Chemistry Honors Midterm Review
A Review for the Chemistry Honors Midterm. BrawwRRR
Questions and Answers
- 1.
Chemical Properties..
- A.
Include changes of state of a substance
- B.
Includes mass and color
- C.
Include changes that alter the identity of a substance
- D.
Can be observed w/o altering the identity of a substance.
Correct Answer
C. Include changes that alter the identity of a substanceExplanation
Chemical properties refer to changes that alter the identity of a substance. This means that when a substance undergoes a chemical change, it transforms into a different substance with different properties. This is different from physical properties, such as changes in state, mass, or color, which do not alter the identity of the substance. Chemical properties can be observed without necessarily altering the identity of the substance, as they involve reactions or interactions with other substances.Rate this question:
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- 2.
A physical change occurs when a
- A.
Peach spoils
- B.
Copper bowl tarnishes
- C.
Bracelet turns your wrist green
- D.
Glue gun melts a glue stick
Correct Answer
D. Glue gun melts a glue stickExplanation
The given options describe various examples of physical changes. A physical change refers to a change in the physical properties of a substance without altering its chemical composition. In this case, the glue gun melting a glue stick is an example of a physical change because the glue stick undergoes a change in its physical state from solid to liquid due to the application of heat.Rate this question:
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- 3.
The state of matter in which a material has neither a definite shape nor a definite volume is the
- A.
Gaseous state
- B.
Liquid state
- C.
Elemental state
- D.
Solid state
Correct Answer
A. Gaseous stateExplanation
The gaseous state is characterized by the absence of a definite shape and volume. In this state, the particles of the material are highly energetic and move freely, filling the space available to them. Unlike solids and liquids, gases do not have a fixed shape and can expand to fill any container. Therefore, the gaseous state is the correct answer for a material that lacks both a definite shape and a definite volume.Rate this question:
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- 4.
The state of matter in which a material has a definite volume but no definite shape is the
- A.
Gaseous state
- B.
Solid state
- C.
Frozen state
- D.
Liquid state
Correct Answer
D. Liquid stateExplanation
A material in the liquid state has a definite volume, meaning it occupies a specific amount of space, but it does not have a definite shape. This is because the particles in a liquid are loosely packed and can move around freely, allowing the liquid to take the shape of its container. In contrast, a material in the solid state has both a definite volume and a definite shape, while a material in the gaseous state has neither a definite volume nor a definite shape. The frozen state refers to a specific condition of matter where a liquid has solidified due to low temperatures, so it does not fit the description of having a definite volume but no definite shape.Rate this question:
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- 5.
A heterogeneous mixture is
- A.
A uniform mixture
- B.
A non-uniform mixture
Correct Answer
B. A non-uniform mixtureExplanation
A heterogeneous mixture refers to a mixture that is not uniform throughout, meaning that its composition varies from one region to another. This can be observed visually, as different components of the mixture may be visible or separated into distinct phases. Therefore, the correct answer is "a non-uniform mixture" because it accurately describes the characteristic of a heterogeneous mixture.Rate this question:
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- 6.
A quantity that describes the concentration of matter is
- A.
Weight
- B.
Density
- C.
Volume
- D.
Mass
Correct Answer
B. DensityExplanation
Density is the correct answer because it is a measure of how much mass is contained within a given volume. It is a measure of the concentration of matter, as it tells us how much mass is packed into a certain amount of space. Weight, volume, and mass are related to density, but they do not directly describe the concentration of matter. Weight is the force exerted on an object due to gravity, volume is the amount of space an object occupies, and mass is the amount of matter in an object.Rate this question:
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- 7.
For numbers less than 0.1, such as 0.06, the zeros to the right of the decimal point but before the first nonzero digit
- A.
Are significant.
- B.
Show the decimal place of the first digit.
- C.
Show that the zero on the left side of the decimal is not significant.
- D.
Show uncertainty
Correct Answer
B. Show the decimal place of the first digit.Explanation
The zeros to the right of the decimal point but before the first nonzero digit in numbers less than 0.1 indicate the decimal place of the first digit. This means that the zeros are significant and help determine the accuracy and precision of the number.Rate this question:
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- 8.
