Atomic Model
The atomic model is a scientific theory that describes the structure of an atom. It proposes that atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in specific energy levels or shells. This model helps to explain the behavior and properties of elements and is fundamental to understanding the nature of matter.
8 Key excerpts on "Atomic Model"
- Mark Kernion, Joseph A. Mascetta(Authors)
- 2021(Publication Date)
- Barrons Educational Services(Publisher)
...Rutherford realized, however, that protons, by themselves, could not account for the entire mass of the nucleus. He predicted the existence of a new nuclear particle that would be neutral and would account for the missing mass. In 1932, James Chadwick (England) discovered this particle, the neutron. BOHR MODEL In 1913, Neils Bohr (Denmark) proposed his model of the atom. This pictured the atom as having a dense, positively charged nucleus and negatively charged electrons in specific spherical orbits, also called energy levels or shells, around this nucleus. These shells are arranged concentrically around the nucleus, and each shell is designated by a number: 1, 2, 3,. … The closer to the nucleus, the less energy an electron needs in one of these shells, but it has to gain energy to go from one shell to another that is farther away from the nucleus. Because of its simplicity and general ability to explain chemical change, the Bohr model still has some usefulness today. Principal Energy Level Maximum Number of Electrons (2 n 2) 1 2 2 8 3 18 4 32 5 32 COMPONENTS OF ATOMIC STRUCTURE The following table lists the basic particles of the atom. When these components are used in the Bohr model, we show the protons and neutrons in the nucleus. These particles are known as nucleons. The electrons are shown in the shells. The number of protons in the nucleus of an atom determines the atomic number. All atoms of the same element have the same number of protons and therefore the same atomic number; atoms of different elements have different atomic numbers. Thus, the atomic number identifies the element. An English scientist, Henry Moseley, first determined the atomic numbers of the elements through the use of X-rays. Since the actual masses of subatomic particles and atoms themselves are very small numbers when expressed in grams, scientists use atomic mass units instead...
eBook - ePubChemistry
Concepts and Problems, A Self-Teaching Guide
- Richard Post, Chad Snyder, Clifford C. Houk(Authors)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...Later, we will use this arrangement in discussing chemical bonding, chemical reactions, and chemical properties. QUANTUM Atomic Model The model we discuss has evolved from the study of quantum mechanics (a theoretical mathematical approach to the study of atomic and molecular structure). We do not attempt an in-depth presentation here. Instead, we present some of the basic concepts so you may use them later in this book or build upon them in other chemistry courses. Keep in mind that we are studying the basic model of a very complex theory. A good way to help you remember the model is to compare it to an apartment building. An apartment building has different floors, different apartments on each floor, and different rooms within each apartment. We can look upon the electrons of an atom as rather peculiar apartment dwellers. Electrons prefer the floor closest to the ground and the smallest apartments. Electrons also prefer to live one to a room until each room in an apartment has one occupant. The electrons will then pair up until each room has two. Each room in the apartment can hold only two electrons. Apartment buildings may have several floors. The model we discuss has several floors, but only the first seven floors will be occupied. All the electrons of the elements known today will fit within seven floors of the building. Additional floors are available but will be occupied only in special cases. The floors in the apartment building are called shells in the electron model and are numbered 1 through 7. According to what you have just read, what shell will be occupied first by electrons? _________ Answer: shell 1 (the first floor) Each shell (or floor) in the model has one or more apartments, which are called subshells. These subshells are apartments of four sizes: s, p, d, and f. An s subshell (apartment) has only a single room. A p subshell has three rooms. A d subshell has five rooms, while an f subshell has seven rooms...
eBook - ePub- Kevin R. Reel(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
...It was clear that a more complex model was needed to explain atoms with multiple electrons. • Electrons give off energy in the form of electromagnetic radiation when they move from a higher level, or an excited state, to a lower level. The energy represented by light, using Planck’s equation, represents the difference between the two energy levels of the electron. de Broglie • Louis de Broglie identified the wave characteristics of matter by combining Einstein’s relationship between mass and energy (E = mc 2) and the relationship between velocity and the wavelength of light (E = hv). • This shows that all particles with momentum have a corresponding wave nature. Heisenberg • Werner Heisenberg, in the early 20th century, said that it is impossible to simultaneously know both the position and the momentum of an electron. • For small particles, such as electrons, this uncertainty suggests that we need a wave model, rather than a Newtonian model, to understand their behavior. Schrödinger • Erwin Schrödinger, in the early 20th century, attributed a wave function to electrons. • The wave function describes the probability of where an electron might exist. The regions of high probability are called orbitals, even though they are more like clouds than orbits. • The orbital of each electron is described in Schrödinger’s equation. These orbitals can be described as s, p, d, or f orbitals, as used in electron configurations described later in this chapter. ATOMIC MASS, ATOMIC NUMBER, ISOTOPES Atomic Mass • The mass of an atom consists of the cumulative mass of all the particles in the atom, which includes protons, neutrons, and electrons. • The mass of the electrons is insignificant relative to the mass of protons or neutrons. Therefore, the atomic mass is calculated by adding up the masses of the protons and neutrons. • Example: A helium atom consists of two protons and two electrons. It would have an atomic mass of 4 amu...
