A.P. Biology Chapter 2 (Chemistry Review)

Stable elements have 8 electrons because they follow the octet rule, which states that atoms tend to gain, lose, or share electrons in order to achieve a full outer shell of 8 electrons. This stability is achieved by filling the s and p orbitals of the outermost energy level. Therefore, elements that have 8 electrons in their outermost energy level are considered stable.

Positive ions are called cations. Cations are formed when an atom loses one or more electrons, resulting in a net positive charge. These ions are attracted to the cathode (hence the name cation) during electrolysis and are typically formed by metals. An example of a cation is the sodium ion, Na+, which forms when a sodium atom loses one electron.

Negative ions are called anions. Anions are formed when an atom gains one or more electrons, resulting in a negatively charged ion. Cations, on the other hand, are positive ions formed when an atom loses one or more electrons. Canions and Ations are not valid terms used to describe negative ions.

The correct answer is Carbon, Oxygen, Hydrogen, Nitrogen. These four elements are considered macroelements because they are required in relatively large amounts by living organisms. Carbon is the basis for organic molecules, while oxygen is essential for respiration. Hydrogen is a component of water and many organic compounds, and nitrogen is crucial for the synthesis of proteins and nucleic acids.

A single covalent non-polar bond is indicated by one dash (-). In a covalent bond, two atoms share a pair of electrons. A single dash represents the sharing of one electron pair between two atoms, indicating a single covalent bond. Non-polar bonds occur when the electrons are shared equally between the atoms, resulting in a balanced distribution of charge. Therefore, a single dash (-) is used to represent a single covalent non-polar bond.

A polar covalent bond is formed when two atoms share electrons, but the electrons are unequally shared between the two atoms. This occurs when one atom has a higher electronegativity than the other, causing it to attract the shared electrons more strongly. As a result, one end of the bond becomes slightly negative (due to the higher electron density) and the other end becomes slightly positive. This unequal distribution of charge creates a polarity in the bond, making it polar.

A non-polar covalent bond is formed when two atoms share electrons equally. In this type of bond, the electronegativity of both atoms is similar, resulting in a balanced distribution of electrons. As a result, there is no separation of charge, and the molecule is electrically neutral. Therefore, non-polar is the correct answer as it describes a covalent bond where electrons are equally shared.

Polar covalent bonds and non-polar covalent bonds do not mix because they have different levels of electron sharing. In a polar covalent bond, the electrons are unequally shared between the atoms, creating partial positive and negative charges. In a non-polar covalent bond, the electrons are equally shared. Due to this difference in electron distribution, polar and non-polar covalent bonds do not mix.

The atomic mass is the sum of the number of protons and neutrons in an atom. Protons have a positive charge and are found in the nucleus of an atom, while neutrons have no charge and are also located in the nucleus. Electrons, on the other hand, have a negative charge and orbit around the nucleus. Therefore, the correct answer is the sum of the number of protons and neutrons, as it represents the total mass of an atom.

Isotopes are atoms that have the same number of protons but different numbers of neutrons. This means that they have the same atomic number but different atomic masses. Isotopes of an element have similar chemical properties but may have different physical properties, such as stability and radioactivity. The answer "Atoms with different numbers of neutrons" correctly describes isotopes.

Isotopes are variants of an element with different numbers of neutrons. They decay over time, but the process takes a very long time. The half-life of an isotope is the time it takes for half of the sample to decay. However, even after many half-lives, there will still be a tiny amount of the isotope remaining. Therefore, the amount of grams of an isotope will never hit zero, making "Never" the correct answer.

Noble/inert gases have 8 valence electrons. These gases, such as helium, neon, and argon, have full outer electron shells, making them stable and less likely to react with other elements. This stability is due to the fact that their outermost energy level is completely filled with electrons, resulting in a balanced and satisfied electron configuration. Consequently, noble gases rarely form chemical bonds with other elements, as they already have the desired number of valence electrons.

When an atom lacks 8 valence electrons, it will seek to obtain them by bonding with other atoms. This is because atoms tend to be more stable when they have a full outermost energy level, which typically consists of 8 electrons. By bonding with other atoms, an atom can share or transfer electrons to achieve this stable configuration. This process allows the atom to fulfill the octet rule and become more chemically stable.

All of the above options, iron, iodine, and zinc, are considered trace elements. Trace elements are essential minerals that are required by the body in small amounts. Iron is necessary for the production of red blood cells and oxygen transport. Iodine is crucial for the production of thyroid hormones, which regulate metabolism. Zinc plays a role in various bodily functions, including immune function, wound healing, and DNA synthesis. Therefore, all three elements are classified as trace elements.

The number of neutrons in an atom can be found by subtracting the atomic number (which represents the number of protons) from the atomic mass. Neutrons are uncharged particles found in the nucleus of an atom, and their number can vary for different isotopes of the same element. Therefore, subtracting the atomic number from the atomic mass gives the number of neutrons in the atom.

The correct answer is 96% because macroelements are essential nutrients that are required by the body in large amounts. These include elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. These elements are found in various compounds in the body, such as carbohydrates, lipids, proteins, and nucleic acids. Together, these macroelements make up approximately 96% of the body's composition.

