Atoms, Molecules and IonsChapter 2

Daltons Atomic Theory (1808) Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions. 2.1

22.1

8 X2Y2.1

J.J. Thomson, measured mass/charge of e- (1906 Nobel Prize in Physics)2.2

Cathode Ray Tube2.2

e- charge = -1.60 x 10-19 CThomsons charge/mass of e- = -1.76 x 108 C/g e- mass = 9.10 x 10-28 gMeasured mass of e- (1923 Nobel Prize in Physics)2.2

Everybody Has Avogadros Number!But Where Did it Come From?It was NOT just picked! It was MEASURED.One of the better methods of measuring this number was the Millikan Oil Drop ExperimentSince then we have found even better ways of measuring using x-ray technology

(Uranium compound)2.2

2.2

The modern view of the atom was developed by Ernest Rutherford (1871-1937).

atoms positive charge is concentrated in the nucleusproton (p) has opposite (+) charge of electron (-)mass of p is 1840 x mass of e- (1.67 x 10-24 g) particle velocity ~ 1.4 x 107 m/s(~5% speed of light)(1908 Nobel Prize in Chemistry)2.2

atomic radius ~ 100 pm = 1 x 10-10 mnuclear radius ~ 5 x 10-3 pm = 5 x 10-15 mRutherfords Model of the Atom2.2If the atom is the Houston Astrodome, then the nucleus is a marble on the 50-yard line.

Chadwicks Experiment (1932)H atoms - 1 p; He atoms - 2 pmass He/mass H should = 2measured mass He/mass H = 4neutron (n) is neutral (charge = 0)n mass ~ p mass = 1.67 x 10-24 g2.2

mass p = mass n = 1840 x mass e-2.2

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutronsIsotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei2.3

2.3

6 protons, 8 (14 - 6) neutrons, 6 electrons6 protons, 5 (11 - 6) neutrons, 6 electronsDo You Understand Isotopes?2.3

2.4

Chemistry In ActionNatural abundance of elements in Earths crustNatural abundance of elements in human body2.4

A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bondsA diatomic molecule contains only two atomsH2, N2, O2, Br2, HCl, COA polyatomic molecule contains more than two atomsO3, H2O, NH3, CH42.5

ELEMENTS THAT EXIST AS DIATOMIC MOLECULESRemember:BrINClHOFThese elements only exist as PAIRS. Note that when they combine to make compounds, they are no longer elements so they are no longer in pairs!

An ion is an atom, or group of atoms, that has a net positive or negative charge.cation ion with a positive chargeIf a neutral atom loses one or more electronsit becomes a cation.anion ion with a negative chargeIf a neutral atom gains one or more electronsit becomes an anion.2.5

Forming Cations & AnionsA CATION forms when an atom loses one or more electrons.An ANION forms when an atom gains one or more electronsMg --> Mg2+ + 2 e-F + e- --> F-

A monatomic ion contains only one atomA polyatomic ion contains more than one atom2.5Na+, Cl-, Ca2+, O2-, Al3+, N3-OH-, CN-, NH4+, NO3-

13 protons, 10 (13 3) electrons34 protons, 36 (34 + 2) electronsDo You Understand Ions?2.5

2.5

2.6

A molecular formula shows the exact number of atoms of each element in the smallest unit of a substanceAn empirical formula shows the simplest whole-number ratio of the atoms in a substanceH2OC6H12O6CH2OO3ON2H4NH22.6

ionic compounds consist of a combination of cation(s) and an anion(s) the formula is always the same as the empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zeroThe ionic compound NaCl2.6

Formula of Ionic CompoundsAl2O32.6Al3+O2-CaBr2Ca2+Br-Na2CO3Na+CO32-

2.6

2.7

Examples of Older Names of Cations formed from Transition Metals(memorize these!!)From Zumdahl

Chemical NomenclatureIonic Compoundsoften a metal + nonmetalanion (nonmetal), add ide to element nameBaCl2barium chlorideK2Opotassium oxideMg(OH)2magnesium hydroxideKNO3potassium nitrate2.7

Transition metal ionic compoundsindicate charge on metal with Roman numeralsFeCl22 Cl- -2 so Fe is +2iron(II) chloride FeCl33 Cl- -3 so Fe is +3iron(III) chloride Cr2S33 S-2 -6 so Cr is +3 (6/2)chromium(III) sulfide2.7

Molecular compoundsnonmetals or nonmetals + metalloidscommon namesH2O, NH3, CH4, C60element further left in periodic table is 1stelement closest to bottom of group is 1stif more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atomlast element ends in ide2.7

HIhydrogen iodideNF3nitrogen trifluorideSO2sulfur dioxideN2Cl4dinitrogen tetrachlorideNO2nitrogen dioxideN2Odinitrogen monoxideMolecular Compounds2.7

2.7

An acid can be defined as a substance that yields hydrogen ions (H+) when dissolved in water.HClPure substance, hydrogen chlorideDissolved in water (H+ Cl-), hydrochloric acidAn oxoacid is an acid that contains hydrogen, oxygen, and another element.2.7HNO3

2.7

2.7

2.7

A base can be defined as a substance that yields hydroxide ions (OH-) when dissolved in water.2.7

2.7

Mixed PracticeDinitrogen monoxidePotassium sulfideCopper (II) nitrateDichlorine heptoxideChromium (III) sulfateFerric sulfiteCalcium oxideBarium carbonateIodine monochlorideN2OK2SCu(NO3)2Cl2O7Cr2(SO4)3Fe2(SO3)3CaOBaCO3ICl

Mixed PracticeBaI2P4S3Ca(OH)2FeCO3Na2Cr2O7I2O5Cu(ClO4)2CS2B2Cl4Barium iodideTetraphosphorus trisulfideCalcium hydroxideIron (II) carbonateSodium dichromateDiiodine pentoxideCupric perchlorateCarbon disulfideDiboron tetrachloride