Chemical Formulas Keynote

Writing Formulas and Naming Ionic & Covalent Compounds ©2005 Douglas Gilliland Honors Physical Science @ Sarasota High Sarasota, Florida

Chemical Compounds

An atom consist of a positively charged nucleus (protons and neutrons) and orbiting electrons.

Atoms of elements are not chemically stable until they have 8 electrons (octet rule).

Atoms gain, lose or share electrons with other atoms to be come chemically stable ( have 8 valence electrons ).

Six valence electrons.

Eight valence

Not chemically stable.

-2

8+

Oxygen Atom

electrons.

8+

stable.

Oxide Ion

Chemically

Types of Compounds I o n i c - occurs when a metal loses all

its valence electrons to a nonmetal. Metal becomes a cation, nonmetal an anion. C o v a l e n t - two nonmetals share electrons. Neither loses or gains

electrons - they share electrons. Neither atom becomes and ion.

Ionic Compounds

Crystalline Lattice

Burning Magnesium 2Mg + O2 ! 2MgO

20+

+

-2

+2 8+

Magnesium Atom + Oxygen Atom

20+

!

+

Magnesium Ion

+

8+ Oxide Ion

Reaction between sodium + chlorine

2Na + Cl2 ! 2NaCl

11+

+

17+

Sodium Atom

+

Chlorine Atom

11+ !

+

Sodium Ion

-

+

17+

+

Chloride Ion

Ionic Compounds Includes a metal and a nonmetal. Metal loses e- and becomes a cation (+). Nonmetal gains e- and becomes an anion(-). Metal comes first followed by nonmetal. Change the name of the nonmetal to -ide. Examples: nitride, sulfide, fluoride, oxide,

bromide, iodide, chloride, telluride, phosphide.

Valence electrons are electrons in the outer energy level of an atom. Metals have between 1-3 valence electrons. Nonmetals have between 5-7 valence electrons.

Lose e-

Cations (+ ions)

Gain eAnions (- ions)

The valence of an elements is the charge it takes when it loses or gains electrons.

Metal atoms lose electrons and become + ions (cations) Nonmetals gain electrons and become - ions (anions) +1

+2

Transition Metals Multiple valences

+3 -4 -3 -2 -1

0

The 5 Steps for writing an ionic compound formula: Write the symbols of the two elements. Write the valence of each as superscripts. Drop the positive and negative signs. Crisscross the superscripts so they become subscripts.

Reduce when possible.

Formula for boron oxide 1. Write the symbols of the two elements.

B O

Formula for boron oxide 2. Write the valence for each element.

+3

-2

B O

Formula for boron oxide 3. Drop the positive & negative sign.

3

B O

2

Formula for boron oxide 4. Crisscross the superscripts so they become subscripts.

3

B O

2

Formula for boron oxide 4. Crisscross the superscripts so they become subscripts.

B O 2

3

Formula for boron oxide 5. Reduce subscripts when possible. (not possible here)

B O 2

3

Examples of Reduction Ca 2S 2 ! CaS Ge 2 O4 ! Ge O2 Be2Te 3 ! can’t reduce Al 3 N 3 ! AlN

Sn 2 O4 ! SnO 2

Most Transition elements have 2 valences. Roman numerals are used in the name to show the valence on the ion. !" 12

$% 13 12

# 14 13

Period 4 Transition Metals () 15 12

&' 13 15

*+ 16 12

(, 16 12

-. 16 12

(/ 16 17

0' 16

Examples: Mn Manganese(IV) Mn +4

Fe

+2

Iron(II)

Fe

+3

Cu Copper(I) Cu +1

+6

+2

Manganese(VI) Iron(III) Copper(II)

Examples of Transition Metals +2

Iron(II) Fe +3 Iron(III) Fe +1 Copper(I) Cu +2 Copper(II)Cu +2 Manganese(II) Mn +4 Manganese(IV)Mn

Naming compounds with a transition metal. formula

name

Fe2 O 3

Iron(III) oxide

ZnCl 2

Zinc(II) chloride

AgCl

Silver(I) chloride

Cu 3 P2

Copper(II) phosphide

PbS2

Lead(IV) sulfide

MnO2

Manganese(IV) oxide

Polyatomic Ions -1

Polyatomic (many atom) ions are covalent molecules with a charge. They behave as if they were a single atom ion.

