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.
How do you determine a nonpolar covalent bond through electronegativities?
A nonpolar covalent bond would have two of the same element or two elements with a difference in electronegativities being .4 or less.
Ex: H-H
Percent Abundance
Relative abundance as a percent
What are ionic compounds made up of? Covalent compounds?
A metal and nonmetal when they lose or gain electrons to form ions; Two nonmetals
When doing any math equations or anything what should you remember?
Significant figures/ SIG FIGS
What is the charge for this column/ element on the periodic table?
- Column 1
- Column 2
- Column 15
- Column 16
- Column 17
- Al, Ga, In
- Zn, Cd
- Ag
- 1+
- 2+
- 3-
- 2-
- 1-
- 3+
- 2+
- 1+
What type of elements typically have things in common?
Elements in the same column tend to have similar properties
If an ion is Ca^2+ how many electrons does it have and how do you write an electron configuration for it? What if it’s O ^ 2-?
When it says plus _____ you are really subtracting and now calcium has 18 electrons so write the configuration like you are writing it for Argon.
When it says minus ______ you are really adding electrons so oxygen now has 10 so write the configuration like you are writing it for neon.
WHEN WRITING CONFIGURATIONS FOR IONS REMOVE THE ELECTRONS FROM THE HIGHEST ORBITAL FIRST.
ex: Fe2+ is 1s2 2s2 2p6 3s2 3p6 3d6 instead of 1s2 2s2 2p6 3s2 3p6 4s2 3d4 because you remove the higher orbital first(4s2).
What is the most electronegative element and why?
F; fluorine because it has a small radius and only 2 energy levels so a small amount of electrons shielding from the 1s electrons so the nuclear charge is high. So there is a really strong pull.
A sample of sodium bromide, NaBr, has a mass percentage of sodium of 22.34%.
a) If the sample of sodium bromide were contaminated with sodium chloride, NaCl, would the mass
percentage of Na in the sample be higher or lower than the pure sample? Justify your claim.
b) If the sample of sodium bromide were contaminated with sodium iodide, NaI, would the mass
percentage of Na in the sample be higher or lower than the pure sample? Justify your claim.
a) Higher because if you find the mass percentage of Na in NaCl ( Na mass/ NaCl mass) it is a higher percentage than 22.34%
b) Lower because NaI mass percentage of Na is 15.34%
Noble gas electron configuration
Put the noble gas preceding your element in brackets with the element number- numbers after noble gas as the superscript and finish the configuration after the gas. If you are writing the configuration for a noble gas then you have to put the noble gas before that one in brackets.
ex: Calcium noble gas configuration: [Ar] ^18 4s^2
What does a high binding/ionization energy mean?
That those electrons have a greater coulombic attraction to the nucleus because they are harder to remove because they are closer to the nucleus.
How do you determine a polar covalent bond through electronegativities?
A polar covalent bond would have a difference in values and the electrons are shared unequally. The atom that is more electronegative will obtain a partial negative charge and the one that is less electronegative will obtain a partial positive.
Ex: H-Br
Which electrons would be hardest to remove?
The electrons closest to the nucleus/ lowest energy orbitals
What should you always do before solving a PES question?
ALWAYS READ THE X AXIS. The 1s2 peak will be on the side with the higher binding energy.
If a question says “Which element would release more energy when it gains an electron?” what are you looking for?
You are looking for an element with a higher nuclear charge or just a smaller element because these atoms hold on to their electrons tighter therefore would release more energy when gaining an electron
Mass Percentage/ Percent Composition Formula
Mass of Substance or Element / Total Mass of Mixture times 100
Second ionization energy
Energy to remove a second electronfrom the atom and so on for each electron
How do you write electron configurations with d and f blocks included?
The d block is the transition metals. It starts with 3d and goes down. Include d and f blocks in the same order as you do for all the other ones.
The f block is the elements on the very bottom of the periodic table. It starts with 4f and the one under it is 5f.
D AND F BLOCK WILL NEVER BE VALENCE ELECTRONS
Why are valence electrons easy to remove?
They experience less of the nuclear pull(pull from the nucleus) because the core electrons block the nucleus attraction from the valence electrons
What does a high relative abundance mean for an isotope?
The isotope with the highest relative abundance is going to be the average atomic mass and the most naturally occuring isotope
How can you tell that a hydrate reaction has been heated a sufficient number of times?
The mass will become constant which ensures all water has been removed from the sample
What are outer electrons called in an atom?
Valence electrons/ Bonding electrons
How do you determine the number of atoms in a mole?
It is Avogadro’s number. This is on the equation sheet.
Why are noble gases known as being unreactive?
They have filled valence shells
Where are nonmetals on the periodic table? Metals?
Nonmetals: columns 14-18
Metals: everything else
A different student heats a hydrate in an uncovered crucible, and some of the solid spatters out of the crucible. This spattering will have what effect on the calculated mass of the water lost by the hydrate? Justify your answer.
The calculated mass (or moles) of water lost by the hydrate will be too large because the mass of the solid that was lost will be assumed to be water when it actually included some MgCl2 as well.