A non-polar double bond occurs when two pairs of electrons are equally shared between two atoms. In this type of bond, the electronegativity difference between the atoms is negligible, resulting in an equal pull on the shared electrons. As a result, the bond is non-polar, meaning there is no separation of charge across the bond.

Radioisotopes are used for various purposes, including dating fossils, tracing things, and treating cancer. These isotopes are used in radiometric dating techniques to determine the age of fossils and geological materials. They are also employed in tracing processes, such as tracking the movement of substances in biological systems or industrial processes. Additionally, radioisotopes are utilized in cancer treatment through techniques like radiation therapy, where high-energy radiation is directed at cancer cells to destroy them.

The halflife of an isotope refers to the amount of time it takes for half of the radioisotope to decay or undergo radioactive decay, resulting in the destruction of half of the isotope's atoms. This process involves the release of radiation and the transformation of the isotope into a different element. The halflife is a characteristic property of each isotope and can vary widely depending on the specific isotope in question.

Elements are the simplest category of matter because they cannot be broken down into smaller substances by chemical means. They are composed of atoms, each with its unique number of protons, neutrons, and electrons. Elements are the building blocks of all matter and are represented by symbols on the periodic table. Examples of elements include oxygen, hydrogen, carbon, and gold.

Covalent bonding refers to the type of chemical bonding where two nonmetals share electrons. In this type of bond, the atoms involved have similar electronegativity, which means they have similar tendencies to attract electrons. As a result, they share electrons in order to achieve a more stable electron configuration. This sharing of electrons creates a strong bond between the atoms, allowing them to form molecules.

not-available-via-ai

Oxidation is a chemical reaction in which a substance loses electrons. This process can occur when a substance reacts with oxygen or when it loses electrons to another substance. Therefore, the correct answer is "Electrons are lost".

The half-life of Carbon 14 is 5,000 years. This means that it takes 5,000 years for half of the Carbon 14 atoms in a sample to decay. After another 5,000 years, half of the remaining Carbon 14 atoms will decay, and so on. This property of Carbon 14 is used in radiocarbon dating to determine the age of organic materials.

When energy is added to an atom, the electrons within the atom absorb this energy. As a result, the electrons speed up and move to a higher energy level, specifically to an outer energy level. However, these electrons eventually fall back to their original energy level. During this process, they release the excess energy in the form of light or transfer it to another atom.

Ionic bonds occur between a metal and a nonmetal. In this type of bond, the metal atom loses one or more electrons from its outermost shell, resulting in a positive charge. On the other hand, the nonmetal atom gains these electrons, leading to a negative charge. The attraction between the positive and negative ions then forms the ionic bond. Therefore, the correct answer is "Metal loses electrons and becomes positive, nonmetal gains electrons and becomes negative."

Microelements refer to trace elements that are present in the body in very small amounts. These elements include minerals like iron, zinc, copper, and iodine, which are essential for various physiological processes. While the exact percentage may vary depending on individual factors, it is generally accepted that approximately 4% of the body is composed of microelements. These elements play crucial roles in enzyme function, metabolism, and overall health, despite being present in such small quantities.

Ionic bonding is a type of chemical bond that occurs between a metal and a nonmetal. In this type of bond, one atom (typically the metal) loses electrons and becomes a positively charged ion, while the other atom (typically the nonmetal) gains those electrons and becomes a negatively charged ion. The attraction between the oppositely charged ions then holds the atoms together, forming an ionic bond.

Reduction refers to a chemical reaction where electrons are gained. This occurs when a substance accepts electrons from another substance, resulting in a decrease in the oxidation state of the substance gaining electrons. In this case, the correct answer states that reduction involves the gaining of electrons, which aligns with the definition of reduction in chemistry.

Valence electrons are the outermost electrons of an atom, which are involved in chemical reactions. This means that they are responsible for the atom's ability to form bonds with other atoms and participate in chemical reactions. Therefore, the correct answer is "Both A and C" because valence electrons refer to the outermost electrons and those that are involved in chemical reactions.

Trace elements are present in very small amounts in the human body, but they play important roles in various biological processes. These elements include minerals like iron, zinc, copper, and iodine. Since the question asks about the percentage of the body made up of trace elements, the correct answer would be ~4%. This implies that although trace elements are present in small quantities, they still contribute to the overall composition and functioning of the body.

Both A and B are correct because an unstable isotope is commonly referred to as a radioactive isotope or a radioisotope. These terms are used interchangeably to describe isotopes that undergo radioactive decay, emitting radiation in the process.

The correct answer is Calcium, Potassium, Phosphorus, Sulfur, Sodium, Chlorine. These six elements are considered microelements because they are required by plants in smaller quantities compared to macronutrients like carbon, oxygen, hydrogen, and nitrogen. Calcium is essential for cell wall formation, potassium regulates water balance, phosphorus is involved in energy transfer, sulfur is important for protein synthesis, sodium helps in osmotic regulation, and chlorine is required for photosynthesis.

not-available-via-ai

The atomic number refers to the number of protons in an atom. This is because the number of protons determines the element's identity. Additionally, the number of electrons in an atom, if it is not an ion, is also equal to the atomic number. Therefore, the correct answer is both a and b.