eBook - ePub- Colin Salter(Author)
- 2021(Publication Date)
- Pavilion(Publisher)
...Niels Bohr (1885–1962) Model of the atom When Ernest Rutherford published his inspired model of the atom in 1911, it galvanized the atomic physics community. As other scientists looked at it through the prism of their own research, it proved accurate but incomplete. One, Danish scientist Niels Bohr, saw its implications for quantum theory. M ax Planck first proposed the quantum, the minimum amount of any agent in a reaction which was required to make the reaction work, in 1900. Planck applied the idea particularly to electromagnetic radiation, a field in which Niels Bohr completed his PhD in the summer of 1911. Bohr’s research was in the electrons and magnetism of metal elements, and he had concluded that the latter could not be explained by the former alone. In September of that year Bohr travelled to England to meet the great minds of that country’s universities. He impressed Rutherford sufficiently to be invited to join him for a year in post-doctoral research at Manchester University. Bohr combined Rutherford’s ideas with Max Planck’s and proposed an Atomic Model in which electrons not only orbited around a neutron as Rutherford had suggested; they did so at different distances, like the planets around the Sun, and were capable of dropping from an outer orbit to an inner one by shedding a quantum of electromagnetic energy. Rutherford was one of the first to applaud the Bohr Model. It was also enthusiastically received by the younger generation of nuclear physicists, including Albert Einstein, Max Born and Enrico Fermi. The model won admirers because it explained reactions and properties which other models, even Rutherford’s, could not. Better still, it could be used to predict the outcomes of experiments yet to be conducted; and the Bohr Model formed the basis of quantum theory for the next twelve years, until the development of quantum mechanics. He was awarded the Nobel Prize for physics in 1922. Neils Bohr with Albert Einstein in the 1920s...
eBook - ePubRadiation Detection
Concepts, Methods, and Devices
- Douglas McGregor, J. Kenneth Shultis(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
...The number of electrons in an atom equals its atomic number Z and determines its position in the Periodic Table. The chemical properties are determined by the number and arrangement of the electrons. Each element in the table is formed by adding one electron to that of the preceding element in the Periodic Table in such a way that the electron is most tightly bound to the atom. The arrangement of the electrons for the elements with electrons in only the first four shells is shown in Table 3.3. Table 3.3. Electron shell arrangement for the lightest elements. 3.4.7 Success of Quantum Mechanics Quantum mechanics has been an extremely powerful tool for describing the energy levels and the distributions of atomic electrons around a nucleus. Each energy level and configuration is uniquely defined by four quantum numbers: n the principal quantum number, ℓ the orbital angular momentum quantum number, m ℓ the z -component of the angular momentum, and m s = ±1/2, the electron spin number. These numbers arise naturally from the analytical solution of the wave equation (as modified by Dirac to include special relativity effects) and thus avoid the ad hoc introduction of orbital quantum numbers required in earlier Atomic Models. Inside the nucleus, quantum mechanics is also thought to govern. However, the nuclear forces holding the neutrons and protons together are much more complicated than the electromagnetic forces binding electrons to the nucleus. Consequently, much work continues in the application of quantum mechanics (and its more general successor quantum electrodynamics) to predicting energy and configuration states of nucleons. Nonetheless, the fact that electronic energy levels of an atom and nuclear excited states are discrete with very specific configurations is a key concept in modern physics...
