Atoms
In models used to illustrate atomic structure, where are neutrons located and what is their electrical charge?
A. Outside the nucleus; negative charge.
B. Inside the nucleus; neutral charge.
C. Inside the nucleus; positive charge.
D. Outside the nucleus; neutral charge.
B. Inside the nucleus; neutral charge.
Elements Helium (He) and Krypton (Kr) are placed in the same column on the right side of the Periodic Table. How are their properties similar?
A. Both are nonreactive gases at room temperature.
B. Both are highly reactive metals at room temperature.
C. Both are highly reactive liquids at room temperature.
D. Both are nonreactive solids at room temperature.
A. Both are nonreactive gases at room temperature.
A student is classifying a pure substance where every atom is identical. Based on the arrangement of its atoms, how should this substance be classified?
A) Compound
B) Mixture
C) Element
D) Solution
C) Element
A scientist conducts two experiments on a piece of solid copper. In the first experiment, the scientist heats the copper until it melts. In the second experiment, the scientist hammers the copper into a thin sheet (change in shape). How are these changes classified?
A) Both are chemical changes, because energy was required.
B) Both are physical changes, because the chemical composition of the copper remains unchanged.
C) The melting is a physical change, and the hammering is a chemical change.
D) The melting is a chemical change, and the hammering is a physical change.
B) Both are physical changes, because the chemical composition of the copper remains unchanged.
A balanced chemical equation serves as a model to show how atoms are rearranged during a chemical reaction. What specific requirement must a balanced equation meet to support the Law of Conservation of Mass?
A. The number of molecules in the reactants must equal the number of molecules in the products.
B. The atoms must change size and chemical identity during the reaction.
C. The total number of atoms for each element must be equal in the reactants and the products.
D. The total mass of the products must be greater than the total mass of the reactants.
A. The number of molecules in the reactants must equal the number of molecules in the products.
When comparing protons and electrons in an atomic model, what are the primary differences?
A. Protons have a neutral charge, while electrons have a positive charge.
B. Protons are found in the nucleus with a positive charge, while electrons are found outside the nucleus with a negative charge.
C. Electrons are much larger than protons in comparative size.
D. Protons and electrons are both found in the nucleus.
B. Protons are found in the nucleus with a positive charge, while electrons are found outside the nucleus with a negative charge.
An unidentified element is a pure solid that is metallic and reacts vigorously when placed in water. Where is this element most likely located on the Periodic Table?
A. At the top of the table, because it is a solid.
B. On the left side of the table, due to its metallic and high reactivity.
C. On the right side of the table, where nonmetals are found.
D. At the bottom of the table, in the transition metals section.
B. On the left side of the table, due to its metallic and high reactivity.
Methane is a pure substance that exists as a gas at room temperature. Each methane molecule is composed of one carbon atom chemically bonded to four hydrogen atoms. How is methane classified based on the atomic arrangement described?
A) As a homogeneous mixture
B) As an element
C) As a compound
D) As a heterogeneous mixture
C) As a compound
A piece of metal is placed in an unknown liquid. Observations show the liquid produces a rapid color change and a large volume of gas. Based on these observations, how should the change that occurred be classified?
A) As a physical change, because the metal's shape was not altered.
B) As a chemical change, because the formation of a gas and a color change are evidence of a chemical reaction.
C) As a physical change, because energy must have been absorbed.
D) As a chemical change, because the state of matter changed.
B) As a chemical change, because the formation of a gas and a color change are evidence of a chemical reaction.
Terry's teacher draws a symbolic model of a chemical reaction, where the squares (□), circles (∘), and triangles (△) represent different elements:
△□2+2∘ ---> △∘2+2□
Terry claims this model does not support the Law of Conservation of Mass. Which statement is the best evidence to prove Terry’s claim is false and the law is supported?
