Week 3: Atomic Theory Flashcards
Atom
Building blocks of matter; smallest particle of an element that still possesses the chemical properties of that element. An element is any quantity of one type of atom. Bohr’s model demonstrates the atom as a mini solar system, with protons and neutrons in the center of the nucleus, and electrons orbit the nucleus in their respective energy shells (energy levels)
Nucleus
Center of the atom that contains protons and neutrons. Because it contains all the protons and neutrons, the nucleus contains most of the mass. The nucleus of a stable atom has a + charge
Nucleons
Particles inside the nucleus of an atom. Protons and neutrons are considered nucleons.
Subatomic Particles
Protons, neutrons, electrons
Proton
Carry a + electric charge; each atom has its own specific number of protons. The number of protons identifies the atom and is referred to as the atomic number (Z number). The periodic table lists atoms in ascending order according to the atoms’ atomic numbers
Neutrons
Carry no charge and are electrically neutral; If an atom gains or loses neutrons, the atom is called an isotope
Electrons
Carry a negative electric charge; when an atom’s number of protons matches the number of electrons, the atom is neutral or stable. Electrons orbit the nucleus in energy levels (energy shells)
- number of electrons = number of protons
Quarks
Sub nuclear structures that make up protons and neutrons
Gluons
Hold quarks together
Electron shells (energy levels)
Electrons orbit the atom’s nucleus in a
continuous motion and reside in a specific orbit that is determined by its distance from the nucleus
The orbital shell closest to the nucleus is called the K-shell. From there, depending on the mass of the atom, it may have K, L, M, N, O, P, Q shells
The orbital shell closest to the nucleus is called the __-shell
K
Each energy level has an electron binding energy measured in keV (kiloelectron volts). The binding energy of an electron is
the amount of energy needed to remove the electron from the atom
The closer an electron is to the positively charged nucleus, the more _______ it is bound to its shell and the more difficult it is to remove the electron from the atom.
tightly
The more protons an atom has, the _________ the + charge of the nucleus, thus the ________ the binding energy in each energy level
stronger, stronger
Binding energy example:
To remove an electron from the K shell of barium, a photon entering the atom would need at least 37.1 keV of energy to remove the electron due to its binding energy that holds it in place.
To calculate the K shell’s characteristic radiation, subtract the K shell binding energy – L shell binding energy.
37 keV – 6 keV= 31 keV secondary photon produced due to the characteristic cascade.
Photoelectric interaction and characteristic radiation production
The horizontal rows (periods) of the periodic table groups atoms according to
Their energy levels
For example, atoms in Period 6 all contain 6 energy levels (K, L, M, N, O, P).
Valence shell
Refers to the outermost shell of an atom. If an atom has 3 energy levels, (K, L, M), the valence shell would be the M shell
Valence
Refers to the number of electrons in an atom’s outermost shell and determines the chemical combining characteristics of the atom
The vertical columns groups the periodic table groups atoms according to
An atom’s valence
For example, atoms in Group 2 have 2 electrons in their valence shell and have a valence of +2
Electrons, Valence shells, Valences
• Atoms with 1, 2, or 3 electrons in the valence shell have a valence of +1, +2, and +3. These atoms will freely give up their valence electrons to combine with another atom to form a compound; Groups 1, 2, and 3 of the periodic table
• Atoms with 4 electrons in the valence shell have a valence of +/-4; Group 4 of the periodic table
• Atoms with 5, 6, or 7 electrons in the valence shell have a valence of -3, -2, and -1 and they will freely accept electrons to form a chemical bond because atoms prefer to be stable with atoms in the outermost shell; Groups 5, 6, and 7 of the periodic table.
• Atoms that contain exactly 8 electrons in the outermost shell are considered inert and chemically stable with a valence of 0; Group 8 of the periodic table.
Atoms that contain exactly __ electrons in the outermost shell are considered inert and chemically stable with a valence of 0. What group on the periodic table are considered stable?
8
Group 8 of the periodic table
Ionization
The process of adding or removing an electron from an atom. If an atom gains or loses an electron, it is called an ion and is said to be ionized. In an ion pair, the ejected electron and the resulting positively charged atom together are called an ion pair
When an electron is removed from an atom, the atom becomes a ________ ion because it possess an extra ________ charge
positive, positive
When an electron is added to an atom, the atom becomes a _________ ion because it possesses an extra _________ charge
negative, negative
Radiation with energies of approximately ___ eV and higher can ionize an atom
10
Examples of ionizing radiation are
High energy ultraviolet rays, x-rays, and gamma rays
Excitation
Occurs when radiation measured at 10 eV or less doesn’t ionize an atom, but rather transfers energy to an atom and moves the electron(s) of an atom to a higher energy state
Excitation example
Coherent scatter (classical scatter or unmodified scatter):
• Thomson- incoming photon vibrates (excites) 1 electron in the atom
• Rayleigh- incoming photon vibrates (excites) all electrons in the atom
How to read elements on the periodic table
The atom is represented by X in the example atom, where the atomic number (Z number) represents the number of protons in the nucleus. The atomic mass number (A number) represents the number of protons and neutrons in the nucleus
-Example: Carbon (C) has an atomic number (Z number) of 6 which means there are 6 protons in the nucleus. It has an atomic mass number (A number) of 12 which represents the number of protons and neutrons in the nucleus (6 protons and 6 neutrons)
Molecule
2 or more atoms chemically combined. A compound is any quantity of one type of molecule
Ionic bond
Molecule formed when 2 or more atoms ionize each other to create an electrostatic bond
Example- NaCl; Na has a +1 valence (1 electron in its outer shell), Cl has a -1 valence (7 electrons in its outer shell). Na gives its valence electron to Cl, with Na now being a + ion, and Cl now being a – ion. The two ions are attracted to each other due to opposite charges
Covalent bond
Chemical union between atoms formed by sharing one or more pairs of electrons
Example- H₂0; Hydrogen has a valence of +1 (1 electron in the outer shell), and Oxygen has a valence of -2 (6 electrons in the outer shell). Oxygen has room for 2 hydrogen atoms and will share electrons so that Oxygen has 8 electrons in its outer shell
Electromagnetic radiation (EM (electromagnetic energy)
type of energy emitted and transferred through space in the form of waves
Electromagnetic spectrum
Electromagnetic energy spans a continuum of wide ranges of magnitudes of energy. The electromagnetic spectrum details all the various forms of EM radiation
X-rays and gamma rays are types of _________ electromagnetic radiation
ionizing
X-rays and gamma rays have similar
wavelengths, frequencies, and similar energy measured in electron volts (eV)
X-rays are produced in __________________________, while gamma rays are emitted spontaneously from ____________________
Diagnostic imaging systems, radioactive materials
T or F: Given an x-ray and gamma ray of equal energy traveling through space, they would be indistinguishable
True
Wave-particle duality
In studying electromagnetic radiation (EM), scientists found that under certain circumstances EM behaved as a wave, and at other times EM behaved as a particle
Frequency
Number of waves that pass a particular point in a given time frame
-The unit of frequency is the hertz (Hz), or cycles per second (cps).
