Unit 4: Atoms Flashcards Preview

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Flashcards in Unit 4: Atoms Deck (46):


a tiny particle that is the fundamental building block of all substances and whose properties determine the properties of an element made up only of those atoms.


Atomic Mass

the measure of the mass of an atom, generally the sum of the protons and neutrons; this term is used when referring to a single atom or atoms of a single isotope.


Atomic Nucleus

the positively charged core of an atom, which is composed of positively charged protons and electrically neutral neutrons.


Atomic Number

the number of protons in every atom of an element.



a tiny part of an atom with a negative electrical charge.



atoms of the same element that differ in the number of neutrons in the nucleus.



a neutral particle with approximately the same mass as a proton, found in nuclei of atoms along with protons, composed of one up quark and two down quarks



a positively charged particle found in the nuclei of atoms, composed of two up quark and one down quark.


Atomic Structure

the structure of an atom, theoretically consisting of a positively charged nucleus surrounded and neutralized by negatively charged electrons revolving in orbits at varying distances from the nucleus.


Atomic Number

the number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table.



A quark is one of the fundamental subatomic particles in physics. They join to form hadrons, such as protons and neutrons, which are components of the nuclei of atoms; ; theoretically, six types of quarks exist and their existence has been demonstrated experimentally



collective term for protons and neutrons.


Subatomic Particles

a particle smaller than an atom (e.g., a neutron) or a cluster of such particles (e.g., an alpha particle).



any elementary particle that is subject to the strong interaction. Hadrons are subdivided into baryons and mesons.



any of the subatomic particles (such as protons and neutrons) that are made up of quarks and are subject to the strong force. They are subdivided into baryons and mesons.



a subatomic particle of a class that is thought to bind quarks together.


Strong Interaction (Strong Nuclear Force)

As its name implies, the strong force is the strongest force of the four fundamental interactions. It is responsible for binding quarks together in clusters to make more familiar subatomic particles, such as protons and neutrons. It also holds together the atomic nucleus and underlies interactions between all particles containing quarks.

Simple: The strong nuclear force is the nuclear binding force, the force that provides the attraction between protons and neutrons and holds an atom's nucleus together.


Four Fundamental Interactions

Strong Interaction, Electromagnetism, Weak Interaction, Gravitation


Confinement (Color Confinement)

the phenomena that color charged particles (such as quarks and gluons) cannot be isolated, and therefore cannot be directly observed in normal conditions below the Hagedorn temperature of approx. 2 trillion kelvin.


Hagedorn Temperature

temperature in theoretical physics where hadronic matter (i.e. ordinary matter) is no longer stable, and must either "evaporate" or convert into quark matter


Composite Particles

A subatomic particle that is composed of two or more elementary particles. The protons and neutrons in the nucleus of an atom are composite particles, as they are composed of quarks; electrons orbiting the nucleus are not composite particles.


Residual Strong Force

The strong nuclear force is so strong that it actually goes beyond one proton or neutron and pulls on quarks inside other protons and neutrons. This force is called residual strong interaction because it is from the strong force. The residual strong interaction holds the atomic nucleus together and is the missing force that you can't recognize until you know about quarks.


Up Quarks

Up quarks are particles with a positive two-thirds charge.


Down Quarks

Down quarks are particles with a negative one-third charge.


Radioactive Decay

Radioactive decay (also known as nuclear decay or radioactivity) is the stochastic (random) process occurring in an unstable atomic nuclei - that is, one lacking enough binding energy to hold the nucleus together due to an excess of either protons or neutrons. During this process the unstable atomic nucleus loses energy in terms of mass in its rest frame by emitting radiation; such as alpha, beta or gamma particles.


Radioactive Decay

Radioactive decay (also known as nuclear decay or radioactivity) is the stochastic (random) process occurring in an unstable atomic nuclei - that is, one lacking enough binding energy to hold the nucleus together due to an excess of either protons or neutrons. During this process the unstable atomic nucleus loses energy in terms of mass in its rest frame by emitting radiation; such as alpha, beta or gamma particles.

