Week 3: Atomic Theory

Question 1

Atom

Answer 1

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)

Question 2

Nucleus

Answer 2

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

Question 3

Nucleons

Answer 3

Particles inside the nucleus of an atom. Protons and neutrons are considered nucleons.

Question 4

Subatomic Particles

Answer 4

Protons, neutrons, electrons

Question 5

Proton

Answer 5

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

Question 6

Neutrons

Answer 6

Carry no charge and are electrically neutral; If an atom gains or loses neutrons, the atom is called an isotope

Question 7

Electrons

Answer 7

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

Question 8

Quarks

Answer 8

Sub nuclear structures that make up protons and neutrons

Question 9

Gluons

Answer 9

Hold quarks together

Question 10

Electron shells (energy levels)

Answer 10

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

Question 11

The orbital shell closest to the nucleus is called the __-shell

Answer 11

K

Question 12

Each energy level has an electron binding energy measured in keV (kiloelectron volts). The binding energy of an electron is

Answer 12

the amount of energy needed to remove the electron from the atom

Question 13

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.

Answer 13

tightly

Question 14

The more protons an atom has, the _________ the + charge of the nucleus, thus the ________ the binding energy in each energy level

Answer 14

stronger, stronger

Question 15

Binding energy example:

Answer 15

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.

Question 16

Photoelectric interaction and characteristic radiation production

Answer 16

Question 17

The horizontal rows (periods) of the periodic table groups atoms according to

Answer 17

Their energy levels

For example, atoms in Period 6 all contain 6 energy levels (K, L, M, N, O, P).

Question 18

Valence shell

Answer 18

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

Question 19

Valence

Answer 19

Refers to the number of electrons in an atom’s outermost shell and determines the chemical combining characteristics of the atom

Question 20

The vertical columns groups the periodic table groups atoms according to

Answer 20

An atom’s valence

For example, atoms in Group 2 have 2 electrons in their valence shell and have a valence of +2

Question 21

Electrons, Valence shells, Valences

Answer 21

• 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.

Question 22

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?

Answer 22

8

Group 8 of the periodic table

Question 23

Ionization

Answer 23

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

Question 24

When an electron is removed from an atom, the atom becomes a ________ ion because it possess an extra ________ charge

Answer 24

positive, positive

Question 25

When an electron is added to an atom, the atom becomes a _________ ion because it possesses an extra _________ charge

Answer 25

negative, negative

Question 26

Radiation with energies of approximately ___ eV and higher can ionize an atom

Answer 26

10

Question 27

Examples of ionizing radiation are

Answer 27

ultraviolet rays, x-rays, and gamma rays

Question 28

Excitation

Answer 28

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

Question 29

Excitation example

Answer 29

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

Question 30

How to read elements on the periodic table

Answer 30

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)

Question 31

Molecule

Answer 31

2 or more atoms chemically combined. A compound is any quantity of one type of molecule

Question 32

Ionic bond

Answer 32

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

Question 33

Covalent bond

Answer 33

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

Question 34

Electromagnetic radiation (EM (electromagnetic energy)

Answer 34

type of energy emitted and transferred through space in the form of waves

Question 35

Electromagnetic spectrum

Answer 35

Electromagnetic energy spans a continuum of wide ranges of magnitudes of energy. The electromagnetic spectrum details all the various forms of EM radiation

Question 36

X-rays and gamma rays are types of _________ electromagnetic radiation

Answer 36

ionizing

Question 37

X-rays and gamma rays have similar

Answer 37

wavelengths, frequencies, and similar energy measured in electron volts (eV)

Question 38

X-rays are produced in __________________________, while gamma rays are emitted spontaneously from ____________________

Answer 38

Diagnostic imaging systems, radioactive materials

Question 39

T or F: Given an x-ray and gamma ray of equal energy traveling through space, they would be indistinguishable

Answer 39

True

Question 40

Wave-particle duality

Answer 40

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

Question 41

Frequency

Answer 41

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)

Question 42

Wavelength

Answer 42

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)

Question 43

Energy

Answer 43

Measured in electron volts (eV), the higher the frequency, the higher the energy

-Photon energy and frequency are directly proportional

Question 44

Velocity

Answer 44

EM energy always moves at the speed of light, regardless of a photon’s frequency and wavelength

Question 45

Particulate radiation

Answer 45

Subatomic particles (protons, neutrons, electrons) are capable of ionizing when in motion containing sufficient energy

*alpha and beta particles are also particulate radiation

Question 46

Alpha particles

Answer 46

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

Question 47

Beta particles

Answer 47

Only difference between a beta particle and electron is their origin. Beta particles originate in the nuclei of radioactive atoms.

Question 48

Neutrons (fast neutron therapy)

Answer 48

Particulate radiation that can be used to treat tumors

Question 49

Protons (proton therapy)

Answer 49

Particulate radiation that can be used to treat tumors

Question 50

Nonionizing radiation (excitation) occurs when

Answer 50

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

Question 51

Ionizing radiation

Answer 51

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

Question 52

Ionizing radiation examples

Answer 52

Compton scatter and photoelectric absorption

Question 53

Radioactive decay (radioactivity)

Answer 53

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.

Question 54

The nucleus of radionuclides can emit

Answer 54

beta particles, alpha particles, and gamma rays

Ex: uranium decays to radium which decays to radon

Question 55

Alpha emission

Answer 55

Violent process in which an alpha particle (2 protons & 2 neutrons bound together) is emitted from the nucleus of a radionuclide

Question 56

Beta emission

Answer 56

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.

Question 57

Gamma emission

Answer 57

radionuclide emits gamma rays from the nucleus to try to stabilize itself

Question 58

Virtually all radioisotopes are capable of transformation by ______ emission, but
only heavy radioisotopes are capable of _______ emission

Answer 58

beta, alpha

*Some radioisotopes are pure beta emitters or pure alpha emitters, but most emit gamma rays simultaneously with the particle emission

Question 59

Radioactive half-life

Answer 59

time required for a radionuclide’s radioactivity to be reduced to ½ its original value

Question 60

T or F: Radioactivity is here one day and gone the next

Answer 60

False, radioisotopes disintegrate into stable isotopes of different elements at a decreasing rate so that the quantity of radioactive material never quite reaches zero

Question 61

12 fundamental x-ray properties

Answer 61

1. X-rays are highly penetrating, invisible rays that are a form of electromagnetic radiation.
2. X-rays are electrically neutral and, therefore, not affected by either electric or magnetic fields.
3. X-rays can be produced over a wide variety of energies and wavelengths (polyenergetic and heterogenous).
4. X-rays release very small amounts of heat upon passing through matter.
5. X-rays travel in straight lines.
6. X-rays travel at the speed of light (3x10⁸ meters per second in a vacuum).
7. X-rays can ionize matter.
8. X-rays can cause fluorescence (the emission of light) of certain crystals.
9. X-rays cannot be focused by a lens.
10. X-rays affect photographic film.
11. X-rays produce chemical and biological changes in matter through ionization and excitation.
12. X-rays produce secondary and scatter radiation.

Question 62

The periodic table lists atoms in _________ order according to the atoms’ atomic numbers

Answer 62

Ascending

Question 63

If an atom gains or loses neutrons, the atom is called an

Answer 63

isotope

Question 64

when an atom’s number of protons matches the number of electrons, the atom is

Answer 64

neutral or stable

Question 65

If an atom gains or loses an electron, it is called an _____ and is said to be ionized

Answer 65

ion

Question 66

Beta and alpha particles come from the

Answer 66

Nucleus