The Atom. the number of subatomic particles determines the properties of atoms (and defines what is called elements )

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1 formed by subatomic particles: neutrons (neutral), protons (+), electrons ( ) electrons move through the atomic volume, and are held there by the (VERY dense) nucleus The Atom = m He = m The atoms may be charged or neutral (how?) mass range: to kg (how?) size range: 62 pm (He) to 520 pm (Cs) the number of subatomic particles determines the properties of atoms (and defines what is called elements )

2 Is it possible to have atoms of the same element with different mass?(isotopes!) Is it possible to have atoms of the same element with different number of e? (ions!) Each element has a unique Z Z = number of p+ What property do radioactive elements share? Can you find other elements usually known as pollutants?

3 Why isotopes? Isotopes are great probes for: - past climate: water can be found as H216O, H217O and H218O but H216O (that is, the light isotope) evaporates preferentially. A signal of high H218O in the ocean (at a given time) indicates that a lot of water had evaporated, but not returned to the ocean! (how could this happen?) - human diet: where does our food come from? different plants have a different isotope content What other uses of isotopes do you know that can have an application in environmental sciences?

4 Jahren and Kraft (2008) *mention UCSB project Children of the corn

5 Can we get energy from atoms?... fusion and fission Your local (still active) G star SUN; Orion Arm, MW X ray picture (pictures not to scale) Your local (retired) nuclear plant TROJAN; Rainier, OR BW picture The sun is a mass of incandescent gas A gigantic nuclear furnace Where hydrogen is built into helium At a temperature of millions of degrees Yo ho, it's hot, the sun is not A place where we could live But here on Earth there'd be no life Without the light it gives We need its light We need its heat We need its energy Without the sun, without a doubt There'd be no you and me They Might Be Giants Why does the Sun shine

6 Oxygen commons.wikimedia.org It's impossible to known for sure the position of an e. e will be more likely located in a place defined by the atomic orbitals (represented as clouds). Orbitals have names depending on: how close are they to the nucleus, their shape, and their orientation. FYI: its impossible to exactly solve the equations to describe the orbitals for atoms with more than 1 e! (so we make approximations) 1s 2p 3p darmstadt.de/ak/immel/script/redirect.cgi?filename= darmstadt.de/ak/immel/tutorials/orbitals/index.html 3d

7 Each orbital can be occupied by 2 electrons. Each orbital has a particular energy level. e fill orbitals in such a way that they will occupy the next available orbital with the lowest energy level (Pauling exclusion principle). * quanta of energy When forming molecules, atoms will tend to have electronic configurations such that their outer orbital is full, that is with 8 e Can you find this numbers in your periodic table?

8 What would happen to e that receives EM energy? It depends! (quantum states, spontaneous emission, electron binding energy, photoionization) Energy of EM waves: a wave consists of quanta of energy (photons). Energy of a photon depends on the frequency: E = hf = hc/λ h = (33) J s = (10) ev s c = m s 1 What kind of EM radiation do you need to photoionize the electron of an H atom given that its binding energy is 13.6 ev? To what environmental problems can this be related?

9 UV radiation and DNA In spite of this sunscreen effect, UV radiation can directly and indirectly damage DNA molecules. 1. Direct damage DNA and RNA bases subject to radiation return from the excited state to the lowest electronic ground state in a very short time. Bases have the ability to transform the energy in EM radiation into vibrational energy and dissipate it as heat. 2. Indirect damage, which occurs through the production of free radicals and reactive O species, is responsible for 92% of melanoma cases What is a free radical?

10 Atoms interact with each other: chemical bonds Most elements occur in nature combined with the same element, or most common, with other elements. Exceptions: noble gases (He, etc.), some metals (Au, Cu, Ag, Pt). A chemical bond refers to the interaction that holds atoms together. This interaction occurs through the sharing or transfer of e from one atom to another. Bonds make atoms function as a unit. There are different kinds of bonds, depending if the e are shared or transferred and on how many e are shared.

11 Electronegativity: how attached am I to my electrons? Electronegativity of an atom will determine the kind of bond Which atoms are more likely to interact?

12 Types of chemical bonds Depending on the difference in electronegativity between the atoms, bonds can be: a) covalent: e are shared b) polar: e are shared but tend to be closer to the most electronegative atom Copyright 2000 Houghton Mifflin c) ionic: e are transfered

13 ... one example of ionic bond: table salt (NaCl)! Salt crystal Na loses its outer e turning into a cation (positive ion). Cl receives the e from Na turning into an anion (negative ion). Na+ and Cl have outer shell stable configurations. Na+ and Cl are kept together by electrostatic interactions. Which represents Na+? which represents Cl? why? chemistry.co.uk/odyssey/screenshots.html

14 ... examples of (single) covalent bonds: hydrocarbons! Methane CH4 Why is octane relevant for this class? Octane C?H?

15 ... examples of (double) covalent bonds: more hydrocarbons! Ethylene Ethylene is the most produced organic compound in the world; global production of ethylene exceeded 107 million metric tonnes per year in (Wikipedia) Q. What can you do with ethylene? Is ethylene a renewable material?

16 polyethylene foam and foam tape A. You can do polyethylene! polyethylene tubing Polyethylene There is no significant What else from your daily life is made of polyethylene? What are the alternatives? polyethylene bottles polyethylene tanks Risk to your health She used to be beautiful once as well Plastic Bag Middle Class Polyethylene Radiohead polyethylene (B side to OK computer)

17 Bonding energy I Bonded atoms are more stable than separated atoms.

18 Bonding energy II Beware! 1 double C=C bond = 614 kj/mol 2 single C C bonds = 696 kj/mol

19 Mole A mole is a chemical unit to denote the quantity of a substance. (Beware: the official definition is more subtle) If you have a mole of atoms, it means that you have 6.02 x atoms. If you have a mole of molecules, it means that you have 6.02 x molecules. 1 mole of pennies distributed globally would make us all trillionaires! Julie Wright, AS222d 2007 TA something useful: the molar mass (M) M = the mass of a mol of a substance Assuming 7 billion (7x109) people in the world, how many pennies correspond per person?

20 Molar mass The molar mass of an element corresponds to the standard atomic weight of the element multiplied by the constant Mu = 1g/mol What is the molar mass of Carbon? Atomic weight of Carbon =? M(C) =? Where can you get the standard atomic weight of the element? Why would you like to multiply something by 1? The molar mass of a molecule corresponds to the sum of the standard atomic weight of the elements that make the molecule, multiplied by the constant Mu = 1g/mol What is the molar mass of Methane?

21 What is the bonding energy found in the 107 metric million tons of ethylene (C2H4) produced in 2005? a) what is the bonding energy of 1 mol of ethylene 1 double C C bond =? 4 single C H bonds =? total =? b) how many moles of ethylene are they in 107 million tons of ethylene molar mass of ethylene =? 1 metric ton = 1000 kg Compare your answer to the global use of energy from fossil fuels and renewable energies (3.8 x 1020 Joules per year in 1999 Physics Today, April 2002).

22 Energy of reaction To calculate the energy of a reaction: find the chemical formulas for the substances of interest write down the reaction be sure the equation is balanced assume you will break all the bonds on the reactants (use energy), and that you will form all the bonds of the products (release energy) subtract the energy used (left side of the equation) to the energy released (right)

23 Lets burn some methane.. CH4 + 2O2 CO2 + 2H2O Where is the burning of CH4 used as an alternative source of energy? today/2008/10/10/ Why negative values? How much methane do we need to supply the requirements of annual global use of energy?