The rays produced in a cathode tube in early experiments were
- A.
Unaffected by a magnetic field.
- B.
Deflected away from a negative plate.
- C.
Found to carry a positive charge
- D.
Striking the cathode.
Correct Answer
B. Deflected away from a negative plate.Explanation
The correct answer is "deflected away from a negative plate." In early experiments with cathode tubes, it was observed that the rays produced in the tube were deflected away from a negative plate. This suggests that the rays carried a negative charge, as like charges repel each other. This observation provided evidence for the existence of negatively charged particles, which were later identified as electrons.Rate this question:
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- 9.
A positively charged particle with mass 1.673 x 10-24 g is a(n)
- A.
Proton
- B.
Neutron
- C.
Electron
- D.
Positron
Correct Answer
A. ProtonExplanation
The given question states that the positively charged particle has a mass of 1.673 x 10-24 g. This mass is consistent with the mass of a proton, which is approximately 1.673 x 10-24 g. Therefore, the correct answer is proton.Rate this question:
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- 10.
If electromagnetic radiation A has a lower frequency than electromagnetic radiation B, then compared to B the wavelength of A is
- A.
Longer
- B.
Shorter
- C.
Equal
- D.
Exactly half the length of B's wavelength
Correct Answer
A. LongerExplanation
If electromagnetic radiation A has a lower frequency than electromagnetic radiation B, it means that A has fewer waves passing a given point in a given time compared to B. Since the speed of light is constant, the wavelength is inversely proportional to the frequency. Therefore, if A has a lower frequency, it must have a longer wavelength compared to B.Rate this question:
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- 11.
The wave model of light did not explain
- A.
The frequency of light
- B.
The continuous spectrum.
- C.
Interference.
- D.
The photoelectric effect
Correct Answer
D. The photoelectric effectExplanation
The wave model of light did not explain the photoelectric effect. The photoelectric effect refers to the phenomenon where light, when incident on certain materials, can cause the emission of electrons. This effect cannot be explained by the wave model of light alone, as it suggests that light is a continuous wave. However, the photoelectric effect can be better understood by considering light as composed of discrete particles called photons, which carry energy and interact with electrons in the material. This particle-like behavior of light is explained by the quantum theory of light.Rate this question:
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- 12.
For an electron in an atom to change from the ground state to an excited state,
- A.
Energy must be released.
- B.
Energy must be absorbed
- C.
Radiation must be emitted.
- D.
The electron must make a transition from a higher to a lower energy level
Correct Answer
B. Energy must be absorbedExplanation
When an electron in an atom transitions from the ground state to an excited state, it moves to a higher energy level. This requires the absorption of energy from an external source. Therefore, the correct answer is that energy must be absorbed.Rate this question:
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- 13.
For the/sublevel, the number of orbitals is
- A.
5
- B.
7
- C.
9
- D.
18
Correct Answer
B. 7Explanation
The number of orbitals for the sublevel is 7. This is because the sublevel is referring to the d sublevel, which has 5 orbitals. However, when combined with the s and p sublevels, which have 1 and 3 orbitals respectively, the total number of orbitals becomes 7.Rate this question:
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- 14.
Which of the following elements is the most electronegative?
- A.
Oxygen
- B.
Fluorine
- C.
Chlorine
- D.
Nitrogen
Correct Answer
B. FluorineExplanation
Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond. Fluorine has the highest electronegativity of all elements due to its small atomic size and high effective nuclear charge. This means that fluorine has a strong tendency to gain electrons, making it highly reactive.Rate this question:
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- 15.
The electron configuration for the carbon atom (C) is Is2 2S2 2p2. The atomic number of carbon is
- A.
3
- B.
6
- C.
11
- D.
12
Correct Answer
B. 6Explanation
The electron configuration for carbon is Is2 2S2 2p2, which means that there are 6 electrons in total. The atomic number of an element corresponds to the number of protons in its nucleus, and since each electron has a charge of -1, the number of electrons is equal to the number of protons. Therefore, the atomic number of carbon is 6.Rate this question:
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- 16.
Mendeleev noticed that properties of elements usually repeated at regular intervals when the elements were arranged in order of increasing
- A.
Atomic number
- B.
Density
- C.
