Correct answer: Oxygen and sulfur have the same number of valence electrons.

Why?:

Oxygen and sulfur are in the same column of the periodic table. They belong to group VIA or group 16. Elements belonging to the same group have similar properties. In the case of sulfur and oxygen, they both have six valence electrons. In effect, they are both capable of accepting two more electrons to have a complete set of eight valence electrons. The valence electrons are responsible for the properties of the elements.

Answering this question:

Write the electron configuration of each of the elements. For sulfur, it is 1s², 2s², 2p⁶, 3s², 3p⁴ because it has 16 electrons. For oxygen, it is 1s², 2s², 2p⁴ because it has 8 electrons. It can be observed that sulfur has 6 electrons in its 3^rd energy level. Oxygen has 6 electrons in its 2^nd energy level. They both have 6 electrons in their valence energy level. With this, both elements are capable of forming 2 bonds with other atoms. Thus, they form compounds with similar molecular structures.

So, oxygen and sulfur form compounds with similar molecular structure because they both have 6 valence electrons.

Correct answer: Ethanol is liquid at room temperature with a boiling point of 78.2˚C.

Why?:

Why is ethanol liquid at room temperature with at boiling point of 78.2˚ C when hydrocarbons of a similar size like propane and butane are gases? The answer lies in the additional intermolecular forces that attract ethanol molecules to one another. Hydrocarbons do not experience this. Ethanol participates in hydrogen bonding with other ethanol molecules. It is a polar molecule that is attracted to other ethanol molecules through dipole-dipole interactions. Finally, ethanol also experiences attraction to other ethanol molecules through induced dipole-dipole interactions (also called dispersion forces or Van der Waals forces). In contrast, hydrocarbons are only attracted to each other through induced dipole-dipole interactions. This weaker attraction results in a lower boiling point.

Answering this question:

Always remember that if a hydrogen atom is bonded to oxygen, nitrogen, or fluorine, it is a hydrogen bond. Hydrogen bonds are strong bonds. Ethanol has this in its O-H functional group. Besides the hydrogen bonding in it, it is also capable of having bonds with other ethanol molecules. This contributes to the stronger bonds ethanol contains.

So ethanol is liquid at room temperature and it has a boiling point of 78.2˚C due to its strong intermolecular forces and its chemical bonds.

Why?:

A water molecule is composed of two hydrogen atoms bonded to one oxygen atom. Considering the two lone pairs of electrons on oxygen, a water molecule has a bent structure. Each oxygen-hydrogen bond is almost 105˚. This is because of the strong electron-electron repulsion brought about by the two lone pairs of electrons on oxygen. When an anion is in a solution, a water molecule positions itself such that the partially positive hydrogen atom is directed towards the negatively charged anion. The oxygen atom will be as far as possible from the anion due to electron-electron repulsion.

In this illustration, the dashed lines represent the attraction between the negatively charged chloride ion and one of the partially positive hydrogen of each water molecule.

Answering this question:

Always remember that an oxygen atom is much more electronegative than the hydrogen atom. Oxygen will pull the electrons towards itself, making it partially negative. It also makes the hydrogen atom partially positive. In the presence of a negatively charged ion, the oxygen atom will tend to stay away. Like charges repel, unlike charges attract. Therefore hydrogen atom will be directed towards the negative ion.

So the illustration is a picture of how water molecules position themselves in the presence of an anion.

Correct answer: (1) water

Why?:

The substance with the greatest intermolecular forces that bind the molecules together will have the lowest vapor pressure. In the conversion of a liquid state of a substance to its vapor phase, intermolecular bonds need to be broken. Those that are bound together by strong intermolecular bonds are less likely to vaporize compared with their other counterparts of weaker intermolecular bonds. An example of a strong intermolecular bond is hydrogen bond. This is a bond between a hydrogen atom and fluorine, oxygen or a nitrogen atom. Water, ethanoic acid, and ethanol all have OH groups. They are all capable of hydrogen bonding. Propanone does not have an OH group.

Answering this question:

It would be necessary to remember the functional groups of all these molecules. Common to water (H₂O), ethanoic acid (CH₃CH₂COOH), and ethanol (CH₃CH₂OH) are O-H bonds. It is a hydrogen bond. Propanone is a ketone and does not contain an O-H bond. So (3) can be eliminated.

