ch 2

Which statement best describes a hydrogen bond?

- A strong covalent bond in which hydrogen atoms share electrons with highly electronegative atoms such as oxygen or nitrogen

- An ionic bond that results when a hydrogen atom completely transfers an electron to another atom, forming charged ions

- A repulsive force that arises between hydrogen atoms due to overlapping electron clouds that cause molecular instability

- A type of molecular interaction that only occurs in organic molecules containing hydrogen and carbon atoms

- A weak attraction between a hydrogen atom in one molecule and an electronegative atom in another molecule

A weak attraction between a hydrogen atom in one molecule and an electronegative atom in another molecule

(A hydrogen bond is a weak attraction between a hydrogen atom (already bonded to a highly electronegative atom) and another electronegative atom (usually O, N, or F). Hydrogen bonding is critical in DNA structure and water's properties.)

Which statement best describes the difference between polar and nonpolar covalent bonds?

- Polar covalent bonds only occur in ionic compounds, while nonpolar covalent bonds occur in molecular compounds

- Nonpolar covalent bonds occur between metals, while polar covalent bonds occur between nonmetals

- Polar covalent bonds do not involve electron sharing, while nonpolar covalent bonds involve complete electron transfer

- Polar covalent bonds involve unequal sharing of electrons, while nonpolar covalent bonds involve equal sharing

- Nonpolar covalent bonds can only form between identical atoms, while polar covalent bonds form between any elements

Polar covalent bonds involve unequal sharing of electrons, while nonpolar covalent bonds involve equal sharing

(A polar covalent bond occurs when electrons are shared unequally due to differences in electronegativity (e.g., H₂O), while a nonpolar covalent bond involves equal electron sharing (e.g., O₂). Polar molecules have partial charges, making them more reactive in biological systems.)

What is a covalent bond?

- A bond that results from the complete transfer of electrons from one atom to another

- A force of attraction between two oppositely charged ions

- A chemical bond in which two atoms share one or more pairs of electrons

- A weak interaction that occurs between polar molecules without electron sharing

- A bond that occurs when one atom donates protons to another atom

A chemical bond in which two atoms share one or more pairs of electrons

(A covalent bond occurs when two atoms share electrons to achieve a stable configuration. This type of bond is common in organic molecules like water (H₂O) and carbon dioxide (CO₂), where atoms form stable structures by sharing electrons.)

What is meant by the term "half-life" in radioactive decay?

- The time it takes for all radioactive atoms in a sample to decay completely

- The amount of energy released by a radioactive isotope as it decays

- The time it takes for an isotope to become completely non-radioactive

- The time required for half of a radioactive substance to decay into a more stable form

- The average time a radioactive element exists before becoming inert

The time required for half of a radioactive substance to decay into a more stable form

(Half-life is the time it takes for half of a given sample of a radioactive isotope to decay into a more stable form. This concept is crucial in nuclear physics, medicine, and radiometric dating techniques.)

What is a van der Waals interaction?

- A strong and permanent molecular attraction that occurs between molecules with opposite charges, forming highly stable bonds

- A bond that forms through the complete transfer of electrons from one atom to another, resulting in charged ions

- A weak attraction between molecules due to temporary dipoles caused by fluctuating electron distributions in their electron clouds

- A type of weak hydrogen bond that helps stabilize complex protein structures and contributes to molecular stability

- A force of attraction that occurs primarily in gases at high pressure and low temperature due to increased molecular motion

A weak attraction between molecules due to temporary dipoles caused by fluctuating electron distributions in their electron clouds

(Van der Waals interactions are weak forces that arise from temporary shifts in electron clouds, creating momentary dipoles. These interactions are significant in large molecules like proteins and lipids.)

Which statement best defines a chemical reaction?

- A phase change in which a substance moves between solid, liquid, and gas states without undergoing any transformation in its chemical structure

- A process in which substances undergo changes that alter their chemical composition by breaking and forming new chemical bonds, leading to different molecular structures

- A reaction in which atoms are either created or destroyed, leading to the formation of entirely new elements within a chemical system

- A process that only rearranges molecules physically but does not involve the breaking or formation of chemical bonds between atoms

- A physical process in which the shape of a molecule is altered, but the molecular composition and atomic structure remain unchanged

A process in which substances undergo changes that alter their chemical composition by breaking and forming new chemical bonds, leading to different molecular structures

(A chemical reaction involves breaking and forming chemical bonds to create new substances. Reactants are converted into products, and energy may be absorbed or released.)

Why do atoms form chemical bonds?

