Atoms, nuclear decay, electronic structure, and atomic chemical behavior
Neutrons, protons, isotopes
- Carbon-12 (or 12C) contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 amu (six protons and six neutrons).- Carbon-14 (or 14C) contains six protons, eight neutrons, and six electrons; its atomic mass is 14 AMU (six protons and eight neutrons).
Neutrons, protons, isotopes
An atom is the smallest unit of matter that retains all of the chemical properties of an element. Atoms combine to form molecules, which then interact to form solids, gases, or liquids. For example, water is composed of hydrogen and oxygen atoms that have combined to form water molecules. See jackwestin.com.`
Classical Experiment-The Millikan Oil Drop Experiment
A charged oil droplet is put into an electric field and becomes suspended. In addition other droplets fall. An electron is added to an oil droplet and ionized by impact before getting to the electric field. Because the droplets are suspended in the electric field, the gravitational force cancels the electric field. The charge of an electron has a fixed numerical value that is the same for all electrons. The value for this fundamental unit of charge is 1.6x10-19 C.
Classical Experiment-Mass spectrometry
A mass spectrometer is designed to measure the charge to mass ratio for a charged particle. This is accomplished by sending a particle into a perpendicular magnetic field and observing the degree to which it curves. The degree of arcing (radius of curvature) for a particle can vary with mass, initial velocity, magnitude of charge, and the strength of the magnetic field. As the momentum increases, (either mass or initial velocity) the particle deflects less, so the radius of curvature increases. As the charge magnitude increases, the force causing deflection increases, so the particle deflects more, causing the radius of curvature to decrease. By comparing the curvature of for an atomic or molecule ion to a known standard, the mass of the unknown ion can be determined. The mass spectrometer is used in general chemistry to determine the isotopic abundance. See equation and photo in BR Atomic theory on page #77.
Mass spectrometer
A particle's mass can be calculated based on parameters such as how long it takes to travel a certain distance or its angle of travel. Mass spectrometers are so accurate that they can determine the types of elements in a compound or measure the differences between the mass of different isotopes of the same atom. See jackwestin.com.
Classical Experiment-Rutherford Experiment
A thin strip of gold foil lies perpendicular to an incoming stream of alpha particles. The stream of alpha particles first passes through a small pore in a lead plate to create a straight, thin beam of particles. The beam then strikes a gold strip that is surrounding by a zinc sulfide band that luminesces if it is struck by alpha particles. He reasoned that many of the alpha particles would ricochet off the gold foil but that did not happen and the particles struck the zinc sulfide band. Results indicate that the atom is predominantly a dense nuclei with all of the mass centrally located which is known as the plum pudding model.
Radioactive decay
Alpha particles are equivalent to a helium (He) nuclei, made of two protons and neutrons. Beta radiation is the emission a beta particle, most commonly an electron. Positrons, the antiparticle of electrons, are also beta particles and can also be emitted by beta radiation. Gamma radiation is high-energy electromagnetic waves. Alpha decay is seen only in heavier elements greater than atomic number 52, tellurium. The other two types of decay are seen in all of the elements.
Atomic number, atomic weight-Key Points
An atom is composed of two regions: the nucleus, which is in the centre of the atom and contains protons and neutrons, and the outer region of the atom, which holds its electrons in orbit around the nucleus. Charges of proton (+1), neutrons (0) and electron (-1). Neutral atoms of each element contain an equal number of protons and electrons. Proton and Neutron have approximately the same mass, about 1.67 × 10-24 grams, or one atomic mass unit (AMU) or one Dalton. Atomic mass is the sum of the mass of protons and neutrons of that atom.
Neutrons, protons, isotopes
Atoms are made up of sub-atomic particles called protons, neutrons, and electrons, which are responsible for the mass and charge of atoms. An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons. And the outer region of the atom, which holds its electrons in orbit around the nucleus. The number of protons is equal to the number of electrons in neutral atoms. This is the atomic number. Proton is positively charged (+1), a neutron is neutral in charge, and the electron is negatively charged (-1).
