Ch.4 The Atom Flashcards
What is matter?
Anything that has shape or form and occupies space
What is a substance?
Any material with a definite and constant composition
What is the simplest form of a substance?
An Element
What is an element?
A substance that cannot be broken down into any simpler substance by ordinary means.
What is an element comprised of?
A group of identical atoms that share specific chemical behavior.
What is the smallest single unit of an element?
An Atom
What is a compound?
- A substance in which atoms of different elements are chemically bound together.
- It does not require two different elements to bind, but two different atoms.
Describe a mixture.
- The combination of two or more substances in such a way that they are NOT chemically bound together.
- Mixtures are mechanically stirred together and given time seperate.
What is a molecule?
- Any time two or more atoms are chemically bound together.
- It is the smallest unit of any chemical compound.
What determines if elements are chemically bound together?
- By the sharing of their electrons in the outermost shells.
- Can only be separated by chemically separating them from each-other by interacting with other chemicals
What is an atomic number comprised of?
- protons
- otherwise known as the Z number
What are the 2 basic elements radiographers should know?
- Hydrogen-H-1
- Helium-He-2
What are the 3 elements in the body radiographers should know?
Carbon-C-6
Oxygen-O-8
Calcium-Ca-20
What x-ray filter element should radiographers know?
Aluminum- Al- 13
What contrast agent element should radiographers know?
Iodine-I-53
What image receptor elements should radiographers know?
Barium-Ba-56
What X-ray tube elements should radiographers know?
Tungsten-W-74
Rhenium-Re-75
What sheilding elements should radiographers know?
Lead-Pb-82
What radioactive elements should radiographers know?
Uranium-U-92
What are atoms mostly comprised of?
empty space
What are the positive charges in the nucleus?
protons
What does the law of periodicity state?
That the properties of elements are periodic functions of their atomic mass.
Why are neutrons relatively unstable?
- They decay, especially when they are outside of an atomic nucleus.
- They fall apart into their component proton and electron.
Describe Beta Radiation.
When a neutron decays it breaks apart into a proton and electron. Because the electron is so much smaller in mass than the proton it is ejected at a high speed from the larger particle thus creating beta radiation.
-This is a natural form of radioactivity.
How are electrons configured outside of the nucleus?
In shells orbiting the nucleus.
Describe the shells that orbit the nucleus.
- up to 7 shells arranged like the layers of an onion
- concentric circles
- labeled alphabetically from K-P
What are the two rules of electron configuration?
- 2N’2
2. octet rule
Describe the 2N’2 rule.
The maximum number of electrons which can occupy a shell under any conditions is equal to 2N’2 where N is the shell number.
-“K” is shell 1 so N=1
What is the principle quantum number?
the shell number
Describe the octet rule.
The outermost shell of an atom can never hold more than 8 electrons.
- This rule overrides rule #1
- only sets a maximum number allowed in a shell not a minimum
What do the shells set up around the nucleus?
It sets up a negative screen around the nucleus which shields other electrons from outside of the atom from the positive pull of the nucleus.
Because of the screening of the positive pull of the nucleus, neutral atoms with exactly 8 electron in the outermost shell have no tendency at all to connect with other atoms, these atoms are said to be…
chemically inert
What is special about inert elements?
They do not combine with other elements to form compunds
Which elements are inert?
Noble gases such as helium, neon, argon etc
Describe covalent bonding.
When two atoms come together because they both have an odd number of electrons which leaves a hole in the screen around the nucleus where the positive pull of the nucleus can be felt by outside electrons or other atoms.
- They literally share their unpaired electrons
- Both electrons, one from each atom, goes back and forth sharing the unpaired electron which fills its suborbitals
What is the most common form of chemical boding between atoms?
Covalent bonding
What is an ion?
Any electrically charged particle
Describe a positive ion.
- an atom that loses an electron through a chemical process, such as with x radiation
- has enough energy to eject electrons out of its shells
- has a net electric charge of +1
If covalent bonding is a short distance phenomenon, what is ionic bonding?
A long distance phenomenon
Describe Ionization.
- the gain or loss of an electron by an atom
- if an electron gains too much energy it cant stay in its orbit and is ejected
What happens when numerous ionizations occur?
It frees up many electrons, those electrons can be attracted to a positively charged plate and flow down a wire creating an electrical current.
-This is the fundamental basis of most imaging and detection devices for x-rays
What is another way ionization can occur?
- From the physical collision between particles
- This type occurs in the X-ray tube anode during the production of the x-ray beam
Describe what happens in the X-ray tube in regards to ionization.
- A high speed electron from the hot cathode filament is accelerated toward the anode disc.
- When the electron smashes into the disc it can physically collide with an orbital electron in a tungsten or rhenium atom causing it to ricochet out of the atom, thus ionizing the atom.
What are nucleons?
All of the large particles comprising the atomic nucleus, including the protons and neutrons
The sum total of protons plus neutrons (the number of nucleons) is called what?
The atomic mass
- under each element on the periodic chart
What are gluons?
Additional particles in the nucleus that mediate the strong nuclear force that flows between all the protons and neutrons to hold the nucleus together.
-add to the weight of the nucleus
A-Z=N is what?
total nucleons (atomic mass) - protons (atomic number) = neutrons in the atom
The splitting of atomic nuclei into smaller fragments is what?
Nuclear Fission
The forcing together of two smaller nuclei to form a single larger nucleus is what?
Nuclear Fusion
-occurs in stars and sun
Both nuclear fission and fusion processes result in what?
The release of large amounts of energy that can be used for power
Describe ground state of an atom.
- the ideal number of neutrons in the nucleus which results in the most stable configuration, this positions the nucleus as a whole at its lowest possible energy state.
- all nuclei seek this low energy state just as all objects seek out their lowest point in a gravity field
What causes an atom to become unstable?
By having too few or too many neutrons in its nucleus
An unstable nucleus is also referred to as what?
a radioactive nucleus
Define a radioisotope.
any atom that is radioactive because it has too few or too many neutrons
T/F: There is a range of neutrons that can be held within the nucleus without making it unstable or radioactive
True
What is radioactive decay?
- the loss of any mass or energy from the nucleus of an atom.
- can alter the number of protons in the nucleus thus changing the identity of the element.
Define Transmutation.
The changing of one element into another by radioactive decay.
What three naturally occurring types of radiation allow the nucleus to lose some of its energy in order for the element to seek a more stable nuclear configuration by emitting the radiation?
- Alpha radiation-consisting of particles
- Beta radiation- consisting of particles
- Gamma radiation- consisting of electromagnetic radiation
Describe the alpha radiation in an unstable nucleus.
- large alpha particles are emitted by very unstable nuclei
- each alpha particle has 2 protons with 2 neutrons that break off the nucleus
- the Z# drops by 2 and the A number drops by 4
- leads to a new element-2 columns to the left on the periodic table
Describe beta radiation in an unstable nucleus.
- occurs when the nucleus is moderately unstable
- most efficient way to reach its ground state
- small particles identical to electrons but travel at high speeds
- a neutron decays creating a proton and electron
- the electron is easier to move so it leaves the nucleus at high speed leaving the proton behind creating beta radiation
What are the transmutation effects that beta radiation has on the atom?
- atom has an extra proton increasing the Z# by 1=A#up1
- atom lost a neutron so the N# goes down by 1
- element
