Do Elements exist?

Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivity.

Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal 2.4

Periodic Table Nonmetals are on the right side of the periodic table (with the exception of H).

Periodic Table Metalloids border the stair-step line (with the exception of Al and Po).

Periodic Table Metals are on the left side of the chart.

A molecule is an aggregate of two or more nonmetals in a definite arrangement held together by chemical bonds H2H2 H2OH2ONH 3 CH 4 A diatomic molecule contains only two atoms H 2, N 2, O 2, Br 2, HCl, CO A polyatomic molecule contains more than two atoms O 3, H 2 O, NH 3, CH 4 2.5

A molecular formula shows the exact number of atoms of each element in the individual molecules which are held together by weak attractive forces. An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2 2.6

Diatomic Molecules These seven elements occur naturally as molecules containing two atoms.

A molecule as we saw in a previous slide. How can we name these? Remember the Law of multiple proportions. H2H2 H2OH2ONH 3 CH 4 H 2, N 2, O 2, Br 2, HCl, CO 2.5

Nomenclature of Binary Molecular Compounds The lowest or most to the left atom is usually listed first. A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed.)

Nomenclature of Binary Compounds The ending is changed to - ide. –CO 2 : carbon dioxide –CCl 4 : carbon tetrachloride

Nomenclature of Binary Compounds If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often condensed: N 2 O 5 : dinitrogen pentoxide

HIhydrogen iodide NF 3 nitrogen trifluoride SO 2 sulfur dioxide N 2 Cl 4 dinitrogen tetrachloride NO 2 nitrogen dioxide N2ON2Odinitrogen monoxide Molecular Compounds 2.7 TOXIC ! Laughing Gas

An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5

Common Cations

Common Anions

Patterns in Oxyanion Nomenclature When there are two oxyanions involving the same element: –The one with fewer oxygens ends in -ite NO 2 − : nitrite ; SO 3 2− : sulfite –The one with more oxygens ends in -ate NO 3 − : nitrate; SO 4 2− : sulfate

A monatomic ion contains only one atom A polyatomic ion contains more than one atom 2.5 Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -

13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in Al ? 3+3+ How many protons and electrons are in Se ?

“Always Ions” When atoms lose or gain electrons, they become ions. –Cations are positive and are formed by metals. –Anions are negative and are formed by nonmetals. –Some elements only have one stable ionic state! Zn 2+ Ag +

ionic compounds consist of a combination of cations and an anions the formula is reported as an empirical formula the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl 2.6

Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: –The charge on the cation becomes the subscript on the anion. –The charge on the anion becomes the subscript on the cation. –If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.

Formula of Ionic Compounds Al 2 O x +3 = +63 x -2 = -6 Al 3+ O 2- CaBr 2 1 x +2 = +22 x -1 = -2 Ca 2+ Br - Na 2 CO 3 1 x +2 = +21 x -2 = -2 Na + CO 3 2-

Inorganic Nomenclature Write the name of the cation. If the anion is an monoatomic ion, change its ending to -ide; if the anion is a polyatomic ion … do you want to memorize 400+ of these? If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses.

Inorganic Nomenclature Link to Activity

Acid Nomenclature An anion with H +. If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro- : –HCl: hydrochloric acid –HBr: hydrobromic acid –HI: hydroiodic acid

Acid Nomenclature An anion with H +. If the anion in the acid ends in -ite, change the ending to -ous acid: –HClO: hypochlorous acid –HClO 2 : chlorous acid

Acid Nomenclature An anion with H +. If the anion in the acid ends in -ate, change the ending to -ic acid: –HClO 3 : chloric acid –HClO 4 : perchloric acid

Polyatomic Ions Revisited 2.7 Note: These names have meaning and can be “calculated.”

Oxidation Number or State The charge the atom would have in a compound if electrons were completely transferred. Electron Book Keeping Method. 1.Free elements in their standard state have an oxidation number of zero. Na, Be, K, Pb, H 2, O 2, P 4 = 0 2.In monatomic ions, the oxidation number is equal to the charge on the ion. Li +, Li = +1; Fe 3+, Fe = +3; O 2-, O = -2 3.The oxidation number of oxygen is usually –2. In H 2 O 2 and O 2 2- it is –1. 4.4

4.The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds. In these cases, its oxidation number is –1. 6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion. 5.Group IA metals are +1, IIA metals are +2 and fluorine is always –1. HCO 3 - O = -2H = +1 3x(-2) ? = -1 C = +4 Oxidation numbers of all the elements in HCO 3 - ? 4.4

NaIO 3 Na = +1 O = -2 3x(-2) ? = 0 I = +5 IF 7 F = -1 7x(-1) + ? = 0 I = +7 K 2 Cr 2 O 7 O = -2K = +1 7x(-2) + 2x(+1) + 2x(?) = 0 Cr = +6 Oxidation numbers of all the elements in the following ? 4.4

+6 Column 6 … Hmmmm Do You Understand Oxidation State? 2.5 What is the oxidation state of Sulfur in Sulfate? What Column is Sulfur in on the periodic table?

+5 Column 5 … Hmmmm Do You Understand Oxidation State? 2.5 What is the oxidation state of Phosphorous in Phosphate? What Column is Phosphorous in on the periodic table?

Some Polyatomic Ions 2.7 Calculate the O.S. for the “ates” and “ites.” Is there a pattern?

Patterns PerchlorateClO 4 - ChlorateClO 3 - ChloriteClO 2 - HypochloriteClO - ChlorideCl - Do you seen any patterns?

Chemical Nomenclature Ionic Compounds –Cation is a metal ion or ammonium ion (NH 4 + ) –Anion (nonmetal), add “ide” to element name, or a complex ion (“ate”, “ite”, etc) BaCl 2 barium chloride K2OK2O potassium oxide Mg(OH) 2 magnesium hydroxide KNO 3 potassium nitrate 2.7

Transition metal ionic compounds –indicate charge on metal with Roman numerals FeCl 2 2 Cl - -2 so Fe is +2 iron(II) chloride FeCl 3 3 Cl - -3 so Fe is +3 iron(III) chloride Cr 2 S 3 3 S so Cr is +3 (6/2)chromium(III) sulfide 2.7