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CEM 141
Exam 3 Flashcards
| Question | Answer |
|---|---|
| what is our evidence that atoms exist? | we have advanced microscopes to "see" atoms |
| do isolated atoms or molecules exist in a state (solid, liquid, gas)? | no |
| do isolated atoms or molecules have melting or boiling points? | no |
| when atoms interact to form larger collections, they have ________. | emergent properties |
| emergent properties belong to a collection of atoms but not what? | the individual components |
| the properties of the products of a chemical reaction are ________. | emergent |
| we ________ predict the properties of a product from the properties of the reactants. (can/can't) | can't they are unrelated |
| the properties of any substance depend on the ________ that exist within that substance. | bonding/interactions |
| the reaction between two hydrogen atoms is much ________ then the reaction between two helium atoms. | stronger |
| what is the cause of both LDF's and covalent bonds? | electrostatic attraction |
| the difference between the electrostatic attraction of LDF's and covalent bonds is ________. | the magnitude of the attraction |
| why do bonds form between atoms? | because the valence electrons are attracted to the nuclei of other atoms |
| in a covalent bond each nucleus is attracting ________. | both electrons |
| in a covalent bond the ________ is the most stable distance between atoms (ionization energy is lowest potential energy). | bond length |
| when bonds form energy is ________ to the ________. | released, surroundings |
| why are only valence electrons involved in bonding? | because valence electrons are in the outermost shell and are easiest to attract things because they are not receiving as strong of an attractive force from the nucleus |
| molecular orbital theory - | electrons are waves and can therefore combine constructively and destructively |
| in molecular orbital theory ________ combine to give ________. | n molecular orbitals, n molecular orbitals |
| when atomic orbitals combine ________ bonding molecular orbitals form. | constructivley |
| bonding molecular orbitals are _________ energy than the atomic orbitals. | lower |
| electrons in bonding orbitals make the species ________. | stable |
| when atomic orbitals combine ________ antibonding molecular orbitals form. | destructivley |
| antibonding orbitals are ________ energy than the atomic orbitals. | higher |
| electrons in antibonding orbitals make the species less ________. | stable |
| molecular orbitals can also only hold ________. | two electrons |
| by combining atoms, the energy of the system ________ to become more stable | decreases |
| two electrons in a bonding orbital make ________. | one bond |
| two electrons in a bonding molecular orbital are ________ but two electrons in an antibonding molecular orbital would ________ the stablization. | stabilizing, cancel out |
| is there stabilization between two He atoms? | no |
| in H2 only the ________ molecular orbital is occupied leading to a net stabilization of the interaction. | bonding |
| to break the bond, enough energy has to be ________ to raise an electron to the antibonding orbital. | added |
| if a photon hits the H bonding orbital it moves _______ to an antibonding orbital, this makes it unstable and causes the bond to _______. | one electron, break |
| why can hydrogen atoms form a covalent bond, but helium atoms cannot? | hydrogen can fill the bonding orbital, helium fills both the bonding and antibonding so there's no stabilization so a bond cannot form |
| what happens to the molecule when the electron is promoted to the antibonding orbital? | the bond holding the molecule together was broken because it now is unstable |
| why is energy required to break a covalent bond? | because the attractive force of the nucleus is holding it together, so you need to add energy in order to overcome the attractive force |
| what pattern do you see regarding mp and bp of elements relative to types of bonding and interactions overcome during a phase change? | elements in an extended network take the most energy and have higher mp and bp, they are held together by metalic bonding/covalent bonds. elemental forms with lower mp and bp are made of either discreate atoms or small molecules with LDF's between them |
| what are the properties of metals? | shiny, conduct electricity and heat, malleable and ductile |
| as the number of molecular orbitals increases the energy gap between them ________. | decreases |
| energy can move ________ between molecular orbitals. | freely |
| electrons can move ________ over the whole system. | freely |
| when a metal absorbs a photon what happens? | it immediately releases a photon of the same energy which is why metals shine |
| because atoms can move with respect to one another metals are ________. | malleable and ductile |
| because electrons can move around freely metals _______. | conduct electricity |
| when melting or boiling something are you absorbing or releasing energy? | absorbing because you are breaking interactions |
| when breaking an interaction where does that energy come from? | the surroundings |
| when melting or boiling where are the attracting that are being overcome? | between particles |
| the magnitude of the mp and bp provides an estimate of the ________ of the attractive interactions between particles. | strength |
