EXAM 1 Flashcards
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Identify the similarities between atoms, molecules, elements, and compounds.
consist of charged particles called protons, neutrons, and electrons. They are all matter. Both molecules and compounds are formed by chemical bonding. Atoms and Elements are pure.
Identify differences between molecules, atoms, elements, compounds
Atoms are the most basic unit, while molecules and compounds are more complex. Elements are pure, compounds and molecules are not. Molecules can be identical atoms, where compounds cannot.
Define a Atom and Key Concepts.
smallest unit of an element that retains the properties of an element. It consists of a nucleus and an electron cloud. Atoms are not bonded, existing as a singular unit, they are building blocks of matter, and atoms of a similar element share the same number of protons.
Define a Molecule and Key Concepts
two or more atoms are chemically bonded together. They can be of the same element (H, O, etc) or different elements (H2O, CO2). They have distinct properties and are held together by covalent bonds.
Define a Element and Key Concepts
a pure substance that consists entirely of one atom. Each element is defined by a # of protons in the nuclei of the atom (the atomic #). Elements are the simplest form of matter that cannot be broken down by chemical means.
Define a Compound and Key Concepts
a substance made up of two or more different elements that are chemically bonded together in a fixed ratio. Compounds can be classified as either molecular (held together by covalent bonds) or ionic (held together by ionic bonds). Examples include H2O, NaCl, and CO2. Compounds MUST consist of AT LEAST two different elements (unlike molecules). Compounds have SPECIFIC ratios. Lastly, compounds have different properties than individual elements that compose them.
How does the Brownian motion prove the existence of atoms?
random, erratic movement of tiny particles suspended in a fluid (pollen in water). These particles were in constant collision with much smaller, invisible entities
How does John Daltons Atomic Theory (1803) prove the existence of atoms?
proposed that matter is composed on “atoms”. His theory is based on observations of chemical reactions, where substances combined in definite proportions, suggesting that they were made of distinct particles.
How does the “Law of Definite Proportions” prove the existence of atoms?
– in chemical reactions, elements combined in fixed ratios (ex 2:1 in water), which implies that compounds are formed from individual atoms in specific numbers. Modern technology such as STM which can directly image individual atoms
What was an experiment that proved the existence of electrons?
II and V
Thomson Cathode Ray Experiment (1897) – JJ Thomson discovered the electron by studying the behavior of cathode rays in a vacuum tube. When the rays were exposed to electric and magnetic fields, they deflected in a way indicating the presence of a negatively charged particle much lighter than an atom.
What experiment proved the existence of a nucleus? Where will the majority of the alpha particles be detected (point I, II, or III) and why?
III and VI
in the back (III) particles go straight through the atom, because it is mostly empty space
Rutherford’s Gold Foil Experiment (1909) – Ernest Rutherford he directed alpha particles at a thin gold foil. Most particles passed through, but some were deflected at large angles, with a few even bouncing back. This could only be explained if most of the atom’s mass and its positive charge were concentrated in a small, dense nucleus at the center of the atom. Most atoms passed through, but deflection occurred around the nucleus.
Explain why the model of an atom changed over time
As scientist preformed more research with advanced technology, there was room for more experimental evidence which revealed aspects of atomic structure that the models in the past didn’t explain or couldn’t, prompting the development of more accurate models.
Explain how a scientific theory differs from everyday use of the term “theory”.
A scientific theory is developed through repeated observations, experiments, and data analysis. It is typically used to explain and predict phenomena and is subject to change as further research is developed. A scientific theory explains, predicts, is consistently supported, and can be modified or replaced. In normal media terms, the word “theory” is just a guess or casual idea.
In summary, in the context of science (like in CLUE: Chemistry, Life, the Universe, and Everything), the term “theory” has a much more specific, reliable, and evidence-backed meaning than in casual conversation. It represents a comprehensive and substantiated explanation of natural events, built on rigorous experimentation and data analysis.
Compare the parts of the various atomic theories that stayed the same over time and those that changed
In CLUE: Chemistry, Life, the Universe, and Everything, the core idea that matter is made of atoms has remained consistent throughout various atomic theories. What changed over time were the details about atomic structure, such as the discovery of subatomic particles (electrons, protons, neutrons) and the arrangement of these particles within the atom. As new experimental evidence emerged, theories adapted, with key shifts occurring from Dalton’s indivisible atom to the modern quantum mechanical model that incorporates the wave-particle duality of electrons.
Develop a scientific question, a scientific explanation, and use evidence and data to make an argument
Scientific Question:
How does the concentration of reactants affect the rate of a chemical reaction?
Scientific Explanation:
The rate of a chemical reaction increases when the concentration of reactants is higher. This is because more particles are present in a given space, which means there are more chances for the particles to collide and react. The more collisions that happen, the faster the reaction occurs.
Evidence and Data:
In an experiment with vinegar and baking soda, when you use more baking soda (higher concentration), the reaction happens faster. This is because with more baking soda, there are more particles that can collide with the vinegar, making the reaction go quicker. So, the more of a substance you have, the faster the reaction.
