Chapter 2 Test - AP Biology

Carbon, hydrogen, nitrogen, and oxygen make up approximately 96% of living matter. These elements are essential for the formation of organic compounds, such as carbohydrates, lipids, proteins, and nucleic acids, which are the building blocks of life. Carbon serves as the backbone for organic molecules, while hydrogen and oxygen are present in water and other essential compounds. Nitrogen is a key component of proteins and nucleic acids, which are vital for cellular function and genetic information. Therefore, these four elements are crucial for the structure and function of living organisms.

Isotopes are different atomic forms of an element that contain the same number of protons but a different number of neutrons. This means that isotopes have the same atomic number (number of protons) but different atomic masses (sum of protons and neutrons). Isotopes can have varying stability and may exhibit different physical and chemical properties due to the difference in their atomic masses.

Hydrogen-3, also known as tritium, is a radioactive isotope of hydrogen. The question asks for the difference between hydrogen-1 and hydrogen-3. Hydrogen-3 has two more neutrons than hydrogen-1. This means that while both isotopes have one proton, hydrogen-3 has two neutrons whereas hydrogen-1 has none. This difference in neutron count is what sets hydrogen-3 apart from hydrogen-1.

The mass number of an element represents the total number of protons and neutrons in an atom of that element. Protons and neutrons are the two types of particles found in the nucleus of an atom, and they contribute to the mass of the atom. Electrons, on the other hand, have a negligible mass compared to protons and neutrons and do not significantly contribute to the mass number. Therefore, adding together the number of protons and neutrons in an atom of an element provides a good approximation of its mass number.

Isotopes of the same element have the same number of protons because they belong to the same element. However, they have different numbers of neutrons, which gives them different atomic masses. Electrons are not involved in determining the atomic mass of an element, so they are not different between isotopes of the same element. Therefore, the correct answer is neutrons.

A covalent bond is likely to be polar when one of the atoms sharing electrons is much more electronegative than the other atom. This is because electronegativity is the measure of an atom's ability to attract electrons towards itself. When one atom is much more electronegative, it will attract the shared electrons more strongly, resulting in an uneven distribution of electron density in the bond. As a result, one end of the bond will be slightly more negative (due to the higher electron density) and the other end will be slightly more positive. This creates a separation of charge, making the bond polar.

Atoms whose outer electron shells contain eight electrons tend to be stable and chemically nonreactive, or inert. This is because having a full outer electron shell satisfies the octet rule, which states that atoms are most stable when they have a full set of eight valence electrons. Atoms with a full outer electron shell do not readily gain, lose, or share electrons, making them chemically nonreactive or inert.

Isotopes of the same element differ from each other in terms of the number of neutrons they contain. While the number of protons and electrons remains the same, isotopes have varying numbers of neutrons. This difference in neutron count leads to variations in the atomic mass of the isotopes, but their chemical properties and valence electron distribution remain the same. Additionally, the amount of radioactivity is not a defining characteristic of isotopes, as some isotopes may be radioactive while others are stable.

An ionic bond is formed when there is a transfer of electron(s) between atoms. In this type of bond, one atom loses electron(s) and becomes positively charged (cation), while the other atom gains electron(s) and becomes negatively charged (anion). The attraction between these opposite charges results in the formation of an ionic bond.

The number of protons in an atom's nucleus is indicated by its atomic number. The atomic number represents the unique identity of an element and determines its placement on the periodic table. It is equal to the number of protons in the nucleus, which defines the element's chemical properties. Atomic mass, atomic weight, mass weight, and mass number are not directly related to the number of protons in an atom's nucleus.

The atomic mass of an atom is determined by the sum of the number of protons and neutrons in its nucleus. In this case, the atom has 15 protons and 16 neutrons, resulting in an atomic mass of 31 daltons.

The atomic number of an atom represents the number of protons in its nucleus, which in this case is 9. The mass number, on the other hand, represents the sum of protons and neutrons in the nucleus, which is 19. Since the atomic mass is the average mass of all the isotopes of an element, and isotopes have different numbers of neutrons, the atomic mass is not equal to the mass number. Therefore, the atomic mass of an atom with an atomic number of 9 and a mass number of 19 would be approximately 19 daltons.

