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Chemistry Regents June 2010 - Question 02 |
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Written by The Chemistry Wizard
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Correct Answer: 3
Why: Carbon is an element located in group 14 of the periodic table. Like most other known elements, they are composed of a positively charged nucleus orbited by negatively charged electrons; therefore, the nucleus is the positively charged center of the atom. The nucleus is both positively charged and contains most of the mass of the atom, usually referred to as the atomic mass. The nucleus is composed of protons and neutrons for most elements, hydrogen being the exception, as its nucleus is composed of one proton and no neutrons.
Based on that information, the nucleus of carbon is composed of protons and neutrons. Carbon 12, the most common form of carbon, is composed of six (6) protons and six (6) neutrons, giving an atomic mass of approximately 12 (the mass of the electrons being negligible in comparison).
Answering the Question:
To answer this question, an understanding of atomic structure is necessary; although, knowledge of the structure of carbon is not necessary. The structure of the atom is such that it is composed of a central positively charged nucleus surrounded by orbiting negatively charged electrons. With that is mind, answer (4) and answer (2) would be immediately eliminated: answer (4) because the nucleus is not composed of protons and electrons, and answer (2) because neutrons have no charge and, therefore, would not be the only subatomic particles present in the nucleus of an atom. Answer (1) is also not possible as hydrogen is the only element with a nucleus that does not have neutrons associated with it. Therefore, the correct answer is answer (3), protons and neutrons. |
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Last Updated on Wednesday, 08 June 2011 11:18 |
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Chemistry Regents June 2010 - Question 03 |
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Written by The Chemistry Wizard
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Correct Answer: 3
Why? Helium is an element found in group 18 of the periodic table along with the other noble or inert gasses. The helium atom, like most other atoms, is composed of three primary subatomic particles. These are the positively charged protons, the neutral neutrons and the negatively charged electrons. Helium has two protons, two neutrons and two electrons, the nucleus, containing the protons and neutrons and having a positive charge, while the orbiting electrons are negatively charged.
Answering the Question:
The question asks "which part of helium is positively charged?" To answer this question, knowledge of general atomic structure is required. Helium is composed of the same atomic structure governing most other elements. Protons are the only positively charged particles in atoms and protons, along with neutrons, form the nucleus of most atoms.
Therefore, answer (1) could not be correct, as electrons are not positively charged. Answer (2) refers to the neutral nucleus, which is also not positively charged. Answer (4) does not referring to a charged particle at all, but refers to the general area in which electrons may be found around atoms. Answer (3) refers to the nucleus, which is composed of both protons and neutrons. Although neutrons do not have a charge, protons do have a positive charge, giving the nucleus a positive charge. Therefore, the answer is three (3) the nucleus. |
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Last Updated on Wednesday, 08 June 2011 11:19 |
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Chemistry Regents June 2010 - Question 04 |
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Written by The Chemistry Wizard
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Correct Answer: 3
Why? An atom is composed of a number of sub-atomic particles, they are: protons, neutrons and electrons. The protons and neutrons make up the nucleus of the atom, while the electrons orbit the nucleus. Both the nucleus and electrons are charged particles and help to stabilize each other, often being compared to a sun being orbited by planets. The nucleus is responsible for almost all the mass of an atom and is used to categories atoms into specific elements.
Answering the Question:
Looking at each of the possible answers in turn:
Answer (1) suggests an alpha particle. An alpha particle is in effect a helium ion, which is composed of two (2) protons and two (2) neutrons; therefore, it has a higher mass than a single proton.
Answer (2), an electron, is negatively charged and has significantly less mass than a proton. According to the current models of the atom, most of the mass of an atom is contained within the nucleus and not in the orbiting electrons. As the proton is a major component of the nucleus, it would, therefore, not be possible for a proton and an electron to have approximately equal mass.
Answer (4), a positron, is the only particle of opposite charge that is also equal in mass to an electron. This means a positron's mass is also significantly less than a proton. Answer (3), a neutron, is the other component that makes up the nucleus of an atom, for all but hydrogen. The neutron and proton give the atom its mass. Though electrically neutral, the neutron is close in mass to that of a proton. Therefore, the best possible answer is (3). |
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Last Updated on Wednesday, 08 June 2011 11:19 |
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Chemistry Regents June 2010 - Question 05 |
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Written by The Chemistry Wizard
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Correct Answer: 1
Why? Carbon is a group 14 element on the periodic table. It has six (6) protons and six (6) neutrons in its most common form, and is tetravalent, meaning it will make four (4) electrons available for the formation of covalent bonds. Carbon has many physical forms called allotropes, the most popular of which are graphite and diamond.
