Gen Chem 1: Fundamentals Flashcards
in SI units, density is expressed in _______
whereas in chemistry, density is usually expressed as ________
SI units: kg/m3
chemistry: g/cm3
to convert,
multiply g/cm3 by 1000 → kg/m3
divide kg/m3 by 1000 → g/cm3
density of water
1 g/cm3
1000kg/m3
density = ?/?
mass/volume
nano-
10-9
micro-
10<span>-6</span>
milli-
10-3
centi-
10-2
kilo-
103
mega-
106
1L=_______cm3
1000cm3
1 mL = ? cc
1 mL = 1 cc (cubic cm)
cc aka cm3
1 Å = ? m
1 Å = 10-10
what does the formula weight refer to?
the sum of the atomic weights of all the atoms in the molecule
we use the term molecular weight MW when the compound exists as discrete molecules
we use the term formula weight when the compound exists as an ionic compound.
how do you find moles of a substance in a molecule?
moles = mass in grams / MW
MW= total mass of molecule
what does percentage composition by mass (aka percent mass composition) refer to? how is it calculated?
the percentage of the compound’s mass that is made up of a given molecule
- tip: use the empirical formula, which will give you the same answer as molecular formula but is shorter*
e. g. C2H2N
find the percent mass of carbon from ^
given: atomic mass of C is 12 g/mol and molecular weight of ^ is 40
%Composition=mass of element in formula/molar mass x100
%Composition = (2x12)/40 x 100
how many oxygen atoms in 5H2O?
5
the 5 in front denotes that there is 5 of each component
How do you find the empirical formula from the percentage composition by mass?
- assume there is 100g of the substance so that the percentages you are given in the problem can equal that number in grams
- find the moles of the components using moles=mass in grams (assumed to equal the percentage)/ MW.
- divide the ratios found for each component. the resulting ratio is the ratio of the component that the first ratio belong to / component that the second ratio belonged to.
- plug that ratio into your emprical formula
nuclear binding energy
the energy relealsed by the protons and neutrons (called nucleon) when they came together to form a nucleus.
equal to the force required to break the nucleus into its respective nucleons
not all nuclei contain protons and neutrons
the mass of a combined nucleus is less than the sum of the mass of all the nucleons taken individually. why?
because then a nucleus comes together, some mass is converted to energy
the difference is called the mass defect, Δm
Δm
mass defect
the difference between total mass of separate nucleons and mass of nucleus
its mass-energy equivalent (found by Einstein’s formula) is the nuclear binding energy
how can you find the nuclear binding energy, EB from the mass defect?
through Einstein’s equation for mass-energy equivalence: EB=(Δm)c2
c=speed of light
amu
atomic mass unit: weight of an atom
e.g. C is 12 and 1 amu is 1/12 of carbon’s amu (by convention)
divide the _________formula by the greatest common factor to get the _________formula
molecular
empirical
polyatomic ions
ions with more than one atom
e.g. NH4+
T/F : molecular weight is grams per mole
true
What effect does vaccuum distillation have on boiling point?
Lowers Boiling Point
boiling occurs when the Pvapor of the substance in question equals the Patm. Typically, we boil substances by increasing the temperature, thereby increasing Pvap. Alternatively, however, we can lower boiling point by reducing Patm, which can be accomplished through the introduction of a vacuum. Vacuum distillation is often used when components have very high boiling points and would otherwise be difficult to distill.
What’s the difference between Bohr model and Quantum model of electron density?
Bohr: electrons in an atom orbit the nucleus in circular paths where distance from nucleus corresponds to energy of electrons. Only certain orbitals at certain distances are allowed. If an electron absorbs energy that is exactly equal to the difference in energy between it’s current state and that of the next, then it moves up into the next higher energy orbital and visa cersa. The name of the unit of energy released or absorbed is called a photon. Only specific energies (as seen by wavelengths) occur.
Quantum: accounts for the interactions seen in atoms with many electrons. It organizes “quantizes” the electrons by shell, subshell, orbital, and spin (these all fall into the category of “quantum numbers” which help add specificity to the locations of electrons.
what are the components of the quantum model of the atom?
1. Energy Shell
- denotes energy level: high the energy level, higher the energy
- analogous to circular orbits of Bohr model
- denoted by 1n, 2n, 3n
2. Subshell:
- describes the probability of finding an electron within the given subshell.
- composed of more than one orbital of the same energy
- denoted by letters s, p, d, or f
3. Orbital
- each orbital has different orientation in space and the orientation increased by 2 in each successive subshell.
- denoted by 1s, 2s, 3s for S subshell; px, py, pz for p orbitals.