Radioactive decay-Key Terms
Electron: Each electron has a negative charge (-1) with weight so small it's normally negligible as compared to proton or neutron. Positron: antiparticle counterpart of an electron. Has a charge of +1. Radioactive decay: the process by which an unstable atomic nucleus loses energy by radiation Mean lifetime: represents the average lifetime of an atomic nucleus in a radioactive sample
Radioactive decay-Key Terms
Half-life: the time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay Radioisotope: a radioactive isotope Exponential: is a specific way that a quantity may increase over time. Proton: Positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element. It weighs one amu. Neutron: A subatomic particle forming part of the nucleus of an atom. It has no charge. It is equal in mass to a proton, or it weighs one amu.
Radioactive decay-Key Terms
Isotope: a variant of a particular chemical element, which shares the same number of protons as other atoms of the element, but differs in its number of neutrons. Alpha particle: a particle consisting of two protons and two neutrons bound together, identical to a helium nucleus. Beta particle: a high energy electron released during beta decay. Gamma-ray: a high-energy wave of electromagnetic energy. Penetrating power: the energy with which the radiation particles are ejected from the atom.
Mass spectrometer
Mass Spectrometer is a device to measure mass. First, the sample is vapourised into a gaseous state. The gaseous samples are then ionized. Ionizationis the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or ions. Once the sample is ionized, it is passed through an electric or magnetic field where it accelerates and deflects and is separated out based on its mass. The charged particles are detected at the end by Faraday collectors and the relative current generated by these ions will indicate its relative abundance.
Mass spectrometer-Key Points
Mass spectrometers work on samples in a gaseous state. An ion source ionizes the gaseous samples. Mass analyzers separate ionized samples according to their mass-to-charge ratio. A particle's mass can be calculated very accurately based on parameters such as how long it takes to travel a certain distance or its angle of travel. Mass spectrometers are so accurate that they can determine the types of elements in a compound or measure the differences between the mass of different isotopes of the same atom.
Radioactive decay
Nuclear chemistry is the chemistry that the nucleus of an atom can undergo. Includes nuclear decay and nuclear capture. Nuclear decay is the process of particle loss from the nucleus that results in a different nucleus. May also be referred to as fission. Nuclear capture is the process of particle gain by the nucleus that results in a different nucleus. AKA fusion.
Radioactive decay
Particles with a mass of less than 56 amu undergo fusion, while particles with mass greater than 56 amu undergo fission. Particles considered to be lost or gained include: alpha particles (helium nucleus), beta particles (an electron), positrons (a positively charged particle with the mass of an electron), neutrons, and neutrinos (an uncharged particle with the mass of an electron).
Atomic number, atomic weight
Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams, which scientists define as one atomic mass unit (AMU). Together, the number of protons and the number of neutrons determine an element's mass number.
Radioactive decay
Radioactive decay occurs when an unstable atomic nucleus emits particles or light waves. Isotopes are atoms of the same element (thereby having the same number of protons) which differ in the number of neutrons in their nucleus. Some isotopes of a given element are more unstable than others, causing a nuclear reaction which releases energy to achieve a more stable nuclear configuration. Such isotopes are radioactive, and are referred to as "radioisotopes."
Radioactive decay-Key Points
Radioactive decay occurs when an unstable atomic nucleus loses energy by emitting energy in the form of emitted particles or electromagnetic waves, called radiation. Alpha particles carry a positive charge, beta particles carry a negative charge, and gamma rays are neutral. An alpha particle is made up of two protons and two neutrons bound together. Beta particles are high energy electrons or positrons. Beta radiation occurs when a neutron turns into a proton releasing an electron. Gamma rays are waves of electromagnetic energy or photons. The atomic mass number (A) and atomic number (Z) can be used to calculate the properties of an atom after radioactive decay.
Radioactive decay
Some isotopes are unstable and will undergo radioactive decay to become other elements. The radioactive decay rate is exponential and is characterized by constants, such as half-life, as well as the activity and number of particles. The half-life (t1/2) is the time taken for the activity of a given amount of a radioactive substance to decay to half of its initial value. λ, pronounced "lambda," is the decay constant, which is the inverse of the mean lifetime (tau). See jackwestin.com and notecard.
