Atoms, Elements, and the Periodic Table - MCAT Physical
Card 0 of 504
An isotope of an element __________.
- has all the chemical characteristics of the element
- can be stable, or non-radioactive
- is designated by the atomic number of the element
- contributes to the atomic mass of the element, as shown on the periodic table, in proportion to its abundance
- all of the above
An isotope of an element __________.
- has all the chemical characteristics of the element
- can be stable, or non-radioactive
- is designated by the atomic number of the element
- contributes to the atomic mass of the element, as shown on the periodic table, in proportion to its abundance
- all of the above
The correct answer is 5. An isotope is a form of an element with a different number of neutrons in the nucleus. Because the proton number (atomic number) is the same, the electron configuration is the same and therefore the atom behaves chemically in an identical manner to other atoms of the same element. Many isotopes are stable, and indeed that is how elements such as chlorine come to have average atomic masses in between integers; chlorine at 35.45 g/mole is a weighted average of the two stable isotopes, chlorine-35 and chlorine-37. Unstable isotopes of any element undergo decay at various rates. Unless they persist in some quantifiable amount, they aren’t really “there” to participate in the weighted average of an atomic mass.
The correct answer is 5. An isotope is a form of an element with a different number of neutrons in the nucleus. Because the proton number (atomic number) is the same, the electron configuration is the same and therefore the atom behaves chemically in an identical manner to other atoms of the same element. Many isotopes are stable, and indeed that is how elements such as chlorine come to have average atomic masses in between integers; chlorine at 35.45 g/mole is a weighted average of the two stable isotopes, chlorine-35 and chlorine-37. Unstable isotopes of any element undergo decay at various rates. Unless they persist in some quantifiable amount, they aren’t really “there” to participate in the weighted average of an atomic mass.
Compare your answer with the correct one above
Which of the following combination of particles accurately describes the above element?
Which of the following combination of particles accurately describes the above element?
The lower number next to the atomic symbol gives the number of protons, 29. The upper number gives the number of protons plus neutrons, so the number of neutrons is given by the difference between upper and lower numbers: 64 - 29 = 35. Finally, this is a neutral isotope since no net charge is noted, so the number of electrons must equal the number of protons, 29.
The lower number next to the atomic symbol gives the number of protons, 29. The upper number gives the number of protons plus neutrons, so the number of neutrons is given by the difference between upper and lower numbers: 64 - 29 = 35. Finally, this is a neutral isotope since no net charge is noted, so the number of electrons must equal the number of protons, 29.
Compare your answer with the correct one above
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist studying the reaction above is surprised to find traces of Xe-124 in his analysis of the reaction. How is Xe-124 different from Xe-135?
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist studying the reaction above is surprised to find traces of Xe-124 in his analysis of the reaction. How is Xe-124 different from Xe-135?
Xe-135 and Xe-124 are isotopes of xenon, not ions. Ions have charges, while isotopes have varying atomic mass numbers; thus, Xe-135 is a more massive isotope of xenon than is Xe-124.
Note that this change in mass can only be attributed to neutron numbers. Changing proton number would alter the elemental identity. Changing electron number would not alter the mass, and would create a charge discrepancy.
Xe-135 and Xe-124 are isotopes of xenon, not ions. Ions have charges, while isotopes have varying atomic mass numbers; thus, Xe-135 is a more massive isotope of xenon than is Xe-124.
Note that this change in mass can only be attributed to neutron numbers. Changing proton number would alter the elemental identity. Changing electron number would not alter the mass, and would create a charge discrepancy.
Compare your answer with the correct one above
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist is studying atomic radius within a sample of radioactive flourine sourced from a nuclear reactor similar to the one described in the passage. Which of the following changes is likely to result in the largest atomic radius found in the sample?
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
A scientist is studying atomic radius within a sample of radioactive flourine sourced from a nuclear reactor similar to the one described in the passage. Which of the following changes is likely to result in the largest atomic radius found in the sample?
Adding an electron to flourine results in a flourine anion. Anions generally have larger atomic radii than do their original atomic counterparts, and relative to their cation counterparts. Addition or substraction of neutrons has less of an impact due to their neutral charges and location in the nucelus. Adding a proton would increase the charge in the nucleus, convert flourine to neon, and pull the existing electrons in more tightly, decreasing radius.
Adding an electron to flourine results in a flourine anion. Anions generally have larger atomic radii than do their original atomic counterparts, and relative to their cation counterparts. Addition or substraction of neutrons has less of an impact due to their neutral charges and location in the nucelus. Adding a proton would increase the charge in the nucleus, convert flourine to neon, and pull the existing electrons in more tightly, decreasing radius.
