Units 20-21 Flashcards
When does the probable location of the electron change within the orbital?
When the total energy (kinetic and potential) of the electron is changed.
This happens as it comes into contact with other atoms.
Molecular orbitals
New orbital shapes that become possible when two atoms are brought closer together. Now there are two atomic nuclei (positive) attracting the negative electrons of each other’s atom.
Standing electron probability waves for MOLECULES.
When do atoms bond together? What condition must be present?
If the electrons from the two different atoms can achieve a lower energy arrangement in their orbitals than when they were isolated, the atoms will bond together.
True or False: It is possible for two atoms to have a lower-energy standing wave pattern than when they are isolated. This creates a bond between the atoms.
True
True or False: When atoms bond, the energy difference is released as photons or heat.
True
Why is energy required to break a bond?
Because you would have to return two atoms to a higher energy arrangement. (they got lower to bond)
Bonding molecular orbitals
Orbitals that have high electron probability BETWEEN the atomic nuclei (positive part) within the newly bonded molecule.
When there is a high density of electrons between the nuclei, it helps hold the nuclei together, contributing to the strength of the bond between the atoms.
Anti-bonding molecular orbitals
Orbitals that have low (or no) electron probability between atomic nuclei in a molecule. There is high electron density in areas NOT between the nuclei.
This type of bond, with electrons in the anti-bonding orbital pull the nuclei apart, weakening the bond between them.
What is another name for anti-bonding molecular orbitals
Non-bonding
Do non-bonding orbitals differ from anti-bonding orbitals?
Tiny bit. They do nothing to strengthen or weaken the bond.
Where is the electron density of a non-bonding orbital?
Equal number between and not between the atoms.
What two things determine if a chemical bond will form?
- Energy
- Entropy
True or False: Two materials are likely to react spontaneously if by doing so, they can achieve a lower energy state.
True
True or False: Energy and entropy play against each other in bonding.
True
Metallic bonding (or strong bonds)
A large number of atoms collectively share their electrons. Takes place in metals.
This is why metal has strength.
True or False: Processes that increase entropy proceed spontaneously
True
True or False: Processes that minimize energy proceed spontaneously
True
How many ways can bonds form?
3
Valence electrons
Electrons in the highest energy, outermost quantum shell of an atom.
True or False: Only the valence electrons are involved in chemical reactions
True
Cations
Atoms, or groups of atoms, bound together that have a net positive charge.
True or False: In cations, the number of electrons is less than the number of protons
True
Anions
Atoms, or groups of atoms, that have a net negative charge.
True or False: In anions, the number of electrons is GREATER than the number of protons
True
Ionic bonding
Bonding between metals and nonmetals where nonmetals completely gain electrons from metals.
Metal atoms lose electrons, forming positive ions, and the non-metal atoms gain electrons, forming negative ions.
Covalent bonding
Bonding between atoms accomplished by sharing electrons to achieve low-energy arrangement of the electrons between the nuclei.
Basically sharing electrons.
True or False: The result of ionic bonding is cation and anion atoms.
True
Reactants
The starting materials in a chemical reaction.
Left side
Which side of the equation do reactants go on?
Left side
Products
Materials produced in a chemical reaction
Right side
Which side of the equation do products go on?
Right side
True or False: The matter on the left side (proportions) should be equal to the matter on the right side of the equation
True
Why does the matter on the left side of the equation have to equal the matter on the right side?
Conservation of mass
If the matter doesn’t change in a chemical reaction, what does?
The arrangement of the molecules
Rates of reactions
The speed at which reactions are consumed and products are produced in a chemical reaction.
What are the two things that tell us if a reaction has occurred.
- How quickly reactants disappear
OR - How quickly products are produced.
Collision
Two atom get close enough that their orbitals overlap
What influences reaction rates?
Collision rates
(and energy and entropies involved in collisions)
What determines collision rates?
- Density/concentration of molecules
- Speed, which is determined by temperature.
Potential energy surface
A diagram plotting the total energy of reactants and products.
Plot of the electrical potential energy between reactants.
Transition state
The critical point that separates reactants from products on a potential energy surface.