Classical Experiment-The Thomson Experiment
The Thomson experiment demonstrated the existence of opposite charges in an atom and that charge is fixed in terms of quantity. Thomson deflected a stream of charged particles (electrons) using an external electric field (the parallel plates of a capacitor). Because the stream of particles bent in a uniform fashion, Thomson concluded that there was a consistent charge to mass ratio for the particles. Thomson observed that when he applied an electric field (positively charged plate on one side and a negatively charged plate on the other) perpendicular to the electron beam he could deflect the beam the exact amount each time. The magnitude of deflection depends on the strength of the field (charge on the plates and the distance between the plates) and the mass of the electron. Reversing the plates of the external field gets deflection of the same magnitude, but in the opposite direction. Thomson concluded that there are two types of charges that oppose each other a positive and a negative charge and that electrons have a fixed charge-to-mass ratio measured as 1.76x108 C/g.
Atomic number, atomic weight
The atomic number is equal to the number of protons in an atom's nucleus. The atomic mass is the sum of the mass of protons and neutrons.
Radioactive decay
The half-life of a sample of material is the period of time required for 50% of the concentration of material to decay to a different possibly more stable form. It is most common to see half-lives associated with first order decay. However, zero order decay does exist. For first-order process, the half-life is constant regardless of the concentration. As the concentration decreases, the duration of the half-life remains the same. For zero-order process, the half-life is directly proportional to the concentration. As the concentration decreases, so does the duration of the half-life. For a second-order process, the half-life is indirectly proportional to the concentration of the compound. As the concentration decreases, the length of the half-life increases. Refer to BR Atomic Theory page #124-#125. When a problem asks how much time passes until a certain percentage of the original quantity remains, it is easiest to figure how many half-lives are required to reach that percentage and then convert the quantity of half-lives to total time.
Nuclear forces, binding energy
The mass defect states that the mass of every nucleus is small. Results from matter being converted to energy. The strong nuclear force hold the nucleons (protons and neutrons) together and is extremely strong, however it only acts over short distances. The nucleons must get close together making the bound system at a lower energy level than the unbound system. Once matter is converted into energy in the form of light, heat, or other electromagnetic radiation. Intermediate nuclei is more stable than larger or small nuclei. There are four forces that must be accounted for and they are the strong and weak nuclear force, the gravitational force, and the electrostatic force.
Nuclear forces, binding energy
The nuclear force is the force between two or more parts of atomic nuclei. The parts are neutrons and protons, which collectively are called nucleons. The nuclear force is responsible for the binding of protons and neutrons into atomic nuclei. The nuclear force is powerfully attractive at distances of about 1 femtometer (fm), rapidly decreases to insignificance at distances beyond about 2.5 fm, and becomes repulsive at very short distances less than 0.7 fm. The nuclear force is a strong interaction that binds together particles called quarks into nucleons.
Nuclear forces, binding energy
The nuclear force is the force that is responsible for the binding of protons and neutrons into atomic nuclei.
Nuclear forces, binding energy-Key Points
The nuclear force is the force that is responsible for the binding of protons and neutrons. The nuclear force is insignificance at distances beyond about 2.5 fm, repulsive at very short distances less than 0.7 fm. The binding energy of nuclei is always a positive number while the mass of an atom 's nucleus is always less than the sum of the individual masses of the constituent protons and neutrons when separated.
Neutrons, protons, isotopes
The number of neutrons can vary in the nucleus to produce isotopes, which are atoms of the same element that have different numbers of neutrons. Despite having different numbers of neutrons, isotopes of the same element have very similar physical and chemical properties. Some isotopes are unstable and will undergo radioactive decay to become other elements.
Atomic number, atomic weight
The number of protons determines an element's atomic number (Z) and distinguishes one element from another. For example, carbon's atomic number (Z) is six because it has 6 protons. The number of neutrons can vary in the nucleus to produce isotopes, which are atoms of the same element that have different numbers of neutrons. The average atomic mass of an atom takes into account all its naturally occurring isotopes.
Neutrons, protons, isotopes-Key Points
The number of protons determines an element's atomic number and is used to distinguish one element from another. The number of neutrons is variable, resulting in isotopes, which are different forms of the same atom that vary only in the number of neutrons they possess. The atomic mass is calculated by obtaining the mean of the mass numbers for its isotopes. Some isotopes are unstable and will undergo radioactive decay to become other elements.
Neutrons, protons, isotopes
The number of protons determines an element's atomic number. The number of neutrons is variable, resulting in isotopes, which are different forms of the same atom.
Neutrons, protons, isotopes
The predictable half-life of different decaying isotopes allows scientists to date material based on its isotopic composition, such as with Carbon-14 dating.