Periodic trend for electronegativity
- Electronegativity decreases as you move down a column because there is a greater distance from the nucleus and less of a pull
- Electronegativity increases as you move across a period because nuclear charge is increasing and the nucleus’ pull is stronger.
A student is given two samples, each a mixture of only NaCl and KCl but in different proportions. Which of the following pieces of information could be used to determine which mixture has the higher proportion of KCl ?
- The volume of each mixture
- The mass of Cl in each mixture
- The number of isotopes of Na and K
- The reaction of each mixture with water
- The mass of Cl in each mixture
because based on the average atomic masses of the elements, the mass proportion of Cl in KCl is less than it is in NaCl. The mixture that has the higher proportion of KCl will have the smaller mass of Cl.
.
Molecular formula
Actual formula of a substance
Consider the two chemical species S and S2-.
- Explain why the radius of the S2− ion is larger than the radius of the S atom.
- Which of the two species would be attracted into a magnetic field? Explain.
- The S2- ion is larger because it is gaining more electrons which causes electron-electron repulsion causing the electron cloud and the atomic radius to expand.
- S would be attracted into a magnetic field because it has unpaired electrons in its 3p orbital whereas S2- has no unpaired electrons and is not attracted to a magnetic field.
Devise a method to separate a mixture of sand, salt and iron filings.
You could use a magnet to get the iron filings. You could get water to dissolve the salt and then you would be left with sand to filter out. Also, you could evaporate the water to get the salt.
How do you write an excited state electron configuration?
- Identify the ground-state electron configuration for the element.
- Change one or more electrons to higher energy orbitals( ex: change the 2p superscript to 5 and add in a 3p) following the normal rules for filling orbitals. Meaning that you can’t have stuff that doesn’t exist(ex: 2p^7).
- Ensure the total number of electrons remains the SAME, but reflect the excited state by showing electrons in orbitals of higher energy than in the ground state.
Two different ionic compounds each contain only copper and chlorine. Both compounds are powders, one white and one brown. An elemental analysis is performed on each powder. Which of the following questions about the compounds is most likely to be answered by the results of the analysis?
- What is the density of each pure compound?
- What is the formula unit of each compound?
- What is the chemical reactivity of each compound?
- Which of the two compounds is more soluble in water?
- What is the formula unit of each compound?
because from the elemental analysis, the moles of copper and chlorine can be calculated, then the mole ratio of copper to chlorine can be calculated. This ratio is the formula unit of the ionic compound.
Electronegativity
How tight an atom’s nucleus holds on to its electrons. High electronegativities are going to be small atoms.
Periodic trend for Ionization energy
- Ionization energy decreases as you move down a group bc electrons are further away from the nucleus and have a lower Coulombic attraction
- Ionization energy increases as you move across a period. As you move across there are more protons and a smaller radius due to nuclear charge. Higher nuclear charge equals higher ionization energy.
Why does a greater nuclear charge make electrons harder to remove?
Nuclear charge is the total positive charge of the protons in an atom’s nucleus. Each proton has a positive charge, so the more protons there are, the stronger the nucleus’s positive charge. The stronger nucleus holds the electrons closer, which means it takes more energy to remove those electrons.
More protons = stronger nucleus = harder to remove electrons!
Coulomb’s Law
There is a greater force of attraction between electrons and the nucleus with small atoms that hace large charges.
If you know the mass and identity of a sample, what other information do you need in order to find the number of each atom in the sample?
The molar mass of the element and Avogadro’s number
How do you determine number of ____ in an isotope when all you have access to is a mass spectrum?
- Protons
- Neutrons
- Mass
- Relative Abundance
- Element number on periodic table
- Mass of isotope- protons
- Available on x-axis of spectrum
- Available above bars on graph
If I had a photoelectron spectroscopy of nitrogen and one for oxygen, explain why there is a difference in energy for the 2s peaks.
This is due to the increased nuclear charge of oxygen. Oxygen has 8 protons, while nitrogen has 7. That means oxygen’s nucleus has a stronger positive charge. This stronger pull attracts the negatively charged electrons more tightly toward the nucleus. The 2s electrons are relatively close to the nucleus, so they feel this stronger pull directly. In oxygen, the stronger nuclear charge holds the 2s electrons closer, which means it takes more energy to remove those electrons. That’s why the 2s peak in oxygen’s photoelectron spectroscopy appears at a higher energy than nitrogen’s.
How do you determine the formula of a hydrated compound?
Do moles of water divided by moles of sample to get the number that goes in front of the water. The formula otherwise is (sample) times nH2O. N will be your factor- make sure to round to the nearest whole number.
What charge do ____ have?
- Protons
- Neutrons
- Electrons
- Nucleus of atom
- Positive
- Neutral( zero)
- Negative
- Positive bc inside the nucleus are protons and neutrons only
What are ways to test if something is ionic or not?
- You could test the melting/boiling points and if they are quite high then they are ionic.
- If the solution conducts electricity then it is ionic.
What is the equation for wavelength that is not on the equation sheet?
E= hc/ wavelength
How do you determine which bond has a greater bond dipole?
