Atoms And Molecules
ElementsChem101 - Lecture 2 Elements are pure substancescontaining only one kind of atom(homoatomic). There are at last count 114 elements.(Your book indicates 112.).Atoms and Molecules- 88 of these are naturally occurring.ElementsElements An alphabetic listing of the elementsis found inside the back cover of yourTextbook.Table 2.1:University of Wisconsin-Eau ClaireChem101 - Lecture 23University of Wisconsin-Eau ClaireChem101 - Lecture 22University of Wisconsin-Eau ClaireChem101 - Lecture 24ElementsElements On the inside of the front cover of youbook is a tabular arrangement of theelements. On the inside of the front cover of youbook is a tabular arrangement of theelements.- This arrangement is called the PeriodicTable.- You will learn this semester that there isa great deal of significance to thisarrangement.- This arrangement is called the PeriodicTable. The resource page at the Chem101website provides links for severalother periodic tables.University of Wisconsin-Eau ClaireChem101 - Lecture 25University of Wisconsin-Eau ClaireChem101 - Lecture 261
Elements as Pure Substances“Seeing” Atoms As pure substances, each element has awell-defined set of physical characteristics. Up until the 1970’s no one had ever seen anatom.- Hydrogen is a clear, colorless, flammablediatomic (H 2) gas.- Nitrogen is a clear, colorless, nonflammablediatomic gas (N2).- Sulfur is a yellow, amorphous polyatomic (S 8)solid.- Sodium is a highly reactive, soft, metallic solid(Na).- Atoms were theoretic objects that could explainthe properties of matter. In 1981, the invention of the ScanningTunneling Microscopy (STM) allowed us tonow “see” atoms.- The inventors received the Nobel Prize for theirinvention in 1986. The web-based periodic tables given on theResources page list characteristc physicalproperties of the elements.University of Wisconsin-Eau ClaireChem101 - Lecture 27University of Wisconsin-Eau Claire“Seeing” Atoms“Seeing” Atoms How an STM works: How an STM works:University of Wisconsin-Eau ClaireChem101 - Lecture 29University of Wisconsin-Eau Claire“Seeing” Atoms“Seeing” Atoms Silicon crystal lattice Nickel crystal latticeUniversity of Wisconsin-Eau ClaireChem101 - Lecture 211University of Wisconsin-Eau ClaireChem101 - Lecture 28Chem101 - Lecture 210Chem101 - Lecture 2122
“Seeing” Atoms“Seeing” Atoms Xenon atom on a nickel crystal lattice Scientists at IBM have learned how toarrange atoms on a surface. Xenon atoms on a nickel crystal latticeUniversity of Wisconsin-Eau ClaireChem101 - Lecture 2University of Wisconsin-Eau Claire13“Seeing” AtomsChem101 - Lecture 214Chemical Symbols for Elements Carbon monoxide molecules on a platinumcrystal lattice Each element has a unique one or twocharacter symbol (Table 2.1 andPeriodic Table)- The first letter of the symbol is alwayscapitalized.- The second letter, if there is one, isalways lower case.University of Wisconsin-Eau ClaireChem101 - Lecture 2University of Wisconsin-Eau Claire15Chem101 - Lecture 2Chemical Symbols for ElementsCompounds Most of the symbols are derived fromthe element’s English name: Compounds are pure substanceswhose molecules contain more thanone type of atom (heteroatomic) There are millions of differentcompounds.- H (Hydrogen), C (Carbon), Ca(Calcium), O (Oxygen), Cl (Chlorine) Some of the symbols are derived fromthe element’s German or Latin name:16- Au (Gold, aurum), Ag (Silver,argentum), Na (Sodium, natrium), Cu(Copper, cuprum), Fe (Iron, ferrum)University of Wisconsin-Eau ClaireChem101 - Lecture 217University of Wisconsin-Eau ClaireChem101 - Lecture 2183
