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CW 3: Students should be able to describe and model a structure of an atom in terms of the nucleus, protons, neutrons and electrons, comparing mass and charge of protons, neutrons and electrons.

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NOS 1
CW 1,2,4,5,

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Being Numerate (BN)
Being Literate (BL)
Communicating (C)
Working with others (WWO)
Managing information and thinking (MI+T)

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subatomic particle, any of various self-contained units of matter or energy that are the fundamental constituents of all matter. Subatomic particles include electrons, the negatively charged, almost massless particles that nevertheless account for most of the size of the atom, and they include the heavier building blocks of the small but very dense nucleus of the atom, the positively charged protons and the electrically neutral neutrons. But these basic atomic components are by no means the only known subatomic particles. Protons and neutrons, for instance, are themselves made up of elementary particles called quarks, and the electron is only one member of a class of elementary particles that also includes the muon and the neutrino. More-unusual subatomic particles-such as the positron, the antimatter counterpart of the electron-have been detected and characterized in cosmic ray interactions in Earth's atmosphere. The field of subatomic particles has expanded dramatically with the construction of powerful particle accelerators to study high-energy collisions of electrons, protons, and other particles with matter. As particles collide at high energy, the collision energy becomes available for the creation of subatomic particles such as mesons and hyperons. Finally, completing the revolution that began in the early 20th century with theories of the equivalence of matter and energy, the study of subatomic particles has been transformed by the discovery that the actions of forces are due to the exchange of "force" particles such as photons and gluons. More than 200 subatomic particles have been detected-most of them highly unstable, existing for less than a millionth of a second-as a result of collisions produced in cosmic ray reactions or particle accelerator experiments. Theoretical and experimental research in particle physics, the study of subatomic particles and their properties, has given scientists a clearer understanding of the nature of matter and energy and of the origin of the universe.

The current understanding of the state of particle physics is integrated within a conceptual framework known as the Standard Model. The Standard Model provides a classification scheme for all the known subatomic particles based on theoretical descriptions of the basic forces of matter.

Basic concepts of particle physics

The divisible atom

The physical study of subatomic particles became possible only during the 20th century, with the development of increasingly sophisticated apparatuses to probe matter at scales of 10 −15 metre and less (that is, at distances comparable to the diameter of the proton or neutron). Yet the basic philosophy of the subject now known as particle physics dates to at least 500 bce, when the Greek philosopher Leucippus and his pupil Democritus put forward the notion that matter consists of invisibly small, indivisible particles, which they called atoms. For more than 2,000 years the idea of atoms lay largely neglected, while the opposing view that matter consists of four elements-earth, fire, air, and water-held sway. But by the beginning of the 19th century the atomic theory of matter had returned to favour, strengthened in particular by the work of John Dalton, an English chemist whose studies suggested that each chemical element consists of its own unique kind of atom. As such, Dalton's atoms are still the atoms of modern physics. By the close of the century, however, the first indications began to emerge that atoms are not indivisible, as Leucippus and Democritus had imagined, but that they instead contain smaller particles.

In 1896 the French physicist Henri Becquerel discovered radioactivity, and in the following year J.J. Thomson, a professor of physics at the University of Cambridge in England, demonstrated the existence of tiny particles much smaller in mass than hydrogen, the lightest atom. Thomson had discovered the first subatomic particle, the electron. Six years later Ernest Rutherford and Frederick Soddy, working at McGill University in Montreal, found that radioactivity occurs when atoms of one type transmute into those of another kind. The idea of atoms as immutable, indivisible objects had become untenable.

The basic structure of the atom became apparent in 1911, when Rutherford showed that most of the mass of an atom lies concentrated at its centre, in a tiny nucleus. Rutherford postulated that the atom resembled a miniature solar system, with light, negatively charged electrons orbiting the dense, positively charged nucleus, just as the planets orbit the Sun. The Danish theorist Niels Bohr refined this model in 1913 by incorporating the new ideas of quantization that had been developed by the German physicist Max Planck at the turn of the century. Planck had theorized that electromagnetic radiation, such as light, occurs in discrete bundles, or " quanta," of energy now known as photons. Bohr postulated that electrons circled the nucleus in orbits of fixed size and energy and that an electron could jump from one orbit to another only by emitting or absorbing specific quanta of energy. By thus incorporating quantization into his theory of the atom, Bohr introduced one of the basic elements of modern particle physics and prompted wider acceptance of quantization to explain atomic and subatomic phenomena.

Size

Subatomic particles play two vital roles in the structure of matter. They are both the basic building blocks of the universe and the mortar that binds the blocks. Although the particles that fulfill these different roles are of two distinct types, they do share some common characteristics, foremost of which is size.