Reactivity
- D.
Atomic mass
Correct Answer
D. Atomic massExplanation
Mendeleev noticed that properties of elements usually repeated at regular intervals when the elements were arranged in order of increasing atomic mass. This observation led him to develop the periodic table, where elements are arranged in order of increasing atomic mass. The periodic table allows for the classification and organization of elements based on their similar properties and helps in predicting the properties of undiscovered elements. Therefore, atomic mass is the correct answer as it is a crucial factor in understanding the periodicity of element properties.Rate this question:
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- 17.
Mendeleev did not always list elements in his periodic table in order of increasing atomic mass because he grouped together elements with similar
- A.
Properties
- B.
Atomic numbers
- C.
Densities
- D.
Colors
Correct Answer
A. PropertiesExplanation
Mendeleev did not always list elements in his periodic table in order of increasing atomic mass because he grouped together elements with similar properties. This means that he prioritized organizing elements based on their chemical behavior and characteristics rather than solely focusing on their atomic mass. By doing so, Mendeleev was able to identify patterns and trends among elements, which laid the foundation for the modern periodic table. This approach allowed for a more comprehensive understanding of the relationships between different elements and facilitated the prediction of properties for undiscovered elements.Rate this question:
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- 18.
What are the radioactive elements with atomic numbers from 90 to 103 in the periodic table called?
- A.
The noble gases
- B.
The lanthanides
- C.
The actinides
- D.
The rare-earth elements
Correct Answer
C. The actinidesExplanation
The correct answer is the actinides. The actinides are a series of radioactive elements in the periodic table with atomic numbers ranging from 90 to 103. They are located in the f-block of the periodic table and are known for their unstable and radioactive nature. These elements include uranium, plutonium, and americium, among others.Rate this question:
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- 19.
The periodic law states that the physical and chemical properties of elements are periodic functions oftheir atomic
- A.
Masses
- B.
Numbers
- C.
Radii
- D.
Structures
Correct Answer
B. NumbersExplanation
The periodic law states that the physical and chemical properties of elements are periodic functions of their atomic numbers. This means that as the atomic number increases, there is a periodic repetition of properties. This is because the atomic number determines the number of protons in the nucleus, which in turn determines the arrangement of electrons and the element's chemical behavior. By organizing elements in order of increasing atomic number, the periodic table allows us to observe patterns in their properties and make predictions about unknown elements.Rate this question:
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- 20.
Within the p-block elements, the elements at the top of the table, compared with those at the bottom,
- A.
Have larger radii
- B.
Are more metallic
- C.
Have lower ionization energies
- D.
Are less metallic
Correct Answer
D. Are less metallicExplanation
The elements at the top of the p-block have smaller radii, higher ionization energies, and are less metallic compared to those at the bottom. This is because, as you move down the p-block, the atomic size increases due to the addition of new energy levels, resulting in larger radii. The increased atomic size leads to a decrease in ionization energy, as the outermost electrons are farther from the nucleus and are therefore easier to remove. Additionally, the elements at the bottom of the p-block have more loosely held valence electrons, making them more metallic compared to the elements at the top.Rate this question:
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- 21.
Which orbitals are characteristic of the lanthanide elements?
- A.
D orbitals
- B.
S orbitals
- C.
F orbitals
- D.
P orbitals
Correct Answer
C. F orbitalsExplanation
The lanthanide elements are known for their unique electronic configurations, which involve the filling of the 4f orbitals. These f orbitals are part of the inner transition metals and are responsible for the characteristic properties of the lanthanides, such as their colorful compounds and strong paramagnetism. The d orbitals are found in the transition metals, while the s and p orbitals are typically associated with the main group elements. Therefore, the f orbitals are the correct answer for this question.Rate this question:
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- 22.
A neutral group of atoms held together by covalent bonds is a
- A.
Molecular formula
- B.
Chemical formula
- C.
Compound
- D.
Molecule
Correct Answer
D. MoleculeExplanation
A neutral group of atoms held together by covalent bonds is referred to as a molecule. In a covalent bond, atoms share electrons to achieve a stable electron configuration. A molecule is formed when two or more atoms join together through covalent bonding. It is important to note that a molecule can be represented by a molecular formula, which indicates the types and number of atoms present in the molecule. Therefore, the correct answer is molecule.Rate this question:
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- 23.
