Chem 003 Midterm

Front 1

Atoms (what they are, and what they're composed of)

Back 1

• Atoms are the minimal expression of matter that can be determined by Chemical methods.
• They are composed of subatomic particles but these are not chemically stable and can be produced only by Physical means.
• Every atom is composed primarily of:
o Protons
o Neutrons
o Electrons

Front 2

Subatomic Particles (name them and enumerate their respective charges/masses)

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• Protons are located in the nucleus, carry one positive charge and unit of atomic mass.
o The number of protons in an atom is called the Atomic number.
• Neutrons are also nuclear but carry no mass and have a mass of roughly one unit.
o The number of protons and neutrons in an atom is referred as the Mass number.
• Electrons form the external layers of the atom, carry one negative charge and almost have no mass.

Front 3

Periodic Table (who created it and how it is arranged)

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• The periodic table was proposed by A. Mendeleiev (1850s) as a compact form to arrange the known atoms according to similarities in their chemical characteristics.
o From Russia, but came to Paris to work at the Academy of Science.
• The atoms are arranged according to their atomic number (number of protons in the nucleus of the atoms) and fall into 18 primary columns (or groups).
• All elements within a group share similar chemical characteristics.
o Example: In Column 1A (which starts with Hydrogen), as you move down the column, the elements become less and less explosive, but all of them still have the capability to explode.
o Example: In Column 1B (which starts with Copper), as you move down the column, the elements become less and less conductive, but all of them still have the capability of conducting electricity.

Front 4

Electrons (describe their arrangement and the associated concept of energy levels)

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• Electrons are arranged in energy levels or shells around the nucleus. Electrons that are closer to the nucleus belong to a lower energy level.
• Energy levels have maximum electron capacities and are more stable when fully occupied.
o The first level (innermost, lowest energy) can hold two electrons (Period 1: H, He).
o The second level can hold up to eight electrons (Period 2: Li, Be, B, C, N, O, F, Ne).
o The number of outer electrons defines the group number.

Front 5

Orbitals (describe them and identify the creator behind the concept)

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• Neils Bohr – designed a version of mathematics for dealing with electrons.
• Orbitals – the shape by which electrons travel around their nuclei.
o 2 electrons in first level (s).
o 6 electrons in second level (p).
o 10 electrons in third level (d).
o 14 electrons in fourth level (f).

Front 6

Molecules (describe them, their arrangement, and the types of them)

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• Molecules are combination of atoms in defined proportions and geometry.
• Molecules can be composed of only one type of atoms (H2) or as many as you can imagine (ClFBrC6H10).
o Monoelemental – one type of element in the molecule.
o Polyelemental – multiple types of elements in the molecule.
• Atomic composition is not the only factor that distinguishes molecules, geometry also counts.
o Isomers – Two molecules with the same formula but different spatial arrangement.

Front 7

Chemical Bonds (describe them and the types of them)

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• In order to form molecules, the atoms need to interact with each other to form a stable chemical bond.
• Types of bonds:
o Covalent – when two atoms share one or more pair of electrons.
• Covalent bonds can be single (one pair of shared electrons), double (two pairs) or triple (three pairs).
o Ionic – long range electrostatic attractions.
• The covalent bond is generally governed by Lewis’ Octet rule.

Front 8

Octet Rule (describe it in detail)

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• Octet Rule – for all atoms except for Hydrogen and Helium, the most stable configuration is the one in which the number of electrons in the most external layer of electrons is eight.
• For Hydrogen and Helium the most stable configuration requires only two electrons.
• The outermost layer of electrons is called the valence layer and has as many electrons as the group in which the element is found in the periodic table.

Front 9

Chemical Reactions (describe them and their processes in detail)

Back 9

• Chemical reactions are the processes by which one chemical compound (molecule) interacts with a second chemical compound to form a new molecule.
• The initial molecules are called the reagents, while the final molecules are called the products.
• Whenever a chemical reaction occurs, certain bonds in the reagents need to broken and new bonds need to form to yield the products.