Compounds as Pure SubstancesMolecular Formulas for Compounds As pure substances, each compoundhas a well-defined set of physicalcharacteristics. Molecular or Chemical formulas areused to indicate the chemicalcomposition of a compound’smolecule. In a molecular formula, the chemicalsymbols of all of the elementscontained in the compound are listed.- Dihydrogen oxide (H2O) is a clear,colorless liquid.- Methane (CH4) is a clear, colorless,flammable gas.- Acetic acid (C2H4O2) is a crystallinewhite solid.University of Wisconsin-Eau ClaireChem101 - Lecture 2- Subscripts are used to indicate thenumbers of atoms of each elementcontained in each molecule of thecompound.University of Wisconsin-Eau Claire19Molecular Formulas for CompoundsChem101 - Lecture 220Exercise 2.5 For example:- The molecular formula for water is H2OEach molecule of water contains two hydrogen(H) atoms and one oxygen (O) atom.Determine the number of each type of atom inmolecules represented by the following formulas:a.b.c.d.- The molecular formula for methane is CH4Each molecule of water contains one carbon (C)atom and four hydrogen (H) atoms.sulfur trioxide (SO 3)nitric acid (HNO 3)ammonia (NH 3)propane (C 3H8)- The molecular formula for acetic acid isC2H4O2Each molecule of acetic acid contains twocarbon (C) atoms, four hydrogen (H) atoms andtwo oxygen (O) atoms.University of Wisconsin-Eau ClaireChem101 - Lecture 2University of Wisconsin-Eau Claire21Chem101 - Lecture 2Inside the AtomInside the Atom Atoms are the limit of chemicalsubdivision in matter. Each element has a different type ofatom. All atoms are made of three differentsubatomic particles.- These were discovered in the latter partof the 19th and early part of the 20thcentury.- Each with different chemical andphysical properties The three subatomic particles include: To understand how different types ofatoms can have different chemical andphysical properties, we need to knowwhat atoms are made of.University of Wisconsin-Eau ClaireChem101 - Lecture 222- The proton- The electron- The neutron23University of Wisconsin-Eau ClaireChem101 - Lecture 2244
Inside the AtomInside the Atom The protons and neutrons contributeessentially all of the mass to an atom. The protons contribute all of the positivecharge, while the electrons contribute all ofthe negative charge. Each of these particles havedistinguishable physical properties,the important ones being mass andelectrical charge.- In a neutral atom the net charge is zero,therefore the numbers of protons and electronsare equal.Characteristic PropertiesParticleCommonSymbolsCharge{ }Mass {g}RelativeMassElectronProtone–p, p , H 11 9.07 x 10–281/18361Neutronn01.67 x 101.67 x 10–24–24Characteristic PropertiesParticleCommonSymbolsCharge{ }Mass {g}RelativeMassElectronProtone–p, p , H 11 9.07 x 10–281.67 x 10–241/18361Neutronn01.67 x 10–2411University of Wisconsin-Eau ClaireChem101 - Lecture 2University of Wisconsin-Eau Claire25Chem101 - Lecture 226Inside the AtomInside the Atom The protons and neutrons are tightlybound together and located in thecenter of the atom in a region calledthe nucleus. The electrons surround the nucleus. The popular model of an atom shown onthe previous slide is somewhat misleading.- The electrons are not hard spheres that whirlabout the nucleus, but rather should bethought of as a cloud that surrounds thenucleus.NucleusNucleus(comprising theprotons and neutrons)(comprising theprotons and neutrons)ElectronsAre located outside ofthe nucleusUniversity of Wisconsin-Eau ClaireChem101 - Lecture 2ElectronsAre located outside ofthe nucleusUniversity of Wisconsin-Eau Claire27Chem101 - Lecture 228Inside the AtomInside the Atom The popular model of an atom shown onthe previous slide is also misleading.NucleusElectron Cloud(mass andpositive charge)(negative charge)- The volume occupied by the nucleus, whichcontains essentially all of the mass, is quitesmall compare to that occupied by theelectrons.- The diameter of the nucleus is approximately1/100,000 the radius of the electron cloud.The electron cloudwould extend 1km toWater Street!If the nucleus were1 cm in diameterUniversity of Wisconsin-Eau ClaireChem101 - Lecture 229University of Wisconsin-Eau ClaireChem101 - Lecture 2305
