Chemistry Notes for CHE101 Chapter 2 PDF

Chapter 2 Atoms, Molecules & Ions  Two Schools of Thought Democritus Zeno All matter is made Matter is infinitely of small particles divisible called atoms  Who was correct? Matter is made of atoms Atoms can be divided into subatomic particles… But after division they l...

Chapter 2 Atoms, Molecules & Ions  Two Schools of Thought Democritus Zeno All matter is made Matter is infinitely of small particles divisible called atoms  Who was correct? Matter is made of atoms Atoms can be divided into subatomic particles… But after division they lose their characteristic properties and become just a pile of electrons, protons and neutrons  Three Kinds of Matter Elements Compounds Mixtures  Pure Substances versus Mixtures Pure substance Mixture Always has same ratio Can have different of atom types ratios of atom types It’s an element or It’s homogenous compound (smooth/transparent) or heterogeneous (chunky/translucent) Classification of Matter Classification of Matter Pure Substance? Classification of Matter Pure Substance? Yes No  Classification of Matter Pure Substance? Yes No Number of atom types  Classification of Matter Pure Substance? Yes No Number of atom types Only 1 Element  Classification of Matter Pure Substance? Yes No Number of atom types Only 1 2 or more Element Compound  Classification of Matter Pure Substance? Yes No Number of atom types Mixture Only 1 2 or more Element Compound  Classification of Matter Pure Substance? Yes No Number of atom types Mixture Chunky? Yes No Only 1 2 or more Element Compound  Classification of Matter Pure Substance? Yes No Number of atom types Mixture Chunky? Yes No Only 1 2 or more Element Compound Heterogeneous  Classification of Matter Pure Substance? Yes No Number of atom types Mixture Chunky? Yes No Only 1 2 or more Element Compound Heterogeneous Homogeneous Samples... Native copper (Cu) a metallic element Sulfur (S) a nonmetallic ……………………………element Lithium (Li) a metallic ……………………………element Galena a compound – a.k.a. lead(II) sulfide Belt Mountain ore a heterogeneous mixture  Elements 118 known at this time; 94 occur in nature Most only discovered in last 200 years The periodic table lists the atomic symbols for the elements Learn those on the handout for Monday’s quiz (spelling counts!) Here are all their names pronounced for you! http://www.privatehand.com/flash/elements.html Fun info about each element at http://www.periodicvideos.com  Element Forms Monatomic elements He, Ne, Ar, Kr, Xe, Rn Diatomic molecules H2, N2, O2, F2, Cl2, Br2, I2 Polyatomic molecules P4, S8  Element Forms Network elements C* (graphite, diamond) Metals (e.g., Cu, Au, Fe) There is no such entity as a molecule for network elements * C60, one type of buckyball, is a molecule Mixtures... Can be separated by physical means Common methods include filtration (coffee) evaporation (salt) distillation (vinegar) fractional crystallization (fresh water ice out of sea water)  What is Gatorade? 1. An element 2. A compound 3. A homogeneous mixture 4. A heterogeneous mixture Element, Compound or Mixture? Gatorade - it’s a HETEROGENEOUS (murky) MIXTURE of sugar, water flavoring, electrolyte salts, etc. Baking soda, NaHCO3 Cl2 gas  What is baking soda, NaHCO3? 1. An element 2. A compound 3. A homogeneous mixture 4. A heterogeneous mixture Element, Compound or Mixture? Gatorade - it’s a HETEROGENEOUS (murky) MIXTURE of sugar, water flavoring, electrolyte salts, etc. Baking soda, NaHCO3 - it’s a COMPOUND named sodium bicarbonate or sodium hydrogen carbonate Cl2 gas  What is chlorine gas, Cl2? 1. An element 2. A compound 3. A homogeneous mixture 4. A heterogeneous mixture Element, Compound or Mixture? Gatorade - it’s a HETEROGENEOUS (murky) MIXTURE of sugar, water flavoring, electrolyte salts, etc. Baking soda, NaHCO3 - it’s a COMPOUND named sodium bicarbonate or sodium hydrogen carbonate Cl2 gas - it’s an ELEMENT since only one kind of atom is present Dalton’s Atomic Theory John Dalton (English chemist) proposed theory in 1808 Built on Lavoisier’s conservation of mass Matter is neither created nor destroyed Used Proust’s law of constant composition Compounds always have same atom ratio  Atoms are tiny Size range 7.4 x 10-11 m for hydrogen (74 pm) 5.2 x 10-10 m for cesium (520 pm) Mass range 1.67 x 10-24 g for hydrogen 3.95 x 10-22 g for uranium Silicon atoms arranged on a face of a crystal. It is impossible to "see" atoms this way using ordinary light. The image was made by a Scanning Tunneling Microscope, a device that "feels" the cloud of electrons that form the outer surface of atoms. http://www.aip.org/history/einstein/atoms.htm Atoms are built from... Protons Electrons Neutrons But what holds them together?  