A chemical bond formed by the attraction between positive ions and surrounding mobile electrons is a(n)
- A.
Nonpolar covalent bond
- B.
Ionic bond
- C.
Polar covalent bond.
- D.
Metallic bond
Correct Answer
D. Metallic bondExplanation
A metallic bond is formed by the attraction between positive ions and the surrounding mobile electrons. In this type of bond, the valence electrons are not localized between specific atoms but are free to move throughout the entire metal lattice. This allows for the conductivity of electricity and heat in metals. Therefore, the correct answer is a metallic bond.Rate this question:
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- 24.
According to VSEPR theory, the electrostatic repulsion between electron pairs surrounding an atom causes
- A.
An electron sea to form.
- B.
Positive ions to form.
- C.
These pairs to be separated as far as possible
- D.
Light to reflect
Correct Answer
C. These pairs to be separated as far as possibleExplanation
According to VSEPR theory, electron pairs surrounding an atom repel each other due to their negative charge. To minimize this repulsion, the electron pairs arrange themselves as far apart as possible. This results in a geometric arrangement of electron pairs around the central atom, which determines the shape of the molecule. Therefore, the correct answer is that these pairs are separated as far as possible.Rate this question:
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- 25.
The following molecules contain polar bonds. The only polar molecule is
- A.
CCI4•
- B.
CO2•
- C.
NH3•
- D.
CH4•
Correct Answer
C. NH3•Explanation
NH3 is the only polar molecule among the given options. This is because it has a trigonal pyramidal molecular geometry with a lone pair of electrons on the central nitrogen atom. The electronegativity difference between nitrogen and hydrogen atoms creates polar bonds, and the lone pair further contributes to the polarity of the molecule. In contrast, CCl4, CO2, and CH4 have symmetrical molecular geometries or no significant electronegativity differences, resulting in nonpolar molecules.Rate this question:
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- 26.
In one experiment, magnesium metal is melted. In a second experiment, magnesium metal is burned. Classify the change in each experiment as chemical or physical. Explain your reasoning.
Correct Answer
In the first experiment, a physical change occurred. The chemical properties of magnesium were unchanged. In the second experiment, a chemical change occurred. A new substance with its own chemical properties was formed.Explanation
In the first experiment, the change is classified as a physical change because the state of magnesium changed from solid to liquid, but its chemical properties remained the same. Physical changes involve a change in the physical state or appearance of a substance without altering its chemical composition.
In the second experiment, the change is classified as a chemical change because the magnesium metal was burned, resulting in the formation of a new substance with its own chemical properties. Chemical changes involve a rearrangement of atoms and the formation of new substances with different chemical properties.Rate this question:
- 27.
Explain the difference between a pure substance and a homogeneous mixture. Use an example
Correct Answer
A homogeneous mixture can be separated by physical means, whereas a pure substance cannot. For example, salt can be removed from a salt-water mixture by evaporating the water, but to separate water into hydrogen and oxygen requires chemical meansExplanation
A pure substance refers to a substance that is made up of only one type of element or compound. It cannot be separated into other substances by physical means. On the other hand, a homogeneous mixture is a mixture that has a uniform composition throughout and can be separated into its components by physical means. The example given illustrates this difference. In a salt-water mixture, the salt can be separated from the water by evaporating the water, which is a physical process. However, to separate water into its components of hydrogen and oxygen, a chemical process such as electrolysis is required.Rate this question:
- 28.
Xenon is generally unreactive. How is its low reactivity related to its position in the periodic table?
Correct Answer
Xenon is a noble gas. It is located in the same group in the periodic table as other noble gases. All noble gases have low reactivities.Explanation
The low reactivity of xenon is related to its position in the periodic table because it is a noble gas. Noble gases, including xenon, are located in the same group in the periodic table. Noble gases have full valence electron shells, making them stable and unreactive. They do not readily form chemical bonds with other elements, which is why they have low reactivities. Therefore, xenon's low reactivity can be attributed to its position as a noble gas in the periodic table.Rate this question:
- 29.
