Atomic Structure & Periodic Table Flashcards
Neutral atoms have…
The number of electrons outside the nucleus is equal to the number of protons inside the nucleus. Electrons are held in the atom by the electrical attraction of the positively charged nucleus
What is an Atom?
The smallest unit of any element. All atoms have a central nucleus which contains protons and neutrons known as nucleons. Each proton has an electric charge of +1; neutrons have no charge. Outside the nucleus are electrons each have an electric charge of -1
What is the atomic number of an atom?
Symbol= Z
Number of protons
Shown in a subscript before the element
Mass of proton and neutron
An electron?
Each have a mass slightly more than one atomic mass unit (1 amu =1.66x10^-27 kg)
An electron has a mass that’s only 0.05% the mass of either a proton or a neutron
All the mass of an atom is due to the nucleus
Atomic mass equals
A=Z+N
Atomic mass is written as a super sub script before the elements
Isotopes
If two atoms of the same element differ in their numbers of neutrons they are called isotopes.
This affects only the mass number.
And item would seven neutrons and a mass number of 12 is an isotope of what element? A. Boron B. Nitrogen C. Magnesium D. Potassium
A. Boron
A equals 12
N equals 7
So Z would equal 5 which is the atomic number
Remember the atomic number is not affected in an isotope
Are elements found in their one form in nature?
Elements exist naturally as a collection of the isotopes. The atomic weight of an element is a weighted average of the masses of its naturally occurring isotopes.
In order to get the weighted average the isotopes are multiplied by the percentages which they occur in the natural world and then added
Atomic weight of an element or the weighted average is found on the periodic table
What are ions?
What a neutral atom gains or loses electrons, it becomes charged, and the resulting atom is called an ion.
For each electron it gains, and atom acquires a charge of -1 unit, and for each electron it loses an atom acquires a charge of a +1 unit. A negatively charged ion is called an anion, while a positively charged ion is called a cation.
What is the strong nuclear force?
Protons and neutrons in the nucleus are held together by force called the strong nuclear force. It is stronger than the electrical force between charged particles, since for all atoms besides hydrogen, the strong nuclear force must overcome the electrical repulsion between the protons.
In fact, of the four fundamental forces of nature, the strong nuclear force is the most powerful even though it only works over extremely short distances.
Unstable nuclei are?
Said to be radioactive, and they undergo a transformation to make them more stable altering the number and ratio of protons and neutrons or just lowering their energy.
Such a process is called radioactive decay, and there are three types alpha, beta, and gamma.
The nucleus that undergoes radioactive decay is known as the parent.
And the resulting more stable nucleus is known as the daughter.
What are the three types of radioactive decay?
Alpha, beta, gamma
What is alpha decay?
When a large nucleus wants to become more stable by reducing the number of protons and neutrons, it emits an alpha particle.
An alpha particle, denoted by 4/2 (alpha sign), consist of two protons and two neutrons.
Alpha decay reduces the parents atomic number by 2 and the mass number by 4
Polonium-210 decaying to it’s more stable form as lead-206 is an example of what type of decay?
Alpha decay.
it is an alpha-emitter
What magnitude of energy do alpha particles emit from the parent nucleus?
High energy.
This energy is quickly lost as the particle travels through matter of air. As a result the particles do not typically travel far, and can be stopped by the outer layers of human skin or a piece of paper.
What is beta decay?
There are three types of beta decay: β-, β+, and electron capture. Each type of beta decay involves the conversion of a neutron into a proton, or vice versa, through the action of the week nuclear force.
Beta particles are more dangerous than alpha particles since they are significantly less massive. They therefore have more energy and a greater penetrating ability. However, they can be stopped by aluminum for foil or a centimeter of plastic or glass
β- Decay
When an unstable nucleus contains too many neutrons, it may convert a neutron into a proton and an electron (which is also know as a beta- particle) which is ejected.
The atomic number of the resulting daughter nucleus is 1 greater than the radioactive parent nucleus, but the mass number remains the same.
The isotope carbon – 14, the decay of which is the basis of radiocarbon dating of archaeological artifacts, is an example of a radioactive nucleus that undergoes beta- decay
14/6C —–> 14/7C (0/-1 beta is ejected)
This is the most common beta decay so if mentioned on MCAT WITHOUT SPECIFICATION, it’s beta-
Electron capture
Another way for an unstable nucleus to increase its number of neutrons is to capture an electron from the closest electron shell (the n=1 shell) and use it in the conversion of a proton into a neutron.
Just like positron emission, electron capture causes the atomic number to be reduced by 1 while the mass number remains the same.
51/24Cr + 0/-1e- —–> 51/23V
(Loses proton because it’s converted into neutron)
β+ Decay
Also know as Positron Emission
When an unstable nucleus contains too few neutrons, it converts a proton into a neutron and a positron, which is ejected. This is known as Beta+ decay.
-The positron is the electron’s anti-particle; it’s identical to and electronics at its charge is positive.
–The atomic number of the resulting daughter nucleus is 1 less than the radioactive parent nucleus, but the mass number remains the same.
18/9F—-> 18/8O. (0/+1 beta ejected)
Gamma decay
A nucleus in an excited state—which is usually the case after a nucleus has undergone alpha or any type of beta decay— can “relax” to its ground state by emitting energy in the form of one or more photons of electromagnetic radiation. These photons are called Gamma photons (symbolized by gamma symbol y) and have a high frequency and energy.
