1.2 Mass Spectroscopy1.2 Mass Spectroscopy
• LT: Explain the quantitative relationship between the mass spectrum of an element and the masses of the element's isotopes.
Isotopes Isotopes are atoms of the same element having different
masses due to varying numbers of neutrons.
Isotope Protons Electrons Neutrons Nucleus
Hydrogen–1
% in nature
isotopes of that element.
number of protons in the nucleus of
each atom of that element.
Element # of protons Atomic # (Z)
Carbon 6 6
Phosphorus 15 15
Gold 79 79
protons and neutrons in the nucleus
of an isotope.
Mass # = p+ + n0
Oxygen - 10
- 33 42
- 31 15
Mass Spectrometry
• Mass spectrometry provides mass to charge ratio and provides us with information to determine the molecular mass of atoms/molecules in a sample.
• High-energy electrons bombard the sample, causing it to ionize
• An electric field separates the ions based on their mass to charge ratio this data is compiled into a mass spectrum
• (it separates isotopes by mass)
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Mass Spectrometry
• The relative size of the peaks indicates the relative number of particles
1.2 Closure
• Mass Spec…
• LT: Explain the quantitative relationship between the elemental composition by mass and the empirical formula of a pure substance.
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Formulas (continued)
Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio).
Molecular:
H2O
1. Base calculation on 100 grams of compound.
2. Determine moles of each element in 100 grams of compound.
3. Divide each value of moles by the smallest of the values.
4. Multiply each number by an integer to obtain all whole numbers.
Empirical Formula Determination

12.01 g C
g H
g O
Empirical Formula Determination (part 2)
Divide each value of moles by the smallest of the values.
Carbon:
Hydrogen:
Oxygen:
Empirical Formula Determination (part 3)
Multiply each number by an integer to obtain all whole numbers.
Carbon: 1.50 Hydrogen: 2.50 Oxygen: 1.00 x 2 x 2 x 2
3 5 2
Empirical formula: C3H5O2
Finding the Molecular Formula The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?
1. Find the formula mass of C3H5O2
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
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Finding the Molecular Formula The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
2. Divide the molecular mass by the mass given by the emipirical formula.
146 2
73
Finding the Molecular Formula The empirical formula for adipic acid is C3H5O2. The molecular mass of adipic acid is 146 g/mol. What is the molecular formula of adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
3. Multiply the empirical formula by this number to get the molecular formula.
(C3H5O2) x 2 = C6H10O4
Percent Composition
PERCENT COMPOSITION BY MASS: Because compounds must have a constant composition, it is possible to find the percent by mass of each element in the compound:
% composition = mass of element
mass of compound ´100%
% Composition example 1
Ammonium is used extensively in the production of fertilizer, where the ammonia is converted in ammonium nitrate. Find the percent nitrogen in ammonium nitrate.
% composition = mass of element
mass of compound ´100%
% composition = mass of element
mass of compound ´100%
• LT: Explain the quantitative relationship between the elemental composition by mass and the composition of substances in a mixture.
• Gravimetric Analysis Lab
– Then, we mixed with water to dissolve all ions.
– Finally, we mixed with another chemical that would create one precipitate that we could filter out and measure.
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1.5 Electron Configuration
• LT: Represent the electron configuration of an element or ions of an element using the Aufbau principle.
Quantum Mechanical Model of the Atom
Mathematical laws can identify the regions outside of the nucleus where electrons are most likely to be found.
These laws are beyond the scope of this class…
Heisenberg Uncertainty Principle
The more certain you are about where the electron is, the less certain you can be about where it is going.
The more certain you are about where the electron is going, the less certain you can be about where it is.
“One cannot simultaneously determine both the position and momentum of an electron.”
Werner Heisenberg
Quantum Numbers
Each electron in an atom has a unique set of 4 quantum numbers which describe it. (**Not Tested!)
Principal quantum number
Electron Energy Level (Shell)
Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. “n” is also known as the Principle Quantum number
Number of electrons that can fit in a shell: 2n2
Orbital shapes are defined as the surface that contains 90% of the total electron probability.
An orbital is a region within an energy level where there is a probability of finding an electron.
Electron Orbitals
The angular momentum quantum number, generally symbolized by l, denotes the orbital (subshell) in which the electron is located.
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The s orbital (l = 0) has a spherical shape centered around the origin of the three axes in space.
s Orbital shape
There are three dumbbell-shaped p orbitals (l = 1) in each energy level above n = 1, each assigned to its own axis (x, y and z) in space.
p orbital shape
Things get a bit more complicated with the five d orbitals (l = 2) that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells”
…and a “dumbell with a donut”!
d orbital shapes Shape of f (l = 3) orbitals
Energy Level (n)
1 s 1 2 2
2 s p
1 3 5 7
2 6 10 14
32
Energy Levels, Sublevels, Electrons Magnetic Quantum Number The magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.
