# CHAPTER 2 ATOMS and MOLECULES. Periodic Table Atomic Mass – number below the element – not whole numbers because the masses are averages of the masses.

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CHAPTER 2 ATOMS and MOLECULES

Periodic Table Atomic Mass – number below the element – not whole numbers because the masses are averages of the masses of the different isotopes of the elements

Ions Are charged species Result when elements gain electrons or lose electrons

2 Types of Ions Anions – (-) charged Example:F - Cations – (+) charged Example:Na +

Highly Important! Gain of electrons makes element (-)=anion Loss of electrons makes element (+)=cation

Charges When elements combine, they have to be in the form of IONS. Cations and anions combine to form compounds. For a neutral compound, the sum of the charges must be ZERO. For a polyatomic ion, the sum of the charges must equal the charge of the ION.

Isotopes Are atoms of a given element that differ in the number of neutrons and consequently in atomic mass.

Example Isotopes% Abundance 12 C 98.89 % 13 C 1.11 % 14 C 11 C

– For example, the mass of C = 12.01 a.m.u is the average of the masses of 12 C, 13 C and 14 C.

Determination of Aver. Mass Ave. Mass = [(% Abund./100) (atomic mass)] + [(% Abund./100) (atomic mass)]

Take Note: If there are more than 2 isotopes, then formula has to be re-adjusted

Sample Problem 1 Assume that element Uus is synthesized and that it has the following stable isotopes: – 284 Uus (283.4 a.m.u.)34.6 % – 285 Uus (284.7 a.m.u.)21.2 % – 288 Uus (287.8 a.m.u.)44.20 %

Solution Ave. Mass of Uus = [ 284 Uus](283.4 a.m.u.)(0.346) [ 285 Uus] +(284.7 a.m.u.)(0.212) [ 288 Uus] +(287.8 a.m.u.)(0.4420) = 97.92 + 60.36 + 127.21 = 285.49 a.m.u (FINAL ANS.)

Oxidation Numbers Is the charge of the ions (elements in their ion form) Is a form of electron accounting Compounds have total charge of zero (positive charge equals negative charge)

Oxidation States Are the partial charges of the ions. Some ions have more than one oxidation states.

Oxidation States - generally depend upon the how the element follows the octet rule Octet Rule – rule allowing elements to follow the noble gas configuration

Nomenclature - naming of compounds

Periodic Table Rows (Left to Right) - periods Columns (top to bottom) - groups

Rule 1 – IONIC COMPOUNDS Metals w/ Fixed Oxidation States – Name metal or first element as is - Anion always ends in “–ide”

Terminal element or anion O-oxideP - phosphide N-nitrideSe - selenide S -sulfideCl - chloride F-fluorideI - iodide Br - bromideC - carbide

Note Only elements that come directly from the periodic table WILL end in –IDE. POLYATOMIC IONS will be named AS IS.

Name the following: CaO- NaCl- MgO- CaS- Na 3 N-

Answers: CaO-calcium oxide NaCl-sodium chloride MgO- magnesium oxide CaS- calcium sulfide Na 3 N-sodium nitride

Where do the subscripts come from? Answer:From the oxidation states of the ions. Remember:Ions are the species that combine. Target:Compounds! (No charges!)

Second Rule II. Ionic Compounds - Metals with no fixed oxidation states (Transition Metals) except for Ag, Zn and Al Metal(Roman #) + 1 st syllable + ide – Use Roman numerals after the metal to indicate oxidation state

Name the following: Copper (I) sulfide Iron (II) oxide Tin (II) iodide Iron (III) nitride

Answers: Copper (I) sulfideCu 2 S Iron (II) oxideFeO Tin (II) iodideSnI 2 Iron (III) nitrideFeN

What about…….? Cesium hydroxide Iron (III) acetate Lithium phosphate Aluminum Sulfite Lead (II) sulfate Silver nitrate

POLYATOMIC IONS Consist of more than 1 element. Have charges. Ex. SO 4 2-, SO 3 2-, PO 4 3-,PO 3 3-

Rule 3 – Covalent Compounds III. For Non-metals (grps IV, V, VI VII), use prefixes. Mono – 1Hepta - 7 Di - 2Octa - 8 Tri – 3Nona - 9 Tetra – 4Deca - 10 Penta – 5 Hexa - 6

Rule 3 – Covalent Compounds (only have Non- Metals) Name 1 st element as is. Use prefix, if necessary. Prefix + 1 st element + prefix + 1 st syllable of anion + ide

Name the following compounds CO 2 - carbon dioxide N 2 O – dinitrogen oxide SO 3 – sulfur trioxide N 2 O 5 – dinitrogen pentoxide P 2 S 5 – diphosphorus pentasulfide CO – carbon monoxide

Naming Acids I. Acids without Oxygen – Use hydro + 1 st syllable + “- ic acid” Example: HCl = hydrochloric acid HCN = hydrocyanic acid HBr = hydrobromic acid

II. Acids with oxygen Polyatomic “ate” converts to “ic” + acid Polyatomic “ite” converts to “ous” + acid - H 2 SO 3 sulfurous acid – H 2 SO 4 sulfuric acid – HNO 3 nitric acid – HNO 2 nitrous acid – H 3 PO 4 phosphoric acid

Trick! If anion ends in “ – ate”, acid ends in “ – ic” Example: HClO 4 perchlorateperchloric acid HClO 3 chloratechloric acid

Trick! If anion ends in “ – ite”, acid ends in “ – ous” Example: HClO 2 chloritechlorous acid HClOhypochloritehypochlorous acid

Name the following: HBrO 4 (perbromate) HBrO 3 (bromate) HBrO 2 (bromite) HBrO(hypobromite)

Pure Acids (not diluted) Simply use Rule 3. Use prefixes, if necessary.

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