- To achieve a stable electron configuration by filling or emptying their valence shell

- To increase their atomic mass and change into a different element

- To absorb additional protons into their nucleus for stability

- To remove excess electrons that make them unstable

- To create new atoms by fusing together at the subatomic level

To achieve a stable electron configuration by filling or emptying their valence shell

(Atoms form chemical bonds to achieve a stable electron configuration, typically following the octet rule (eight valence electrons). They can share (covalent), donate (ionic), or pool electrons (metallic bonding) to reach a lower-energy, stable state.)

Which of the following best defines an element in biological systems?

- A substance that cannot be broken down into simpler substances by chemical reactions

- A compound composed of two or more atoms bonded together

- A molecule that is made up of different types of atoms

- A mixture of different substances in a solution

- A structure composed of protons, neutrons, and electrons that can combine to form molecules

A substance that cannot be broken down into simpler substances by chemical reactions

(An element is a pure substance consisting of only one type of atom. It cannot be broken down into a simpler substance through chemical reactions. Each element has unique properties determined by the number of protons in its nucleus. Examples include oxygen (O), carbon (C), and hydrogen (H).)

How does a single covalent bond differ from a double or triple bond?

- A single bond forms between metal atoms, while double and triple bonds only form between nonmetals

- Single bonds always form between atoms of different elements, while double and triple bonds form between identical atoms

- A single bond results in a complete transfer of electrons, while double and triple bonds result in partial electron sharing

- Single bonds are weaker than double and triple bonds, but they involve more electron transfer

- A single bond involves one shared electron pair, while double and triple bonds involve two and three shared pairs, respectively

A single bond involves one shared electron pair, while double and triple bonds involve two and three shared pairs, respectively

(A single covalent bond involves one shared electron pair (e.g., H₂), a double bond involves two shared pairs (e.g., O₂), and a triple bond involves three shared pairs (e.g., N₂). Double and triple bonds are stronger and shorter than single bonds due to increased electron sharing.)

Which statement best describes an ion?

- An atom or molecule that has gained or lost electrons

- A charged nucleus surrounded by a neutral electron cloud

- A molecule held together by covalent bonds

- An atom with a different number of neutrons than protons

- An atom with an equal number of protons and electrons

An atom or molecule that has gained or lost electrons

(An ion is an atom or molecule with a net charge due to the gain or loss of electrons. Cations are positively charged (lost electrons), and anions are negatively charged (gained electrons). Examples include Na⁺ and Cl⁻.)

Which statement accurately defines a trace element in biological systems?

- Any element present in the body that is not involved in chemical reactions

- An element that makes up the majority of an organism's mass

- A compound necessary for cellular respiration and metabolism

- An element required in very small amounts but crucial for life.

- An element that organisms can survive without in their diet

An element required in very small amounts but crucial for life.

(Trace elements, such as iron, zinc, and iodine, are required by organisms in minute quantities but play essential roles in enzymatic functions, hormone production, and cellular processes. Despite their small amounts, deficiencies can lead to significant health issues.)

What does the mass number of an atom represent?

- The number of protons in the nucleus

- The sum of protons and electrons in a neutral atom

- The total number of protons and neutrons in the nucleus

- The average atomic mass of all isotopes of an element

- The number of valence electrons in an atom

The total number of protons and neutrons in the nucleus

(The mass number of an atom is the sum of protons and neutrons. Electrons are too small to affect mass. For example, carbon-12 has 6 protons and 6 neutrons, giving it a mass number of 12.)

Which of the following is the correct combination of major bulk elements found in living organisms?

- Carbon, hydrogen, oxygen, and nitrogen

- Sodium, potassium, chlorine, calcium, and magnesium

- Carbon, hydrogen, phosphorus, oxygen

- Iron, zinc, copper, manganese, and iodine

- Oxygen, carbon, phosphorus, and sulfur

Carbon, hydrogen, oxygen, and nitrogen

(The six major bulk elements—carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur—make up most of the mass of living organisms. In the General Biology level, usually only 4 (C, H, O, and N) are mentioned. They are essential for forming biomolecules such as proteins, nucleic acids, lipids, and carbohydrates.)

Which of the following best describes the valence shell of an atom?

- The energy level closest to the nucleus, where core electrons are located

- A region where only protons and neutrons interact

- The outermost energy level that contains electrons available for bonding

- The sum of all electrons in an atom, determining its overall charge

- A completely filled electron shell that prevents atoms from reacting

The outermost energy level that contains electrons available for bonding

(The valence shell is the highest occupied energy level of an atom, containing electrons that participate in chemical bonding. Elements with full valence shells (e.g., noble gases) are chemically inert, while others react to achieve a stable electron configuration.)