How can you use the periodic table to make a prediction about the properties of xenon and helium, both in Group 18?
Correct Answer
In the periodic table, elements in the same column have similar properties. Because helium and xenon are located in the same group, their properties are similar.Explanation
The periodic table is organized in a way that elements in the same column, or group, have similar properties. Since helium and xenon are both located in Group 18, they are expected to have similar properties. This is because elements in this group have a full outer electron shell, making them stable and unreactive. Both helium and xenon are noble gases, which means they are odorless, colorless, and have low boiling and melting points. Therefore, based on their group placement in the periodic table, it can be predicted that helium and xenon will have similar properties.Rate this question:
- 30.
Give an example of a region of the periodic table that acts as a bridge between two other regions. What does this tell you about the properties of the bridging elements?
Correct Answer
Metalloids form a region that bridges metals and nonmetals. Metalloids have properties of both metals and nonmetals.Explanation
Metalloids, such as boron, silicon, and germanium, are located in a region of the periodic table that acts as a bridge between metals and nonmetals. This suggests that metalloids possess properties of both metals and nonmetals. They exhibit characteristics of metals, such as being able to conduct electricity and heat, while also displaying nonmetallic properties, such as being brittle and having lower melting points. The presence of metalloids in this transitional region highlights their unique nature and the intermediate properties they possess.Rate this question:
- 31.
What are the first steps scientists take to analyze the cause of a disease?
Correct Answer
Scientists must first observe the symptoms of the disease. Then they form a hypothesis and design an experiment with a control and variables to test their hypothesis about the probable cause of the disease.Explanation
Scientists first observe the symptoms of the disease to gather information about its characteristics and manifestations. Based on these observations, they form a hypothesis, which is a proposed explanation for the cause of the disease. To test their hypothesis, scientists design an experiment that includes a control group and variables that can be manipulated. The control group serves as a baseline for comparison, while the variables are factors that scientists believe may be related to the cause of the disease. Through this experimental approach, scientists can gather data and analyze it to determine the probable cause of the disease.Rate this question:
- 32.
Note the differences between qualitative and quantitative observations.
Correct Answer
In qualitative observations, the data are descriptive and non-numerical. In quantitative observations, the data are numerical.Explanation
The explanation provided accurately describes the differences between qualitative and quantitative observations. Qualitative observations involve descriptive information that cannot be measured or expressed numerically, while quantitative observations involve numerical data that can be measured and analyzed. This explanation highlights the key distinctions between the two types of observations and provides a clear understanding of their characteristics.Rate this question:
- 33.
Compare and contrast a model with a written theory
Correct Answer
A written theory is a broad generalization used to explain observations. A model is a visual, verbal, or mathematical theory that illustrates or explains abstract concepts.Explanation
A written theory and a model both serve the purpose of explaining concepts or observations. However, a written theory is a broad generalization that is expressed through words, while a model can be visual, verbal, or mathematical in nature. A model provides a more tangible representation of abstract concepts, making it easier to understand and visualize.Rate this question:
- 34.
How is a theory different from a hypothesis?
Correct Answer
A theory is a broad generalization based on observations, reasoning, and data that is used to explain a phenomenon and predict future events. A hypothesis is an educated assumption based on observation and data. When tested, a hypothesis may become a theory.Explanation
A theory is a broad generalization that is used to explain a phenomenon and predict future events. It is based on observations, reasoning, and data. On the other hand, a hypothesis is an educated assumption that is based on observation and data. A hypothesis is a starting point for scientific investigation, whereas a theory is a well-established explanation that has been extensively tested and supported by evidence. It is possible for a hypothesis to become a theory if it is rigorously tested and consistently supported by evidence.Rate this question:
- 35.
Explain why pictures of atoms and molecules are models.
Correct Answer
The pictures represent the atoms and molecules and are consistent with what we know about their behavior. They are not true representations because atoms and molecules are not hard, colored spheresExplanation
The answer states that pictures of atoms and molecules are models because they represent the atoms and molecules in a way that is consistent with what we know about their behavior. It also mentions that these pictures are not true representations because atoms and molecules are not hard, colored spheres. This explanation suggests that the pictures serve as a simplified representation or visual interpretation of atoms and molecules, helping us understand their behavior and structure.Rate this question:
- 36.
