CEM 141 - Introduction to Chemistry

This set of flashcards covers key vocabulary and concepts from the CEM 141 Introduction to Chemistry lecture notes.

Chemistry

The scientific study of the properties, composition, and behavior of matter.

Atoms

The smallest unit of matter that retains the properties of an element.

Matter

Anything that has mass and takes up space.

Emergent Properties

Properties that arise from the interactions between individual components in a system.

Scientific Method

A systematic approach to experimentation and observation to validate or refute scientific theories.

Model

A representation, such as a diagram or equation, that helps explain or predict phenomena.

Claim

A statement or assertion that can be tested and supported with evidence.

Evidence

Data or information that supports a claim or hypothesis.

Theory

A well-substantiated explanation of an aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

Scientific Law

A statement that describes a consistent and universal relationship observed in nature.

Covalent Bond

A chemical bond formed when two atoms share electrons.

Intermolecular Forces

Forces of attraction or repulsion between molecules.

Kinetic Energy (KE)

The energy of an object due to its motion.

Potential Energy (PE)

The energy stored in an object due to its position or configuration.

Thermal Energy

The total kinetic energy of the particles in a system caused by their temperature.

London Dispersion Forces

Weak intermolecular forces that arise from temporary shifts in electron density within molecules.

Electrostatic Forces

Forces that occur between charged particles, such as electrons and protons.

Atomic Radius

The distance from the nucleus to the outermost shell of an electron in an atom.

Chemistry

The scientific study of the properties, composition, and behavior of matter.

Atoms

The smallest unit of matter that retains the properties of an element.

Matter

Anything that has mass and takes up space.

Emergent Properties

Properties that arise from the interactions between individual components in a system.

Scientific Method

A systematic approach to experimentation and observation to validate or refute scientific theories.

Model

A representation, such as a diagram or equation, that helps explain or predict phenomena.

Claim

A statement or assertion that can be tested and supported with evidence.

Evidence

Data or information that supports a claim or hypothesis.

Theory

A well-substantiated explanation of an aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.

Scientific Law

A statement that describes a consistent and universal relationship observed in nature.

Covalent Bond

A chemical bond formed when two atoms share electrons.

Intermolecular Forces

Forces of attraction or repulsion between molecules.

Kinetic Energy (KE)

The energy of an object due to its motion.

Potential Energy (PE)

The energy stored in an object due to its position or configuration.

Thermal Energy

The total kinetic energy of the particles in a system caused by their temperature.

London Dispersion Forces

Weak intermolecular forces that arise from temporary shifts in electron density within molecules.

Electrostatic Forces

Forces that occur between charged particles, such as electrons and protons.

Atomic Radius

The distance from the nucleus to the outermost shell of an electron in an atom.

Solid

A state of matter characterized by a definite shape and volume, with particles arranged in fixed positions.

Liquid

A state of matter characterized by a definite volume but an indefinite shape, with particles that can move past one another.

Gas

A state of matter characterized by an indefinite shape and volume, with particles that are far apart and move randomly.

Plasma

An ionized gas, consisting of positive ions and free electrons, forming at very high temperatures.

Pure Substance

Matter that has a uniform and definite composition, either an element or a compound.

Mixture

A physical combination of two or more substances that are not chemically bonded and retain their individual properties.

Homogeneous Mixture (Solution)

A mixture with a uniform composition throughout, where components are evenly distributed.

Heterogeneous Mixture

A mixture with a non-uniform composition, where individual components can be distinguished.

Element

A pure substance consisting only of atoms that all have the same number of protons in their atomic nuclei.

Compound

A pure substance consisting of two or more different chemical elements chemically bonded together in a fixed ratio.

Physical Property

A characteristic of matter that can be observed or measured without changing the substance's chemical identity (e.g., density, melting point).

Chemical Property

A characteristic of matter that describes its ability to participate in chemical reactions and form new substances (e.g., flammability, reactivity).

Physical Change

A type of change in which the form of matter is altered but not its chemical identity (e.g., melting ice).

Chemical Change (Chemical Reaction)

A process that involves rearrangement of the structure of molecules or ions, resulting in the formation of new substances (e.g., burning wood).

Proton

A subatomic particle with a positive charge (+1) located in the atomic nucleus.

Neutron

A subatomic particle with no charge (0) located in the atomic nucleus.

Electron

A subatomic particle with a negative charge (-1) orbiting the atomic nucleus in shells or orbitals.

Atomic Number (Z)

The number of protons in the nucleus of an atom, uniquely identifying an element.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus.

Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons, leading to different mass numbers.

Density (\rho)

The measure of mass per unit volume of a substance, calculated as \rho = \frac{m}{V}.

Hypothesis

A testable prediction or an educated guess that explains an observation and serves as a starting point for experimentation.

On what date and during what specific time frame was the "Alternate Examination 1" for Chemistry 141 Fall 2025 administered?