Compare your answer with the correct one above
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
How is a nuclear reaction, as described in the passage, different from a chemcial reaction?
In the operation of nuclear reactors, engineers make use of substances known as neutron poisons. These are used to help store nuclear waste and slow nuclear reactions, but are also generated naturally in nuclear chain reactions as a by-product. This natural by-product can stop the desirable chain reaction present in a nuclear reactor used for power generation.
For example, in nuclear power plants, U-235 is used as a fuel. U-235 absorbs a neutron, and subsequently generates neutrons (which power the chain reaction) and Xe-135. Xe-135 is a well-known neutron poison, and thus can impact the continued chain reaction of a nuclear power plant if it becomes over abundant during power generation.
To help account for this, engineers have developed measurements to quantify the impact of Xe-135 on nuclear operations. For instance, the time during which there is an inability to start a reactor due to the buildup of Xe-135 is referred to as the precluded start-up time. Also, the amount of time that the reactor cannot override the effects of built up Xe-135 is called poison outage time. Perhaps the most important measure that engineers have developed is the _neutron absorption capacity (_σ), which is measured in units of barns and is a function of microscopic cross section. Xe-135 has a neutron absorption capacity of 2.00 * 106 barns, while another common poison, Sm-149, has a neutron absorption capacity of 74,500 barns.
How is a nuclear reaction, as described in the passage, different from a chemcial reaction?
Nuclear reactions are unique because they can involve the change of one atom to another, by changing the atomic number. Chemical reactions, by and large, keep atomic number constant, but often vary the ionic state of atoms. In this way, chemical reactions can be thought of as generally involving electrons, while nuclear reactions generally involve protons and neutrons.
Nuclear reactions are unique because they can involve the change of one atom to another, by changing the atomic number. Chemical reactions, by and large, keep atomic number constant, but often vary the ionic state of atoms. In this way, chemical reactions can be thought of as generally involving electrons, while nuclear reactions generally involve protons and neutrons.
Compare your answer with the correct one above
The isotope 
has _________ protons, _________ neutrons, and _________ electrons.
The isotope
The lower number, the atomic number, indicates the number of protons. The upper number, the mass number, indicates the sum of protons and neutrons. The number of neutrons would be equal to the number of protons subtracted from the total mass number. In a neutral atom, the number of protons and electrons is equal in order to balance charge.
The atomic number of iodine is 53, meaning there must be 53 protons. The total mass number is 131.
The remaining mass must come from neutrons; thus there are 78 neutrons. Since the atom is neutral, the electrons will balance the protons. In total, there are 53 protons, 78 neutrons, and 53 electrons.
The lower number, the atomic number, indicates the number of protons. The upper number, the mass number, indicates the sum of protons and neutrons. The number of neutrons would be equal to the number of protons subtracted from the total mass number. In a neutral atom, the number of protons and electrons is equal in order to balance charge.
The atomic number of iodine is 53, meaning there must be 53 protons. The total mass number is 131.
The remaining mass must come from neutrons; thus there are 78 neutrons. Since the atom is neutral, the electrons will balance the protons. In total, there are 53 protons, 78 neutrons, and 53 electrons.
Compare your answer with the correct one above
Suppose 0.5 moles of each of the following atoms is dissolved in 500 mL of water: calcium, oxygen, chlorine, barium, and silver. Which of the following resulting reactions is possible?
Suppose 0.5 moles of each of the following atoms is dissolved in 500 mL of water: calcium, oxygen, chlorine, barium, and silver. Which of the following resulting reactions is possible?
Although it appears that one must know solubility rules to answer this question, that is not the case. All but one of the answer choices employs incorrect charges. The periodic table can be used to predict charges of common ions. They are as follows: 
, 
, 
, 
, and 
. Next, recognize that an ionic compound is formed from a cation (positive) and an anion (negative), and that the total positive charge must equal the total negative charge for a neutral compound. That leaves the reaction between silver and oxygen as the only possible choice.
Although it appears that one must know solubility rules to answer this question, that is not the case. All but one of the answer choices employs incorrect charges. The periodic table can be used to predict charges of common ions. They are as follows:
Compare your answer with the correct one above
Which of the following atoms has the same number of neutrons as an atom of 
?
Which of the following atoms has the same number of neutrons as an atom of
In order to find the number of neutrons in an atom when givien isotopic notation, simply subtract the bottom number (atomic number or number of protons) from the top number (mass number or number of protons and neutrons). Doing this with the question atom reveals that it contains 28 neutrons. The only other atom that has this amount is 
.
In order to find the number of neutrons in an atom when givien isotopic notation, simply subtract the bottom number (atomic number or number of protons) from the top number (mass number or number of protons and neutrons). Doing this with the question atom reveals that it contains 28 neutrons. The only other atom that has this amount is
Compare your answer with the correct one above
Which of the following is not true of halogens?