What would be the most appropriate SI unit for expressing the mass of a single brick?
Correct Answer
The mass of a brick should be expressed in kilogramsExplanation
The most appropriate SI unit for expressing the mass of a single brick is kilograms. Kilograms is the standard unit of mass in the International System of Units (SI). It is a more practical and commonly used unit for measuring the mass of objects, including bricks. Other units such as grams or metric tons may also be used, but kilograms is the most suitable unit for expressing the mass of a single brick.Rate this question:
- 37.
Why are only seven basic SI units needed to express almost any measured quantity?
Correct Answer
The base units are combined to form derived units.Explanation
The seven basic SI units are needed to express almost any measured quantity because they serve as the foundation for all other units. These base units, such as the meter, kilogram, and second, can be combined in various ways to create derived units, which are used to measure more complex quantities. For example, the unit of speed is derived by dividing the unit of distance (meter) by the unit of time (second). By combining these base units, we can express a wide range of measurements in a consistent and standardized manner.Rate this question:
- 38.
Give an example to show how SI units can be adjusted to measure the mass, length, or volume of very small or very large objects.
Correct Answer
The prefix milli- is used with the base unit gram to express the mass of a tiny objectExplanation
The prefix milli- represents one thousandth of a unit. By using the prefix milli- with the base unit gram, we can express the mass of a tiny object. For example, if we have an object that weighs 0.001 grams, we can say that its mass is 1 milligram. This allows us to accurately measure and express the mass of very small objects.Rate this question:
- 39.
Distinguish between mass and weight.
Correct Answer
Mass is the amount of matter in something. Weight depends on Earth's gravitational attraction on the object.Explanation
The explanation provided accurately distinguishes between mass and weight. It states that mass refers to the amount of matter in an object, while weight is influenced by Earth's gravitational pull on the object. This explanation highlights the key difference between the two concepts, emphasizing that mass is an intrinsic property of an object, while weight is a force exerted on the object due to gravity.Rate this question:
- 40.
Distinguish between precision and accuracy
Correct Answer
Precision is how close a set of measurements of the same quantity are. Accuracy is how close a measurement is to the true value.Explanation
Precision and accuracy are two different concepts in the field of measurement. Precision refers to the consistency and repeatability of a set of measurements of the same quantity. It indicates how close the measurements are to each other. On the other hand, accuracy refers to how close a single measurement is to the true value or the accepted reference value. It indicates the absence of systematic errors in the measurement process. In summary, precision focuses on the consistency among measurements, while accuracy focuses on the proximity of a measurement to the true value.Rate this question:
- 41.
Explain the importance of significant figures when working with measurements and calculated quantities based on actual measurements.
Correct Answer
Significant figures identify the digits in a measurement that are certain, along with one estimated digit. When using measurements in calculations, your result must reflect the precision of the least precise measurementExplanation
Significant figures are important when working with measurements and calculated quantities because they indicate the level of precision in a measurement. They identify the digits that are certain and the estimated digit. When performing calculations using measurements, the result should reflect the precision of the least precise measurement. This means that the final answer should have the same number of significant figures as the measurement with the fewest significant figures. This ensures that the calculated result is not falsely precise or accurate beyond the limitations of the original measurements.Rate this question:
- 42.
In a calculation based on measured quantities, why must the number of significant figures in the result be limited?
Correct Answer
The number of significant figures must reflect the precision of the measurements that were used in the calculation. If significant figures are not considered, the answer might appear to be far more precise than it actually is.Explanation
The number of significant figures in the result must be limited because it is important to accurately represent the precision of the measurements used in the calculation. If the significant figures are not considered, the answer may falsely appear to be more precise than it actually is. This can lead to misleading or incorrect conclusions based on the calculated result.Rate this question:
- 43.
How has Dalton's theory about atomic particles been modified by modern science?
Correct Answer
The discovery of subatomic particles proved that atoms are divisible. Dalton believed that atoms were indivisible.Explanation
Dalton's theory about atomic particles has been modified by modern science through the discovery of subatomic particles. This discovery proved that atoms are divisible, contrary to Dalton's belief that atoms were indivisible. This modification in Dalton's theory acknowledges the existence of smaller particles within atoms and their ability to be divided.Rate this question:
- 44.