| the temperature of the phase change tells you about the ________ of interaction you are overcoming. | strength |
| covalent bonds are present only when atomic orbitals interact ________. | constructivley |
| LDF's are caused by ________ charge distribution. | fluctuating |
| when carbon melts the particles that are moving are atoms and they are held together by _______. | networks |
| what are the allotropes in carbon? | diamond and graphite |
| properties of diamond: | high mp, hard, brittle, translucent, does not conduct electricity |
| properties of graphite: | high mp, soft, slippery, grey, shiny, conducts electricity |
| diamond and graphite are made only of ________. | carbon atoms |
| we explain why diamond and graphite have different properties through _______. | bonding |
| each carbon atoms forms 4 bonds to 4 identical carbon atoms, we call this geometry a ________. | tetrahedral |
| the C-C-C-C bond angle is ________. | 109 degrees |
| if we wanted to melt diamond it would ________ and become CO2. | oxidize |
| to explain the bonding in carbon we need to use a different model of bonding known as ________. | valence bond theory |
| in the valence bond theory model, we assume that the atomic orbitals ________ to form bonds. | overlap |
| where the atomic orbitals overlap is where you find the ________. | valence electrons |
| details of molecular orbitals: | atomic orbitals combine to form an equal number of molecular orbitals electrons are delocalized |
| details of valence bond: | atomic orbitals overlap to form a bond the greater the overlap the stronger the bond each bond is made up of two electrons electrons are localized in the bond |
| how can carbon form 4 identical bonds in diamond? | it uses 4 hybrid orbitals n atomic orbitals give n hybrid orbitals |
| in normal carbon atom orbitals are ________ apart and they have more than one orbital. | 90 degrees |
| how many atomic orbitals must combine to make 4 hybrid orbitals? | four |
| hybrid orbital for carbon: | sp3 one s orbital and 3 p orbitals |
| what type of bonds exist between metals at room temp? | metallic bonds |
| in diamond atomic orbitals ________ to form bonding orbitals. | hybridize |
| when hybrid orbitals combine there is a large gap between the ________ and the ________ molecular orbitals. | bonding, antibonding |
| sp3 hybrid orbitals are called ________ bonds. | sigma |
| sigma bonds form when atomic orbitals overlap ________. | end-to-end |
| both diamond and graphite are ________ carbon, the differences in properties are due to the differences in ________. | pure, bonding |
| in graphite in one sheet how many carbon atoms is each carbon atom attached to? | three |
| in graphite how many orbitals should hybridize to form 3 bonds? | three |
| bonding in graphite is one _________ and two ________. | s orbital, p orbitals |
| the bonding in graphite makes a geometry called ________. | trigonal planar |
| a C-C-C bond is ________ degrees. | 120 |
| when the sp2 hybrid orbitals combine they form ________ bonding molecular orbitals. | sigma |
| is a sp2 bond there is a ________ left over. | p orbital |
| the left-over p orbitals (one on each carbon) combine side to side to form a large number of molecular orbitals also known as a ________. | pi bond |
| side to side overlap of atomic orbitals gives you a ________. | pi bond |
| in graphite the unhybridized p-orbitals overlap side to side to form ________. | pi bonds |
| what types of interactions exist between sheets? | LDF's |
| bonds are ________ from each other. | equidistant |
| when drawing a Lewis structure with cations n+ ________ n electrons. | remove |
| when drawing a Lewis structure with anions with n- ________ n electrons. | add |
| rules for drawing Lewis structures: | 1. count valence electrons (use group number) 2. skeleton structure - use number of bonds |
| how many bonds does column 7A form? | 1 |
| how many bonds does column 6A form? | 2 |
| how many bonds does column 5A form? | 3 |
| how many bonds does column 4A form? | 4 |
| how many bonds does column 3A form? | 3 |
| how many bonds does column 1A form? | 1 |
| what is the information missing from a Lewis structure? | the shape of the molecule |
| structural ________ have the same formula, but different connectivity. (Therefore, different properties) | isomers |
| how are isomers the same? | number of each type of atom chemical formula |
| how are isomers different? | connectivity between atoms properties |
| what best describes CH4 and C2H6? | molecules |
| atoms and molecules are considered ________. | discreate you can see exactly how many atoms they have |
| what happens when a molecular substance boils? | forces BETWEEN molecules are overcome |
| the stick structure shows bonds ________ atoms. | between |
| single bonds allow ________ rotation. | free |
| single bonds are ________. | sigma bonds |
| the generic formula applies if there are no ________ bonds. | double/triple |
| what is the generic formula? | CnH2n+2 |
| true or false: you can't rotate around double bonds because it would break the pi bond. | true |
| alkenes contain ________ double bond. | C-C |
| what hybridized orbitals are used to form a double bond? | sp2 |
| double bonds contain: | one sigma bond and one pi bond |