-Represented by the Greek symbol (ν)
Wavelength
Distance between two successive points on a wave. It is usually measured from crest to crest or trough to trough
-Represented by the Greek symbol (λ)
Energy
Measured in electron volts (eV), the higher the frequency, the higher the energy
-Photon energy and frequency are directly proportional
Velocity
EM energy always moves at the speed of light, regardless of a photon’s frequency and wavelength
Particulate radiation
Subatomic particles (protons, neutrons, electrons) are capable of ionizing when in motion containing sufficient energy
*alpha and beta particles are also particulate radiation
Alpha particles
Particles emitted as a result of radioactive decay. They are comparative to the helium nucleus because the alpha particle consists of two protons and two neutrons bound together
Beta particles
Only difference between a beta particle and electron is their origin. Beta particles originate in the nuclei of radioactive atoms.
Neutrons (fast neutron therapy)
Particulate radiation that can be used to treat tumors
Protons (proton therapy)
Particulate radiation that can be used to treat tumors
Nonionizing radiation (excitation) occurs when
radiation measured at 10 eV or less doesn’t ionize an atom, but rather transfers energy to an atom and moves the electron(s) of an atom to a higher energy state
Example: coherent scatter (classical scatter or unmodified scatter): Thomson or Rayleigh
Ionizing radiation
Can dislodge electrons inside of atoms and occurs when a photon’s energy measures 10 eV or more and it enters an atom. The more atoms a substance has and the higher the Z number of those atoms, the higher probability of ionization if a photon has enough energy to overcome an electron’s binding energy
Ionizing radiation examples
Compton scatter and photoelectric absorption
Radioactive decay (radioactivity)
Occurs with an abnormally excited atom with an unstable nucleus. To reach stability, the nucleus emits particles and energy and transforms itself into another atom through radioactive decay. The atoms involved are radionuclides.
The nucleus of radionuclides can emit
beta particles, alpha particles, and gamma rays
Ex: uranium decays to radium which decays to radon
Alpha emission
Violent process in which an alpha particle (2 protons & 2 neutrons bound together) is emitted from the nucleus of a radionuclide
Beta emission
Occurs more frequently than alpha emission. Radionuclide creates an electron in the nucleus that is ejected with high kinetic energy and escapes from the atom. Simultaneously, a neutron undergoes conversion to a proton. The result of beta emission is to increase the atomic number of the radionuclide by 1, which changes the atom to a different atom.
Gamma emission
radionuclide emits gamma rays from the nucleus to try to stabilize itself
Virtually all radioisotopes are capable of transformation by ______ emission, but
only heavy radioisotopes are capable of _______ emission
beta, alpha
*Some radioisotopes are pure beta emitters or pure alpha emitters, but most emit gamma rays simultaneously with the particle emission
Radioactive half-life
time required for a radionuclide’s radioactivity to be reduced to ½ its original value
T or F: Radioactivity is here one day and gone the next
False, radioisotopes disintegrate into stable isotopes of different elements at a decreasing rate so that the quantity of radioactive material never quite reaches zero
12 fundamental x-ray properties
- X-rays are highly penetrating, invisible rays that are a form of electromagnetic radiation.
- X-rays are electrically neutral and, therefore, not affected by either electric or magnetic fields.
- X-rays can be produced over a wide variety of energies and wavelengths (polyenergetic and heterogenous).
- X-rays release very small amounts of heat upon passing through matter.
- X-rays travel in straight lines.
- X-rays travel at the speed of light (3x10⁸ meters per second in a vacuum).
- X-rays can ionize matter.
- X-rays can cause fluorescence (the emission of light) of certain crystals.
- X-rays cannot be focused by a lens.
- X-rays affect photographic film.
- X-rays produce chemical and biological changes in matter through ionization and excitation.
- X-rays produce secondary and scatter radiation.
The periodic table lists atoms in _________ order according to the atoms’ atomic numbers
Ascending
If an atom gains or loses neutrons, the atom is called an
isotope
when an atom’s number of protons matches the number of electrons, the atom is
neutral or stable
If an atom gains or loses an electron, it is called an _____ and is said to be ionized
ion
Beta and alpha particles come from the
Nucleus