Gamma photons or gamma rays have neither mass nor charge, and can therefore penetrate matter most effectively. A few inches of lead or about a meter of concrete. Most Scana race there each action from a radioactive Adam changes neither the atomic number nor the mass number of the nucleus.
31/14Si–beat neg. D–> 31/15P*—gamma D–>31/15P+0/0y emitted
* means in excited stage
Alpha and beta decay changes the identity of the element, gamma doesn’t. Gamma decay is simply the expulsion of energy.
What happens during gamma decay?
Brings an excited nucleus to a lower energy level, doesn’t change mass number or atomic number.
What happens during alpha decay?
Decreases the number of neutrons and protons in large nucleus, subtract 4 from the mass number and subtract 2 from the atomic number.
What happens during positron emission?
Increases the number of neutrons, decreases the number of protons, and subtract 1 from the atomic number.
What happens during β- decay?
Decreases the number of neutrons, increases the number of protons, and adds 1 to the atomic number.
What happens during electron capture?
Increases the number of neutrons, decreases the number of protons, subtract 1 from the atomic number.
Americium-241 is used to provide intracavitary radiation for the treatment of malignancies. This radioisotope is known to undergo alpha decay. What is the daughter nucleus?
247Np
Alpha decay reduces atomic mass by 4 and atomic number by 2
Radioactive calcium-47, a known β- emitter, is administered in the form of 47CaCL2 by IV as a diagnostic tool to study calcium metabolism. What is the daughter nucleus of 47Ca?
A. 46K
B. 47K
C. 47Ca+
D. 47ScD. 47Sc
Adds 1 proton and atomic weight doesn’t change.
Vitamin B12 can be prepared with radioactive cobalt (58Co), a known bet+ emitter, and administered orally as a diagnostic tool to test for defects in intestinal vitamin B12 absorption. What is the daughter nucleus of 58Co?
A. 57Fe
B. 58Fe
C. 59Fe
D. 59Ni
B. 58Fe
Reduces atomic mass by 1 but atomic weight stays the same
A certain radioactive isotope is administered orally as a diagnostic tool to study pancreatic function and intestinal fat absorption. This radioisotope is known to undergo beta- decay, and the daughter nucleus is xenon – 131. What is the parent radioisotope?
A. 131Cs
B. 131I
C. 132I
D. 132Xe
B. 131I
Since xenon-131 is the daughter we are reversing the process. Instead of adding a proton to atomic number, subtract 1 proton to get the parent.
which mode of radioactive decay causes change in the mass number of the parent nucleus?
Alpha decay
One of the naturally occurring radioactive series begins with radioactive 238U. It undergoes a series of decays, one of which is: alpha, beta, beta, alpha, alpha, alpha, alpha, alpha, beta, beta, alpha, beta, alpha, beta. What is the final resulting nuclide of the series of decays?
A. 204Pb
B. 204Pt
C. 206Pb
D. 206Pt
C. 206Pb
Alpha: -4/-2
Beta-: 0/+1
What is a half-life?
Different radioactive nuclei decay at different rates. The half-life, which is denoted by t1/2, of a radioactive substance is the time it takes for one-half of some a sample of the substance to decay.
Thus, the shorter the half-life, the faster the decay. The amount of radioactive substance decreases exponentially with time.
The shorter the half-life….
The greater the decay constant, and the more rapidly the sample decays
Cesium-137 has a half-life of 30 years. How long will it take for only 0.3 g to remain from a sample that had an original mass of 2.4 g?
90 years
2.4–30yrs–> 1.2–30yrs–> .6–30yrs–>.3
30x3=90
If 58Ca has a half-life of 72 days, approximately what percentage of the radioisotope will still remain in the patient after a year?
A. 3%
B. 5%
C. 8%
D. 10%
A. 3%
360 days/72 days=5 half-lives
(1/2)^5 equals 1/32 of the original amount administered.
1/32—>3/100 about 3%
Iodinated oleochemicals acid, containing radioactive iodine-131, is administered orally to study a patient’s pancreatic function. If 131I has a half-life of 8 days, how long after the procedure will the amount of 131I remaining in the patient’s body be reduced to 1/5 it’s initial value?
A. 19 days
B. 32 days
C. 40 days
D. 256 days
A. 19 days
1/5 is between 1/4 and 1/8
1/4=25%=2t
1/8=12.5%=3t
So about 2 half-lives occurred, so 8 days times 2 is 16.
What is the usual half-life percentages of remaining substance?
Time. Amount remaining t(1/2)=1 half-life. 1/2=50% t(1/2)=2 half-life. 1/4=25% t(1/2)=3 half-life. 1/8=12.5% t(1/2)=4 half-life. 1/16=6.25%
What is an Emission Spectrum?
A glass filled with a small sample of an element in gaseous form. When electric current passed through the glass, the gas begins to glow with a color characteristic of that particular element.
If the light emitted by the gas is then passed through the prism, which will separate the light into it’s compliment wavelengths
Basically shows which wavelengths are emitted by the element.
The emission spectrum gives an energetic fingerprint of the element because it consists of a unique sequence of bright lines that correspond with the specific wavelengths and energies.