The atomic number of an element represents the number of protons in the nucleus of its atom. Since the given information states that the calcium atom has an atomic number of 20, it means that it must have 20 protons. The atomic mass of an element represents the total number of protons and neutrons in its atom. However, the information provided does not specify the number of neutrons in the calcium atom. Therefore, the correct answer is 20 protons.

The atomic mass of an element is the average mass of all the isotopes of that element, taking into account their relative abundance. Oxygen has three naturally occurring isotopes: oxygen-16, oxygen-17, and oxygen-18. Oxygen-16 is the most abundant isotope, with a relative abundance of about 99.76%. Oxygen-17 and oxygen-18 have lower abundances of about 0.04% and 0.20% respectively. The atomic mass of an oxygen atom is calculated by multiplying the mass of each isotope by its relative abundance and summing them up. In this case, the atomic mass of oxygen is approximately 16 daltons, which is closer to the mass of oxygen-16 (16 atomic mass units) due to its high abundance.

The maximum number of electrons in the 1s orbital of an atom is 2 because the 1s orbital can only hold a maximum of 2 electrons according to the Pauli exclusion principle. This principle states that each orbital can hold a maximum of 2 electrons with opposite spins. Therefore, the 1s orbital can accommodate 2 electrons, one with spin up and the other with spin down.

Covalent bonds involve the sharing of electrons between atoms, meaning that the atoms involved in the bond share their electrons in order to achieve a stable electron configuration. Ionic bonds, on the other hand, involve the electrical attraction between atoms. In an ionic bond, one atom transfers electrons to another atom, resulting in the formation of ions with opposite charges that are attracted to each other. This difference in the way electrons are shared or transferred is what distinguishes covalent bonds from ionic bonds.

Carbon-12 and carbon-14 are isotopes of carbon. Isotopes have the same number of protons but different numbers of neutrons. Since carbon-12 has 6 protons, carbon-14 also has 6 protons. The only difference between the two isotopes is the number of neutrons. Carbon-12 has 6 neutrons, while carbon-14 has 8 neutrons. Therefore, the correct answer is that carbon-14 has two more neutrons than carbon-12.

The reactivity of an atom depends on the presence of unpaired electrons in the outer valence shell of the atom. Unpaired electrons are more likely to form chemical bonds with other atoms, leading to chemical reactions and increased reactivity. The number of valence shells, number of orbitals, number of electrons in each orbital, and presence of hybridized orbitals are not direct factors that determine reactivity.

H2O contains the strongest polar covalent bond among the given molecules. This is because H2O is a polar molecule due to the electronegativity difference between oxygen and hydrogen atoms. Oxygen is more electronegative than hydrogen, causing the oxygen atom to attract the shared electrons more strongly. As a result, there is an uneven distribution of charge in the molecule, with the oxygen atom being slightly negative and the hydrogen atoms being slightly positive. This unequal sharing of electrons creates a strong polar covalent bond in H2O.

The statement mentioned in the answer is false because protons have a positive charge, not a negative charge, and electrons have a negative charge, not a positive charge.

An atom of sulfur has 6 electrons in its valence shell. The valence shell is the outermost shell of an atom, and sulfur is in group 16 of the periodic table, also known as the oxygen family. Elements in this group have 6 valence electrons. Therefore, sulfur also has 6 electrons in its valence shell.

The atomic number of an atom represents the number of protons in its nucleus. In a neutral atom, the number of electrons is equal to the number of protons. Therefore, an atom with atomic number 12 would have 12 electrons. The electrons are arranged in different energy levels or shells around the nucleus. The outermost shell, also known as the valence shell, can hold a maximum of 8 electrons. In this case, the outermost electron shell of the atom with atomic number 12 would have 2 electrons, as it is the closest to the nucleus and can only accommodate a maximum of 2 electrons.

A covalent chemical bond is formed when the outer-shell electrons of two atoms are shared. This sharing allows both atoms to satisfactorily fill their outer electron shells, which is a more stable configuration. By sharing electrons, the atoms are able to achieve a full outer shell and become more stable, rather than one atom losing electrons and the other gaining them. This is the nature of a covalent bond, where electrons are shared between atoms rather than transferred completely.

A polar covalent bond forms when one of the atoms in a molecule has a greater affinity for electrons than the other atom. This means that one atom is more electronegative and attracts the shared electrons more strongly, creating a partial negative charge on that atom and a partial positive charge on the other atom. This unequal sharing of electrons results in a polar covalent bond. The other options are incorrect because they do not describe the conditions necessary for a polar covalent bond to form.