Radioactive decay
The relationship between the half-life and the decay constant shows that highly radioactive substances rapidly transform to daughter nuclides, while those that radiate weakly take longer to transform. We can measure exponential decay and the half-life of a radioactive substance using the equation below: See jackwestin.com and notecard.
Radioactive decay
The three types of radiation have different levels of penetrating power. Penetrating power refers to the energy with which the radiation particles are ejected from the atom. The higher the energy, the more the particles of light produced by radioactive decay will penetrate a substance. Alpha particles are stopped by paper, beta particles stopped by thin aluminium foil, and the most penetrating gamma is only stopped by thick lead and concrete.
Classical Experiments
There are 3 experiments that are important: the Thomson experiment (used to determine the sign of charges), the Millikan oil drop experiment (used to determine the magnitude of charge) and the Rutherford experiment (used to determine the location of dense particles).
Radioactive decay
There are many types of emitted particles and radiation that radioisotopes produce when they decay. The types we will discuss here are alpha, beta, and gamma. Alpha particles carry a positive charge, beta particles carry a negative charge, and gamma rays are neutral. See jackwestin.com and notecard.
Radioactive decay
To calculate the atomic properties of an atom before and after radioactive decay, two important quantities are used - the atomic mass number A (number of protons + neutrons), and the atomic number Z (number of protons). These numbers must balance before and after decay. For example, if a Uranium-238 atom (A=238, Z=92) undergoes alpha decay, then it must become Thorium-234 (A=234, Z=90) because it lost an alpha particle (He, A=4, Z=2).
Nuclear forces, binding energy
To disassemble a nucleus into unbound protons and neutrons would require working against the nuclear force. Conversely, energy is released when a nucleus is created from free nucleons or other nuclei—known as the nuclear binding energy. The binding energy of nuclei is always a positive number since all nuclei require net energy to separate into individual protons and neutrons. Because of mass-energy equivalence (i.e., Einstein's famous formula E=mc2), releasing this energy causes the mass of the nucleus to be lower than the total mass of the individual nucleons (leading to "mass deficit"). Binding energy is the energy used in nuclear power plants and nuclear weapons.
Neutrons, protons, isotopes-Key Terms
element: atoms with the same number of protons molecules: where atoms of the same element bond together subatomic: particles that are smaller than atoms nucleus: the centre of the cell containing protons and neutrons AMU: an atomic mass unit is defined as precisely 1/12 the mass of an atom of carbon-12 half-life: the time it takes for half of the original concentration of an isotope to decay back to its more stable form.
Mass spectrometer-Key Terms
ionization: any process that leads to the dissociation of a neutral atom or molecule into charged particles (ions). mass-to-charge ratio: the best way to separate ions in a mass spectrometer. This number is calculated by dividing the weight of the ion by its charge. mass spectrometers: an analytical technique that measures the mass-to-charge ratio of ions. The results are typically presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio Faraday collectors: is a metal (conductive) cup designed to catch charged particles in a vacuum
Atomic number, atomic weight-Key Terms
mass number: the sum of the number of protons and the number of neutrons in an atom. isotope: any of two or more forms of an element where the atoms have the same number of protons, but a different number of neutrons within their nuclei. atomic mass: the sum of the mass of protons and neutrons of that atom. half-life: the time it takes for half of the initial concentration of an isotope to decay back to its more stable form. atomic number: the number of protons in the nucleus of an atom AMU: an atomic mass unit is defined as precisely 1/12 the mass of an atom of carbon-12
Nuclear forces, binding energy
nucleus: the massive, positively charged central part of an atom, made up of protons and neutrons quark: in the Standard Model, an elementary subatomic particle that forms matter. Quarks are never found alone in nature but combine to form hadrons, such as protons and neutrons nuclear force: a force that acts between the protons and neutrons of atoms nuclear binding energy: the minimum energy that would be required to disassemble the nucleus of an atom
Neutrons, protons, isotopes-Key Terms
radioactive decay: the process by which an unstable atomic nucleus loses energy by radiation atom: The smallest possible amount of matter which still retains its identity as a chemical element, consisting of a nucleus surrounded by electrons. proton: Positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element. It weighs 1 amu. neutron: A subatomic particle forming part of the nucleus of an atom. It has no charge. It is equal in mass to a proton, or it weighs 1 amu. electron: Each electron has a negative charge (-1) with weight so small it's normally negligible as compared to proton or neutron.