This just means the bond with the bigger difference in electronegativity.
Properties of Ionic Substances
- High melting and boiling points bc ionic bonds must be broken to melt the sollid and this requires high temps bc the particles need enough kinetic energy
- Hard
- Conducts electricity when melted- The ions are fixed in place so they need to be melted and free to move.
- Soluble in polar solvents and insoluble in non-polar solvents
When does metallic bonding occur?
Between metal atoms; one type of metal, pure substance, alloy
Why do metallic attractions occur? What will get you the strongest attraction?
This is due to metallic cations being attracted to a delocalized sea of valence electrons.
Smaller metallic cations and more valence electrons
Properties of Metallic Substances
- Shiny
- Conducts heat and electricity
- Loses electrons to form cations
- Low electronegativities
Properties of nonmetals
- Poor conductors
- Form anions by gaining electrons
- High electronegativities
Periodic Trend for nonmetallic character
Increases going across the period
Decreases going down the group
Periodic Trend for metallic character
Decreases going across the period
Increases going down the group
If something says to write it in “increasing polarity or __________” what does that mean?
Write it from smallest to largest
Bond length; What type of element will have a longer bond length?
The separation between atoms at which the potential energy is the lowest. Larger atomic radii increases bond length.
The more bonds you have the _______er they are and _____er bond energies they have.
short, large
Bond order
Single, double, or triple bond
Why does increasing bond order increase bond energy?
If you have a triple bond(for example) there are more electrons involved and greater coulombic attraction so it is harder to break the bond. Also the bond length is shorter.
Lattice energy; What gives you a higher lattice energy?
Energy required to separate ions in ionic compounds
Larger charges and smaller radii because more attraction and harder to separate ions
How do you graph a potential energy graph?
Use ex: If the graph has C (double bond) C, how would you graph C-C and C(triple bond C)?
C-C has a longer bond length and weaker bond energy than the double bond. So, make it to the right of the double bond because the x-axis is bond length. Also, make it drop less than the double bond because it has less energy.
C(triple bond) C has shorter bond length and stronger bond energy than the double bond. So, make it to the left of the double bond and the lowest drop.
How do you determine stronger bond energy just by looking at periodic table?
The farther away they are, the weaker they are. Also, the smaller the atoms the more overlap you can have.
What will the structure of an ionic solid be?
It will be in an array that MAXIMIZES the attractive forces among cations and anions while MINIMIZING the repulsive forces
- Opposite charged ions adjacent to one another
How do you determine the stronger ionic bond?
The higher the charges and the smaller the radius. Also, this goes along with melting points. The ionic bond with higher charge and smaller radius will have a higher melting point.
Interstitial Alloys
Where you have atoms of different radii; The smaller atoms fill the small spaces between the larger atoms
Substitional Alloys
Where you have atoms of similar radii; One atom substitutes for the other in the lattice
What does a delocalized sea of valence electrons mean?
It means the electrons do not have to stay with just one atom but they are able to move throughout the entire substance
In a Lewis diagram, which elements may have an expanded octet? Which ones are allowed to have less than an octet?
Any nonmetal in periods 3 or greater as a central atom only
H, Be, and B
How to draw a lewis diagram?
- Create a skeleton structure where you make sure everything has an octet. The atom in the middle tends to be the most electronegative.
- Add double and triple bonds if needed after counting the amount of electrons
What is different for a lewis diagram for an ion?
It will be in brackets with its charge written on the outside
Formal Charge Equation
valence electrons of element - (# lone pairs + # bonds connected(amount of lines))
TO CHECK YOUR CALCULATION, THE FORMAL CHARGE FOR A MOLECULE SHOULD BE ZERO AND FOR POLYATOMIC IONS, IT SHOULD EQUAL THE CHARGE
Purpose of formal charge
Helps you determine which structure is most valid. The most valid structure will have formal charge as close to zero for all atoms. Negative formal charges will be placed on the most electronegative atom
Resonance structures- how to draw them? How to determine bond length?
Draw all structures possible and draw arrows in between. To determine bond length, do bond lines/ bonding domains.
Which one has more electron-electron repulsion: bonds or lone pairs?
Lone pairs and they tend to compress the angle between bonding atoms
What is the molecular geometry for:
2 bonds, no lone pairs
3 bonds no lone pairs
3 bonds and 1 lone pair
4 bonds and no lone pairs
3 bonds and 1 lone pair
2 bonds and 2 lone pairs
5 bonds and 0 linear pairs
2 bonds and 3 linear pairs
6 bonds and no lone pairs
- Linear
- Trigonal Planar
- Bent
- Tetrahedral
- Trigonal Pyramidal
- Bent
- Trigonal Bipyramidal
- Linear
- Octahedral
When to use sp, sp^2, sp^3?
Sp is for 2 bonds
Sp2 is for 3 bonds
Sp3 is for 4 bonds
Single bond also known as
- strength
Sigma bonds
- really strong
Double and triple bonds also known as
Double- one sigma and 1 pi
Triple- one sigma and 2 pi
Pi bonds
pull the atoms closer together