| use valence bond theory to explain why rotation is possible around single bonds. | sigma bonds formed when atomic/hybrid orbitals overlap directly between two nuclei (end-to-end) when bond rotates the overlap stays the same, so the bond is not broken. |
| use valence bond theory to explain why rotation is not possible around double bonds. | double bonds contain one sigma and one pi bond. pi bonds formed from side-to-side overlap of parallel p-orbitals and result in overlap occurring above and below plane of nuclei. if it were to rotate it would break the pi bond therefore break entire bond |
| triple bonds form ________ hybridized orbitals. | sp |
| triple bonds consist of ________ and ________. | one sigma bond, two pi bonds |
| what is the equation for formal charge? | formal charge = valence electrons from free atom - number of bonds to atom in the structure - number of non-bonded electrons on atom in the structure (lone pairs) |
| the valence shell electron pair repulsion helps figure out the ________ of the molecules from the Lewis structure. | shape |
| lone pairs, single bonds, double bonds, triple bonds each count as ________ center. | one |
| 2 electron centers are a _________ geometry with ________ hybridization. | linear, sp |
| three centers make up a ________ geometry with ________ hybridization. | trigonal planar, sp2 |
| four centers make up a ________ geometry with ________ hybridization. | tetrahedral, sp3 |
| five centers make up a ________ geometry with _________ hybridization. | trigonal pyramidal, sp3d |
| six centers make up a ________ geometry with ________ hybridization. | octahedral, sp3d2 |
| every electron center requires a ________. | hybrid orbital |
| electron center geometry is ________ always same as the molecular shape. | NOT |
| to determine the ________ of a molecule, consider only the positions of atom, not lone pairs. | shape |
| ENC: | charge of the nucleus experienced by the valence electrons |
| to calculate the ENC : | to calculate the ENC : |
| an atom that has a high ENC attracts its own ________ strongly. | valence electrons |
| electronegativity: | ability of an element to attract electrons to itself in a bond |
| true or false: noble gases are not electronegative because they don't form bonds. | true |
| electronegativity depends on ________ and ________. | ENC, size of orbitals |
| when two atoms of different electronegativities bond, the electrons are _________. | not shared equally |
| when electrons are not shared equally this results in a ________ we say the bond is ________. | dipole, polar |
| bond dipoles are ________ quantities. | vector |
| what is important in order to tell if a molecule is polar. | the shape of the molecule |
| do molecules interact with other molecules? | yes |
| melting and boiling points ca tell us about how ________ the atoms or molecules are interacting. | strongly |
| what is the strength order for IMF's? | LDF's < dipole-dipole < H-bonding |
| what is the bond angle for tetrahedral? | 109 degrees |
| what is the bond angle for linear? | 180 degrees |
| what is the bond angle for trigonal planar? | 120 degrees |
| dipole-dipole interactions are present in ________ substances. | polar |
| what effect would increasing molecular polarity have on strength of the IMF? | it would increase |
| what effect would increasing the molecular polarity have on melting point and boiling point of substances? | it increases |
| polar molecules have ________ intermolecular interactions than similarly sized non-polar molecules. | stronger |
| hydrogen bonding interactions are ________. | IMF's |
| true or false: hydrogen bonding is present in almost all molecules. | false it is present between two specific types of molecules |
| H-bond must contain H covalently bonded to either ________. | N, O, or F |
| in H-bond the H atom has a large ________. | positive dipole |
| the N, O, or F must contain a _______ and this atom has a large ________. | lone pair, negative dipole |
| compounds with H-bonding also have ________ and ________. | dipole-dipole, LDF's |
| H-bonding is a ________. | interaction NOT a bond |
| LDF's: | temporary interactions between an instantaneous dipole and the subsequently induced dipole. |
| when drawing LDF's make sure you label the ________. | dipoles |
| ________ should be indicated on both electron clouds using partial positives and partial negatives. | temporary dipoles |
| dipole-dipole interactions: | an interaction between molecular dipoles of two molecules |
| hydrogen-bonding interactions: | directed interaction between a lone pair on a very electronegative atom. molecule (O, N, or F) is covalently bonded to a hydrogen. |
| molecules with the highest bp have the ________ to overcome. which take the most ________ to overcome. | strongest interaction, energy |
| where does the energy come from when breaking an interaction? | other molecules and atoms in the surroundings transferred when molecules collide |
| bent shape: | contains three molecules where one has a lone pair |
| trigonal planar: | contains four molecules with 3 bonds around the central atom and no lone pairs |
| if a molecule has no lone pairs around the central atom, then the ________ is the same as the geometry. | shape |
| trigonal pyramidial: | contains four molecules with three bonds and a lone pair around the central atom |
| linear: | contains three atoms which two bonds around the central atom and no lone pairs |