Monday, September 29th, 2025, from 6:30am to 7:50am.

How many questions are present on "this part of the exam," and what is the total point value for this section?

There are twenty questions, each worth 4 points, totaling 80 points.

Which essential reference materials are permitted to be attached to the exam paper for student use during the examination?

A Periodic Table and a few equations.

Identify three categories of electronic devices that are explicitly prohibited from being accessed or used as calculators during the examination.

Cell phones, smart watches, and other devices such as computers or iPads.

What two distinct physical items must a student hand in precisely upon completion of the examination?

Both the answer (bubble) sheet and the exam paper.

What specific student identification detail must be correctly marked on the answer sheet for proper processing?

The Student PID box.

Under what condition, and from whom, can students retrieve their exam questions after the examination has concluded?

Questions can be picked up from their lecture instructor later the same week.

What is the official policy regarding the posting, selling, or distribution of this specific examination material to unauthorized individuals or platforms?

The course instructors do not give permission for this exam to be posted online, sold, or distributed to others, as it is exclusively for students enrolled in CEM 141 Fall 2025.

For which specific chemistry course and academic semester was this particular "Alternate Examination 1" designed?

Chemistry 141 Fall 2025.

What must students present to show their identity when exiting the examination room?

Show your ID.

How is O_2 accurately classified in terms of its composition and structure?

It is an element and a molecule.

Which experimental observation provided the most compelling evidence for the positive charge concentrated in the atomic nucleus?

Rutherford's gold foil experiment, where a small percentage of alpha particles were significantly deflected upon passing through a thin gold foil.

Thomson's cathode ray tube experiment revolutionized the atomic model by demonstrating what key characteristic of atomic structure?

The observation that the cathode ray bends toward a positively charged plate, revealing the existence of negatively charged subatomic particles (electrons) and indicating that atoms are divisible, contrary to Dalton's initial beliefs.

Evaluate the following statements regarding the nature of a scientific theory:

I. It is an observation that is always true.

II. It predicts the results of future experiments and observations.

III. Once it is established it remains unchanged.

IV. It must be changed if its predictions are not borne out by experiment.

V. It is an explanation of a phenomenon based on the best evidence available.

Which of these statements are true?

Statements II, IV, and V are true. A scientific theory predicts, is subject to revision based on new evidence, and provides an explanation of phenomena.

Considering fundamental forces, which of these statements is accurate when comparing gravitational and electrostatic forces?

Electrostatic forces can be both attractive and repulsive, while gravitational forces are only attractive.

Analyze the potential energy diagram for two subatomic particles that shows potential energy decreasing as the objects get closer until a very short distance, where it sharply increases. What can be inferred about the charges of these particles and their interactions?

The curve indicates that the particles experience an attractive interaction at longer distances (potential energy decreases as they approach) and a repulsive interaction at very close distances (potential energy increases sharply), characteristic of two opposite charges.

Is an attractive force possible between two entirely neutral atoms, and if so, what mechanism accounts for it?

Yes, an attractive force exists between two neutral atoms. This is due to London Dispersion Forces, which arise from temporary shifts in electron density creating instantaneous dipoles that induce dipoles in neighboring atoms, leading to a weak attraction.

When two atoms approach each other so closely that their electron clouds begin to overlap significantly, what change occurs in the kinetic energy of the system, and why?

The kinetic energy decreases because the atoms slow down due to increasing repulsive forces between the overlapping negatively charged electron clouds.

Which visual representation would best depict krypton (Kr) in its liquid state, considering the arrangement and movement of its atoms?

A representation showing particles that are closely packed but still possess the ability to move past one another, indicating a definite volume but an indefinite shape.

Helium has an extremely low boiling point of 4.5\text{ K}. When helium undergoes condensation (a phase change from gas to liquid), how is energy transferred at the atomic level?

Energy is removed from the system as the helium atoms lose kinetic energy to form liquid, typically by colliding with surrounding particles and transferring energy away.

Rank the following substances from weakest to strongest in terms of the London Dispersion Forces (LDFs) they exhibit: He, Xe, and I_2.

He < Xe < I_2. The strength of London Dispersion Forces increases with an increase in electron cloud size and molar mass.

Among He, Ne, O2, and Cl2, which substance is predicted to have the lowest boiling point, and what type of intermolecular interaction is overcome during its boiling process?

Helium (He) will have the lowest boiling point. When it boils, London Dispersion Forces are broken.

Compare a system of two nitrogen atoms to a system of two argon atoms at room temperature. Which system demonstrates stronger interatomic interactions, and what is the underlying reason?

A system of two nitrogen atoms (N_2) exhibits stronger interactions because two nitrogen atoms form a strong covalent bond, which is much more robust than the weak London Dispersion Forces found between two individual argon atoms.

Which statement accurately describes a shared characteristic of both London Dispersion Forces and covalent bonds?

They are both attractive electrostatic interactions.