Which principle is used in radiometric dating to determine the age of rocks and fossils?

- Measuring the mass of an element to see how much has decayed

- Measuring the ratio of parent and daughter isotopes based on their known half-lives

- Identifying the presence of radioactive isotopes and estimating their energy output

- Comparing the total amount of radioactive material to the non-radioactive material in a sample

- Using chemical reactions to determine how much radioactive material remains in a fossil

Measuring the ratio of parent and daughter isotopes based on their known half-lives

(Radiometric dating estimates an object's age by measuring the proportion of parent and daughter isotopes, using their known half-lives. Carbon-14 dating is used for recent fossils, while uranium-lead dating is used for ancient rocks.)

What does an atom's atomic number represent?

- The number of neutrons in the nucleus

- The sum of protons and neutrons

- The number of protons in the nucleus

- The number of electrons in a neutral atom

- The atomic weight

The number of protons in the nucleus

(The atomic number is the number of protons in an atom's nucleus, which defines the element. For example, carbon always has 6 protons, giving it an atomic number of 6. The number of neutrons or electrons can vary, but the atomic number remains constant.)

What is electronegativity?

- The total number of electrons an atom has

- An atom's ability to attract electrons in a chemical bond

- The overall charge of an atom after bonding

- The energy required to remove an electron from an atom

- The number of valence electrons an atom possesses

An atom's ability to attract electrons in a chemical bond

(Electronegativity measures an atom's tendency to attract shared electrons. It increases across a period and decreases down a group in the periodic table. Oxygen (O), Nitrogen (N), and fluorine (F) are highly electronegative, leading to strong polar bonds.)

What does a Lewis dot structure represent?

- The valence electrons of an atom or molecule using dots around element symbols

- The complete arrangement of all electrons in an atom, including core electrons

- The molecular shape and geometry of a compound

- The energy levels and orbitals occupied by electrons in an atom

- A diagram that shows the movement of electrons in a chemical reaction

The valence electrons of an atom or molecule using dots around element symbols

(A Lewis dot structure uses dots around an element's symbol to show valence electrons. It helps predict bonding behavior, electron sharing, and molecular structure.)

Which of the following best describes a radioactive tracer?

- A substance that emits radiation capable of completely sterilizing biological samples

-A highly toxic radioactive substance that damages biological tissues

- A radioactive isotope used to track the movement of substances in a biological or chemical system

- A radioactive isotope that accumulates in the bones and causes long-term exposure effects

- A stable isotope used in experiments to prevent contamination

A radioactive isotope used to track the movement of substances in a biological or chemical system

(Radioactive tracers use isotopes such as carbon-14 or technetium-99m to follow chemical pathways in medical imaging, metabolic studies, and ecological tracking. These tracers help visualize processes without significantly altering them.)

What characteristic of an atom determines its identity as a specific element?

- The number of protons in the nucleus

- The number of neutrons in the nucleus

- The total mass of the atom

- The arrangement of electrons in the outer shell

- All of the above.

The number of protons in the nucleus

(The atomic number, which is the number of protons in an atom's nucleus, uniquely identifies an element. While neutrons can vary (creating isotopes), the proton count remains constant for a given element. For example, all carbon atoms have six protons, even if their neutron numbers differ.)

How does the periodic table relate to the number of valence electrons in an element?

- Elements in the same period (row) have the same number of valence electrons

- The atomic number directly determines the number of valence electrons

- Transition metals always have a full valence shell, making them nonreactive

- Elements in the same group (column) have the same number of valence electrons

- Noble gases have incomplete valence shells, causing them to react with other elements

Elements in the same group (column) have the same number of valence electrons

(Elements in the same group (vertical column) of the periodic table have the same number of valence electrons, leading to similar chemical properties. For example, all Group 1 elements (alkali metals) have one valence electron and react similarly.)

Which statement correctly describes chemical equilibrium?

- A condition in which a chemical reaction has completely stopped, meaning that no further changes occur to the reactants or products at any point

- A state in which the forward and reverse reactions occur at the same rate, resulting in no net change in reactant and product concentrations over time in a closed system

- The specific point at which all reactants have been fully converted into products, leaving no remaining unreacted substances in the system

- A state where products continuously form in an ongoing reaction, but the reverse reaction does not take place or influence the system's stability

- A chemical system in which only the forward reaction is favored indefinitely, preventing the formation of any reverse reaction under standard conditions

A state in which the forward and reverse reactions occur at the same rate, resulting in no net change in reactant and product concentrations over time in a closed system

(Chemical equilibrium occurs when the forward and reverse reactions proceed at the same rate, leading to stable concentrations of reactants and products. It is dynamic, meaning reactions still occur, but no net change is observed.)