What is the relationship between isotopes, mass number, and neutrons?
Correct Answer
Isotopes are atoms of the same element with different numbers of neutrons and therefore different mass numbers.Explanation
The relationship between isotopes, mass number, and neutrons is that isotopes are atoms of the same element that have different numbers of neutrons, which results in different mass numbers. Isotopes have the same number of protons, which determines the element they belong to, but the varying number of neutrons gives them different mass numbers. This means that isotopes of an element have slightly different atomic masses due to the differing number of neutrons.Rate this question:
- 45.
Why do chemists work with moles instead of individual atoms?
Correct Answer
A mole is a collection of atoms that is large enough to measure in the laboratory. A single atom is too small.Explanation
Chemists work with moles instead of individual atoms because a mole is a more practical unit for measuring substances in the laboratory. A mole represents a large number of atoms, making it easier to work with and measure quantities of substances. On the other hand, individual atoms are extremely small and difficult to handle and measure accurately. By using moles, chemists can work with more manageable quantities and perform experiments more effectively.Rate this question:
- 46.
Explain Louis de Broglie's contribution to the quantum model of the atom
Correct Answer
If light has a particle nature, de Broglie reasoned, could particles have a wave nature? He compared the behavior of Bohr's quantized electron orbits to the known behavior of waves. Finally, he hypothesized that electrons are confined to the space around an atomic nucleus and that electron waves exist only at specific energies.Explanation
Louis de Broglie's contribution to the quantum model of the atom was the proposal that particles, such as electrons, could also exhibit wave-like behavior. He made this suggestion based on the idea that if light, which was known to have a particle nature, could also exhibit wave-like properties, then the reverse could also be true for particles. De Broglie compared the behavior of Bohr's quantized electron orbits to the known behavior of waves, leading him to hypothesize that electrons are confined to the space around an atomic nucleus and that electron waves exist only at specific energies.Rate this question:
- 47.
What do quantum numbers describe?
Correct Answer
Three of the quantum numbers describe the location of an electron, and the fourth gives its spin.Explanation
Quantum numbers are a set of values used to describe the characteristics and properties of electrons in an atom. Three of these quantum numbers, namely the principal quantum number, azimuthal quantum number, and magnetic quantum number, provide information about the location and energy levels of electrons within an atom. The fourth quantum number, known as the spin quantum number, describes the spin orientation of an electron. Together, these quantum numbers help define the unique quantum state of an electron within an atom.Rate this question:
- 48.
How does the figure above illustrate Hund's rule?
Correct Answer
According to Hund's rule, the arrangement of electrons with the maximum number of unpaired electrons is the most stable arrangement.Explanation
Hund's rule states that when filling orbitals of equal energy, electrons will occupy separate orbitals with parallel spins before pairing up. This is illustrated in the figure above by showing each orbital being filled with one electron before any orbital is paired up. This arrangement maximizes the number of unpaired electrons, which is considered the most stable arrangement according to Hund's rule.Rate this question:
- 49.
How does the figure above illustrate the Pauli exclusion principle?
Correct Answer
According to the Pauli exclusion principle, no two electrons can have the same set of four quantum numbers. Therefore, no more than two electrons can occupy an orbital, and these two must have opposite spins.Explanation
The figure above illustrates the Pauli exclusion principle by showing the arrangement of electrons in different orbitals. It demonstrates that no more than two electrons can occupy an orbital, and these two electrons must have opposite spins. This is in line with the principle that states that no two electrons can have the same set of four quantum numbers.Rate this question:
- 50.
Use the electron configuration for nitrogen, Is2 2S2 2p3, to state how many electrons are in each main energy level.
Correct Answer
The principal quantum number n describes the energy level that an electron occupies. In a nitrogen atom, n = 1 for two electrons and n = 2 for five electrons.Explanation
The electron configuration for nitrogen, Is2 2S2 2p3, indicates that there are two electrons in the first energy level (n=1), two electrons in the second energy level (n=2), and three electrons in the p sublevel of the second energy level. Therefore, in total, there are five electrons in the second energy level.Rate this question:
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