CEM #3 – Flashcards
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What holds ions together in the solid?
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The force of attraction between the electrons and protons.
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What factors affect the strength of the interaction between ions in a solid.
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The size of the ions and the size of the charge affect the strength of the interaction.
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What would need to happen if you wanted to melt NaCl?
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You would have to add a certain amount of energy to break the force of attraction between the atoms.
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What is the difference between ionic and covalent bonds?
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The electrons are transferred in an ionic bond; they aren't shared or fought over like in a covalent bond.
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Does NaCl have "bonds"?
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No, because ionic bonds are attraction between two ions of opposite charges rather than a bond. Ionic bonds are not directional and don't share electrons like bonds.
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Does NaCl have molecules in it?
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No
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Why doesn't solid NaCl conduct electricity, but solid Al does?
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solid NaCl has fixed ions, not able to move to conduct electricity, while Al has free delocalized electrons, free to move and conduct electricity
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Why does molten (liquid) NaCl conduct electricity?
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in molten state, the ions are free; they have been liberated and they are able t move around
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Does Aluminum have to be heated to conduct electricity?
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No, because the electrons already move freely in Aluminum
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The bigger the ionic charge..
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the higher the melting point
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What does thermal energy depend on?
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how much material you have
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What does temperature depend on?
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it only depends on the average KE of the particles
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Can an individual gas particle have a temperature?
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No, you have to have more than one particle
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Do all the atoms in a gas move at the same speed at a given temperature?
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No, because collisions are random, so certain gas particles move at high speeds and some at low speeds. Some particles may have not collided with as many other particles, so their speeds are different.
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One molecule can have ___ but not a _____.
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KE, temperature
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What happens to the average velocity of a gas if the temperature increases?
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it increases
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What happens to velocity as mass increases?
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it decreases
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When gas molecules collide why don't they stick together?
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They have too much energy, so they overcome the attractive interactions.
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What would happen if the gas molecules did stick together?
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the substance would no longer be a gas
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Why don't we smell molecules immediately when you open a container ?
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because the molecules collide with each other and therefore don't move in a straight line
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Simple Ionic Compound
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contains one element with low electronegativity (metal) and one element with high electronegativity (non-metal).
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In simple ionic compounds which element gains an electron?
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the non-metal
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Why does the non-metal gain an electron?
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since the non-metal has a higher effective nuclear charge, it pulls the electron towards it strongly
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Noble gas configuration
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a trade-off between energy required to gain or lose electrons, and stabilization of the system when ionic bonds are formed.
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Cations
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losing an electron
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what charge are cations?
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always positive
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what charge are anions?
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always negative
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Why do cations form?
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because highly charged ions form stringer bonds, which are more stable
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Cations are _____ than corresponding atoms.
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smaller
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Anions are _____ than corresponding atoms.
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larger
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Anions
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gaining an electron
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In anions, what does the charge correspond with?
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corresponds to gain of electrons to the next filled (sub) shell (i.e. noble gas configuration)
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In cations, what does the charge correspond with?
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corresponds to loss of electrons back to "core". (valence electrons)
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lattice energy
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energy released when an ionic lattice forms from ions in the gas phase
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What makes a stronger attraction when dealing with lattice energy?
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more charge and smaller ions
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What happens to the lattice energy when there is a stronger attraction?
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it increases
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How does atoms interact?
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electrostatically
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What happens when atoms interact?
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the system becomes more stable and loses energy to surroundings
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The way atoms interact depends on what?
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the arrangement of electrons (valence electrons)
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When atoms interact the properties are what?
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emergent: arising casually or unexpectedly
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What do properties of materials depend on?
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type of bond, spatial arrangement of atoms, and interactions between molecules.
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What allows us to make predictions about types of interactions?
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temperature of phase changes
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Energy always moves from a _____ object to a ______ object.
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hotter, colder (heat moves)
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What is the lowest possible temperature?
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0K (absolute zero)
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Units of temperature
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Celsius, Kelvin, Fahrenheit
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Temperature
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average kinetic energy (measure of hotness)
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Which bond allows free rotation of the bonded atoms?
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sigma bonds
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What type of bond can't rotate?
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double bond (pi)
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triple bond
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pi bond plus sigma bond
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What happens to the bonds when a substance is being boiled?
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the bonds are being spread further apart (not broken)
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Formal charge=
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valence electrons on free atom - # bonds to atoms - non-bonded electrons
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What helps determine the shape of molecules from the lewis structure?
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valence shell electron pair repulsion
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How do you determine the shape of a molecule?
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consider the arrangement of the atoms
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What happens to the valence electrons when an atom has a high effective nuclear charge?
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the atom attracts its own valence electrons strongly
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Electronegativity
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ability of an element to attract electrons to itself in bond
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Do noble gases have electronegativity?
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no, because they do not form bonds
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What does electronegativity depend on?
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effective nuclear charge
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Electronegativity __________ across the periodic table.
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increases
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Electronegativity __________ down the periodic table.
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decreases
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Polar bonds
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When two atoms of different electronegativities bond, the electrons are not shared equally.
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polar bonds result in what?
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a bond dipole
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What do you use to determine the polarity of a molecule?
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the SHAPE of the molecule
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Types of IMFs
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LDFs, dipole-dipole interactions, hydrogen bonding
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For non-polar molecules what is the only intermolecular force present?
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LDFs
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What IMF is present in all substances?
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LDFs
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What does LDFs depend on?
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size, surface area, and shape
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What must be present in order for hydrogen bonding to occur?
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first must contain H covalently bonded to O, N, or F. second must have O, N, or F with one lone pair.
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What is the strongest IMF?
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hydrogen bonding
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What will have a higher melting point: a bigger hydrogen bonding molecule or a smaller hydrogen bonding molecule?
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bigger hydrogen bonding molecule because the LDF forces increase with size, so more energy will be required to break to larger LDFs.
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Is there such thing as a true ionic bond?
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no
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Thermochemistry
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using temperature changes to determine energy changes
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In order to keep track of energy changes, we need to define what?
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a system and the surroundings
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What do state functions depend on?
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only the initial and final states
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What are state functions denoted by?
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upper case letters
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What do path functions depend on?
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how changes take place
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What are path functions denoted by?
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lower case letters
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Internal Energy E
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sum of all KE and PE of all particles in the system
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First law of thermodynamics
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energy cannot be created or destroyed (but it can be transformed or transferred)
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Endothermic
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heat into the system (q+): the surroundings get cold
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Exothermic
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heat out of the system (q-): the surroundings get hot
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contraction
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work done by surroundings on system (w+)
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expansion
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work done by system on surroundings (w-)
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Enthalpy H
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heat absorbed or emitted during a reaction under constant pressure
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Heat capacity
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amount of energy it takes to change the temperature of a substance
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Specific heat
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energy required to raise 1 g by 1 °C (or 1 K)
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Molar heat capacity
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energy required to raise 1 mol by 1 °C (or 1 K)
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What happens to molar heat capacity as the molar mass increases?
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it increases
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What is the mechanism of adding thermal energy?
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collisions
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When molecules have more energy what is the consequence (what do they do at the molecular level?)
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Move faster, translate, vibrate rotate
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Open system
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can transfer matter and energy (biological systems)
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Closed system
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transfer energy but not matter (a closed container)
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isolated system
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no transfer of matter or energy ( an insulated closed container - hard to do!)
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The temperature does not change until the change of phase is complete. (T/F)
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true