The small size of subatomic particles is perhaps most convincingly expressed not by stating their absolute units of measure but by comparing them with the complex particles of which they are a part. An atom, for instance, is typically 10 −10 metre across, yet almost all of the size of the atom is unoccupied "empty" space available to the point-charge electrons surrounding the nucleus. The distance across an atomic nucleus of average size is roughly 10 −14 metre-only 1 / 10,000 the diameter of the atom. The nucleus, in turn, is made up of positively charged protons and electrically neutral neutrons, collectively referred to as nucleons, and a single nucleon has a diameter of about 10 −15 metre-that is, about 1 / 10 that of the nucleus and 1 / 100,000 that of the atom. (The distance across the nucleon, 10 −15 metre, is known as a fermi, in honour of the Italian-born physicist Enrico Fermi, who did much experimental and theoretical work on the nature of the nucleus and its contents.)

The sizes of atoms, nuclei, and nucleons are measured by firing a beam of electrons at an appropriate target. The higher the energy of the electrons, the farther they penetrate before being deflected by the electric charges within the atom. For example, a beam with an energy of a few hundred electron volts (eV) scatters from the electrons in a target atom. The way in which the beam is scattered ( electron scattering) can then be studied to determine the general distribution of the atomic electrons.

At energies of a few hundred megaelectron volts (MeV; 10 ⁶ eV), electrons in the beam are little affected by atomic electrons; instead, they penetrate the atom and are scattered by the positive nucleus. Therefore, if such a beam is fired at liquid hydrogen, whose atoms contain only single protons in their nuclei, the pattern of scattered electrons reveals the size of the proton. At energies greater than a gigaelectron volt (GeV; 10 ⁹ eV), the electrons penetrate within the protons and neutrons, and their scattering patterns reveal an inner structure. Thus, protons and neutrons are no more indivisible than atoms are; indeed, they contain still smaller particles, which are called quarks.

Quarks are as small as or smaller than physicists can measure. In experiments at very high energies, equivalent to probing protons in a target with electrons accelerated to nearly 50,000 GeV, quarks appear to behave as points in space, with no measurable size; they must therefore be smaller than 10 −18 metre, or less than 1 / 1,000 the size of the individual nucleons they form. Similar experiments show that electrons too are smaller than it is possible to measure.

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Subatomic particle | Definition, Examples, & Classes

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Subatomic particle, any of various self-contained units of matter or energy that are the fundamental constituents of all matter. They include electrons, protons, neutrons, quarks, muons, and neutrinos, as well as antimatter particles such as positrons.

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Subatomic Particles: So That's What's in an Atom

The atom is the smallest part of matter that represents a particular element. For quite a while, the atom was thought to be the smallest part of matter that could exist. But in the latter part of the 19th century and early part of the 20th, scientists discovered that atoms are composed of certain subatomic particles and that, no matter what the element, the same subatomic particles make up the atom. The number of the various subatomic particles is the only thing that varies.

Scientists now recognize that there are many subatomic particles (this really makes physicists salivate). But in order to be successful in chemistry, you really only need to be concerned with the three major subatomic particles:

The following table summarizes the characteristics of these three subatomic particles.
The Three Major Subatomic Particles
In the table, the masses of the subatomic particles are listed in two ways: grams and amu, which stands for atomic mass units. Expressing mass in amu is much easier than using the gram equivalent.

Atomic mass units are based on something called the Carbon 12 scale, a worldwide standard that's been adopted for atomic weights. By international agreement, a carbon atom that contains 6 protons and 6 neutrons has an atomic weight of exactly 12 amu, so 1 amu is 1/12 of this carbon atom. But what do carbon atoms and the number 12 have to do with anything? Because the mass in grams of protons and neutrons are almost exactly the same, both protons and neutrons are said to have a mass of 1 amu. Notice that the mass of an electron is much smaller than that of either a proton or neutron. It takes almost 2,000 electrons to equal the mass of a single proton.

The table also shows the electrical charge associated with each subatomic particle. Matter can be electrically charged in one of two ways: positive or negative. The proton carries one unit of positive charge, the electron carries one unit of negative charge, and the neutron has no charge - it's neutral.

Scientists have discovered through observation that objects with like charges, whether positive or negative, repel each other, and objects with unlike charges attract each other.

The atom itself has no charge. It's neutral. (Well, actually, certain atoms can gain or lose electrons and acquire a charge. Atoms that gain a charge, either positive or negative, are called ions.) So how can an atom be neutral if it contains positively charged protons and negatively charged electrons? Ah, good question. The answer is that there are equal numbers of protons and electrons - equal numbers of positive and negative charges - so they cancel each other out.

The last column in the table lists the location of the three subatomic particles. Protons and neutrons are located in the nucleus, a dense central core in the middle of the atom, while the electrons are located outside the nucleus.

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Subatomic Particles: So That's What's in an Atom - dummies

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The atom is the smallest part of matter that represents a particular element. For quite a while, the atom was thought to be the smallest part of matter that could exist. But in the latter part of the 19th century and early part of the 20th, scientists discovered that atoms are composed of certain subatomic ...

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Atoms Facts

The name atom comes from the Greek word atomos, which means uncuttable; this implies that atoms are the smallest unit and are not dividable. They are often described as the basic unit of matter.

Atoms contain a dense nucleus surrounded by a cloud of electrons, which contain a negative charge.