| IMFs can't be the same ________. | strength |
| H-bonds are limited by the number of ________ to ________ ratio. | hydrogen, lone pair |
| you can tell which H-bond would take more energy to separate based on what information? | which one has more hydrogen bonds in it |
| what is the strongest type of IMF present in liquid He? | LDF's |
| what is the strongest type of IMF present in liquid H2? | LDF's it is nonpolar and covalent bonds are NOT LDF's |
| what is the strongest type of IMF present in liquid CH4? | LDF's it is nonpolar |
| what is the strongest type of IMF present in liquid NH3? | H-bonding it also has LDF's and dipole-dipole interactions |
| what is the strongest type of IMF present in liquid H2O? | H-bonding |
| what is the strongest type of IMF present in liquid CO2? | LDF's nonpolar |
| what is the best explanation for why metals are ductile? | metallic bonds involve delocalized electrons whereas covalent bonds involve localized electrons |
| unlike diamond graphite can conduct electricity because? | in graphite there are unhybridized p-orbitals that extend over the entire sheet forming a delocalized pi bonding network where electrons are free to move |
| what types of bonding would be present in a molecule with a high mp that does not conduct electricity? | there is covalent bonding within the molecules and LDF's between the molecules |
| which would have a higher mp and why? Cl2 or Ar | Cl2 when this substance boils LDF's are overcome and the strength of LDF's depends on the size of the electron cloud |
| how do you tell if a structure is the same or an isomer? | if they have the same formula and same connectivity you can tell if it is an isomer if it has a double bond and is rotated because double bonds can't rotate |
| dipole-dipole interactions are stronger than LDF's due to the presence of ________. | permanent dipoles |
| when a bond is polar the bond dipoles add together to create a _________. | molecular dipole |
| when one element is more electronegative than another the bonding electrons are closer to the ________. | nucleus |
| what do the components of the bonding in diamond represent? | the circles represent carbon atoms, and the lines represent covalent bonds each atom uses sp3 hybrid orbitals to form covalent bonds to four other carbon atoms, the bond angle is about 109 degrees |
| how does the model of bonding in diamond represent that it does not conduct electricity? | uses idea that electrons are localized between the two nuclei that participate in the bond, they aren't mobile |
| to conduct electricity molecules must: | charged particles must be able to move freely in molecular orbitals |
| how does the model of bonding in diamond represent that it has a very high mp? | to melt diamond & allow particles to move relative to one another the strong C-C covalent bonds must break |
| how is the model of bonding in diamond different from that in metals? | bonding in metals is represented by a positive charged neutral atom surrounded in a "sea" of electrons that are delocalized |
| when atoms form new compounds, the properties are _________. | emergent |
| properties of materials depend upon the types of bonds, spatial arrangement of atoms, and the _________ molecules. | interactions between |
| atoms interact _________ – interactions range from IMFs to bonding to ion-ion interactions. | electrostatically |
| the way atoms interact depends on the ________. | arrangement of electrons |
| when atoms interact, the system becomes more ________ and releases energy into the ________. | stable, surroundings |
| all attractive interactions require ________ to overcome. | energy |
| properties (such as mp and bp) allow us to make predictions about types of ________ that are present. | interactions |
| what is the difference between properties of atoms and larger macroscopic materials? | the key difference is due to the ratio between the two and the surface area, IMFs are important for microscopic materials |
| what determines whether a bond or interaction is stable? | it depends on the temperature and the strength of the interaction |
| how does temperature fluctuate the stability of bonds and interactions? | raising the temperature causes bonds to become unstable until the point that they break |
| describe the bonding in metals. | metals have a metallic bond where it is a neutral positive charged nucleus surrounded in a sea of electrons |
| why are metals malleable, ductile, and conductors? | malleable and ductile: the bonding is the same in all directions so the electrons can move around easily without breaking the bonds conductors: they have free moving electrons, so the free moving electrons allow electricity to pass through them |
| compare and contrast the molecular orbital bond and the valence bond model. | MO: describes the molecular orbital formation VB: describes the atomic orbitals and the hybridization |
| bonding in diamond: | sp3, tetrahedral |
| bonding in graphite: | sheets, sp2, trigonal planar |
| when 2 atoms interact with: 1s2 2s2 2p4, how many molecular orbitals are generated? | 10 you have one 1s orbital plus one 2s orbital plus THREE 2p orbitals (don't forget there are three 2p orbitals) so that's 5 and you have 2 atoms so 5 time 2 is 10 |
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mccurdyo
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