Fundamental forces Strong nuclear force Strong but short range (~10-15 m) Electrostatic (electromagnetic) forces Intermediate and midrange (~10-10 m) Gravity Weak but long range (light years!)  Strong nuclear force Used as “glue” between protons and neutrons in the nucleus Protons repel each other, but the strong nuclear force overwhelms the electrostatic repulsion Beyond 83 protons (bismuth), all nuclei become unstable Electrostatic Forces... ⚫ Electrostatic forces are dominant once particles are more than 10-15 m apart ⚫ Protons and electrons are more than 10-15 m apart ELECTROSTATIC INTERACTIONS ARE THE DRIVING FORCE BEHIND CHEMISTRY! Charge behaviors.. Like charges repel + repels + - repels - Unlike charges attract + attracts - Neutral charges are indifferent 0 ignores + and - and 0 The US Office of Naval Research just unveiled its new rail-gun that uses charge repulsion to accelerate a sliding metal conductor between two rails and launch a 28-pound HVP up to 5,600 mph!  The Atomic Nucleus Protons and neutrons are packed into a HIGH density nucleus  The Atomic Nucleus Protons and neutrons are packed into a HIGH density nucleus  The Atomic Nucleus Protons and neutrons are collectively called nucleons Strong nuclear force holds nucleus together Neutrons can be viewed as “proton glue”  Nuclear Density Incredibly dense: 1.8 x 1014 g/cm3 A paper clip with this density would weigh 10,000,000 tons! Neutrons stars have this density As they rapidly spin they give off radio waves and are known as pulsars The electron cloud Electrons move through the space surrounding the nucleus in unknown trajectories The electron cloud Electrons move through the space surrounding the nucleus in unknown trajectories the electron cloud An inaccurate diagram of an atom! http://sciencecabin.com/there-are-three-parts-of-the-atoms/ The electron cloud Atoms are mostly empty space Nuclear diameter: 10-15 m Electron cloud diameter: 10-10 m If the nucleus is pea-sized, the electron cloud is as big as a domed football stadium! Subatomic Particles  Table : Subatomic Particles Particle Symbol amu’s grams Charge  Table : Subatomic Particles Particle Symbol amu’s grams Charge Proton p+ 1.0073 1.673 x 10-24 +1  Table : Subatomic Particles Particle Symbol amu’s grams Charge Proton p+ 1.0073 1.673 x 10-24 +1 Electron e- 0.0005486 9.110 x 10-28 -1  Table : Subatomic Particles Particle Symbol amu’s grams Charge Proton p+ 1.0073 1.673 x 10-24 +1 Electron e- 0.0005486 9.110 x 10-28 -1 Neutron n 1.0087 1.675 x 10-24 0 Atomic Mass Units (amu) Masses of atoms and subatomic particles are so small that they are often expressed on a relative scale 1 amu = 1/12 the mass of a carbon-12 atom = 1.6605 x 10-24 g = 1 dalton (biochemistry) Atomic Number, Z Atom type determined by number of protons in nucleus # of protons = atomic number =Z Atomic numbers are integers that increase through the periodic table Atomic Number, Z Atom type determined by number of protons in nucleus # of protons = atomic number =Z Atomic numbers are integers that increase through the periodic table Neutral Atoms When an atom is uncharged (electrically neutral)… # of protons = # of electrons # of p+ = # of e- Z = # of e-  Consider a neutral copper atom... Number of protons: Z = ?  Consider a neutral copper atom... Number of protons: Z = 29  Consider a neutral copper atom... Number of protons: Z = 29 Number of electrons: ?  Consider a neutral copper atom... Number of protons: Z = 29 Number of electrons: 29  Mass Number, A When weighing chemicals, need to account for neutrons, too. # of neutrons is not fixed for an atom type The first evidence of different masses appeared at the bottom right corner of this J. J. Thomson photographic plate. Two of the patches are both from neon: neon of mass 20 and neon of mass 22.  