Which of the following is not true of halogens?
Elements are generally more reactive the closer they are to the stable noble gas configuration (eight valence electrons). Halogens have seven valence electrons, so only need one more to achieve a full valence shell, thus they are said to have high "electron affinity" since they react easily to gain the final valence electron. All the other options are correct statements about halogens.
Elements are generally more reactive the closer they are to the stable noble gas configuration (eight valence electrons). Halogens have seven valence electrons, so only need one more to achieve a full valence shell, thus they are said to have high "electron affinity" since they react easily to gain the final valence electron. All the other options are correct statements about halogens.
Compare your answer with the correct one above
A mystery element is found in nature. It is very conductive and is able to be hammered into a thin layer without breaking. Based on these properties, where would you least expect to find this element on the periodic table?
A mystery element is found in nature. It is very conductive and is able to be hammered into a thin layer without breaking. Based on these properties, where would you least expect to find this element on the periodic table?
First off, it is important to know that the ability to be hammered into a sheet and conduct electricity are characterisitcs typically reserved for metals. With this in mind, we can check the periodic table, and see where on the table metals reside. Metallic character generally decreases as you go from left to right on the table, which results in nonmetals being found on the right side of the table. As a result, we would not expect to find this element and its metallic characteristics on the right side.
First off, it is important to know that the ability to be hammered into a sheet and conduct electricity are characterisitcs typically reserved for metals. With this in mind, we can check the periodic table, and see where on the table metals reside. Metallic character generally decreases as you go from left to right on the table, which results in nonmetals being found on the right side of the table. As a result, we would not expect to find this element and its metallic characteristics on the right side.
Compare your answer with the correct one above
What class of element is zinc?
What class of element is zinc?
In general, the metals fall on the left side of the periodic table and are separated from the non-metals by the metalloids. Transition metals fall in the d block of the periodic table, in groups (columns) 3-12. Examples of metals, non-metals, transition metals, and metalloids are calcium, oxygen, zinc, and arsenic, respectively.
Alkali metals are a special class of metal only found in group 1 of the periodic table.
In general, the metals fall on the left side of the periodic table and are separated from the non-metals by the metalloids. Transition metals fall in the d block of the periodic table, in groups (columns) 3-12. Examples of metals, non-metals, transition metals, and metalloids are calcium, oxygen, zinc, and arsenic, respectively.
Alkali metals are a special class of metal only found in group 1 of the periodic table.
Compare your answer with the correct one above
What class of element is krypton?
What class of element is krypton?
The non-metals in group 8 are called noble gases because they tend to resist reactions with other atoms. Noble gases are the only elements to have valence octets in their ground states (
).
Halides are the gases in group 7, which are most stable as negative ions to reflect the octet configurations of the noble gases. Lanthanides are the elements in period 6 that have an incomplete f shell. The metalloids are arranged along the diagonal between boron and polonium and divide the periodic table between the metals (to the left) and nonmetals (to the right).
The non-metals in group 8 are called noble gases because they tend to resist reactions with other atoms. Noble gases are the only elements to have valence octets in their ground states (
Halides are the gases in group 7, which are most stable as negative ions to reflect the octet configurations of the noble gases. Lanthanides are the elements in period 6 that have an incomplete f shell. The metalloids are arranged along the diagonal between boron and polonium and divide the periodic table between the metals (to the left) and nonmetals (to the right).
Compare your answer with the correct one above
All of the following elements have the same number of valence electrons except __________.
All of the following elements have the same number of valence electrons except __________.
Beryllium (Be), magnesium (Mg), calcium (Ca), and strontium (Sr) are all alkaline earth metals with two valence electrons.
Rubidium (Rb) is an alkali metal and has only one valence electron.
Beryllium (Be), magnesium (Mg), calcium (Ca), and strontium (Sr) are all alkaline earth metals with two valence electrons.
Rubidium (Rb) is an alkali metal and has only one valence electron.
Compare your answer with the correct one above
Which of the following is true about insulators?
Which of the following is true about insulators?
Good insulators are usually non-metals, in which the electrons are not able to freely move. Insulators, unlike conductors, do not carry current. This is because charges cannot move freely in an insulating material, making this choice the correct answer.
Sound would travel slowest through an insulating material, as there is less ability to compress and propagate the sound wave. Copper is an example of a good conductor, and is a poor insulator.
Good insulators are usually non-metals, in which the electrons are not able to freely move. Insulators, unlike conductors, do not carry current. This is because charges cannot move freely in an insulating material, making this choice the correct answer.
Sound would travel slowest through an insulating material, as there is less ability to compress and propagate the sound wave. Copper is an example of a good conductor, and is a poor insulator.