When two atoms are equally electronegative, it means that they have the same ability to attract electrons. In this case, they will form nonpolar covalent bonds. In a nonpolar covalent bond, the electrons are shared equally between the two atoms, resulting in a balanced distribution of charge and no separation of positive and negative charges. This is different from polar covalent bonds, where the electrons are shared unequally, leading to a partial positive and partial negative charge on the atoms involved. Ionic bonds involve the complete transfer of electrons from one atom to another, while isotopes are different forms of the same element with different numbers of neutrons.

Nitrogen has an atomic number of 7, which means it has 7 electrons. The valence shell of an atom is the outermost shell, and in the case of nitrogen, it is the second shell. The second shell can hold a maximum of 8 electrons, but nitrogen only has 5 electrons in its valence shell, making it the correct answer.

An atom with six electrons in its outer electron shell has a valence of 2. The valence of an atom refers to the number of electrons in the outermost shell, also known as the valence shell. In this case, the atom has six electrons in its outer shell, which means it can either gain two more electrons to achieve a stable octet (eight electrons in the outer shell) or lose six electrons to have an empty outer shell. Both options would result in a valence of 2.

In the ionic bond of sodium chloride, chlorine gains an electron from sodium. This is because chlorine has 7 valence electrons and needs 1 more electron to achieve a stable octet. Sodium, on the other hand, has 1 valence electron and wants to lose it to achieve a stable octet. Therefore, chlorine gains an electron from sodium to fulfill its electron requirement and form a stable ionic bond.

When an atom absorbs sufficient energy, it can cause an electron to move to an electron shell that is farther away from the nucleus. This is because electrons exist at fixed levels of potential energy, and when they gain energy, they can move to higher energy levels or electron shells. This movement is known as an electron transition or excitation. As a result, the electron moves to a shell with a higher energy level, which is farther from the nucleus.

The correct answer is "the existence of unpaired electrons in the valence shell." This is because the reactivity of an atom is determined by its ability to gain, lose, or share electrons in chemical reactions. Unpaired electrons in the outermost shell, known as the valence shell, are more likely to participate in bonding with other atoms, making the atom more reactive. The other options are not directly related to the reactivity of an atom.

When an atom of sulfur (S) reacts with atoms of hydrogen (H), they can form a molecule with the formula H-S-H. This means that a hydrogen atom is bonded to a sulfur atom, and another hydrogen atom is bonded to the other side of the sulfur atom. This molecule is known as hydrogen sulfide (H2S), which is a colorless gas with a strong odor of rotten eggs. So, the correct answer is H-S-H.

The atomic number of carbon is 6, which means it has 6 protons in its nucleus. Carbon-14 is heavier than carbon-12 because it has 8 neutrons in its nucleus, while carbon-12 has only 6 neutrons. The number of neutrons in an atom can vary, resulting in different isotopes of an element. In this case, carbon-14 has more neutrons than carbon-12, making it heavier.

Fluorine has 9 electrons, and its valence shell can hold a maximum of 8 electrons. Therefore, only 1 electron is needed to complete the valence shell of a fluorine atom.

Atoms form molecules when they share electron pairs. This is because when atoms share electrons, they are able to fill their outermost energy levels and achieve a more stable configuration. This sharing of electrons creates a bond between the atoms, resulting in the formation of a molecule. Molecules can be made up of atoms of the same element or different elements, depending on the types of atoms involved in the sharing of electrons.

Iodine is a trace element that is required by humans and other vertebrates. It is essential for the production of thyroid hormones, which regulate metabolism and play a crucial role in growth and development. Although iodine is needed in small amounts, its deficiency can lead to serious health problems, including goiter and intellectual disabilities. Therefore, iodine is an important trace element for maintaining proper thyroid function and overall health in humans and other vertebrates.

The element with atomic number 8 refers to oxygen. Oxygen has 6 valence electrons, and it needs 2 more electrons to complete its octet. Each hydrogen atom has 1 valence electron. Therefore, oxygen can form 2 covalent bonds with hydrogen atoms, where each hydrogen atom shares its electron with oxygen. This allows oxygen to complete its octet and hydrogen to have a stable electron configuration with 2 electrons in its outermost shell.