Front 10

Lavoisier’s Law of Conservation of Mass (describe it and its exceptions)

Back 10

• Lavoisier’s Law of Conservation of Mass – whenever a reaction occurs, certain quantities remain the same.
o Always conserved:
• Number of atoms in reactants = Number of atoms in Identity
• Number of atoms in reactants = Identity of atoms in products
• Total mass of reactants = Total mass of products
o Not necessarily conserved:
• Number of molecules of reactants may or may not equal number of molecules of products
• Volume of reactants may or may not equal volume of products

Front 11

Dry Air (describe its composition)

Back 11

• Nitrogen – 78%
• Oxygen – 21%
• Other gases – 1%

Front 12

Air Pollutants (name them, describe them, and explain why they are prevalent in some cities more than in others)

Back 12

• Carbon Monoxide (CO).
o Combines with permanently with hemoglobin (heme) in the blood.
o Impedes Oxygen transport.
• Ozone (O3).
o A form of Oxygen, produces oxydative damage to lung lining, reducing lung function.
o Ozone becomes a pollutant when it moves from the atmosphere to surface level.
• Nitrogen Oxydes (NO, NO2, N2O3).
• Sulfur Oxydes (SO2, SO3)
o Produced by incomplete fossil combustion.
o Basic components of acid rain.
o Pulmonary irritants, by means of acid production in the surface of pulmonary epithelium.
• Example: petroleum.
• San Francisco has very low amounts of air pollutants because its location on a peninsula and its fogginess allows for pollutants to dissipate.
• Mexico City has very high amounts of air pollutants because its location in a depression traps pollutants inside the city.

Front 13

Risk Assessment (explain the process)

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• Assessing risk is a combination of the evaluation of two factors :
o Exposure to substance/activity
o Toxicity of substance/activity
• The risk is thus indicated as probability of occurring to a particular individual, never a certainty

Front 14

Neuenberg and Helsinki Protocols (describe them)

Back 14

• Neuenberg Protocol – regulates experiments on both human beings and animals.
o Established following WWII.
• Helsinki Protocol – revised version of the protocol.
o Established during the 1950s.

Front 15

Air Quality Index (describe it, what factors determine it, and what it means for us)

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• The Air Quality index is an indicator of how clean or polluted the air is with respect to five major air pollutants:
o Particulate matter, from combustion and industrial processes.
o Carbon monoxide (CO), from incomplete fuel combustion.
• 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
• 2 C8H18 + 17 O2 → 16 CO + 18 H2O
o Sulfur oxides (SOx), from burning of coal
• S + O2 → SO2 (sulfur dioxide)
• 2 SO2 + O2 → 2 SO3 (sulfur trioxide)
• Nitrogen oxides (NOx), side products from internal combustion engines (cars)
o N2 + O2 → 2 NO (nitric oxide)
o 2 NO + O2 → 2 NO2 (nitrogen dioxide)
• Ground-level (tropospheric) ozone, from photochemical smog
o NO2 + sunlight → NO + O (atomic oxygen)
o O2 (molecular oxygen) + O → O3 (ozone)
• Harmful effects of ozone:
o Irritation of the respiratory system
o Reduction of lung function
o Increased sensitivity to lung infections
o Aggravation of chronic conditions (asthma, bronchitis)

Front 16

Isotopes (describe them and how to calculate their atomic mass)

Back 16

• Isotopes are two or more forms of the same element (same number of protons) that differ in the number of neutrons.
o Atomic mass: protons + neutrons
• Atomic number: number of protons
• Number of protons: number of electrons in a neutral atom
• Then for 14C: 6 protons (atomic number), 6 electrons, 8 neutrons (14-6).

Front 17

Double Bonds and Triple Bonds (describe them and provide examples)

Back 17

• Double bond: covalent bond with two pairs of shared electrons.
o Example: O2 (Group 6A)
• Triple bonds: covalent bond with three pairs of shared electrons.
o Example: N2 (Group 5A)

Front 18

Alleotropes (describe them and provide examples)

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• Alleotropes: Forms of the same element that differ in molecular or crystal structure. Examples: diamond and graphite (carbon), O2 and O3.
• The structure of the ozone molecule exemplifies resonance forms: hypothetical extreme arrangements of electrons

Front 19

Radiation (describe it, describe its features, and provide examples of it)

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• Radiation, such as solar energy, can be described as both waves and particles.
• Radiation as waves has two features:
o Wavelength: distance between two successive peaks (λ)
o Frequency: number of waves passing a fixed point in one second (ν). Unit = 1/s or Hz (hertz)
o ν = c / λ , where c (units of distance per second) is the constant speed at which light and other forms of radiation travel.
• Electromagnetic spectrum: range of radiant energy.
Radiation can also be understood as composed of units of energy or photons.
• The two models that describe energy are linked by one equation:
o E (Energy) = h ν = h c / λ
• E = energy of a single photon (J = joule)
• h = Planck’s constant (J . s)
• λ = wavelength
• ν = frequency

Front 20

Energy (describe it in terms of the types of wavelengths that exist)

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Energy
• Types of wavelengths:
o Longer wavelength – microwave – causes the molecules to rotate.
o Medium wavelength – visible – causes the molecules to vibrate.
o Shorter wavelength – ultraviolet – causes the molecules to dissociated.
• When UVs are heated, bonds are broken.
• High energy photons can dissociate molecular bonds.
• A photon must have a precise amount of energy to disrupt a molecular bond.
• This type of energy depends on the type of bond (single, double, triple) and the identity of the atoms involved.