eBook - ePub- Dov M. Gabbay, Paul Thagard, John Woods, Dov M. Gabbay, Paul Thagard, John Woods(Authors)
- 2011(Publication Date)
- North Holland(Publisher)
...Since a full account of the electron requires quantum mechanics, it appears essential to initiate a physical description of a molecule in terms of its sub-atomic constituents, that is, as a collection of electrons and nuclei governed by an appropriate Schrödinger equation. This is so even though the electron plays no role in the (chemical) equations that describe chemical reactions; the irreducible unit of chemical transformations remains the atom. We remark in passing that there is something problematic about molecular structure itself in this setting [ Löwdin, 1988 ]. Suppose the molecule contains A nuclei which, to simplify the discussion, are taken to be distinguishable, and that one nuclear coordinate is fixed in the process of elimination of the centre-of-mass motion. There are then (3 A − 3) coordinates to be determined, whereas there are A (A − 1)/2 internuclear distances in a ‘structure’, and so for A > 6 the system is over-determined. Hence the existence of specific ‘molecular structures’ cannot be taken for granted; there must be further constraints to make the additional internuclear distances compatible with the others 13. 13 If rotation is also separated off there are (3 A − 6) coordinates and the condition for overdetermination becomes A > 4. At a fundamental level the atom is an electrodynamical system because even if it is overall electrically neutral its constituent charges are coupled to the electro-magnetic field. If we assume that the particle speeds are much less than the speed of light, all virtual radiative processes are accounted for by the use of the experimental mass and charge values, and disregard real (energy-conserving) molecule-photon interactions, the QED Hamiltonian in the Coulomb gauge 14 for a system of N electrons and A atomic nuclei reduces to the Coulomb Hamiltonian operator we referred to in §2, (equation (1))...
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...Chapter 5 Atomic Theory and the Periodic Table Development of Atomic Theory Around 400 BCE, the Greek philosopher Democritus theorized that everything is comprised of indivisible particles, or “atomos.” For the next 2,200 years, there was no substantive change in how people viewed matter. However, beginning with John Dalton in the early 1800s, atomic theory evolved with sweeping changes. It is important to remember that no one has actually “seen” an atom, so scientists must utilize the data collected from a myriad of experiments to guide their theories. Dalton John Dalton was the pioneer of modern atomic theory. Dalton proposed that all matter is composed of subunits called atoms, which were essentially solid spheres. There are different types of atoms, called elements. Elements combined together in definite whole-number ratios to form compounds. Dalton also used his mass experiments as a basis for the idea that atoms are never created or destroyed during chemical reactions—they are merely rearranged to form new compounds. TEST TIP The AP exam requires students to evaluate and refine scientific questions. The progression of how different scientists came to understand atomic structure is a classic example of how others used the scientific process to understand something unseen and previously unknown. Thompson J. J. Thompson performed research with cathode ray tubes where he observed the deflection of particles inside the tube. Thompson concluded that atoms are composed of positive and negatively charged particles. He developed the “plum pudding” model of the atom (see Figure 5.1), where electrons were arbitrarily spread throughout an atom that was uniformly composed of positive charges. Figure 5.1. Thompson Model of the Atom Millikan Robert Millikan performed research on the electron. He is best known for his oil-drop experiment where he calculated the charge of an electron based upon a mass-to-charge ratio. Rutherford Ernest Rutherford was a contemporary of J. J...
eBook - ePubParticles, Fields, Space-Time
From Thomson's Electron to Higgs' Boson
- Martin Pohl(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...CHAPTER 4 Atoms and nuclei Shortly after electrons were discovered it was thought that atoms were like little solar systems, made up of a …nucleus and electrons, which went around in “orbits,” much like the planets …around the sun. If you think that’s the way atoms are, then you’re back in 1910. Richard P. Feynman, The Strange Theory of Light and Matter, 1985 [ 457 ] Y OU HAVE NOTED by now that I do not care too much about chronology. I rather care about the continuity or discontinuity of ideas as we follow our reductionist narrative. In this chapter we look at how classical physics arrived at the notion of atoms in the 18th and 19th centuries. And how Rutherford, Geiger and Marsden discovered their substructure. The uncertainty about the ultimate nature of matter is of course much older than physics. Indian and Greek philosophers already disputed whether matter was granular or continuous, made of atoms or made of symmetries. But their theories were based on pure thinking, without much input from Nature itself. So we jump ahead to the beginning of the scientific study of matter, in physics and chemistry, in the 18th century. 4.1 Atomism For many, scientific atomism starts with Daniel Bernoulli’s book “Hydrodynamica” of 1738 [ 3 ]. The bulk of the book deals with the dynamics of fluids as the title says, based on the conservation of energy. This conservation law was then still far from established. In Chapter 10 of his book, Bernoulli introduced the kinetic theory of gases, describing them as made of microscopic rigid bodies in motion, which scatter elastically from one another and from the boundaries of the gas volume. He demonstrated that pressure is caused by their impacts on the boundaries, as we show in Focus Box 4.1. Thus heat was identified as the kinetic energy of the gas atoms or molecules. Gases where only elastic scattering among molecules and with the confining boundaries occurs are called ideal gases. Noble gases are a particularly good example...