Inside the AtomExercise 2.13 The number protons an atom containsdetermines which element it is, thisnumber is called the atomic number and isrepresented by the letter Z.Determine the number of electrons and protonscontained in an atom of the following elements:a.b.c.- On the periodic table the symbols for theelements are arranged according to theiratomic numbers.sulfurAselement number 24 For an electrically neutral atom, thenumber of electrons is equal the number ofprotons.University of Wisconsin-Eau ClaireChem101 - Lecture 2University of Wisconsin-Eau Claire31Chem101 - Lecture 232IsotopesIsotopes The number of neutrons does affect anatom’s mass. The number of neutrons an atom hasdoes not affect its electrical charge,- The sum of the number of protons andneutrons an atom contains is called theatom’s atomic mass number.- The atomic mass number is represented bythe letter A.- Nor does it affect which element an atom is. The number of neutrons in an atom isapproximately equal to the number ofprotons, but it can vary for the differentatoms of a given element.University of Wisconsin-Eau ClaireChem101 - Lecture 2 The different forms of atoms thatelements have due to differences in theirnumber of neutrons are called isotopes.University of Wisconsin-Eau Claire33IsotopesChem101 - Lecture 234Isotopes Each element has its owncharacteristic number of isotopes andrelative abundance of each. For example- Chlorine (Cl) also has two naturally occurringisotopes:one has 18 neutrons and represents 75.78% of all naturallyoccurring chlorinethe other has 20 neutrons and represents the remaining24.22% of all naturally occurring chlorine.- Phosphorus (P) has just one naturally occurringisotope- Magnesium (Mg) has three naturally occurringisotopes:it contains 16 neutrons.- Carbon (C) has two naturally occurring isotopesone has 12 neutrons and represents 78.99% of all naturallyoccurring magnesiumanother has 13 neutrons and represents 10.00% of allnaturally occurring magnesiumand the last has 14 neutrons and represents the remaining11.01% of all naturally occurring magnesium.one has 6 neutrons and represents 98.93% of allnaturally occurring carbonthe other has 7 neutrons and represents the remaining1.07% of all naturally occurring carbonUniversity of Wisconsin-Eau ClaireChem101 - Lecture 235University of Wisconsin-Eau ClaireChem101 - Lecture 2366
IsotopesIsotopes The number of naturally occurringisotopes an element has, and theirnatural abundance, are characteristicproperties of each element. Some isotopes are radioactive- This means that their nuclei areunstableThey fall apart to produce new elementsand in the process release energy- They have been determinedexperimentally.- They can be looked up in the CRCHandbook of Chemistry and Physics.- They can also be found on-line at theWebElements web site:University of Wisconsin-Eau ClaireChem101 - Lecture 2University of Wisconsin-Eau Claire37IsotopesIsotopes The convention used to distinguish oneisotope of an element from another ismodify the element’s chemical symbol: For our previous examples:- Phosphorus: 1531P1213- Carbon:6 C and 6 C3537- Chlorine:17 Cl and 17 Cl2425- Magnesium: 12 Mg , 12 Mg andAZE24- Magnesium: Mg ,Chem101 - Lecture 225Mg andUniversity of Wisconsin-Eau Claire39IsotopesMg26MgChem101 - Lecture 240Exercise 2.15 Another way to represent the differentisotopes of an element is to write outthe name of the element followed bythe atomic mass number:-261238 Since an element’s atomic number isunique, it is not necessary to includeit, for example, for magnesium we canwrite:- Where E is the element’s chemical symbol,- Z is the element’s atomic number,- and A is the element’s atomic mass number.University of Wisconsin-Eau ClaireChem101 - Lecture 2Determine the number of protons, number ofneutrons, and the number of electrons in atoms ofthe following isotopes:phosphorus-31carbon-12 and carbon-13chlorine-35 and chlorine-37magnesium-24, magnesium-25 andmagnesium-26University of Wisconsin-Eau ClaireChem101 - Lecture 241a.73Lib.2210Nec.4420CaUniversity of Wisconsin-Eau ClaireChem101 - Lecture 2427