Compare and contrast gravitational and electrostatic forces
Gravitational and electrostatic forces are both fundamental interactions, but they differ in nature and strength. Gravitational force is always attractive and acts between masses, with its strength being proportional to the masses involved and inversely proportional to the square of the distance between them.
Electrostatic force, on the other hand, acts between charged particles and can be either attractive or repulsive, depending on the nature of the charges (opposite charges attract, like charges repel). Electrostatic forces are significantly stronger than gravitational forces, especially at the atomic scale, where gravitational effects are negligible compared to electrostatic interactions.
Predict and explain the changes in the potential energy, the kinetic energy and the total energy as two positive charges approach each other.
As two positive charges approach each other, the electrostatic potential energy increases because the charges repel each other. This increase in potential energy occurs as the charges get closer, causing them to “push” against one another more strongly. Meanwhile, the kinetic energy of the system increases as the charges accelerate toward each other due to the repulsive force. The total energy, which is the sum of potential and kinetic energy, remains constant if no external forces are acting, according to the law of conservation of energy. As the charges move, potential energy is converted into kinetic energy, keeping the total energy unchanged.
On an atomic level, why do two atoms attract each other as they approach?
The electron cloud on a fluorine molecule is not stationary but fluctuates. As two isolated atoms approach each other, their electrons begin to interact, creating an attractive force due to opposite charges between the atoms’ positive nuclei and negative electron clouds. This attraction brings the atoms closer together.
Why would two isolated atoms repel each other as they get too close?
as the atoms get too close, their electron clouds start to repel each other because like charges (electrons) repel. Additionally, the positively charged nuclei experience repulsion when they get too close, which increases the overall repulsive force and prevents the atoms from merging.
Predict and explain the changes in the potential energy, the kinetic energy and the total energy as two isolated helium (or another noble gas) atoms approach each other
As two helium atoms approach each other, their potential energy decreases due to attraction, and their kinetic energy increases as they accelerate. When the atoms get too close, repulsive forces cause potential energy to rise. Throughout the process, total energy remains constant, with potential and kinetic energy converting between each other.
Explain how energy is transferred at the atomic level (by collisions that can either add energy to the system or remove it).
Energy is transferred during atomic collisions, where particles either gain energy, exciting them and increasing kinetic energy, or lose energy, lowering their kinetic energy. These energy exchanges help regulate the system’s overall energy balance in chemical processes.
Predict/rank the relative London Dispersion Forces between atoms and molecules of different sizes
London Dispersion Forces increase with the size of atoms or molecules. Larger atoms or molecules have more electrons, creating stronger temporary dipoles. Therefore, heavier, larger molecules (like iodine) experience stronger London forces than smaller molecules (like helium).
Relate the strength of London Dispersion Forces to relative melting and boiling points for the noble gases or simple diatomic molecules (H2, N2, O2, F2, Cl2, Br2, and I2).
London Dispersion Forces increase with the size and mass of molecules, as larger molecules have more electrons and can form stronger temporary dipoles. For the noble gases and diatomic molecules, as the size of the molecule increases, so do the London Dispersion Forces, leading to higher melting and boiling points.
Contrast and explain the energy change that occurs when two atoms form an LDF with the energy change that occurs when two atoms form a covalent bond?
The energy released in a covalent bond formation is much greater than the minimal energy change in LDF formation, as covalent bonds result in more stable, lower-energy configurations compared to the temporary interactions seen in LDFs.
Differentiate between London Dispersion Forces and covalent bonding without providing an explanation.
London Dispersion Forces are weak, temporary attractions between atoms or molecules, while covalent bonding is a strong, stable attraction where atoms share electrons.
OR
inside, outside type drawing.
what happens to gravitational force as the mass increases?
increases
what happens to gravitational force as the distance increases?
decreases
energy can be…
transferred (one object to another) and transformed (potential to kinetic)
describe a solid
Molecules packed closely in definite arrangements
Volume and shape independent of container
Incompressible
describe a liquid
melting point
Molecules move in relation to one another
Volume independent of container
No fixed shape
Incompressible
describe a gas
boiling point
Molecules far apart, move with high speed, collide
No fixed volume or shape
Compressible
what makes electron cloud “fluffy”
It can fluctuate momentarily so that the electron density is distorted.
What causes LDF’s to form?
Caused by fluctuations of electron density in the molecule (or atom) forming a dipole. An instantaneous dipole on one helium atom can induce an instantaneous dipole on neighboring atoms, which then attract one another.
How can we get them to stay in the potential minimum?
add energy!
Once atoms are stuck at the potential well, what prevents them from flying apart?
attractive forces between their electrons and nuclei prevent them from flying apart. These forces balance the repulsive forces at a certain distance, creating a stable configuration.
What can the the position of the PE well on the x-axis tell you?
The distance between the atom centers at their most stable point
What can the the depth of the PE well tell you?
How much energy would be needed to overcome the interaction
What would we have to do to break the LDFs between the He atoms (and get them out of the potential well)? Where does the energy go?
To break the LDFs between He atoms, you need to add energy to the system, usually by increasing temperature. The added energy increases the atoms’ kinetic energy, the attractive force is overcome, allowing them to escape the potential well.