Compare your answer with the correct one above
What is a typical characteristic of the halogens?
What is a typical characteristic of the halogens?
Halogens are in the group next to the noble gasses. They have seven valence electrons, and therefore have a high electronegativity. The addition of only a single electron (production of an anion) generates a full valence octet.
Their diameters vary within the group. The diameter can be very small, like fluorine, or large, like iodine. They do not conduct electricity well, as they are non-metals.
Halogens are in the group next to the noble gasses. They have seven valence electrons, and therefore have a high electronegativity. The addition of only a single electron (production of an anion) generates a full valence octet.
Their diameters vary within the group. The diameter can be very small, like fluorine, or large, like iodine. They do not conduct electricity well, as they are non-metals.
Compare your answer with the correct one above
Which of the following is likely to have multiple oxidation states?
Which of the following is likely to have multiple oxidation states?
Transition elements have multiple oxidation states because of the d-orbitals they possess. This allows them to lose or gain electrons in a variety of ways, often leading to the standard characteristics of metals, such as electrical conductivity. Lanthanides and actinides are less commonly tested, but also have the ability to form multiple oxidation states due to their large and variable orbitals. Ytterbium is one of the lanthanides, and has Yb(II) and Yb(III) oxidation states.
Transition elements have multiple oxidation states because of the d-orbitals they possess. This allows them to lose or gain electrons in a variety of ways, often leading to the standard characteristics of metals, such as electrical conductivity. Lanthanides and actinides are less commonly tested, but also have the ability to form multiple oxidation states due to their large and variable orbitals. Ytterbium is one of the lanthanides, and has Yb(II) and Yb(III) oxidation states.
Compare your answer with the correct one above
An unknown element has been studied in the lab. It has been shown to be malleable, ductile, and a good conductor of heat. Which element best fits this description?
An unknown element has been studied in the lab. It has been shown to be malleable, ductile, and a good conductor of heat. Which element best fits this description?
The correct answer is cobalt, since it is the only metal among the answer choices. Metals have all the properties described (malleability, ductility, and conductivity). Sulfur, boron, and silicon do not exhibit these properties to the same extent.
The correct answer is cobalt, since it is the only metal among the answer choices. Metals have all the properties described (malleability, ductility, and conductivity). Sulfur, boron, and silicon do not exhibit these properties to the same extent.
Compare your answer with the correct one above
An element from which of the following groups is most likely to react with a halogen?
An element from which of the following groups is most likely to react with a halogen?
The halogens are the second to last column in the periodic table, meaning that they have an affinity for a single additional electron. Halogens would be most likely to react with alkali metals, which contain only one loosely bound electron in the valence shell. Alkali metals have very low ionization energy, readily losing an electron, while halogens have very high electronegativity, readily gaining an electron. This interaction allows the alkali metals to form ionic bonds with the halogens.
The halogens are the second to last column in the periodic table, meaning that they have an affinity for a single additional electron. Halogens would be most likely to react with alkali metals, which contain only one loosely bound electron in the valence shell. Alkali metals have very low ionization energy, readily losing an electron, while halogens have very high electronegativity, readily gaining an electron. This interaction allows the alkali metals to form ionic bonds with the halogens.
Compare your answer with the correct one above
An unknown element has been shown to be unreactive. It has a low boiling point and an extremely high ionization energy. Which group does the element most likely belong to?
An unknown element has been shown to be unreactive. It has a low boiling point and an extremely high ionization energy. Which group does the element most likely belong to?
The properties described fit well with the noble gases. Alkali and alkaline earth elements are solid at room temperature, meaning that they have a high boiling point. Halogens can be gaseous at room temperature, but are very reactive. Noble gases have low boiling points and rarely act in spontaneous reactions. Their properties are due to their full valence shell, which is the source of their stability. Changes to their electron configuration (such as removing an electron) require large amounts of energy.
The properties described fit well with the noble gases. Alkali and alkaline earth elements are solid at room temperature, meaning that they have a high boiling point. Halogens can be gaseous at room temperature, but are very reactive. Noble gases have low boiling points and rarely act in spontaneous reactions. Their properties are due to their full valence shell, which is the source of their stability. Changes to their electron configuration (such as removing an electron) require large amounts of energy.
Compare your answer with the correct one above
Which of the following is not a property of alkali metals?
Which of the following is not a property of alkali metals?
Alkali metals are much less dense than other metals due to their large radii, which results from having a single loosely bound valence electron. Some of the alkali metals have such low densities that they can float on water.
Alkali metals are much less dense than other metals due to their large radii, which results from having a single loosely bound valence electron. Some of the alkali metals have such low densities that they can float on water.
Compare your answer with the correct one above