Exercise 2.17Relative Masses The mass of an atom cannot bedetermined by simply adding up themass of its constituent protons,neutrons and electrons.Write symbols like those given in Exercise 2.15for the following isotopes:a. cadmium-110b. cobalt-60c. uranium-235- This is because some of the mass isconverted to energy, which is used tohold the nucleus of the atom together. The mass of the atoms for eachelement must be determinedexperimentally.University of Wisconsin-Eau ClaireChem101 - Lecture 243University of Wisconsin-Eau ClaireChem101 - Lecture 2Relative MassesRelative Masses By convention, atomic masses aredetermined by comparing them to themass of the carbon-12 isotope. The unit of mass that is used is calledthe atomic mass unit and isrepresented by the symbol u. The atomic mass unit is equal toexactly 1/12 the mass of the carbon-12isotope. The atomic mass is also called the atomicweight. The atomic weights of the elements are givenon most periodic tables of the elements. The atomic weights given reflect weightedaverage of the masses of the naturallyoccurring isotopes of an element.44- For example, the atomic weight given for carbon is12.01 u instead of exactly 12 u.- This is because naturally occurring carboncomprises98.93 % carbon-12 and 1.07% carbon-13.- A carbon-12 atom weighs exactly 12 u.University of Wisconsin-Eau ClaireChem101 - Lecture 245 Chlorine has two naturally occurring isotopes:chlorine-35 (75.53%) and chlorine-37(24.47%).46Calculate the atomic weight of boron on the basisof the following percent composition and atomicweights of the naturally occurring isotopes.Compare the calculated value with the atomicweight listed for boron in the periodic table.- The atomic weight for chlorine-35 is 34.97 u.- The atomic weight for chlorine-37 is 36.97 u. The average atomic weight for chlorine is100Chem101 - Lecture 2Exercise 2.38Relative Masses(75.53)(34.97u) (24.47)(36.97u)University of Wisconsin-Eau Claireboron-10 19.78% (10.0129 u) 35.45uboron-11 80.22% (11.0093 u) This is the mass reported for chlorine on theperiodic table.University of Wisconsin-Eau ClaireChem101 - Lecture 247University of Wisconsin-Eau ClaireChem101 - Lecture 2488
The MoleThe Mole The atomic mass unit is a very smallunit of mass. A mole is defined as- The number of atoms of an element who’s massin grams is numerically equal to the atom’smass in atomic mass units.- This number is the same for all elements- For example: 1 g of carbon-12 weighs5.0 x 1023 u For example: In the lab we typically use grams asour unit of mass.University of Wisconsin-Eau ClaireChem101 - Lecture 2- The mass of 1 mole of carbon is 12.01 g.- The mass of 1 mole of chlorine is 35.45 g.49University of Wisconsin-Eau ClaireChem101 - Lecture 2The MoleThe Mass of a Mole of Molecules. The number of atoms in a mole of atomsis 6.022 x 1023 mole-1 ( per mole). Pure substances are made of molecules. The mass of a mole of molecules iscalled the molar mass or molecularweight. The molecular weight for a compoundcan be determined from its chemicalformula and the atomic weights of itsconstituent atoms.- This number is called Avogadro’s number.- You can have a mole of any object, like1 dozen (12) or 1 gross (144), it is just anumber.University of Wisconsin-Eau ClaireChem101 - Lecture 251University of Wisconsin-Eau ClaireChem101 - Lecture 25052Exercise 2.29The Mass of a Mole of Molecules. To determined the molecular weight ofH2O:Determine the molecular weights of the followingin u:a. oxygen (O 2)b. carbon monoxide (CO)c. chloric acid (HClO 3)d. glycerine (C 3H8O3)e. sulfur dioxide (SO 2) 1 mol O 16.00 g O 16.00 g O 1 mol H 2 O 1 mol H 2 O 1 mol O - O: 2 mol H 1.008 g H 2.016 g H 1 mol H 2 O 1 mol H 2 O 1 mol H - H: Added together these give the molecularweight for H2O: 16.00 g O 2.016 g H 18.02 g H 2 O 1 mol H 2 O 1 mol H 2 O 1 mol H 2 O University of Wisconsin-Eau ClaireChem101 - Lecture 253University of Wisconsin-Eau ClaireChem101 - Lecture 2549
