Final Exam Q and A
Remember----this is a public pad. : )
i have many questions, the first of them being.. can you re explain the born haber cycle? and how to calculate the answer, the videos you posted confuzzle me.
The born haber cycle is a series of steps in the formation of an ionic bond.----between a metal and a nonmetal
First...the metal must be turned into a gas......The energy needed to change the metal from solid to gas is called the heat of sublimation.
Often ionic bonds from between metals and diatomic nonmetals. If the nonmetal is diatomic, the two atoms must be separated. The energy needed to do this is called the bond energy.
After forming atoms of metal and nonmetal, the metal must lose an electron and the nonmetal must gain. Energy required to pull an electron off of the metal is called ionization energy. The energy
released when an electron is added to a nonmetal is called electron affinity.
After the electrons have been lost by the metal and gained by the nonmetal, the two ions attract each other and slam together. The energy released when they slam together is called lattice
energy. Lattice energy is the driving force behind ionic bond formation. It is very exothermic.
The "slamming together" referenced above is most dramatic when the charge is greatest. For example, MgO will have greater lattice energy than NaCl because of the +2 -2 charges in MgO. NaCl
only has =1 -1. In general, the larger the product when the charges are multiplied, the greater the attraction between the ions, and the greater the lattice energy.
If the two different compounds have the same charges as in KF and NaF, the attraction betweeen the ions is based on size. Smaller ions are able to get closer together, so their attractions are
greater.
Lattice energy affects properties of ionic compounds like boiling point and melting point. Higher lattice energy means the ions attract each other more, so their melting and boiling points will be
higher.
When doing calculations, the energies involved in all of these steps are added up to find the overall heat of reaction.
How do you calculate the lattice energies, and how do you know if the boiling points will be high or low?
as well as hybridization, that still confuses me and how the combine and form and such,.
Hybridization is a term we use to describe "blending" of atomic orbitals. For example, If one s orbital blends with three p orbitals to make four orbitals of equal energy, we say that each of the four new orbitals is called an sp3 hybrid orbital. Hybridization boils down to the number of electron domains. If there are 3 domains, the hybridization is sp2. 4 domains, sp3, etc.
This animation explains: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/hybrv18.swf
Mr howe the homwwork you gave this week is confusing February. 1 2016
I dont understand lattice energy and how to calculate it, the videos on your website havent really helped me much SEE ABOVE
I don't understand number 10 on the Final review test. Can someone please explain?
I don't even see that test. Where is it? Is it just the review questions?
Sorry, the Fall Final Review.
are you talking about this question?
10.
What are the names and valence shell electron configurations of groups 1,2,16,17,18?
Group one (Li, Na, K, etc...) alkali metals one valence electron
Group two alkaline earth metals two valence electrons
group 16 chalcogens six valence electrons
group 17 halogens seven valence electrons
group 18 noble gases eight valence electrons.
Ok, thank you!
Mr. Howe, are we going to have a cheat sheet for the Final tomorrow? NO you can use the periodic table, and your geometry chart
okay, so the salmon colored paper was only for the retake? yes. did you see my question above? Is that the number 10 you were talking about?
yes.
Any other questions right now?
Not at this moment, but as our group we will have more
OK. I will check back later..... Remember, the answers to the question that I posed (like number 10 above) are on the same page....
Do you have any videos of you doing an example calculation of lattice energy problem on your website?
no, but here is a problem from the old test.....
Formation of NaCl Na(s) + ½Cl2(g) ----> NaCl(s)
STEPS NAME OF PROCESS ENERGY
_____1 Na(s) --> Na(g) heat of sublimation +108 kJ
_____2 Na(g) --> Na+(g) + 1e- ionization energy +496 kJ
_____3 Cl2(g) --> 2Cl(g) bond energy +243 kJ ( since there is only one Cl in NaCl, cut this number in half....121.5 kJ)
_____4 Cl(g) + 1e- --> Cl-(g) electron affinity -349 kJ
_____5 Na+(g) + Cl-(g) --> NaCl(s) lattice energy ??? kJ
_____6 Na(s) + ½Cl2(g) --> NaCl(s) heat of reaction -411 kJ
To solve for the ???? kJ....
108 + 496 + 121.5 + -349 + x = -411
x = -787.5
why do elecronegativity and ionization energy increase as you move up and to the right?within a series/period, as you add protons, there is more pull on the electron cloud, so it gets smaller. As you move UP a family, each element has one less energy level, so the atoms get smaller. Smaller atoms have more attraction for electrons, so more and electronegativity. Smaller atoms hold their electrons tighter, so higher ionization energy. Note that the noble gases don't have electronegativites due to their full outer shells.
what is a double replacement reaction? A reaction where the cations change partners. for example ...... NaCl + Pb(NO3)2 --> PbCl2 + NaNO3 after the formulas are written, use coefficients to balance..... 2NaCl + Pb(NO3)2 --> PbCl2 + 2NaNO3
also, i wasnt there for the percipitation lab so what was that about? For the precipitation lab you were to write equations for the reactions like the one above.