Radioactive decay causes new isotopes, or elements, to form.



the process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body


Alpha Decay

Definition: a radioactive process in which an alpha particle is emitted from the nucleus of an atom, decreasing its atomic number by two.

Explanation: An alpha particle is made up of two protons and two neutrons bound together.

It initially escapes from the nucleus of its parent atom, invariably (always) one of the heaviest elements, by quantum mechanical processes and is repelled further from it by electromagnetism, as both the alpha particle and the nucleus are positively charged. The process changes the original atom from which the alpha particle is emitted into a different element.

Its mass number decreases by four and its atomic number by two. For example, uranium-238 will decay to thorium-234.

Sometimes one of these daughter nuclides will also be radioactive, usually decaying further by one of the other processes described below.


Beta Decay

Definition: a radioactive process in which a beta particle is emitted from the nucleus of an atom, raising the atomic number of the atom by one if the particle is negatively charged, lowering it by one if positively charged.

Explanation: Beta decay itself comes in two kinds: β+ and β-.

β- emission occurs by the transformation of one of the nucleus’s neutrons into a proton, an electron and an antineutrino. Byproducts of fission from nuclear reactors often undergo β- decay as they are likely to have an excess of neutrons.

β+ decays is a similar process, but involves a proton changing into a neutron, a positron and a neutrino.


Gamma Decay

Definition: A radioactive process in which an atomic nucleus loses energy by emitting a gamma ray (a stream of high-energy photons). When an element undergoes gamma decay its atomic number and mass number do not change.

Gamma radiation is the most penetrating of the three, and will travel through several centimetres of lead.

Beta particles will be absorbed by a few millimetres of aluminium, while alpha particles will be stopped in their tracks be a few centimetres of air, or a sheet of paper – although this type of radiation does the most damage to materials it hits.


Decay Chain

the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes (radioactive isotopes) do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached.



a distinct kind of atom or nucleus characterized by a specific number of protons and neutrons.



Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of a given element have the same number of protons in each atom.

Isotopes are unstable, give off radiation, and decay at a constant rate.



a subatomic particle with the same mass as an electron and a numerically equal but positive charge.



For each neutrino, there also exists a corresponding antiparticle, called an antineutrino, which also has no electric charge and half-integer spin. Antineutrinos are produced in nuclear beta decay together with a beta particle,

ex: a neutron decays into a proton, electron, and antineutrino.


Decay Chain

A sequence of radioactive decay processes, in which the decay of one element creates a new element that may itself be radioactive. The chain ends when stable atoms are formed. For example, uranium-238 decays into thorium-234, which in turn decays into palladium-234, and so on until stable iron is produced at the end of the chain. Also called decay sequence.



an atomic species in which the atoms all have the same atomic number and mass number.


Three Flavors of Neutrino

There are three flavors of neutrinos; electron, muon, and tau



Definition: a neutral subatomic particle with a mass close to zero and half-integral spin, rarely reacting with normal matter. Three kinds of neutrinos are known, associated with the electron, muon, and tau particle.

Explanation: One of the fundamental particles, neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it.

If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.



the time needed for half of a sample of radioactive material to decay


Radioactive Dating (Radiomatric Dating)

any method of determining the age of earth materials or objects of organic origin based on measurement of either short-lived radioactive elements or the amount of a long-lived radioactive element plus its decay product.



Half-life is the time it takes for half the radioactive nuclei in a sample to undergo radioactive decay.


Nuclear Fission

the splitting of the nucleus of an atom into nuclei of lighter atoms, accompanied by the release of energy.


Nuclear Fusion

a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with mass converted into energy that is released


Nuclear Fission

a nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the emission of neutrons and conversion of mass into energy that is released.


Percent Abundance

the amount of a certain isotope that occurs in a natural sample of an element