A. The arrangement of the symbols changed, showing a chemical reaction occurred.
B. There are different types of molecules in the reactants and products.
C. The model uses the same symbols on both sides, demonstrating conservation of elements.
D. There is an equal number of each symbol in the reactants and products.
D. There is an equal number of each symbol in the reactants and products.
A student drew a model of a neutral beryllium (Be) atom and placed 5 electrons in the nucleus. What error did the student make, based on the requirements for illustrating atomic structure?
A. The model has too many protons, causing it to be incorrectly drawn as neutral.
B. The model should not contain any neutrons.
C. Protons, not electrons, should be located within the nucleus.
D. Electrons should be illustrated as located outside the nucleus.
D. Electrons should be illustrated as located outside the nucleus.
Why are the highly reactive metallic element Lithium (Li) and the highly reactive gaseous element Fluorine (F) placed on opposite sides of the Periodic Table?
A. They are placed opposite because they share similar physical properties.
B. They are placed opposite because their specific chemical behaviors (types of reactivity) and non-metallic vs. metallic physical properties differ significantly.
C. Lithium is nonreactive, while Fluorine is highly reactive.
D. They are only separated because they are in different rows (periods).
B. They are placed opposite because their specific chemical behaviors (types of reactivity) and non-metallic vs. metallic physical properties differ significantly.
A student pours a cloudy liquid through a thin piece of paper and into a beaker. The student observes that the collected liquid is no longer cloudy, indicating separation occurred via filtration. How should the student classify the original cloudy liquid based on its ability to be separated by this physical process?
A) As an element, because filtration changed its state.
B) As a compound, because chemical bonds were broken.
C) As a mixture, because components were separated by physical means.
D) As a compound, because filtration separated it into two pure substances.
C) As a mixture, because components were separated by physical means.
When inflating a hot-air balloon, a flame heats the air, causing the air to expand. This expanding air then applies pressure on the balloon's fabric walls, causing the balloon to change shape. How does the air expanding compare to the balloon changing shape?
A) Both are physical changes, as neither process alters the chemical composition of the air or the balloon fabric.
B) Both are chemical changes, because both involve a change in energy.
C) The air expanding is a chemical change, and the balloon changing shape is a physical change.
D) The air expanding is a physical change, but the balloon changing shape is a chemical change because work is done.
A) Both are physical changes, as neither process alters the chemical composition of the air or the balloon fabric.
In a controlled experiment, a student balances the following chemical equation for the formation of magnesium oxide (MgO) from magnesium (Mg) and oxygen gas (O2):
2Mg + XO2 ---> 2MgO
What must the missing coefficient X be for the equation to illustrate how atoms are rearranged while conserving the total number of atoms, thus supporting the Law of Conservation of Mass?
A. 4
B. 3
C. 2
D. 1
D. 1
How must the comparative sizes of the subatomic particles be illustrated in an atomic model?
A. All three particles must be shown as equal in size.
B. Neutrons must be significantly larger than protons and electrons.
C. Protons and neutrons are relatively large, while electrons are significantly smaller.
D. Electrons must be shown as slightly larger than protons, but smaller than neutrons.
C. Protons and neutrons are relatively large, while electrons are significantly smaller.
Element X is a solid with very low reactivity. Element Y is a gas with very high reactivity. Element Z is a solid with very high reactivity. If these elements were added to the table based on standard rules, which element would most likely be placed in a column with nonreactive gases like Argon?
A. Element X, because of its physical state.
B. Element Y, because of its high reactivity.
C. Element Z, because it is a solid.
D. None of the elements listed, as nonreactive gases form a unique group based on reactivity and state.
D. None of the elements listed, as nonreactive gases form a unique group based on reactivity and state.
Which statement accurately describes the distinction between a pure sample of chlorine gas (Cl2) and a pure sample of water (H2O), according to the classification of matter?
A) Chlorine gas is an element made of different types of atoms, while water is a compound made of one type of atom.
B) Chlorine gas is a mixture, while water is a compound.
C) Chlorine gas is an element composed of only one type of atom, while water is a compound composed of two or more types of atoms chemically bonded together.
D) Both are classified as compounds because they both consist of molecules.
C) Chlorine gas is an element composed of only one type of atom, while water is a compound composed of two or more types of atoms chemically bonded together.