What is usually required to reach a transition state?
Breaking existing chemical bonds.
Which requires energy
True or False: Breaking existing chemical bonds requires energy
True
Activation energy
The energy required to form the transition state
Which form of matter has collisions happening quickly and spontaneously without adding additional energy?
Gases
Why do liquids and solids need an activation energy to begin the reaction?
Because their atoms aren’t hitting hard enough to be broken apart. Collisions aren’t hard enough.
True or False: All collisions result in product formation
False
True or False: Some collisions require a specific orientation.
True
Activation entropy
The disorder required to have successful collisions.
Collisions require certain orientations, but they are happening randomly and will not always hit each other just right. The activation entropy describes the “luck” essentially, or the randomnness working out to cause a successful collision.
Catalyst
A chemical whose presence increases the rate of a chemical reaction without being consumed in the reaction.
They increase the energy or entropy, making it more favorable, without affecting the energies or entropies of the initial reactants or final products.
Enzymes
Protein molecules that function as catalysts in biochemical reactions
Why are enzymes important?
They speed up the reactions happening at room temperature that all life requires. You can’t increase the heat, or life will die. So you have to speed up the natural processes.
How do catalysts work?
By lowering the energy or increasing the entropy of the transition state
Can products react and turn back into their reactants?
yes
True or False: There is nothing special about the direction of a chemical reaction
True
Equilibrium
The condition where the forward and reverse rates of a chemical reaction are equal, so the system experiences no net change.
What is the state that has the most favorable energy and entropy for a chemical system?
Equilibrium
True or False: All natural systems head toward equilibrium
True
What is the ultimate equilibrium?
The heat death of the universe
Which type of reaction has low activation energy, fast or slow?
Fast
Why don’t noble gases react well with other atoms?
They have full shells
True or False: Chemical reactions are very unlikely to occur with antibonding molecular orbitals
True
True or False: Largest molecules give the most energy when breaking apart/forming
True
Which has more energy, the reactants or the products?
Reactants
Energy is given off in the reaction
True or False: In chemistry, a catalyst is specifically a CHEMICAL
True
True or False: A match is a catalyst
FALSE
Not a chemical
True or False: Thermal energy is a catalyst
FALSE
Not a chemical
In the electrolysis process, is there more or less energy in the products?
MORE
More than the reactants, because the electrical current is adding energy
True or False: In equilibrium, the energy is at a minimum and the entropy is at a maximum.
True
What does it mean to have a favorable energy change?
Thermal energy is released. This means the products have a lower overall energy than the reactants, which is favorable.
How does a catalyst affect a reaction?
It lowers the activation energy
True or False: Metals form network solids
True
What does it mean that an element lies on the boundary line between two different kinds of elements?
It can have properties on both sides of the line, depending on the circumstance.
True or False: Metals have high melting and boiling temperatures.
True
Do metals have high or low densities in solid states?
High
Malleability
The characteristic that allows metals to be worked into desirable shapes or drawn out into wires.
True or False: When metal is rolled into very thin sheets, it shatters
False
Opacity
The opposite of being transparent. Visible light is absorbed by an opaque object
True or False: You can see through something opaque
False
True or False: Visible light is ABSORBED by an opaque object
true
Reflectivity
Being capable of producing a reflection
Thermal conductivity
How well a substance conducts heat
True or False: Metals are highly thermal conductive
True
What key factors determine bonding in metals?
- Only involves valence electrons
- Valence electrons of metals have low ionization energies
- Few electrons compared to the total number allowed in their valence orbitals
- Electrons occupy the lowest energy orbitals available
True or False: In metals, electrons are practically shared by all the nuclei (of bonded atoms) rather than belonging to any particular one
True
Delocalized electrons
Electrons in metallic orbitals are not confined to a specific nucleus, and have basically the same probability of being near many nuclei
What is the “sea” of electrons that scientists refer to?
A blue cloud surrounding the nuclei in which electrons are free to travel.
Not a real thing, but because the orbitals interact and overlap with each other so much, it seems like bonded metallic atoms are basically free to move around anywhere near ANY of the nuclei.