Which statement best describes an atomic orbital?

- A fixed circular path in which electrons revolve around the nucleus

- The central part of the atom where electrons and protons are located

- A region around the nucleus where an electron is most likely to be found

- A solid shell surrounding the nucleus that holds all the electrons

- A type of electron that exists only at the highest energy levels of an atom

A region around the nucleus where an electron is most likely to be found

(An atomic orbital is a three-dimensional region around a nucleus where electrons are likely to be found. Unlike the outdated Bohr model, quantum mechanics describes electrons as existing in probability clouds rather than fixed orbits.)

Which subatomic particles make up an atom?

- Protons, neutrons, and electrons

- Nucleus and electron cloud

- Protons and electrons only

- Neutrons and electrons only

- Molecules and ions

Protons, neutrons, and electrons

(Atoms consist of three subatomic particles: protons (positive charge), neutrons (neutral charge), and electrons (negative charge). Protons and neutrons are in the nucleus, while electrons orbit in energy levels around the nucleus.)

Which statement correctly describes isotopes?

- Atoms with the same mass number but different atomic numbers

- Atoms with the same number of electrons but different protons

- Two elements that have identical atomic structures

- Atoms of the same element with different numbers of neutrons

- An atom that has gained or lost electrons and carries a charge

Atoms of the same element with different numbers of neutrons

(Isotopes are variants of an element that have the same number of protons but different numbers of neutrons. For example, carbon-12 and carbon-14 are isotopes of carbon. Some isotopes, like carbon-14, are radioactive.)

What is an energy shell in an atom?

- A region around the nucleus where electrons are organized into different energy levels

- A solid boundary that prevents electrons from escaping the nucleus

- The central part of the atom that contains protons and neutrons

- A charged cloud surrounding the nucleus that randomly holds electrons

- A specific pathway that electrons follow in circular motion around the nucleus

A region around the nucleus where electrons are organized into different energy levels

(An energy shell is an area around an atom's nucleus where electrons exist at specific energy levels. The first shell can hold up to 2 electrons, the second up to 8, and so on. Electrons fill the lowest available energy level before moving to higher ones.)

Which characteristic is common to all noble gases?

- They have full outer electron shells, making them chemically unreactive

- They are highly reactive and form many compounds with other elements

- They are all radioactive due to their atomic structure

- They only exist as ions in natural environments

- They are found only in liquid form under normal atmospheric conditions

They have full outer electron shells, making them chemically unreactive

(Noble gases (helium, neon, argon, krypton, xenon, and radon) have full valence electron shells, making them highly stable and nonreactive. Their lack of chemical reactivity is why they are used in lighting and inert environments.)

Which of the following best describes an ionic bond?

- A chemical bond formed when electrons are completely transferred from one atom to another, creating oppositely charged ions

- A type of bond where two atoms share electrons equally

- A force that holds molecules together by weak interactions, such as hydrogen bonding

- A type of attraction between two neutral atoms based on van der Waals forces

- A bond that only occurs between noble gases and nonmetals

A chemical bond formed when electrons are completely transferred from one atom to another, creating oppositely charged ions

(Ionic bonds form when electrons are transferred between atoms, typically between metals and nonmetals. The resulting ions (e.g., Na⁺ and Cl⁻ in NaCl) are held together by electrostatic attraction. Ionic compounds dissolve in water and conduct electricity when dissolved.)

Which of the following best describes an essential element in biology?

- An element required in large amounts by organisms for survival

- An element necessary for an organism's growth, development, and reproduction

- Any element that exists in living organisms, regardless of function

- An element that contributes to the mass of an organism but has no specific role

- A mineral that must be obtained through the diet but is not required by all living things

An element necessary for an organism's growth, development, and reproduction

(Essential elements are those that organisms require to survive, grow, and reproduce. These include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Deficiencies in essential elements can lead to physiological problems or death.)

How many of the elements are considered bulk elements in life?

- 1

- 2

- 3

- 4

- More than 4

More than 4

(Essential elements is the one that's 4)

? bonds can be broken easily when dissolved in water, but ? bonds are not usually broken easily when dissolved in water.

1. Ionic Bonds

2. Covalent Bonds

Which of the following is/are molecules? Select All That Apply.

- H2O

- Protein

- NH3

- H2SO4

- Carbohydrates

All

(Molecules are combinations of elements, even with no chemical formula Protein and Carbohydrates still are molecules.)

Which of the following is a characteristic of elements?