Of the remaining answer choices, all participate in hydrogen bonding, dipole-dipole interactions, and induced dipole-dipole interactions. However, water is the most polar of the three choices, making its dipole-dipole interactions stronger.

It is beneficial to relate the three probable answers to substances common to us. Propanone is a family of acetone. Acetone is a solvent used in removing nail polish. We know that this is a very volatile liquid. Ethanol is component in alcoholic beverages. If a small amount of an alcoholic beverage is left in an open container, its volume would surely reduce after some time. Water will experience the same if left in an open container. But it would take a longer time for this to happen to water. Therefore among the three, water is the least volatile.

So (1) is the correct answer.

Correct answer: (1)

Why?:

Chloroethene is a substituted hydrocarbon with 1 chlorine atom attached to it. Connecting the two carbon atoms is a double bond. Since it is a substituted hydrocarbon, one of the carbon atoms is attached with a chlorine atom. It does not matter which carbon atom chlorine is attached to because there are only 2 carbon atoms.

The parent hydrocarbon, ethene, is a 2-carbon molecule with a double bond between the 2 carbon atoms. It is a member of the alkene family. The other members of the hydrocarbon family are the alkanes and alkynes. Alkanes have single bonds and no multiple bonds. Alkynes have at least one triple bond.

A Lewis structure shows the number of electrons in the valence shell of an atom. These electrons are represented by dots. When molecules are formed, a covalent bond is formed between atoms. These covalent bonds are made by the sharing of electrons of two atoms. Each of the atoms sharing the electrons assumes sole ownership of the shared electrons. Atoms share electrons to become stable. Most atoms are stable with 8 valence electrons. Hydrogen is stable with 2 valence electrons resembling the noble gas helium.

Answering this question:

Examine each atom in the molecule. Each of the atoms must be stable. It means that carbon must be surrounded with 8 dots, hydrogen with 2, and chlorine with 8 as well. Four dots must be in between the 2 carbon atoms as these represent a double bond. It can be noted that the structure in (2) does not contain a double bond. This can be eliminated. The structure in (4) contains only 1 carbon atom. This can be eliminated. The structure in (3) contains 10 dots surrounding each of the carbon atoms. This is contrary to the octet rule.

Correct answer: (4)

Why?:

Carbon monoxide or CO is a gas composed of 1 atom of oxygen and 1 atom of carbon. There is a 1 to 1 relationship between the numbers of atoms on this molecule. And since it is a gas, it is not bound to other CO molecules. They are very mobile.

Answering this question:

In this question, a particle diagram must contain molecules comprised of black and white circles. Choice (2) can be eliminated. Since CO is a gas and cannot form a network of bonds with other CO molecules, (3) can be eliminated. Choice (1) contains molecules with 3 atoms attached in a single molecule. This can be eliminated as a single CO molecule is composed of just 2 atoms.

This leaves us with (4) as the correct answer.

Why?:

Oxygen has an oxidation state of -2. For this to be balanced in a neutral compound with a metal of a +1 oxidation state, it needs 2 of the metal. With a metal of +2 oxidation state, oxygen needs just 1 of it. For the representative elements, the oxidation states can be easily determined using their group numbers. Representative elements are those that belong to groups 1, 2, 13, 14, 15, 16, 17. In the older version, they are known as the groups IA, IIA, IIIA, IVA, VA, VIA, and VIIA, respectively. Group IA elements have an oxidation state of +1. Group IIA elements have +2, +3 for group IIIA, -3 for group VA, -2 for group VIA, and -1 for group VIIA. Group IVA can either have -4 or +4.  Oxygen is under group VIA.

Answering this question:

The combination of a metal and a nonmetal produces an ionic compound. A simpler technique of coming up with the formula for an ionic compound is the "criss-cross" method. Here, the magnitude of the oxidation state of the metal ion becomes the subscript of the nonmetal element. The magnitude of the oxidation state of the nonmetal ion becomes the subscript of the metal element. When Na⁺¹ combines with O^-2, the 1 from the oxidation state of Na⁺¹ becomes the subscript of O. The 2 from the -2 oxidation state of oxygen becomes the subscript of Na. Thus, the resulting formula is Na₂O. Given the general formula M₂O, it could be easily determined that the oxidation state of M is +1 and that of oxygen is -2. Since the +1 oxidation state is that of an element from group IA or group 1 in the periodic table,

The correct answer is (1).