True or False: In metals, there is a set of energy states so closely spaced that they can be regarded as continuous.
True
True or False: In metallic bonding, atoms have basically lost their negative electrons, so they are ions with net positive charge
True
What causes strong forces/bonding in metals to be so strong?
The strength of the electrostatic attraction between the electrons and the nuclei
Why are metals so conductive of electricity?
Because the electrons aren’t bound to any nuclei, so they’re free to move around more.
Why are metals so conductive of thermal energy?
Heat energy = kinetic energy. The electrons are freer to move in metals, so when one end of the metal heats up, the electrons carry the increased kinetic energy rapidly throughout the rest of the piece.
Why are metals malleable?
Because the fluid-like electrons act like a lubricant between the layers of nuclei (to be a sheet requires metal nuclei to pass over each other).
Why are metals opaque?
Because they can absorb radiation over the entire visible region of the spectrum, as well as infrared and UV). They absorb energy because there are an almost infinite number of energy states due to the moving electrons (discrete spectra stuff) that can match/block light.
Why are metals reflective?
The mobility of the electrons allows them to easily interact with the light waves.
Electrons absorb light, which causes them to oscillate. This oscillation radiates light energy.
Reflections are the radiating oscillations.
Alloy
A combination of two or more metals into a single homogenous substance.
True or False: A true alloy has a specific ratio of metal to metal.
False
What happens to the entropy of a system as two pure metals form an alloy?
It increases
What are the two ways that alloys form?
Atoms from one type of metal are either interspersed with the other, substituting their space because they’re similar in size.
OR
Atoms from one type of metal fill in the gaps between larger atoms of the other.
To be stable, does an alloy need to release or absorb energy upon formation?
releases
True or False: For alloys that release energy, disorder increases in both the system and the surroundings.
True
True or False: When two pure metals are mixed into an alloy, the alloy will be a greater conductor of electricity than either of the two separate metals.
FALSE
The two pure metals are often better at it.
True or False: Alloys have stronger properties than their individual metals.
Falseish
It depends on the property, sometimes it’s weaker
Semiconductor
A solid crystalline substance that conducts electricity better than insulators, but worse than metals. In the middle.
What is unique about semiconductors?
They become better conductors as their temperature increases.
Where are the semiconductors on the periodic table?
Those elements bordering the black staircase separating metals from non-metals.
What is another name for a semiconductor?
Semi-metals
Metalloids
Resistivity
A measure of the resistance to the flow of electrical current.
What is one way to characterize how easily electricity can flow through a quantity?
Resistivity.
The greater the R, the harder it is for the current to flow through it.
True or False: Metals become slightly more resistive as the temperature increases
True
True or False: Semiconductors become slightly more resistive as the temperature increases
False
Band gap
The energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.
Those bands with all the lines. Metals are just one continuous band, but semis and insulators have a gap between the high and low energies.
How big is the semiconductor band gap?
Relatively small.
Valence band
The low energy band of a semiconductor. Unexcited electrons reside here. Completely filled in low energies.
Conduction band
The range of electron energy higher than that of the valence band. It’s high enough to make the electrons free to accelerate under the influence of an electric force - thus making an electric current.
True or False: Semiconductors have the ability to absorb photons whose energy matches or exceeds the band gap energy.
TRUE
Junction
The region that two different semiconductors join together on a semiconductor device
Metallic luster
The high reflectivity or shininess of metals.
N-Type Semiconductor
A semiconductor with extra electrons in the valence band. It is formed by adding a different semiconductor that has more valence electrons than the host semiconductor to the host semiconductor. Phosphorus can be used to create an N-type semiconductor.
P-Type Semiconductor
A semiconductor with vacancies in the conduction band. It is formed by adding a different semiconductor that has fewer valence electrons than the host semiconductor to the host semiconductor. Aluminum can be used to create a P-type semiconductor.
What is the opposite of malleable?
Brittle
Does ionization energy increase or decrease as you move across a row to the right on the periodic table?
Increase
True or False: If electrical resistance is high, thermal conductivity is low. And if resistance is low, thermal conductivity is high. There is an inverse relationship.
TRUE
