the atom mentioned in this paragraph, the first energy level shell has two electrons in its s orbital the only orbital it can have , and second energy level has a maximum of two electrons in its s orbital, plus one electron in its p orbital.
Figure 5. Geometry of orbitals.
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S-orbitals are spherical, p-orbitals are shaped like a dumbbell or figure 8. During the nineteenth century, chemists arranged the then-known elements according to chemical bonding, recognizing that one group the furthermost right column on the Periodic Table, referred to as the Inert Gases or Noble Gases tended to occur in elemental form in other words, not in a molecule with other elements.
It was later determined that this group had outer electron shells containing two as in the case of Helium or eight Neon, Xenon, Radon, Krypton, etc.
As a general rule, for the atoms we are likely to encounter in biological systems, atoms tend to gain or lose their outer electrons to achieve a Noble Gas outer electron shell configuration of two or eight electrons.