A scientist heats a solid piece of copper. The scientist first observes that the copper's density decreases as its temperature increases. If the scientist continues to heat the copper until it melts (a change of state), how is the decrease in density related to the melting process?
A) The decrease in density is a chemical change, while melting is a physical change.
B) Both are chemical changes because heating causes energy transfer.
C) Both are physical changes because, in both instances, the copper's chemical composition remains identical.
D) The decrease in density is a physical change, but the melting is a chemical change because a liquid is formed.
C) Both are physical changes because, in both instances, the copper's chemical composition remains identical.
A student places a piece of limestone (CaCO3) in an open beaker and adds acid. The reaction produces calcium chloride (CaCl2), water (H2O), and carbon dioxide gas (CO2).
If the student measures the mass of the substances left in the open beaker after the reaction stops, the measured mass will be less than the initial mass of the reactants. Why is this result still consistent with the Law of Conservation of Mass?
A. The reaction rearranged atoms so that the total mass of all atoms was reduced, but only in an open system.
B. Mass was transformed into chemical energy, which escaped the beaker.
C. The solid reactant changed its state, which invalidates the Law of Conservation of Mass in an open environment.
D. The atoms were rearranged into a gaseous product that escaped the open system, meaning the total mass of all products (including the gas) remains equal to the initial reactant mass.
D. The atoms were rearranged into a gaseous product that escaped the open system, meaning the total mass of all products (including the gas) remains equal to the initial reactant mass.
In an illustration of a neutral atom, the nucleus contains 15 protons and 16 neutrons. If the location and size of these particles are correctly modeled, which statement must be true about the overall electrical nature of the nucleus?
A. The nucleus is neutral because neutrons cancel out the protons.
B. The nucleus has a net negative charge due to the presence of 16 neutrons.
C. The nucleus is electrically balanced, but the atom as a whole is negative.
D. The nucleus has a net positive charge, contributed solely by the protons.
D. The nucleus has a net positive charge, contributed solely by the protons.
The modern Periodic Table model groups elements primarily into vertical columns (groups). This organization is based on analyzing and interpreting which crucial combination of factors?
A. The atomic number and the year the element was discovered.
B. The element’s density and its comparative size (radius).
C. The elements' physical properties (e.g., state, metallic nature) and their characteristic chemical reactivity.
D. The ratio of protons to neutrons, disregarding chemical behavior.
C. The elements' physical properties (e.g., state, metallic nature) and their characteristic chemical reactivity.
A student creates a diagram showing molecules of salt (sodium chloride) uniformly distributed throughout molecules of water. The student incorrectly classifies the resulting salt water solution as a compound. Why is the student's classification incorrect?
A) It is an element because water is a pure substance.
B) It is an element because salt contains only two atoms.
C) It is a compound because the salt chemically reacts with the water.
D) It is a mixture because the components (salt and water) are not chemically bonded together, even though they are uniformly arranged.
D) It is a mixture because the components (salt and water) are not chemically bonded together, even though they are uniformly arranged.
A student dissolves sugar in hot water, creating a clear solution. After the water cools and evaporates completely, solid sugar crystals remain. Which statement provides the best evidence that dissolving the sugar and evaporating the water were physical changes?
A) Energy was transferred during the process.
B) The sugar changed shape when it crystallized.
C) No evidence of a chemical reaction, such as a color change, gas formation, or precipitate, was observed throughout the process.
D) The volume of the water decreased as it boiled, which is a physical change (change in size).
C) No evidence of a chemical reaction, such as a color change, gas formation, or precipitate, was observed throughout the process.
The synthesis of ammonia (NH3) is modeled by the balanced chemical equation:
N2+3H2 ---> 2NH3
If a chemist starts with 15 molecules of N2 gas in a closed system and enough H2 to complete the reaction, how many total atoms of Nitrogen (N) will be conserved and rearranged into the final product molecules?
A. 15 atoms
B. 30 atoms
C. 45 atoms
D. 90 atoms
B. 30 atoms