Both allotropes are very different. Diamond is the hardest naturally occurring material on earth. It is a poor electrical conductor but an excellent thermal conductor. It is clear (like glass) and used heavily in industry as a result of its hardness. In diamond, the carbon atoms form covalent bonds with each other, utilizing all available electrons to form a tetrahedron monomer for its lattice.
Diagram 1. Showing the lattice structure of diamond
Graphite, on the other hand, is soft enough to rub off on paper, a good electrical conductor but a poor thermal conductor. Graphite is opaque and dark grey to black in appearance. Covalently bonded hexagonal sheets form it, each sheet bonding to the next through weak Van Der Waals forces.
Diagram 2.showing the lattice structure of graphite
Although chemically identical, graphite and diamond display very different structural, chemical and physical properties.
Answering the Question:
Answering this question does not require much knowledge of carbon. Graphite and diamond are very common and popular allotropes of carbon. It would be unlikely that graphite and diamond, both known to be very different, would have the same molecular structure. If they did indeed have the same structure, they would be categorized as isotopes and would share many properties. Therefore, answers (3) and (4) would be eliminated as they both state "the same molecular structure" as a part of the answer. Also, it is unlikely that given the difference in structures, that the properties would remain the same. Therefore, answer (2) would be eliminated, leaving answer (1), different molecular structure and different properties, as the correct answer.
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Last Updated on Wednesday, 08 June 2011 11:20 |
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Chemistry Regents June 2010 - Question 07 |
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Written by The Chemistry Wizard
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Answer: 3
Answering the Question:
Based on the information present in the question, light is being emitted. For this to occur there must be a release of energy, which eliminates answers (1) and (2). Light is a form of energy and can neither be created nor destroyed but changed from one form to another. If light is being emitted (and light is a form of energy), it stands to reason that energy is being emitted or released.
Electrons are negatively charged particles usually orbiting the nucleus of an atom. When electrons are supplied with energy, they become excited and move to a higher energy state, or higher orbit. This means that the distance between the electrons and the nucleus will increase as more energy is supplied to overcome the forced of attraction between the electrons and the nucleus. As energy is released, the electrons no longer have sufficient energy to overcome the force of attraction from the nucleus. This results in an electron entering a lower energy state, hence the answer is (3). |
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Last Updated on Wednesday, 08 June 2011 11:21 |
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Chemistry Regents June 2010 - Question 31 |
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Written by The Chemistry Wizard
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Answer: (1)
Why? An element is defined by the number of protons present in its nucleus. An isotope of an element is an element with the same number of protons, but a different number of neutrons. The periodic table is organized on the basis of number of protons, hydrogen having one, then helium with two, lithium with three and so on. This means that if hydrogen were to suddenly gain a proton, it would cease to be hydrogen and would now be labeled helium. However, if hydrogen gained a neutron, it would be called deuterium, an isotope of hydrogen.
Answering the Question:
Based on the definition of an element and an isotope, only A and D have six protons, meaning they have the same number of protons. This means they can be placed into the same category of element. However they have a different number of neutrons, which makes them isotopes of the same element. Atom X has seven protons, which makes atom X different from any other given atom. Atom Z has eight protons, also makes atom Z different from any other atom listed. Therefore, only answer (1) is correct, as both A and D has the same number of protons. |
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Chemistry Regents June 2010 - Question 32 |
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Written by The Chemistry Wizard
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Answer: (3)
Why? The Lewis electron dot diagram is a theoretical representation showing the free and/or covalently bonded electrons present in an atom or molecule. Group 13 elements have three electrons available for bonding in their valence orbital. These three electrons will participate in covalent bonding with suitable elements or donate unpaired electrons to form a stable ion. The ground state of an atom is the lowest energy state. In general, group 13 elements have three electrons in there valance orbital available for bonding.
Atoms have electrons present in various orbitals around the nucleus. In general the electrons try to achieve a noble gas configuration, which is generally more stable, according to the octet rule. That means on average the system likes to achieve eight electrons in its valence orbital, this sometimes results in donation of electrons or accepting of electrons.
Electrons of atoms are organized into the likely zones, orbiting the nucleus, where they can be found. The zones of the orbiting electrons are called orbitals. Orbitals are the electrical fields generated by the nucleus, which bind the electrons within a particular radius. The exact location of electrons cannot be determined however the probable location of the electrons can be determined.