What is the relationship between thermal energy and temperature?
Thermal energy is a measure of the sum of the kinetic energies (½mv2) of all the atoms.
Temperature T is directly related to average kinetic energy (½mv2) of the atoms.
How do the He atoms in the system “know” the temperature is increased?
The energy is transferred from other atoms that have collided with the walls of the container (that were directly heated).
what is a Van der Waals radii
Atom “sizes” are often listed as Van der Waals radii, which are defined as ½ the distance between the atoms at the potential minimum.
What happens as we increase the temperature? Which processes are phase changes and which are chemical reactions?
As we increase the temperature, the kinetic energy of the molecules increases, weakening the LDFs and eventually overcoming them.
If the temperature increases enough, H₂ molecules can break free from the liquid phase into the gas phase.
Phase changes include melting, freezing, and boiling, while chemical reactions involve the breaking and forming of covalent bonds, like in the case of hydrogen combustion or other reactions.
Which statement about the breaking of a single chemical bond is true?
Energy is absorbed.
Which statement about the forming of a single chemical bond is true?
Energy is released.
Consider the question: Is there an attractive force between a pencil and the earth? Is this a scientific question?
Yes, because It can be tested and answered through observations and experiments.
Which of the following properties ascribed to atoms by the Greek Gods do we still consider valid?
Atoms are in constant motion
Which of the following represents molecules that are compounds?
IV only
Which of the following contains atoms?
dust
Thomson’s cathode ray tube experiment proved false what part of Dalton’s atomic theory?
all atoms are indivisible and indestructible (~electrons)
How would the strength of the electrostatic force change if the distance between two charged objected DECREASED?
electrostatic force will become stronger
The diagram to the right is for two subatomic particles. It is a PE line graph with line pointing down only. What does the curve show?
The PE decreases as the objects get closer , one proton one electron
Which statement best describes the forces that exist between helium atoms in the solid state?
The partial positive end of one atom’s instantaneous dipole attracts the partial negative end of the neighboring atom’s induced dipole. (LDF)
When a covalent bond is formed between two nitrogen atoms
energy is released, a molecule is formed
The London dispersion force between two neon atoms compared to the London dispersion force between two argon atoms where both systems are the most stable is:
weaker, neon has a smaller electron cloud, therefore a smaller separation of charge resulting in a weaker force.
Is the following statement true or false?
When chlorine freezes, London dispersion forces are formed
true, because there are LDFs in BOTH the solid and liquid state, but MORE in the solid state.
Which do you predict to have a HIGHER boiling point, fluorine (F2) or neon (Ne) and why?
F2, bc the LDFs between fluorine molecules are stronger, requiring more energy to overcome.
Consider a system of two atoms with a stable interaction between them (the atoms are stuck in the bottom of the potential energy well). The potential energy curve for this system is shown to the right. What would happen to the system for the potential energy to change from Y to Z?
A third atom from the surroundings would collide with the system, energy would transfer from the surroundings to the system, the interaction between the atoms in system would be overcome
True or False : The kinetic energy increases because the atoms are attracted to each other and are speeding up.
true
what does a deeper well illustrate?
When a well is deeper it illustrates the amount of energy needed to overcome the force. When an atom forms a covalent bond, it requires more energy to sperate the atoms.
Design an experiment that involves what happens when cold milk is added to hot coffee.
Include:
* The question you would answer
* An experimental design that would allow you to answer the question
* The data you would collect
* How you would analyze the data
Question:
How does the temperature of hot coffee change when cold milk is added?
Experimental Design:
Start with 100mL of hot coffee. Add small volumes (5mL) of cold milk. Monitor the temperature as the milk is added.
Data Collection: Collect the temperature of the hot coffee, cold milk, and the coffee/milk mixture. Analysis: Plot the temperature vs. the volume of milk added.
The electron was the first sub-atomic particle that was discovered. Why do you think it was the first?
Electrons are located on the outside of the atom (the nucleus is in the middle). Therefore, it is easier to remove the electrons. Electrons are also charged so they are easier to detect than an uncharged particle (like a neutron) because charged particles can be manipulated with electrical and magnetic fields.
Describe the evidence that was used to support the discovery of the electron. Why was it assumed that electrons exist within atoms, rather than are created in the course of the experiment?
A beam of particles (electrons) was emitted from cathodes (the negative end of the apparatus) composed of many different metals. These “cathode rays” were the same regardless of the types of atoms in the cathode. Therefore, electrons must be a sub-atomic particle that exists in all of the metals that were tested.
Describe a picture of JJ Thomson’s proposed atomic structure and indicate how it differs from Dalton’s model of the atom?
The electrons were embedded in a positively charged blob, together making up the atom. This is similar to how chocolate chips are embedded in a cookie to make up a chocolate chip cookie.
Dalton’s model of the atom was an indivisible
atom that had no subatomic particles.
what is wrong with Rutherford’s model of the atom?
A negatively charged particle moving in an electric field will emit radiation and spiral into the nucleus, causing the atom to implode.
