Answer: 2-8-1

Answering the Question:

Answer: An atom with an excited state of 2-7-2 means that there are electron shells 1, 2 and 3 are in use. An electron shell is the most probable area that an electron could be found orbiting the nucleus of an atom at a point in time. Electron shells are numbered 1, 2, 3...n, each shell is capable of accommodating a fixed number of electrons. Electron shells also have a particular order in which they are filled to achieve a stable configuration.  In shell 1, two electrons can be accommodated; shell 2, eight, and shell 3 can accommodate eighteen. An excited state of 2-7-2 means that the non excited state would be 2-8-1, as shell two would fill to eight before the next shell is used. The 2-7-2 configuration would have resulted from an electron becoming excited and moving to a higher energy shell. The reason for electrical neutrality is that no electrons have been gained or released, simply moved from one shell to another.

Answering the Question:

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.

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.

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.

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:

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:

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.

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:

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.