Electrons fill the orbitals in a particular order 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. Where an s can accommodate 2 electrons, p can accommodate 6, d can accommodate 10 and f can accommodate 14. Group 13 elements all have two s electrons and one p electron in their valence orbital
Answering the Question:
The question asks about the ground state of group 13 elements. To answer this question it is good to have an understanding of the group 13 elements in the periodic table. A very popular group 13 element is aluminum, which ionizes to form Al3+ as a result of the loss of three electrons. This is a good indicator as to how many electrons are present in the ground state of the element. Since three electrons will be lost it would indicate that three electrons are present in the valence orbital. Analyzing the lewis dot diagram, the diagram showing three electrons would be the correct one. Therefore, answer (3) is the correct answer. |
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Chemistry Regents June 2010 - Question 37 |
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Written by The Chemistry Wizard
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Answer: (4)
Why? The element argon is a member of group 18 on the periodic table. This group of elements is referred to as the noble gases. They have attained the most stable electron state for any of the elements in their particular period. Most atoms strive to attain an electron configuration according to the octet rule. The octet rule has to do with a general understanding that atoms will try to attain the most stable electron configuration possible and this is usually achieved when they have a full s2p6 orbital, or eight electrons in their valence orbital, like the noble gases. This holds true for most of the main group elements. The noble gases have achieved this goal and the outer orbital of valence electrons is "full". The results are atoms, which at standard temperature and pressure, will not readily accept or donate an electron.
The main group of elements usually ends with s and p subshells, which can accommodate 2 and 6 electrons respectively. In order to have a full electron shell or octet, it means that the last electron shell have s and p subshells with their maximum number of electrons. Transition metals do not always follow this sure as they do not end with s and p subshells, but rather d and s. The d subshell can accommodate a maximum of 10 electrons, which means the octet rule would no longer apply.
Answering the Question: Analyzing the answers in turn, answer (1) has more protons than neutrons. This could not be the correct answer as protons are not what will determine if an atom is in its ground state. Chemical bonding is usually a result of electromagnetic interactions, between the orbiting electrons and the nuclei of the bonding atom. However, only electrons are "mobile" and will have a ground state, or lowest energy state. This means any answer involving protons and neutrons (atomic nuclei) can be eliminated. Answer two will have a similar result as one, as both answers focus on the number of protons or neutrons. Answers 3 and 4 focus on the number of electrons present in the valence orbital of the atom, and both speak to electron stability. However, answer 3 speaks about two valence electrons, which does not conform to the octet rule. Therefore, answer 4 as the correct answer. |
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Chemistry Regents June 2010 - Question 51 |
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Written by The Chemistry Wizard
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Answer: 2 pairs
Answering the Question:
Carbon dioxide is a naturally occurring molecule that is primarily a result of respiration or living organisms. It is also man made mostly in the form of the burning of fossil fuels and is a major contributor to global warming.
Carbon dioxide (written CO2) is a result of the covalent bonding of one carbon atom with two oxygen atoms. Carbon dioxide is a gas at standard temperature and pressure and sublimes to a solid at -78°C.
Carbon dioxide is composed of one carbon atom covalently bonded to two oxygen atoms, as shown below:
O=C=O
To get an idea of how carbon and oxygen will bond, it helps to determine how many electrons they each have available for bonding. Carbon has an electron configuration of 1s2 2s2 2p2, This means that carbon has 4 electrons in its valence orbital and would be capable to bond with 4 more electrons to attain a noble gas configuration. Oxygen on the other hand has an electron configuration of s2 2s2 2p4, which means it has 6 electrons in its valence orbital and will accept 2 more electrons for bonding in order to achieve a noble gas configuration.
With this in mind, the number of electrons needed for both carbon and oxygen to achieve a stable configuration can be determined. Carbon will require 4 electrons in total; however, an oxygen atom only has space for two. This means carbon will require two oxygen atoms to achiever its stable electron configuration while one carbon atom would be more than sufficient for an oxygen atom.
Therefore, the Lewis electron dot diagram of carbon dioxide would show.
Each "-" represents a pair of electrons. The bond between carbon and one oxygen atom would be C=O meaning that four electrons are being shared or 2 pairs. Therefore, the total number of electron pairs being shared between the carbon atom and one of the oxygen atoms in a carbon dioxide molecule is 2. |
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Chemistry Regents June 2010 - Question 52 |
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Written by The Chemistry Wizard
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Chlorine (Cl) is a member of the group 17 elements of the periodic table, also called the halogens. This group of compounds has 7 electrons in their valence orbitals and will form diatomic molecules in nature. The chlorine atom has 17 electrons and 17 protons, if an additional electron is accepted, which is what happens when a chloride ion is formed, then there are additional forces of repulsion between electrons along with more electrons than protons. This results in a larger atom in theory, as the electrons have to spread out more due to repulsion effects. This is in contrast to the loss of an electron, in which case there will be more protons pulling on fewer electrons, causing the atomic radius to decrease as a result of fewer electrons to repel one another and greater attractive forces since there are more protons. |
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