Front 21

Chapman Cycle (describe it and its processes)

Back 21

• Chapman cycle: explains how ozone is not only created, but is naturally broken as well.
o How to form ozone (O3) molecules:
• O2 molecules need to be broken apart (see * above).
• An O molecule combines with an O2 molecule and becomes O3 (see ** above).
- Requires fast collisions.
o How to break apart ozone (O3) molecules:
• O3 combines with O and breaks apart into 2 O2 (reverse of * above).
- Requires slow collisions.

Front 22

Ultraviolet Rays (describe them, their effects on humans, their effects on plants, and their effects on marine ecosystems, and how knowledge about them was used to discover the hole in the ozone layer)

Back 22

Ultraviolet Rays
• UV can cause skin cancer.
• UV can produce sunburn.
• UV can elicit vitamin D production.
• UV is a major cause of skin aging.
• UV triggers the production of the skin pigment melanin.
• As the absorption of O3 in your region increases, your sensitivity to UV radiation biologically will increase as well.
o Therefore, it is important to avoid locales with strong UV rays in order to protect your skin.
• Effects on plants:
o Physiological and developmental processes of plants are affected by UV-B radiation, even by the amount of UV-B in present-day sunlight.
• UV-B facilitates photosynthesis.
 Excess UV-B, or any UV-C, is bad for plants.
• Effects on marine ecosystems:
o UV-B causes damage to early developmental stages of fish, shrimp, crab, amphibians, and other animals.
o Loss of phytoplankton, which are the foundation of aquatic food webs.
• Phytoplankton productivity is limited to the upper layer of the water column in which there has been sufficient sunlight.
• Exposure to solar UV-B radiation has been shown to reduce survival rates for these organisms.
 The hole in the ozone layer was discovered by the fact that all the phytoplankton (and, hence, all the phytoplanktons’ predators) living under the hole were dying.
Luckily, the hole is finally closing up.

Front 23

Free Radicals (describe them and provide an example of them)

Back 23

• Free radical: unpaired electron that’s reactive and unstable.
• Other naturally occurring free radicals in stratosphere:
o NO (nitrogen oxide).

Front 24

Chlorofluorocarbons (describe them, list their properties, list their uses, and understand its effect on the Earth from a technical perspective)

Back 24

o Chlorofluorocarbons (CFCs): the chemicals of aerosols that are made up of chlorine, fluorine, and carbon (CFCl3), which have caused the hole in the ozone layer.
• CFCs’ properties:
 Nontoxic
 Nonflammable
 Stable
• All the aforementioned properties are also what nitrogen has.
 Boiling point of - 30ºC.
• CFCs’ uses:
 Refrigerant
 Propellants in aerosol spray cans
 Polymer foaming
 Solvents for oil and grease
 Sterilizers for surgical instruments
• No longer a common practice.
• Intact CFC molecules reach the stratosphere:
 CCl2F2 + (UV protons when λ < 220 nm) → CClF2 + Cl
 Cl + O3 → ClO + O2
 ClO + ClO → ClOOCl
 ClOOCl + (UV photons) → ClOO + Cl
 ClOO + (UV photos) → Cl + O2
 End result: 2O3 → 3O2
• • Cl catalyzes the destruction of O3.

Front 25

Catalysts (describe them)

Back 25

 Catalyst: Accelerates a chemical reaction without undergoing permanent change.
• Enzyme: a catalyst in the human body.
 The catalyst participates in a chemical reaction but is regenerated in subsequent steps.
 The net concentration of the catalyst does not change.
 The catalyst can be recycled in many chemical reactions:
• One • Cl atom can catalyze the destruction of up to 1 x 105 O3 molecules!