Exercise 2.44Exercise 2.46Write three relationships (equalities) based on themole concept for each of the following elements(See section 2.7 for some examples):a.b.c.Use a factor derived from the relationshipswritten in Exercise 2.44 and the factor-unitmethod to determine the following (The factorunit method is discussed in Study Skills 2.1.):a. The mass in grams of one bromine atomb. The number ot grams of carbon in2.75 mol of carbonc. The total mass in grams of one-halfAvogadro’s number of silver atomsbrominecarbonsilverUniversity of Wisconsin-Eau ClaireChem101 - Lecture 255University of Wisconsin-Eau ClaireChem101 - Lecture 256Exercise 2.57Urea (CH 4N2O) and ammonium sulfate(N 2H8SO 4) are both used as agriculturalfertilizers. Which one contains the higher masspercentage of nitrogen?University of Wisconsin-Eau ClaireChem101 - Lecture 25710
Isotopes - Chlorine (Cl) also has two naturally occurring isotopes: one has 18 neutrons and represents 75.78% of all naturally occurring chlorine the other has 20 neutrons and represents the remaining 24.22% of all naturally occurring chlorine. - Magnesium (Mg) has three naturally occurring isotopes: one
A. 1.13 1024 atoms B. 1.48 1025 atoms C. 2.44 1022 atoms D. 3.22 1023 atoms E. 6.98 1021 atoms 50. How many atoms are in 7.12 mol of gold, Au? A. –1.18 10 23 atoms B. 244.29 10 atoms C. 8.46 1022 atoms D. 4.70 1024 atoms E. 3.34 1026 atoms 51. How many moles are
CARBON-BASED MOLECULES Reinforcement KEY CONCEPT Carbon-based molecules are the foundation of life. Carbon atoms are the basis of most molecules that make up living things. Many carbon-based molecules are large molecules called polymers that are made of many smaller, repeating molecules called monomers. There are four main types of
Atoms, Molecules, and Ions The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton. Dalton's Postulates Each element is composed of extremely small particles called atoms All atoms of a given element are identical to one another in mass and other
a. nitrogen. c. water. b. carbon dioxide. d. oxygen. ANS: D DIF: 1 OBJ: 6-1.3 21. During the Calvin cycle, carbon-containing molecules are produced from a. carbon atoms from ATP. b. carbon atoms, hydrogen atoms, and oxygen atoms from glucose. c. carbon atoms from carbon dioxide in the air and hydrogen atoms from water.
The forces that hold atoms together in compounds. Covalent bonds result from atoms sharing electrons. Molecule: a collection of covalently-bonded atoms. Figure 2.17: Molecular models of some elementary substances. An elemental substance is composed of molecules containing atoms from only one element.
AJR Ch2 Atoms, Molecules and Ions.docx Slide 1 Chapter 2: Atoms, Molecules, and Ions (Ch2 Chang, Chs 0 and 2 Jespersen) Atoms are the basic building blocks of matter. They are the smallest particles of an element that retain the chemical identity of the element, or, the basic unit of an element that can enter into chemical combination.
o Atoms are made of protons ( charge), neutrons (no charge), and electrons (- charge). o Atoms of the same type always have the same composition. o Atoms can share electrons (or “bond”) and form molecules. o Molecules adapt different shapes: spherical
water (liquid water, solid ice, and gas vapor). 3. You get different phases of water by adding or removing energy to speed up or slow down the molecules 4. The tiniest pieces of water of are molecules. 5. The molecules are made of atoms. 6. The specific atoms that make up water are 2 hydrogen atoms and 1 oxygen atom. 7. Yes, all water molecules .
