Term
| Ratio of Masses in a Pure Sample |
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Definition
- All elements and molecules are made up of atoms
- Substances with the same atomic makeup will have same average masses
- The ratio of masses of the same substance is independent of size of the substance
- Molecules with the same atomic makeup (ex: H2O) will have the same ratio of average atomic masses H2O2 ratio would be different than H2O due to the different chemical makeup
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Term
Question:
A 4.5 gram sample of which of the following would have the greatest mass percent of oxygen?
Li2O (molar mass = 30 g/mol)
MgO (molar mass = 40 g/mol)
SrO (molar mass = 104 g/mol)
Na2O (molar mass = 62 g/mol) |
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Definition
Answer:
A. 16/30 x 100 = 53%
B. 16/40 x 100 = 40%
C. 16/104 x 100 = 15%
D. 16/62 x 100 = 26 % |
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Term
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Definition
Impurities in a substance can change the percent
composition by mass
If more of a certain element is added from an impurity,
then the percent mass of that element will increase andvice versa
When heating a hydrate, the substance is heated
several times to ensure the water is driven off
Then you are simply left with the pure substance and
no excess water
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Term
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Definition
Percent mass can be used to determine the composition of a substance
% mass can also be used to find the empirical formula
The empirical formula is the simplest formula of a substance
It is a ratio between the moles of each element in the substance
Quick steps to solve!
- % to mass
- mass to moles
- divide by the smallest and multiply ‘til whole!)
The molecular formula is the actual formula of a substance
It is a whole number multiple of the empirical formula |
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Term
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Definition
How many moles of carbon are in 88 grams of propand, C3H8?
Molar mass = 44g/mol
2moles of propane in 88g
3 moles of C in 1 mole of propane
2*3 = 6 moles of C |
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Term
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Definition
1stIonization Energy (IE) indicates the strength of the coulombic attraction of
the outermost, easiest to remove, electron to the nucleus:
X(g) + IE X+(g) + e–
1st IE generally increases across a period and decreases down a group
- IE generally increases as #protons increases in same energy level
- IE decreases as e– in higher energy level: increased shielding, e– farther from nucleus
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Term
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Definition
2nd & subsequent IE’s increase as coulombic attraction of remaining e–’s to nucleus increases
X+ + IE X2++ e–
X2++ IE X3++ e–
Large jump in IE when removing less-shielded core electrons |
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Term
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Definition
1st Ionization Energy Energy (IE) decreases from Be to B and Mg to Al
Electron in 2p or 3p shielded by 2s2 or 3s2 electrons, decreasing coulombic attraction despite additional proton in nucleus.
Same effect seen in 3d10-4p, 4d10-5p and 5d10-6p
1st Ionization Energy decreases from N to O and P to S
np4 contains first paired p electrons, e–-e– repulsion decreases coulombic attraction despite additional proton |
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Term
| Chemical Reactivity Using Periodic Trends |
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Definition
Nonmetals have higher electronegativities than metals --> causes the formation of ionic solids
Compounds formed between nonmetals are molecular
Usually gases, liquids, or volatile solids at room temperature
Elements in the 3rd period and below can accommodate a larger number of bonds
The first element in a group (upper most element of a group) forms pi bonds more easily (most significant in 2nd row, non-metals)
Accounts for stronger bonds in molecules containing these elements
Major factor in determining the structures of compounds formed from these elements
Elements in periods 3-6 tend to form only single bonds
Reactivity tends to increase as you go down a group for metals and up a group for non-metals. |
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Term
Question:
Of the elements below, _____ reacts the most violently with water.
A. Na
B. Ba
C. Ca
D. Cs
E. Mg |
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Definition
| Cesium--largest atomic radius, 1 v.e. most loosely held (weak coulombic attraction) |
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Term
Question:
Which of the following groups from the periodic table would be the easiest to oxidize?
A. Halogens
B. Transition Metals
C. Alkali Metals
D. Alkaline Earth Metals |
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Definition
Answer:
Alkali metals--oxidation involves the loss of electrons, so the group of elements that has the lowest ionization energy would be the easiest to oxidize.
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Term
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Definition
Group 1 metals more reactive than group 2 metals
Reactivity increases as you go down a group
Metals on left form basic oxides
Ex. Na2O + H2O → 2 NaOH
Nonmetals on right form form acidic oxides
Ex. SO3 + H2O → H2SO4
Elements in the middle, like Al, Ga, etc can behave amphoterically
If SiO2 can be a ceramic then SnO2 may be as well since both in the same group |
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Term
[image]
Classic Shell Model vs. Quantum |
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Definition
Developed by Schrodinger and the position of an electron is now
represented by a wave equation
Most probable place of finding an electron is called an ORBITAL (90% probability)
Each orbital can only hold 2 electrons with opposing spins (S, P, D & F orbitals)
Evidence for this theory:
Work of DeBroglie and Planck that electron had wavelike characteristics
Heisenberg Uncertainty Principle - impossible to predict exact location of electron- contradicted Bohr
This new evidence caused the Shell Theory to be replaced by the Quantum Mechanical Model of the atom |
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Term
[image]
Shell Model consistent with IE data |
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Definition
The patterns shown by the IE graph can be explained by Coulomb’s law
As atomic number increases, would expect the ionization energy to constantly increase
Graph shows that this is NOT observed. WHY NOT?
The data implies that a shell becomes full at the end of each period
Therefore the next electron added must be in a new shell farther away from the nucleus.
This is supported by the fact that the ionization energy drops despite the addition positive charge in the nucleus |
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Term
Using Spectroscopy
to measure properties associated with
vibrational or electronic motions of molecules
[image] |
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Definition
IR Radiation - detects different types of bonds by analyzing molecular vibrations
UV or X-Ray Radiation
Photoelectron Spectroscopy(PES) Causes electron transitions
Transitions provides info on electron configurations |
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Term
Beer's Law-used to measure the concentration of colored solutions
[image] |
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Definition
A = abc
A = absorbance
a = molar absorptivity (constant for material being tested)
b = path length (cuvette = 1 cm)
c = concentration
(Taken at fixed wavelength) |
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Term
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Definition
Answer:
Based on Beer's Law, for small concentration ranges there is a linear relationship between absorbance and concentration. For an absorbance of 0.4, the corresponding concentration is 0.28M. |
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Term
Stoichiometry
g--> mole: use the periodic table
mole-->mole: use the BALANCED equation
mole--> g: use the periodic table |
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Definition
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Term
Gravimetric Analysis
[image] |
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Definition
Buchner Filtration Apparatus
How much lead (Pb2+) in water?
Pb2+(aq) + 2Cl-(aq) → PbCl2 (s)
By adding excess Cl- to the sample, all of the Pb2+ will precipitate as PbCl2
Solid product is filtered using a Buchner Filter and then dried to remove all water
Mass of PbCl2is then determined
This can be used to calculate the original amount of lead in the water |
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