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Electron Spin The Spin Quantum Number describes the behavior (direction of spin) of an electron within a magnetic field.
Possibilities for electron spin:
Two electrons occupying the same orbital must have opposite spins
Wolfgang Pauli
s p
C. Periodic Patterns ATOMIC ORBITALS • Atomic Orbital: region of
space in which there is a high probability of finding an electron.
• Denoted by letters: s, p, d, and f
• Each atomic orbital corresponds to a specific shape at a specific energy level.
s - spherical
p – dumbbell-shaped
s 1 2
p 3 6
d 5 10
f 7 14
Energy level (n) Max number of Electrons
1 2
2 8
3 18
4 32
d
d
f
Sublevels
Electron Configuration The most stable arrangement of electrons in sublevels and orbitals.
A. General Rules
– “Lazy Tenant Rule”
A. General Rules
• Pauli Exclusion Principle
opposite spins.
A. General Rules
• Hund’s Rule
– Within a sublevel, place one e- per orbital before pairing them.
– “Empty Bus Seat Rule”
B. Notation
• Longhand Configuration
• A/B Group # – total # of valence e-
• Valence electrons are electrons in the outermost energy level. Determines the chemical and physical properties of an element.
• Column within sublevel block – # of e- in sublevel
s-block1st Period
C. Periodic Patterns
1.6 Photoelectron Spectroscopy Coulomb's Law
• a law stating that like charges repel and opposite charges attract, with a force proportional to the product of the charges and inversely proportional to the square of the distance between them.
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• Atomic structure
• Electron configurations
• Ionization energy
• Periodic trends
• Photoelectron spectrophotometers use high-energy radiation (UV or X-rays) to eject electrons from an atom
• The photoelectron spectrophotometer inputs only one type of radiation (with a specific energy)
• Because electrons within an atom are in different energy levels, different electrons can require different amounts of energy to eject – Electrons that are closer to the nucleus are HARDER to remove
(More attraction between protons and electrons) – Valence electrons (outer level) are the EASIEST to remove
• The photoelectron spectrophotometer removes electrons from multiple atoms, so electrons from all levels will be observed (& graphed)
What is measured?
• The “input” energy removes the electron from the atom • Any “leftover” energy determines how fast the electrons is
moving when it leaves the atom
• If only a small amount of energy is needed to remove an electron, a lot of energy is “leftover”
• These electrons will be moving fast
• If a lot of amount of energy is needed to remove an electron, not much energy is “leftover”
• These electrons will be moving slow
Reading PES Graphs
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1.7 Periodic Trends
• Justify all of the trends on the periodic table can be simplified using these two generalizations:
1. Use Zeff to justify trends across a period
2. Use increased distance (greater value of n) to justify trends down a group
Zeff
• Energy levels
Atomic Radius
• Refers to the distance between the nucleus and the outer edge of the electron cloud. It is influenced by the nuclear pull an the number of energy levels.
Atomic Radius
• Atomic radii decrease as atomic numbers increase in any given period.
– Greater effective nuclear charge, Zeff, increases the attractive force of the nucleus and therefore pulls the electron cloud closer to the nucleus resulting in smaller atomic radius.
Atomic Radius
• Atomic radii increases as atomic number increases down a column or group
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Ionization Energy
• Refers to the energy needed to remove an electron from a gaseous atom or ion, i.e. an isolated one, not part of a solid, liquid, or a molecule. It is always endothermic.
Ionization Energy • Ionization energy increases as atomic number
increases in any given period.
Ionization Energy
• Ionization energy decreases as atomic number increases down a column or group.
Electron Affinity
• Is NOT the opposite of ionization energy, but involves the addition of an electron to the gaseous atom, which can be exothermic or endothermic.
• Positive electron affinities indicate that the nucleus is not as effective at attracting the electron, and it must be forced into the atom.
Electronegativity
• An assigned property which indicates the attraction of an atom for the pair of outer shell electrons in a covalent bod with another atom. Electronegativity patterns are the same as electron affinity patterns for the same reasons.
• Focus on the attraction that the nucleus has for electrons.
Electronegativity
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Electronegativity
• Decreases as atomic number increases down a column or group.
Ionic Radius
• The distance from the nucleus to the outer edge of the electron cloud in a charged ion.
• The same radii trends apply once you divide the table into the metal and non-metal sections.
• Positive (metals) ionic radii decrease from left to right with only minor changes in the transition metals
• Negative (nonmetal) ionic radii are larger and they will decrease in radii from left to right.
Ionic Radius
Ionic Radius
Reactivity
• Depends on whether the element reacts by losing electrons (metals) or gaining electrons (non-metals).
Reactivity
• Metals are more reactive as you move down a column.
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Reactivity
• Non-metals are more reactive as you move up a column
1.8 Valence Electrons and Ionic Compounds