The atomic number of an element represents the number of protons in its nucleus. Since the atomic number of phosphorus is 15, it means that it has 15 protons. Additionally, in a neutral atom, the number of protons is equal to the number of electrons. Therefore, phosphorus also has 15 electrons. However, the number of neutrons cannot be determined solely from the atomic number. Hence, the correct answer is B and C only.

Phosphorus has 5 electrons in its valence shell. The valence shell of an atom is the outermost shell that contains electrons, and it determines the atom's reactivity and ability to form chemical bonds. Phosphorus is in Group 15 of the periodic table, which means it has 5 valence electrons. These electrons can participate in chemical reactions and form bonds with other atoms to achieve a stable electron configuration.

Chemical equilibrium is a state in which the forward and reverse reactions occur at the same rate, resulting in no net change in the concentrations of the reactants and products. This means that the concentrations of the reactants and products remain constant over time. The other options do not accurately describe chemical equilibrium.

The four elements most abundant in life - carbon, oxygen, hydrogen, and nitrogen - all have unpaired electrons in their valence shells. This means that they have the potential to form chemical bonds with other elements, allowing for the formation of complex molecules necessary for life. Having unpaired electrons makes these elements highly reactive and versatile in their ability to form bonds.

The mass number of an atom is the total number of protons and neutrons in its nucleus. Since the nitrogen atom has 7 protons and 7 neutrons, its mass number is 14. Atomic mass refers to the average mass of all the isotopes of an element, taking into account their abundance. The atomic mass of nitrogen is approximately 14 daltons, which is consistent with the mass number. Therefore, the correct statement is that the nitrogen atom has a mass number of 14 and an atomic mass of approximately 14 daltons.

When a reaction has attained chemical equilibrium, it means that the rate of the forward reaction is equal to the rate of the reverse reaction. This indicates that the reaction is occurring at a steady state, with no net effect on the concentration of the reactants and products. At equilibrium, the concentrations of the reactants and products may not be equal, but their rates of formation and consumption are balanced.

Atoms whose valence shells are filled with electrons are stable and chemically unreactive or inert. This means that they do not easily form chemical bonds with other atoms. Additionally, these atoms exhibit similar chemical behaviors due to their full valence shells, which results in similar chemical properties. Therefore, the correct answer is C and D only.

The maximum number of electrons in a 2p orbital of an atom is 2. This is because the 2p orbital can accommodate a maximum of 6 electrons, with each suborbital (px, py, pz) holding 2 electrons. Therefore, the correct answer is 2.

Sulfur would exhibit chemical behavior most like that of oxygen because both sulfur and oxygen are in the same group (Group 16) on the periodic table. Elements in the same group have similar electron configurations and therefore exhibit similar chemical behavior. Oxygen is known for its ability to form compounds with other elements, particularly through the sharing of electrons, and sulfur shares this characteristic. Additionally, both oxygen and sulfur are nonmetals, further contributing to their similar chemical behavior.

An atom of neon has 10 protons, which gives it an atomic number of 10. Since the atomic number represents the number of electrons in an atom, neon also has 10 electrons. However, the question specifically asks about the outer electron shell. The first shell of an atom can hold a maximum of 2 electrons, and the second shell can hold a maximum of 8 electrons. Since neon has 10 electrons, it means that the first shell is full with 2 electrons, and the second shell has 8 electrons in its outer electron shell. This makes statement A correct. Neon is also inert, meaning it does not readily react with other elements. Therefore, statement B is also correct. Statement C is incorrect because the atomic mass of neon is 20.18 daltons, not 10.

The given reaction is a reversible reaction, as indicated by the double arrow. Ammonia (NH3) is being formed in the forward reaction, where 3 molecules of hydrogen gas (H2) react with 1 molecule of nitrogen gas (N2) to produce 2 molecules of ammonia. However, ammonia is also being decomposed in the reverse reaction, where 2 molecules of ammonia break down to form 3 molecules of hydrogen gas and 1 molecule of nitrogen gas. Therefore, the statement "Ammonia is being formed and decomposed" is true for this reaction.

A van der Waals interaction is the weak attraction between the nucleus of one molecule and the electrons of a nearby molecule. This type of interaction is due to the temporary fluctuations in electron distribution, which create temporary dipoles in molecules. These temporary dipoles induce opposite dipoles in nearby molecules, leading to an attraction between them. The interaction between the nucleus and electrons is stronger than the attraction between electrons, making it the correct answer.