The interior of the nucleus contains positively charged protons, and almost all atoms' nuclei (with the exception of hydrogen-1) contain neutrally charged neutrons.

Nearly one hundred percent of the mass of an atom (99.94%) is contained in the nucleus.

The mass of the protons and the mass of the neutrons are almost the same.

Electromagnetic force binds the electron cloud to the nucleus.

A nearly identical force can allow atoms to bind together, forming molecules.

Atoms exist as either electrically neutral, or ions.

In an electrically neutral atom, the number of protons equals the number of electrons, thus cancelling each other out.

In an ion, however, there are more of one of particle than the other, making the atom have either a positive or negative charge.

Atoms are classified according to their numbers of protons or neutrons.

The number of protons in the atom will determine its chemical element, and the number of neutrons will determine its isotope.

Every element has at least one isotope, and many elements have multiple isotopes.

The isotopes undergo radioactive decay due to their unstable nuclei.

The scientific field of quantum mechanics has led to a successful model of the atom and its observable properties.

It wasn't until the end of the 19th century and beginning of the 20th century that scientists began to discover subatomic particles contained within the atom.

As researchers discovered the existence and properties of subatomic particles, a debate ensued about the fact that there was actually something smaller than an atom and that atoms could be divided, nullifying its name.

Some proponents wanted to change the name of the atom to reflect this new understanding, but it didn't catch on.

The first understandings of the existence of atoms date back to ancient Greece, and it was Democritus who first used the term "atomos" (atom).

Early scientists in ancient India independently developed theories on the existence of atoms.

In 1661, Robert Boyle first published the theory that all matter was composed of atoms.

The nature and structure of atoms was improved upon beginning in the 18th century with the advances in chemistry.

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Atoms Facts The name atom comes from the Greek word atomos, which means uncuttable; this implies that atoms are the smallest unit and are not dividable. They are often described as the basic unit of matter. Atoms contain a dense nucleus surrounded by a cloud of electrons, which contain a negative charge.

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Learn how and why J. J. Thompson's plum pudding model of an atom was disproved by Rutherford and team through an experiment. Also, know about the different consequences of the experiment and the inferences drawn from them. Watch the video for more information.

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What are Isotopes? | Properties of Matter | Chemistry | FuseSchool

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We have already learned that ions are atoms that are either missing or have extra electrons. Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope. An atom is still the same element if it is missing an electron. The same goes for isotopes. They are still the same element. They are just a little different from every other atom of the same element.

For example, there are a lot of carbon (C) atoms in the Universe. The normal ones are carbon-12. Those atoms have 6 neutrons. There are a few straggler atoms that don't have 6. Those odd ones may have 7 or even 8 neutrons. As you learn more about chemistry, you will probably hear about carbon-14. Carbon-14 actually has 8 neutrons (2 extra). C-14 is considered an isotope of the element carbon.

If you have looked at a periodic table, you may have noticed that the atomic mass of an element is rarely an even number. That happens because of the isotopes. If you are an atom with an extra electron, it's no big deal. Electrons don't have much of a mass when compared to a neutron or proton.

Atomic masses are calculated by figuring out the amounts of each type of atom and isotope there are in the Universe. For carbon, there are a lot of C-12, a couple of C-13, and a few C-14 atoms. When you average out all of the masses, you get a number that is a little bit higher than 12 (the weight of a C-12 atom). The average atomic mass for the element is actually 12.011. Since you never really know which carbon atom you are using in calculations, you should use the average mass of an atom.

Bromine (Br), at atomic number 35, has a greater variety of isotopes. The atomic mass of bromine (Br) is 79.90. There are two main isotopes at 79 and 81, which average out to the 79.90amu value. The 79 has 44 neutrons and the 81 has 46 neutrons. While it won't change the average atomic mass, scientists have made bromine isotopes with masses from 68 to 97. It's all about the number of neutrons. As you move to higher atomic numbers in the periodic table, you will probably find even more isotopes for each element.

If we look at the C-14 atom one more time, we find that C-14 does not last forever. There is a time when it loses its extra neutrons and becomes C-12. The loss of those neutrons is called radioactive decay. That decay happens regularly like a clock. For carbon, the decay happens in a few thousand years (5,730 years). Some elements take longer, and others have a decay that happens over a period of minutes. Archeologists are able to use their knowledge of radioactive decay when they need to know the date of an object they dug up. C-14 locked in an object from several thousand years ago will decay at a certain rate. With their knowledge of chemistry, archeologists can measure how many thousands of years old an object is. This process is called carbon dating.

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We have already learned that ions are atoms that are either missing or have extra electrons. Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope. An atom is still the same element if it is missing an electron.

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The BSCS 5E Instructional model: Origins and Effectiveness

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Inquiry-Based Science Instruction—What Is It and Does It Matter?

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Simplifying inquiry instruction

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Teaching about scientific inquiry and the nature of science: towards a more complete view of science

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Explanation of use of peer review papers

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Explanation of use of peer review papers