Mass Number, A When weighing chemicals, need to account for neutrons, too. # of neutrons is not fixed for an atom type For a specific atom… # of protons + # of neutrons = mass number Z + # of n = A Carbon-12 The most common type of carbon atom 6 protons 6 neutrons 6 p+ + 6 n = 12 (mass number) Carbon-12 The most common type of carbon atom 6 protons 6 neutrons 6 p+ + 6 n = 12 (mass number) Carbon-12 The most common type of carbon atom 6 protons 6 neutrons 6 p+ + 6 n = 12 (mass number) NOTE: electrons ignored -- too light Let's try another... Let’s try another... What’s in a neutral nickel-60 atom?  How many protons in a neutral Ni-60 atom? 1. 60 2. 0 3. 59 4. 28  How many protons in a neutral Ni-60 atom? 1. 60 2. 0 3. 59 4. 28  Lets try another... What’s in a neutral nickel-60 atom? Protons = ? # of protons = atomic number  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28  How many electrons in a neutral Ni-60 atom? 1. 60 2. 0 3. 59 4. 28  How many electrons in a neutral Ni-60 atom? 1. 60 2. 0 3. 59 4. 28  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28 Electrons = ? In a neutral atom # of protons = # of electrons  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28 Electrons = 28  How many neutrons in a neutral Ni-60 atom? 1. 60 2. 32 3. 58 4. 28  How many neutrons in a neutral Ni-60 atom? 1. 60 2. 32 3. 58 4. 28  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28 Electrons = 28 Neutrons = ? Mass number is... # of protons + # of neutrons  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28 Electrons = 28 Neutrons = 60 - 28  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28 Electrons = 28 Neutrons = 60 - 28 = 32  Lets try another... What’s in a neutral nickel-60 atom? Protons = 28 Electrons = 28 Neutrons = 60 - 28 = 32 Shorthand notation: 28 p+, 28 e-, 32 n  Ions Not all atoms are electrically neutral A charged atom (or molecule) is called an ion Ion charge = # of p+’s - # of e-’s  What’s the charge of an atom that has 16 protons and 18 electrons? 1. -2 2. -1 3. 0 4. +2  What’s the charge of an atom that has 16 protons and 18 electrons? 1. -2 2. -1 3. 0 4. +2  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = # of p+’s - # of e-’s  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = # of p+’s - # of e-’s  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - # of e-’s  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - # of e-’s  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - # of e-’s  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - 18  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - 18  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - 18 = -2  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - 18 = -2 Aha! It’s a sulfide ion, S2-  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p +’s - # of e-’s With 16 p+’s, it What’s can only the be acharge of an atom that has sulfur 16 atom and 18 electrons? protons Ion charge = 16 - 18 = -2 Aha! It’s a sulfide ion, S2-  Ions Not all atoms are electrically neutral A charged atom is called an ion The ion charge Ion charge = # of p ’s - # of e-’s + is written as a What’s the charge of an atom that has superscript to 16 protons and 18 electrons? the right, with Ion charge = 16 the - charge18 sign listed last = -2 Aha! It’s a sulfide ion, S2-  Ions Not all atoms are electrically neutral A charged atom is called an ion Ion charge = # of p+’s - # of e-’s What’s the charge of an atom that has 16 protons and 18 electrons? Ion charge = 16 - 18 = -2 Aha! It’s a sulfide ion, S2-  Build atom and Ion https://phet.colorado.edu/sims/html/build-an- atom/latest/build-an-atom_en.html Ions are charged species  Ions are charged species Cations are missing a few electrons  Ions are charged species Cations are missing a few electrons This imparts a positive charge  Ions are charged species Cations are missing a few electrons This imparts a positive charge e.g., Zn2+ 30 protons 28 electrons 2 e-’s missing  Ions are charged species Cations are missing a Anions have a few few electrons extra electrons This imparts a positive charge e.g., Zn2+ 30 protons 28 electrons 2 e-’s missing  Ions are charged species Cations are missing a Anions have a few few electrons extra electrons This imparts a positive This imparts a charge negative charge e.g., Zn2+ 30 protons 28 electrons 2 e-’s missing  Ions are charged species Cations are missing a Anions have a few few electrons extra electrons This imparts a positive This imparts a charge negative charge e.g., Zn2+ e.g., Cl- ion 30 protons 17 protons 28 electrons 18 electrons 2 e-’s missing 1 excess e- How to remember which is which C a t ion See a + ion A n ion A negative ion Hydrogen isotopes Most hydrogen atoms have a nucleus with just 1 proton hydrogen-1 protium About 15 of every 100,000 hydrogen atoms has a neutron as well hydrogen-2 deuterium (D) or heavy hydrogen Deuterium and Harold Urey The neutron was theoretically predicted to exist by Chadwick around 1930 Harold C. Urey ( UM chemistry alum/faculty!) proved the existence of neutrons by isolating deuterium Awarded 1934 Nobel prize He isolated deuterium through fractional distillation of liquid hydrogen Chemists use deuterium all the time in the form of heavy water, D2O Harold Clayton Urey was born in Walkerton, Indiana, on April 29, 1893, as the son of the Rev. Samuel Clayton Urey and Cora Rebecca Reinsehl, and grandson of pioneers who settled in Indiana. His early education in rural schools led to his graduation from high school in 1911 after which he taught for three years in country schools. In 1914 he entered the University of Montana and received his Bachelor of Science degree in Zoology in 1917. He spent two years as a research chemist in industry before returning to Montana as an instructor in Chemistry. In 1921 he entered the University of California to work under Professor Lewis and he was awarded the degree of Ph.D. in Chemistry in 1923. He spent the following year in Copenhagen at Professor Niel Bohr’s Institute for Theoretical Physics as American-Scandinavian Foundation Fellow to Denmark and on his return to the United States he became an Associate in Chemistry at Johns Hopkins University. In 1929 he was appointed Associate Professor in Chemistry at Columbia University and he became Professor in 1934. Professor's Urey's early researches concerned the entropy of diatomic gases and problems of atomic structure, absorption spectra and the structure of molecules. In 1931 he devised a method for the concentration of any possible heavy hydrogen isotopes by the fractional distillation of liquid hydrogen: this led to the discovery of deuterium.  Hydrogen isotopes (Cont’d.) Nuclear reactions create a third isotope with two neutrons in the nucleus hydrogen-3 tritium This is a radioisotope in that it decays and gives off harmful radiation Isotope notation... Isotope notation... All four positions around a symbol can hold information H Isotope notation... Mass number, A H Isotope notation... Mass number, A H Atomic number, Z Isotope notation... Mass number, A Ion charge H Atomic number, Z Isotope notation... Mass number, A Ion charge H Molecular Atomic number, Z formulas Isotope notation... Consider a +1 ion of a deuterium atom H Isotope notation... Consider a +1 ion of a deuterium atom H A deuterium atom has 1 proton in its nucleus Isotope notation... Consider a +1 ion of a deuterium atom 1 H A deuterium atom has 1 proton in its nucleus Isotope notation... Consider a +1 ion of a deuterium atom 1 H Isotope notation... Consider a +1 ion of a deuterium atom 1 H A deuterium atom has a mass number of 2 Isotope notation... Consider a +1 ion of a deuterium atom 2 1 H A deuterium atom has a mass number of 2 Isotope notation... Consider a +1 ion of a deuterium atom 2 1 H Isotope notation... Consider a +1 ion of a deuterium atom 2 1 H A deuterium cation has a charge of +1 Isotope notation... Consider a +1 ion of a deuterium atom 2 + 1 H A deuterium cation has a charge of +1 Isotope notation... Consider a +1 ion of a deuterium atom 2 + 1 H Isotopes of Hydrogen Atomic Weights Atoms of the same type that differ in neutron count are called isotopes Most elements in nature occur as a mixture of several isotopes Isotopes DON’T make much difference in a chemical sense Isotopes DO make a difference in weighing out samples  Weighted Averages Masses listed on periodic table are weighted averages of natural isotopic abundances Chlorine comes in two common forms 75.53% is chlorine-35 24.47% is chlorine-37 Exact masses are Chlorine-35 34.97 Chlorine-37 36.96  Weighted Averages Masses listed on periodic table are weighted averages of natural isotopic abundances Chlorine comes in two common forms 75.53% is chlorine-35 The average MUST be somewhere 24.47% is chlorine-37 between 35 and 37! Exact masses are Chlorine-35 34.97 Chlorine-37 36.96 Example calculation  Example calculation Contribution from Cl-35  Example calculation Contribution from Cl-35 + Contribution from Cl-37  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 (34.97) 