4. Electron Spin
- each electron can be either spin up or spin down
- there can be 2 electrons per orbital, one spin up and one spin down
- when there are 2 electrons, the spin states must be opposed as it is a measure of magnetism
what are the 3 rules for how electons can occupy an orbital?
- Aufbau principle: electrons occupy the lowest energy orbitals available (meaning, that 2 will be filled before S is filled) since the numbers indicate energy levels. It also means that S will be filled before P
- Hund’s Rule: electrons in the same subshell occupy available orbitals singly, before pairing up
- Pauli Exclusion Principle: there can be no more than two electrons in any given orbital.
An s subshell has only one possible orbital orientations. Since only 2 electrons can fill any given orbital, an s subshell can hold no more than __#__ electrons.
1 orbital x 2 electrons = 2 electrons
a d subshell has __#__ possible orbital orientations. a d shell can contain ___#___ electrons
5 (2 more than the p subshell)
10 electrons
an f subshell has ___#__ possible orbital orientations and can have ___#__ total electrons
7 orientations
14 electrons
“diamagnetic” means
an atom has all its electrons spin-paired
A diamagnetic atoms must contain an even number of electrons and ahve all its occupied subshells filled.
T/F diamagnetic atoms are repelled by an externally produced magnetic field
true, because they have no net magnetic field
(all canceled out)
T/F an atom with an odd number of electrons is paramagnetic
true, but not every even numbered atom is diamagnetic because you can have a 2p4 orbital
so it is attracted to externaly produced magentic fields
atoms with the same electron configuration are called
isoelectric
when electrons are removed from an atom its called _________ and they only leave from the _________shell
ionization
valence
T/F: only after all s electrons are lost do d electrons get ionized (ie lost)
True
the d block corresponds to what type of atom?
transition metals (for the most part)
If Ti is 4s23d2 then Ti+ is
4s13d2
because electrons leave in order of highest configuration (n=4) to lowest (n=3)
Chromium has an irregular electron configuration. Why?
because a d subshell can hold a max of 10 electrons, when d5 is reached, it actually becomes more stable. This means that what would be a configuration of [Ar] 4s23d4 is actually [Ar] 4s13d4.
essentially an “s” electron is promoted to d orbital
T/F: atoms in an excited state have additional electrons
FALSE. They have absorbed energy but not addition of electrons.
what pattern is associated with each family/group/column of the periodic table
valence electrons: each element in that group have the same number of valence electrons
halogens are powerful _________ing agents
oxidizing because they share electrons, which results in gain of electrons for the oxidized molecule
Zeff stands for _____
effective nuclear charge: the amount of force felt by the electron after shielding effect is accounted for
Zeff = Z - core electrons
core electrons = Atomic number (Z) - # valence electrons
(represented by group (column number)
https://www.youtube.com/watch?v=hwM4mCj8Oh8
T/F: gravitational forces between electrons and nucleons of an atom are negligible
true
what is the periodic trend for atomic radius
- atomic radius decreases as you move from left to right on the table
- increases as you move down a group
because the number of protons is increasing from left to right but new shells are not being made, so the electrons feel a greater effective nuclear charge, which means that the radius is decreasing.
It increases as you go down a group because new shells are added each period, which increases the atomic radii
equation for coulumb’s law as it applies to atomic theory
Fe ∝ (Zeff + C)/r2
Where Fe is effective nuclear force
and Zeff is effective nuclear charge
r = size of valence shell
**r does NOT equal the atomic radius, in fact the atomic radius can get smaller while valence shell remains unchanged
Which is accurate in terms of atomic radius?
- cation radius < neutral atom radius < anion radius
- neutral atom radius < anion radius < cation radius
- anion radius <neutral></neutral>
</neutral>
cation radius < neutral atom radius < anion radius
because as you remove electrons, the radius gets smaller because the electrons are held more tightly to the nucleus
Moving top to bottom within a group core electrons are added at the same rate as protons. What happens to Zeff , C, and r
^the variables in Coulumbs equation
Zeff and C both remain constant
(C, charge, is determined by number of valence electrons, which remains constant as you move down)
r increases because new shells are added, which increases shielding
T/F: Fe increases as you move down a group
True
because Zeff and C remain constant but r increases (refer to Coulumb equation)
Moving left to right across the periodic table, what happens to Zeff , C and r? What happens to Fe ?
Z<strong>eff</strong> increases because protons are added while core electrons remain the same
C valence electrons are added at the same rate as protons, so charge remains zero
r (size of valence shell) is unchanged since there is no change to core electrons and therefore no increase in shielding
This means that according to the equation (Fe=Zeff + C/r2), Fe increases
what happens to the variables in coulumbs law when you move from positive to negative?