And how do you find an oxidation state? Oxidation state is charge. The charges add up to equal zero in a compound, or they add up to equal the charge on a polyatomic ion. In NO3- the N is 5, and the oxygen is -2. 5 + -6 = -1, which is the charge on the polyatomic ion. In a compound like BaO, the charge on the Ba is +2, and the oxygen is -2. sum = zeron
On 19 how can you tell what element looses electrons and how many electrons it looses? If sodium reacts withAluminum chloride to make elemental sodium chloride and aluminum, what is oxidized? What is reduced? What is the oxidizing agent? What is the reducing agent? 3Na + AlCl3 -----> 3NaCl + Al Na has zero charge on the left( it hasn't combined with anything) , and +1 on the right.
The Al is +3 on the left and zero on the right. so.. the Na lost one electron per atom and the Al gained three per atom. Na was oxidized and the Al+3 is reduced. the reducing agent is Na, and the oxidizing agent is Al+3
On 23 what do you mean by an "excited" electron? An excited electron is an electron that has gained energy an moved away from the nucleus -- we studied these in the flame lab and the spectroscopy lab. and with the light tube demos.
Can you expain how you got your answer on number 30?(sorry for the overload of questions) Nitrogen (III) oxide nitrogen has a + 3 charge in this case, and oxygen has a -2. So, you need two oxygen atoms to make a +6 total and 3 oxygen atoms to make a -6 total. or you could think.....nitrogen gives three electrons and oxygen takes two. in order to make the loss = the gain, you need two nitrogens to give 6 and three oxygen atoms to take six.
I don't understand the explanation given for number 16. In an ion the charges of the atom = the charge on the ion. In the sulfate ion the overall charge is -2. Oxygen must be -2, and there are four of the them to make a total of -8. So....the S must be +6 in order for the overall charge to equal -2. An equation would look like this. -8 + x = -2
hi, can you explain where you will put a double bond if there are more then one open spots? If there is more than one spot to put it the double bond, it can go in any of the spots. We call this resonance, and the double bond becomes molecular, the electrons are delocalized. I showed a short video on benzene.
thanks!
Thanks mr howe your the best! :)
thanks. : )
Any more questions?
nope
Actually yes i do haha sorry, so could you explain to me why Atoms with 4 or less valence electrons will tend to lose them and move to zero. It has to do with energy, and is a complicated answer. The short answer is that if these things happen, as a result of the electon loss and gain and energy changes during bond formation (bond energy or lattice energy) the product will be at the lowest energy state possible. cool beans, thanks
Atoms with 5 or more valence electrons will tend
to gain more electrons to get to 8.
What does polyatomic ion mean? Those groups of atoms at the bottom of your periodic table are called polyatomic ions. they are groups of atoms that act as if they have a single charge.
from the review for the last test, posted on the homework section of the web site:
1. How to determine if two elements would form an ionic or a covalent bond.
You would use the differences in electronegativity. Values will be provided.
If the difference is small, the attraction for electrons is about the same, so the electrons will be shared. ----- covalent bonding
If the difference is large, the bond will be ionic, electrons will be TRANSFERRED.
Specifically, 0- .2 difference = non-polar covalent
.2 - 1.7 = polar covalent
>1.7 = ionic
Also how can you tell the difference between polar and non-polar? And which way the vector or whatever is going?
So for individual bonds, follow the guidelines above.
If there are multiple bonds, then you consider the "charge vectors." Okay electrons will be pulled toward the more electronegative atom. so for example in a molecule like carbon dioxide that is linear, the electrons are pulled toward the oxygens on each end of the molecule. Since it is linear, the vectors would pull against each other and cancel out. In a molecule such as SO2, there is an unshared pair of electrons around the S. This causes the molecule to bend. Since the molecule is bent, the charge vectors don't cancel out when the electrons pull toward the oxygen, and the molecule is polar.
Where can you find the charge of an atom? Atoms have zero charge until they bond with something else. When they bond with another atom, they lose, gain or share electrons. The number of electrons lost gained or shared is called an oxidation state (or charge if the bond is ionic with transfer of electrons).
so how would shared electrons be a postive or negative charge? If there are shared electrons, usually one atom "possesses" the electrons more that the other. for example, N and O form a covalent bond, but O is more electronegative the N. So, the N is considered to donate to the oxygen and have a positive oxidation state. The oxygen would be negative. Chemists call the resulting positive charge of the N a partial positive charge.
So would N have a 0 charge because it didnt gain or loose electrons? If the N is in a bond it will have an oxidation state, unless it is bonded with another N in a totally nonpolar bond. N2
So does that men polarity effects the oxidation state? If so how does it do that? I wouldn't say that polarity affects oxidation state exactly, except that atoms in a polar bond will have oxidation states. As the bond becomes more polar, eventually the bond becomes ionic and that oxidation state becomes more properly referred to as a charge..
Then what gives N a charge if it neither looses or gain electrons? It has a partial charge. In a bond between two atoms such as N and O the O (more electronegative) will attract the shared electrons more, and is considered to be negative. the N partially gives its electrons to the oxygen and is considered to be positive. Thats super confusing but i think i sorta kinda get it-ish for simplicity sake you can think of the oxidation state as a charge, even though in the case described it is a partial charge. so for a compound such as NO, the N would be +2 and oxygen would be -2 Alright cool
What do you do if it was bonded to itself? Like Ov2 here would be no oxidation state.
I need to let the dog out, and do a couple of things, so I will check back in a minute......
Any other questions? I am thinking of calling it a night.......
nope im all good, thanks for the help You're welcome. good night. : )