Front 26

Montreal Protocol (describe it as it relates to contemporary science)

Back 26

• Regulations for CFC use:
 1978: Use of CFCs in spray cans banned in US.
 1987: Montreal Protocol on Substances that Deplete the Ozone Layer:
• Reduction of CFC production.
• Research on atmospheric processes.
• Protection of ozone layer.
 Amendments to the Montreal Protocol:
• CFC production ban.
• Progressive elimination of other ozone-depleting compounds.

Front 27

Greenhouse Gases (what is necessary to be one?)

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• Not all gases in the atmosphere act as greenhouse gases.
o The 2 main components (O2 and N2) are not greenhouse gases (i.e., they cannot absorb I.R. and reflect them back).
• In order to act as greenhouse gases, you need to have a certain non-linear structure that allows for an increase in molecular movement that does not cancel itself.

Front 28

Molecular Symmetry (describe this concept and the reasoning behind it)

Back 28

• Any molecule will arrange its component atoms in such a way so as to have all external bonding and non-bonding pairs of electrons as far as possible to each other.
o This is due to electrostatic repulsion of similarly charged bodies.
• In a diatomic molecule, this means to be in a line (the only possible form).
• In other molecules, it depends on the number of ligands and types of bonds formed.

Front 29

Tetrahedrons (identify the atoms that are classified as this, why they are classified as such, why this occurs, and the consequences of all this)

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• In general, atoms from groups 4A, 5A, and 6A that form molecules with single bonds will adopt a grossly tetrahedrical configuration (109.5º between bonds).
o In H3N, the angle between the atoms decreases to 107.5º because the 2 extra electrons push the atoms closer together.
• Similarly, in H2O, the angle decreases to 104.5º.
• This occurs because even if they are not all joined to four ligands (only 4A atoms do), they have one or two extra pairs of electrons that act as bonding pairs at the repulsion level.
• In fact these free pairs of electrons have a greater repulsion that bonding pairs and will deform the tetrahedron to angles of 107.5º and 104.5º (one or two non-bonding pairs respectively) for the bonding pairs.

Front 30

Avogrado's Number (know its value, describe its significance, and describe the related concept of the mole)

Back 30

Avogrado’s number = 6.02 x 10^23.
• This number seeks to answer the question of how many atoms of 12C will be present in 12 grams of pure carbon.
• Mole – a group of those particles possessing an Avogrado’s number pertaining to them.
o A mole of protons or neutrons thus weigh exactly 1 gram, a mole of 16O grams weighs 16 grams, and so on.

Front 31

Methane (describe its chemical makeup and explain its effects on the Earth)

Back 31

Methane (CH4) – a common greenhouse gas with a greenhouse factor of 30 (compared to 1 of CO2).
• It is produced by decomposition of matter by bacterial action.
• Some big deposits are stored in natural gas reservoirs.
• Gas exploitation and agriculture are the 2 main sources of CH4 today.

Front 32

Energy (define it)

Back 32

Energy – the capacity to do work.

Front 33

Work (define it and understand how to calculate it)

Back 33

Work – what occurs when you produce movement against a force.
• W = -F x d

Front 34

Heat (define it, identify what it is a form off, and provide an example of it)

Back 34

Heat – a form of energy that flows from the higher to the lower temperature body.
• Solar heat – a form of heat that comes from the Sun, that we have only begun recently to harness as energy but have not (yet) made full use of yet.

Front 35

Temperature (define it and identify what it is a measure of)

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Temperature – the property that determines the flow of heat (basically, the heat content indicator).

Front 36

Exothermic and Endothermic Reactions (describe them, know how they contrast each other, and explain how they are similar)

Back 36

• Exothermic – energy of products is less than reactants, thus excess is released to the surroundings.
• Endothermic – energy of products is more than reactants, thus defaults has to be taken from the surroundings.
• The energy released on any chemical reaction is obtained by breaking and forming new bonds.
o In the case of methane’s combustion:
• Break 4 single C-H bonds and 2 double O-O bonds.
• Form 2 double C-O bonds and 4 single H-O bonds.

Front 37

Degrees of Freedom (describe them and explain what varying values of this means)

Back 37

Degrees of freedom – the higher this number is for a molecule, the fewer bonds there are holding it together.
• As this number approaches 0, the molecule becomes more stable.

Front 38

Caveat (describe this concept in terms of how it relates to chemistry

Back 38

Caveat – Latin for “warning”; calculations of chemical matter assume that all bonds are identical, with the same energies of formation.
• This only applies to very small, symmetrical molecules.
• All compounds are gases.
• The activation of a reaction would cause the amount of energy to increase, but the net energy change would result in a low amount of energy for the product.