100  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100 (0.7553 x 34.97) + (0.2447 x 36.96)  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100 (0.7553 x 34.97) + (0.2447 x 36.96) 26.41 + 9.04  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100 (0.7553 x 34.97) + (0.2447 x 36.96) 26.41 + 9.04 Note that contribution from Cl-35  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100 (0.7553 x 34.97) + (0.2447 x 36.96) 26.41 + 9.04 Note that contribution from Cl-35 is about 3 times that from Cl-37  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100 (0.7553 x 34.97) + (0.2447 x 36.96) 26.41 + 9.04 = 35.45  Example calculation Contribution from Cl-35 + Contribution from Cl-37 75.53 24.47 (34.97) + (36.96) 100 100 (0.7553 x 34.97) + (0.2447 x 36.96) 26.41 + 9.04 Weighted average = 35.45 appears on periodic table  Weighted Averages Masses listed on periodic table are weighted averages of natural isotopic abundances Magnesium comes in three common forms 78.70% is magnesium-24 10.13% is magnesium-25 11.17% is magnesium-26 Exact masses are magnesium-24 23.98504 magnesium-25 24.98584 magnesium-26 25.98259  Weighted Averages Masses listed on periodic table are weighted averages of natural isotopic abundances Magnesium comes in three common forms 78.70% is magnesium-24 The average MUST 10.13% is magnesium-25 be somewhere between 24 and 26! 11.17% is magnesium-26 Exact masses are magnesium-24 23.98504 magnesium-25 24.98584 magnesium-26 25.98259  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26 78.70 10.13 (23.98504) + (24.98584) 100 100 + 11.17 (25.98259) 100  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26 78.70 10.13 (23.98504) + (24.98584) 100 100 + 11.17 (25.98259) 100 0.7870 (23.98504) + 0.1013 (24.98584) + 0.1117 (25.98259)  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26 0.7870 (23.98504) + 0.1013 (24.98584) + 0.1117 (25.98259)  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26 0.7870 (23.98504) + 0.1013 (24.98584) + 0.1117 (25.98259) = 18.87623 + 2.53107 + 2.90226  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26 0.7870 (23.98504) + 0.1013 (24.98584) + 0.1117 (25.98259) = 18.87623 + 2.53107 + 2.90226 = 24.30955  Example calculation Contribution from Mg-24 + Contribution from Mg-25 + Contribution from Mg-26 0.7870 (23.98504) + 0.1013 (24.98584) + 0.1117 (25.98259) = 18.87623 + 2.53107 + 2.90226 = 24.30955 = 24.31 (4 sig figs allowed) The Periodic Table As more elements were discovered, researchers noted “triplets” that had similar chemical properties Lithium, sodium, and potassium react vigorously with water Chlorine, bromine, and iodine are all pungent nonmetals  Dmitri Mendeleev Let chemical character dictate placement rather than atomic weight Co (53.9882 amu) before Ni (58.6934 amu) Te (127.60) before I (126.9045 amu) His positioning in 1869 anticipated quantum theory by 60 years An early version of Mendeleev’s periodic table  Here it is commemorated in stone on the side of a Russian science building The Periodic Table Each row is a period  Each row is a period 1  Each row is a period 1 2  Each row is a period 1 2 3  Each row is a period 1 2 3 4  Each row is a period 1 2 3 4 5 6 7 7 periods so far  Each row is a period 1 2 3 4 5 6 7 7 periods so far These actually fit in here!  The Periodic Table It’s not a convenient shape to print when inserted Each column is a family 1A Each column is a family The alkali metal family  Element Families Elements in the same family exhibit similar properties Alkali metals are: soft shiny metals react violently with water to produce alkaline (basic) solutions http://www.youtube.com/watch?v=eCk0lYB_8c0 never found in elemental form  Lessons Learned Recognize the contributions of Zeno, Democritus, Dalton, Urey, Mendeleev and Pauli to our knowledge of atomic structure Distinguish between elements and compounds; pure substances and mixtures; heterogeneous and homogeneous mixtures Name and give symbols of common elements Know fundamental forces - strong nuclear, electrostatic, gravitational  Lessons Learned Explain the composition of different atoms according to the number of protons, neutrons and electrons they contain Know what cations and anions are. Use charge to predict electron numbers and vice versa Understand what isotopes are, how to write isotope notation, and how to use their natural abundances to compute average atomic masses