Do Elements exist?

Periodicity

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

Period 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 H 2 H 2 O NH 3 CH 4 A

diatomic molecule

contains only two atoms H 2 , N 2 , O 2 , Br 2 , HCl, CO A

polyatomic molecule

two atoms contains more than 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

molecular

H 2 O C 6 H 12 O 6 N O 2 3 H 4

empirical

H 2 O CH 2 O O 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.

H 2 H 2 O NH 3 H 2 , N 2 , O 2 , Br 2 , HCl, CO CH 4 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

vowels are often condensed: or

o

and the name of the element begins with a vowel, the two successive N 2 O 5 : dinitrogen pentoxide

HI NF 3 SO 2 N 2 Cl 4 NO 2 N 2 O

Molecular Compounds

hydrogen iodide nitrogen trifluoride sulfur dioxide dinitrogen tetrachloride nitrogen dioxide TOXIC dinitrogen monoxide !

Laughing Gas 2.7

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.

Na 11 protons 11 electrons Na + 11 protons 10 electrons

anion

– ion with a negative charge If a neutral atom

gains

it becomes an anion.

one or more 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 Na + , Cl , Ca 2+ , O 2 , Al 3+ , N 3 A

polyatomic ion

contains more than one atom OH , CN , NH 4 + , NO 3 2.5

Do You Understand Ions?

How many protons and electrons are in 27 13 Al 3 + ?

13 protons, 10 (13 – 3) electrons How many protons and electrons are in 78 34 Se 2 ?

34 protons, 36 (34 + 2) electrons 2.5

“Always Ions”

Ag + Zn 2+ • 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!

ionic compounds

and an anions consist of a combination of cations • 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 2 x +3 = +6 3 x -2 = -6 Al 3+ Al 2 O 3 O 2 1 x +2 = +2 2 x -1 = -2 Ca 2+ CaBr 2 Br

-

1 x +2 = +2 1 x -2 = -2 Na + Na 2 CO 3 CO 3 2

-

2.6

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

NH 4 + CO 3 2 HCO 3 ClO 3 Cr 2 O 7 2 CrO 4 2 Polyatomic Ions Revisited ammonium carbonate bicarbonate chlorate dichromate chromate SO 4 2 SO 3 2 NO 3 NO 2 - SCN - OH sulfate sulfite nitrate nitrite thiocyanate hydroxide Note: These names have meaning and can be “calculated.” 2.7

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 and O 2 2 it is –1 .

usually

–2 . In H 2 O 2 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 .

5. Group IA metals are +1 , IIA metals are +2 always –1 .

and fluorine is 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.

HCO 3 Oxidation numbers of all the elements in HCO 3 ?

O = -2 H = +1 3x( -2) + 1 + ?

= -1 C = +4 4.4

Oxidation numbers of all the elements in the following ?

NaIO Na = +1 I = +5 3 O = -2 3x( -2 ) + 1 + ?

= 0 IF 7 F = -1 7x( -1 ) + ?

= 0 I = +7 K 2 Cr 2 O 7 O = -2 K = +1 7x( -2 ) + 2x( +1 ) + 2x( ?) = 0 Cr = +6 4.4

Do You Understand Oxidation State?

What is the oxidation state of Sulfur in Sulfate?

+6 What Column is Sulfur in on the periodic table?

Column 6 … Hmmmm 2.5

Do You Understand Oxidation State?

What is the oxidation state of Phosphorous in Phosphate?

+5 What Column is Phosphorous in on the periodic table?

Column 5 … Hmmmm 2.5

NH 4 + CO 3 2 HCO 3 ClO 3 Cr 2 O 7 2 CrO 4 2 Some Polyatomic Ions ammonium carbonate bicarbonate chlorate dichromate chromate SO 4 2 SO 3 2 NO 3 NO 2 - SCN - OH sulfate sulfite nitrate nitrite thiocyanate hydroxide Calculate the O.S. for the “ates” and “ites.” Is there a pattern?

2.7

Patterns

• Perchlorate ClO 4 • Chlorate ClO 3 • Chlorite ClO 2 • Hypochlorite ClO • Chloride Cl • Do you seen any patterns?

•

Chemical Nomenclature

Ionic Compounds

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

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