T/F: atomic radius increases with increasing electron charge
true
this means that an anion has a greater atomic radius than a neutral molecule or cation
ionization energy increases/decreases with higher Fe
increases
ionization energy is the force required to remove the outermost electron, so the greater the Fe pulling the electron toward the nucleus, the greater the force required to overcome Fe
IE2 represents ?
the energy required to remove the least tightly bound electron from the cation X+
energy required to remove the least tightly bound electron = “ionization energy”
T/F: Elements with a closed subshell/shell have a greater ionization energy
true
How do you solve this problem?
Notice there’s a huge jump in ionization energy between the second and the third ionization energies.
That means it’s much harder to remove a third electron than the second.
So look for the one that will be in noble gas configuration (very stable) after removing 2 electrons.
Answer is Calcium
in groups where the valence shell is filled, the electron affinity (EA) is a ___pos/neg_____ value
positive value
because energy is required to make it happen, which is less favorable
this is because moving it into an electron configuration that is not completely filled is less stable
examples of these groups are alkaline earth metals and noble gases
electron affinity def
energy change that occurs when one electron is added to an atom in gas phase
aka EA
what are the 9 most electronegative atoms in order from most electronegative to least?
FONCLBrISCH
F>O>N~Cl>Br>I>S>C~H
an alpha particle consists of
2 protons and 2 neutrons
when calculating ground state configurations for atoms, you must do what first?
check to see if it’s a transition metal! if it is, then the electrons that are lost first are from the S orbitals not d orbitals
what is the number for the orbital class associated with the first row of d orbitals
3 (not 4, as is the case for the S orbitals)
what determines the energy level of a given subshell compared to the other subshells
the quantum number
meaning, the number associated with each row of subshells
e.g. 4p2 is higher in energy than 3p2
which of the following has the smallest atomic or ionic radius?
- Cl-
- Ar
- K+
- Ca2+
- Ca2+
even though Ca is to the far left on the periodic table, if it’s 2+ then it’s moved 2 spaces to the left which corresponds to the same configuration as a noble gas, making Ca2+ the farthest ion to the right
What are the nuclear numbers and their symbols?
How do you name polyatomic Ions with multiple oxyanions - Most oxidized
prefix = per-
suffix = -ate
Examples: perchlorate (ClO4-)
How do you name polyatomic Ions with multiple oxyanions - second most oxidized
no prefix
suffix = -ate
Examples:
- Bicarbonate (HCO3-)
- Carbonate (CO₃²)
- Sulfate (SO32-)
- Phosphate (PO43-) and biphosphate (HPO₄³⁻ )
- Acetate (CH₃COO-)
- Nitrate (NO3-)
How do you name Polyatomic Ions with multiple Oxyanions - Second least oxidized
no prefix
suffix = -ite
Examples:
- Nitrite (NO2-)
- Sulfite (SO3-2)
How do you name Polyatomic Ions with multiple Oxyanions - Least oxidized
prefix = hypo-
suffix = -ite
Example: hypochlorite (ClO⁻)
Polyatomic Ions w/o multiple oxygens
NH4+
H3O+
CN-
OH-
Oxidation number of Hydrogen
0 when bonded to carbon
+1 when bonded to element more electronegative than carbon
-1 when bonded to less electronegative element than carbont
how to know what’s less electronegative:
FONClBrISCH (most electronegative to least in order) so anything not on this list gives hydrogen a -1 oxidation state
Oxidation number of oxygen
-2 unless bonded to perchloride (in which case it is usually -1)
*other exception: when paired with other more electronegative elements
Oxidation number of Group 1A Elements in Compounds
+1
oxidation number of Group 2A Elements in Compounds
+2
oxidation numbers of halogens
-1
how to determine how much product will be produced in a given reaction equation (ie the theoretical yield)
Consider two electron transitions. In the first case, an electron falls from n=4 to n=2 giving off a photon of light with wavelength of 488nm. In the second transition, an electron moves from n=3 to n=4, for the second transition we would expect that:
- energy is absorbed/emitted pick one
- the wavelength of the corresponding photon release will be longer/shorter pick one than the first transition
energy (a photon) is absorbed
wavelength of the corresponding photon will be longer
explanation: since the electron transitions between energy levels that are closer together, the ΔE between levels is smaller. By the ΔE=hc/λ equation, ΔE and λ are inversely proportional.
descibe the direction of the periodic trend of mettalic character
increases from top to bottom and from right to left (“towards california”)
mnemonic: california is the golden state and gold is a metal
