Final Flashcards
Isoelectric
When two things have the same number of electrons
Isotope
Atoms with the same number of protons and electrons but different numbers of neutrons and mass numbers
Relative abundance
Percentage of each isotope in the sample
How do you determine empirical formula?
- Assume you have 100g of the sample so you can change percents to grams
- Turn each element into moles
- Then, divide every element by the lowest mole value
- If you are within .1 of a whole number round to the NEAREST whole number, if not MULTIPLY by a FACTOR. to get all whole numbers
- Each value you find is a subscript for the element.
The first ionization energy for potassium, K, is 419 kJ/mol and the second ionization energy for calcium,
Ca, is 1145 kJ/mol. Using concepts from this unit explain why they are different even though they are
isoelectric (have the same number of electrons).
K(g) yields K+(g) + e-
Ca+(g) yields Ca2+(g) + e-
Calcium has a higher nuclear charge because it has more protons than potassium. This means that calcium’s electrons are going to be harder to remove because the nucleus’ pull is stronger.
If I had a photoelectron spectroscopy of nitrogen and one for oxygen, explain why there is a difference in energy for the 2p peaks.
The 2p peak for oxygen has a lower energy peak due to the electron – electron repulsions in the 2p orbital. In oxygen, there’s an extra electron in the p orbital compared to nitrogen, which causes the electrons to “push back” on each other more. This makes it easier to take one of them away because it’s not as tightly held by the nucleus. That’s why oxygen’s 2p binding energy is lower than nitrogen’s.
How do you fill in an orbital diagram?
- Start with the lowest energy levels then build up. Every orbital(box) can only have 2 electrons.
- Each sublevel should have one electron before any are doubled up
- Electrons in the same sublevel need to have an opposite spin
How do you determine an ionic bond through electronegativities?
If there is a large difference in values. If the difference is greater than 1.7 the electrons are not being shared but transferred. Also if you have a nonmetal and metal it will be ionic. The electrons are always being transferred from the least electronegative to the most electronegative.
Periodic trend for Ionic Radius
- Similar to atomic radii. Increases moving down a column and decreases moving across a period
- Cations(positive charge) are always smaller than the parent atoms because they have lost their valence shell and they are smaller.
- Anions(negative charge) are always larger than the parent atom because electrons are being added to teh same valence shell.
Average atomic mass formula
Relative abundance (as a decimal/divided by 100) times mass of isotope for each isotope and then add them all up
How do you determine molecular formula if you have empirical formula?
- Find the molar mass of empirical formula
- Do Molar Mass of solution/ Empirical formula mass
- Multiply all subscripts in empirical formula by value
After finding the atomic mass of an element and you are asked what element that is what do you do?
Go to the periodic table and look for the element with the atomic mass closest to that
Avogadro’s number
Conversion factor to convert between number of particles(molecules, atoms, formula units, ions) and moles
Cation? Anion?
Positively charged ion/ Negatively charged ion
Electron-electron repulsion
In an atom, when more electrons are added to the same space (like the 2p orbital), they start crowding each other, making it harder for each one to feel the full pull of the nucleus. This makes it easier to take one of them away because it’s not as tightly held by the nucleus. Also, a result of electron-electron repulsion is an increased atomic radius/ increased electron cloud.
It’s like trying to listen to a teacher when other kids around you are talking—it’s harder to focus on the pull of the nucleus!
Periodic trend for Atomic Radius
- Atomic radius increases as you move down a column because there are more electron shells.
- Atomic radius decreases as you move across a period because the nuclear charge is increasing and the attraction gets stronger and the nucleus pulls its electrons closer.
What are inner electrons called in an atom?
Core electrons
Ionization energy/ Binding energy
Energy required to remove an electron from a subshell
Empirical formula
Simplest ratio of elements in a compound
What is nonmetals ultimate goal? Metals?
They want to gain enough electrons to fill their octet.
Metals want to give away enough electrons to “be a noble gas”.
What should the relative abundance on a mass spectroscopy equal?
100
In the second experiment, a student is given 2.94 g of a mixture containing anhydrous MgCl2 and KNO3 . To determine the percentage by mass of MgCl2 in the mixture, the student uses excess AgNO3(aq) to precipitate the chloride ion as AgCl(s).
Starting with the 2.94 g sample of the mixture dissolved in water, briefly describe the steps necessary to quantitatively determine the mass of the AgCl precipitate.
- Add excess AgNO3 .
- Separate the AgCl precipitate (by filtration).
- Wash the precipitate and dry the precipitate completely.
- Determine the mass of AgCl by difference.
How can you determine an element from a chart of ionization energies?
You will see a large jump between the ionization energy values and after removing that many electrons you will be rid of all of your valence electrons and determine your element. For example, If you have two valence electrons then you are at s^2(just be careful with that part). You determine where your core electrons start and let’s say for example you have 3 valence electrons, your element will be a +3 ion because it can lose 3 electrons easily.There is such a jump because the core electrons are closer to the nucleus and it takes more energy.
Elemental analysis
Elemental analysis can be used to determine the relative numbers of atoms in a substance and to determine its purity.