Given the balanced equation for water formation: 2H2 + O2 \to 2H_2O, which pictorial representation correctly shows the contents of a reaction container after 2 molecules of hydrogen react with 2 molecules of oxygen?

The representation showing 2 molecules of water (H2O) and 1 unreacted molecule of oxygen (O2), because hydrogen is the limiting reactant and one oxygen molecule remains after all hydrogen reacts.

When ethyne (C2H2) undergoes complete combustion with oxygen to produce carbon dioxide and water, what is the stoichiometric coefficient for oxygen (O_2) in the balanced chemical equation, using the smallest whole numbers?

The balanced equation is 2C2H2 + 5O2 \to 4CO2 + 2H_2O. The coefficient for oxygen is 5.

Which of the following samples contains the largest total number of atoms?

(a) 2.0 mol H2 (b) 1.0 mol H2O

(c) 4.0 mol CH4 (d) 0.75 mol SO3

(c) 4.0 mol CH_4 contains the largest number of atoms. (20.0 moles of atoms in total, compared to 4.0, 3.0, and 3.0 moles of atoms for the other options, respectively).

Nitrogen dioxide (NO2) decomposes according to the reaction: 2NO2 \to 2NO + O2. If 23\text{ g} of NO2 fully decomposes, what mass of oxygen (O_2) will be produced?

8.0\text{ g} of oxygen (O2). (23 g NO2 is approximately 0.50 mol. From stoichiometry, 0.50 mol NO2 yields 0.25 mol O2. 0.25\text{ mol} \times 32.00\text{ g/mol} = 8.0\text{ g})

In an experiment where carbon tetrachloride (CCl4) reacts with excess hydrogen fluoride (HF) to produce dichlorodifluoromethane (CCl2F2) and hydrogen chloride (HCl) in a 1:1 molar ratio (CCl4 \to CCl2F2), 1.80 moles of CCl4 are initially used. If 1.55 moles of CCl2F_2 are experimentally produced, calculate the percent yield of this reaction.

The percent yield is approximately 86\%\n(Actual Yield / Theoretical Yield) \times 100\% = (1.55\text{ mol} / 1.80\text{ mol}) \times 100\% \approx 86\%

When a covalent bond undergoes breakage, what energetic event occurs within the system?

Energy is absorbed from the system.

Which subatomic particle's discovery was primarily responsible for discrediting Dalton's indivisible atom model and leading to Thomson's 'plum pudding' model?

The electron.

Aside from molecular motion, what is the fundamental difference in particle arrangement and interaction that distinguishes liquid water from gaseous steam?

In liquid water, molecules are closely packed but can still move past each other due to stronger intermolecular forces, whereas in gaseous steam, molecules are far apart and move randomly with minimal intermolecular interactions.

Considering the elements found in HF, which specific type of intermolecular force is exceptionally significant in hydrogen fluoride due to the high electronegativity of fluorine and small size of hydrogen?

Hydrogen bonding.

When a chemical bond forms between two atoms, how is the energy of the resulting system typically affected?

Energy is released from the system, leading to a more stable, lower-energy configuration.

If you combine sand and salt thoroughly, what type of mixture is formed, and what property allows for the relatively simple separation of its components?

A heterogeneous mixture is formed. The components can be easily separated through physical means (e.g., dissolving the salt in water, then filtering out the sand, and evaporating the water) because they retain their individual properties and are not chemically bonded.

What observational evidence would provide the strongest indication that the cooking of an egg involves a chemical change, rather than just a physical alteration?

The formation of new substances with different properties (e.g., changes in color, texture, and odor that are irreversible) rather than just a change in state or form.

In a chemical reaction that requires a 2:1 molar ratio of reactant A to reactant B, if you begin with 5\text{ mol} of A and 2\text{ mol} of B, which reactant will be consumed completely first, thereby limiting the amount of product formed?

Reactant B is the limiting reactant. (To react with 2 mol of B, 4 mol of A would be needed, leaving 1 mol of A in excess).

Why do noble gases, such as Neon (Ne), typically exist as isolated individual atoms rather than forming stable molecules or extensive networks under standard temperature and pressure conditions?

Noble gases have a complete or stable valence electron shell, making them very unreactive and disinclined to form chemical bonds with other atoms.

A bowling ball is diligently lifted to a height of 2\text{ meters}. What type of energy has it gained, and how does this energy transform if the ball is subsequently dropped?

The ball has gained potential energy due to its position. As it is dropped, this potential energy is converted into kinetic energy as the ball accelerates downwards.

Distinguish between a scientific law and a scientific theory by explaining their primary scope and purpose in scientific understanding.

A scientific law describes a fundamental, consistent, and often mathematical relationship observed in nature, stating 'what' happens without explaining why (e.g., Law of Conservation of Mass), while a scientific theory is a well-substantiated, comprehensive explanation of 'why' or 'how' a natural phenomenon occurs, incorporating facts, laws, and tested hypotheses.