Correct answer: (1) CH₄

Why?:

A nonpolar molecule has no net dipole moment. This means that the electron cloud between two bonded atoms is equally dispersed between them. Carbon is more electronegative than hydrogen. It has greater pull of the electron cloud towards itself. Each C-H bond has an arrow with the arrowhead pointing towards carbon and the tail on the hydrogen. This arrow represents the pull of the electron cloud towards carbon. Since there are 4 C-H bonds in CH₄, there would be 4 arrows pointing towards carbon. But since the structure of CH₄ is tetrahedral, those 4 arrows, representing forces, will cancel each other. Hence, there is no net dipole moment.

Answering this question:

Try to come up with the Lewis structure of each of the molecules. For HCl, there are just 2 atoms so the structure would be linear. Since chlorine is known to be one of the most electronegative elements in the periodic table, it would have greater pull of the electrons towards itself. The chlorine atom will have a partial negative charge, and hydrogen will have a partial positive charge. Hence, HCl is polar since there is a net dipole moment.

The molecule H₂O would not be linear due to the lone pairs of electrons on oxygen. Lone pairs of electrons carry in them a very strong repulsive force. Its presence would mean staying of the atoms as far apart from each other as possible. Hence, the structure of H₂O is bent. Oxygen is very electronegative. This would pull the electron cloud towards itself. If this pull would be represented by an arrow, there would be two arrows pointing towards oxygen. Those two arrows will not be cancelling each other due to the bent structure of H₂O. Hence, H₂O is polar.

Ammonia, NH₃, is also a polar molecule like H₂O. Nitrogen here contains a lone pair of electrons also. Like water, the pull of electron clouds would be towards nitrogen. And in the structure of NH₃, those pull of electron clouds will not be cancelled out. So there would be a net dipole moment. It is also a polar molecule.

It is also beneficial to note that if a molecule is composed of two different kinds of atoms such as HCl, the pull of electrons would definitely be towards one of them. So this is a polar molecule. Two-membered molecules would be nonpolar if both atoms combined together are the same, such as O₂, H₂, or N₂. Oxygen and chlorine are very electronegative atoms. Unless there are four the same kinds of atoms connected to each of them, their molecules would be polar.

So the correct answer is (1).

Correct answer: (1) 6

Why?:

In the Lewis structure, two shared electrons are represented with a single bond. There are 3 bonds joining together the 2 carbon atoms. Therefore, there are 6 electrons shared by them.

Answering this question:

Always remember that a bond between two atoms represents two electrons shared by both atoms. Just count the number of bonds between the two carbon atoms. Multiply the bonds by 2 electrons since a bond represents two electrons.

Then it leaves us with (1) as the correct answer.

Correct answer: (2) an ionic bond

Why?:

Transfer of electrons from one atom to another results in the formation of charges. If an atom loses electrons, it becomes positively charged as it loses negativity. It is called a cation. When an atom gains electrons, it acquires a negative charge. It is called an anion. Cations and anions are generally known as ions. They have opposing charges. Because of their opposing charges, they become attracted to each other. They then form a bond. Since the attraction arises from two ions with opposing charges, the resulting bond is called an ionic bond.

Answering this question:

A hydrogen bond, as the name implies, involves a hydrogen atom. The question is talking about an atom in general and not just a hydrogen atom. So (1) can just be eliminated immediately. Furthermore, a hydrogen bond only exists if a hydrogen atom bonds with fluorine, oxygen, or nitrogen atoms. A covalent bond occurs by the sharing of electrons and not through their transfer from one atom to another. Since the term "covalent" is mentioned in (3) and (4), these can then be eliminated as well.

Always remember too that losing or gaining electrons involve the formation of charged particles called ions. From the name itself, it could be deduced that the combination of ions form an ionic bond.

So the correct answer is (2).