- All elements are required for life

- Elements are atoms

- Elements are the basic function units of life

- Elements cannot be broken down into other substances

- All of the above

Elements cannot be broken down into other substances

Which elements are the most abundant (making up approximately 96% of living matter)? Select All That Apply.

- Hydrogen

- Calcium

- Nitrogen

- Sodium

- Oxygen

- Carbon

Carbon, Hydrogen, Oxygen, Nitrogen

(CHON)

Electronegativity is ...

- a strength of valency

- an attractive force of an atom for electrons

- a strength of electrons of an atom

- a measurement of ions

- none of the above

an attractive force of an atom for electrons

Bonds found within a molecule are ...

covalent bonds

(Ionic bonds happen with 2 oppositely charged molecules)

Ionic bond is formed ...

between cations (+) and anions (-)

Hydrogen bond is formed ...

between polar molecules

Van der Waals interaction occurs ...

between non-polar molecules

No chemical bond forms ...

between a polar molecule and a non-polar molecule

The smallest unit of matter that still retains the property of an element and that cannot be further broken down by ordinary chemical or physical means is ...

- Element

- Molecule

- Cell

- Elementary particle

- None of the above

None of the above

(It would be an atom)

Which of the following statements is true regarding the element Silicon?

- Silicon becomes a cation

- Silicon becomes an anion

- The mass number of Silicon is 28.086

- ALL Silicon have 14 protons.

- None of the above

ALL Silicon have 14 protons.

Which of the following is/are found in a nucleus? Select All That Apply.

- protons

- neutrons

- electrons

- atoms

- isotopes

protons & neutrons

Which of the following is happening when a chemical reaction takes place? Select All That Apply

- Forming new bonds

- Breaking existing bonds

- Forming new atoms

- Increasing the number of atoms (during a forward reaction, but not a reverse reaction)

- Increasing the number of atoms (during a reverse reaction, but not a forward reaction)

Forming new bonds & Breaking existing bonds

Which of the following takes place at chemical equilibrium? Select All That Apply.

- Forward reaction

- Reverse reaction

- Hydration shell formation

- Formation of reactants

- Formation of products

forward reaction, reverse reaction, formation of reactants, formation of products

What is the name for an atom that has gained extra electron(s)?

- Isotope

- radioactive isotope

- Cation

- Anion

- Chemical bond

Anion

(Cation = + CHARGE, an atom has LOST an electron and therefore results in a POSITIVE charge.)

When a water molecule reacts with a sucrose molecule, it produces one glucose molecule and one fructose molecule. In this chemical reaction, a water molecule is considered to be ...

- a solvent

- a solute

- a catalyst

- a reactant

- a solution

reactant

Which of the following is true about trace elements?

- Trace elements are mainly used to trace back to a common ancestor of different species

- Trace elements are the radioactive isotopes used for radioactive tracer

- Trace elements are any elements which can detect the presence of the small amount of elements in a cell

- Trace elements are used to draw over its lines on a superimposed piece

- None of the above

none of the above

(Trace elements are elements essential/needed for life but in SMALL amounts)

The half-life of carbon-14 is 5730 years. You measure the ratio of carbon-14 to carbon-12 in a fossilized bone to be one-16th of the ratio of a living organism.

How old is this fossilized bone?

- 11,460 years (5730 x 2 years)

- 22,920 years (5730 x 4 years)

- 45,840 years (5730 x 8 years)

- 91,680 years (5730 x 16 years)

- None of the above

22,920 years (5730 x 4 years)

(1/2 -> 1/4 -> 1/8 -> 1/16 so 4 Half Lifes)

Consider one isotope of Silicon, Silicon-29 (Si-29). Which of the following is/are true? Select All That Apply

- Si-29 has 14 protons

- Si-29 has 15 electrons

- Si-29 has 15 neutrons

- Si-29 has 29 subatomic particles

- Si-29 is not Silicon

Si- 14 protons & 15 neutrons

(Si-29 is an isotope so neutron has changed and electron/proton is unaffected; subatomic particles is neutrons, protons & electrons; Si-29 is still silicon)

All living organisms have the same or a very similar carbon-14 to carbon-12 ratio because we constantly consume and excrete all carbon isotopes. However, once we die, we no longer obtain carbon from the environment. Carbon-14 is a known radioactive isotope of carbon.

Thus, the ratio of carbon-14 to carbon-12 in a living organism ______ once it dies.

- becomes smaller

- becomes bigger

- stays the same

- fluctuates

- None of the above since we cannot predict this with our current technology

becomes smaller

(possible because of radioactive dating, we already do this with fossils and we are dead so we don't get anything more it just goes down)