Polyatomic Ions Nitrite

-2 SO2 -2 SO3 -2 CO3

Carbonate

Nitrate

-3 PO4

Phosphate

+1 NH4 -1

Ammonium

-1 NO2

OH

-1 NO3

Hydroxide

Sulfite Sulfate

Treat polyatomic ions as you would any ion - crisscross to

determine the formula. The only difference is that when you have more than one of a specific polyatomic ion in a formula you must encase it in parenthesis.

Writing Formulas

Cation

Anion

Ca

-1 NO3

Mg +2

-3 PO4

+2

Na

+1

+2

Ba

OH

-1

-2 SO4

Compound Ca(NO3)2

Mg 3(PO4)2 NaOH Ba SO4

As in all ionic compounds you must reduce subscripts, but you

cannot change the formula of the polyatomic ion. You can only reduce subscripts outside the parenthesis.

Compounds with Polyatomic ions

Carbonate

-2 CO 3

Sodium carbonate Na 2CO3

Calcium carbonate Ca CO 3

Phosphate

Aluminum carbonate Al 2(CO 3)3

-3 PO4

Sodium phosphate Na 3PO4

Calcium phosphate Ca3(PO3 )2 Aluminum phosphate AlPO 3

Covalent Compounds

Water Molecule

Hydrogen Oxygen Atom Atom

Hydrogen Atom

Covalent Compounds Two nonmetals share electrons so both have 8 valence electrons. Exception: H

Neither takes on a charge - no valence. Must use prefixes in the name. Name tells you the formula. Example: N2O4 is dinitrogen tetraoxide.

You cannot reduce the formulas!!!

Reaction between hydrogen + oxygen

2H2 + O2 ! 2H2O

1+

1+

+

2 Hydrogen Atoms

8+ Oxygen Atom

1+

8+

Water Molecule 1+

The Space Shuttle

Oxygen Hydrogen

Water Vapor Exothermic Reaction

2H2 + O2 ! 2H2O

Covalent Prefixes Mon - 1 Tetra - 4 Di - 2

Pent - 5

Tri - 3

Hex - 6

A prefix tells you the number of atoms of that element in the compound.

Examples of Covalent Compounds

N2O3 Carbon tetrahydride CH 4 Phosphorus pentoxide PO 5 disulfur trifluoride S2F3 Dinitrogen trioxide

Ionic and Covalent Structure Ionic compounds

form a crystalline lattice - a repeating pattern of ions. +3

B ions N-3 ions

Boron nitride

Water

H atoms O atom

Covalent compounds form individual molecules that are not connected to each other.

Naming Binary Compounds Does the compound have a metal?

Yes

No

Covalent

Ionic

(Metal cation + Nonmetal anion)

Place metal first followed by nonmetal ending in -ide

(Two Nonmetals)

Contain a Transition Metal? Place the nonmetal furthest to the left on the periodic table first, then No Yes the other nonmetal ending in -ide. Use Roman Do not use Use prefixes to tell the number of Numerals to tell atoms in the compound Roman the valence of mon(o)-1, di-2, tri-3, tetr(a)-4, Numerals the metal. pent(a)-5, hex-6 Examples: Examples: iron(III) oxide copper(II) chloride manganese(IV) oxide silver(I) chloride

sodium chloride magnesium nitride aluminum fluoride beryllium oxide

Examples: dinitrogen trioxide, nitrogen trichloride, phosphorus pentoxide, sulfur dioxide carbon tetrachloride, dihydrogen oxide

Summing up: Ionic

Ionic bonding occurs between a metal and

a nonmetal. Metals lose all their valence eand become cations. Nonmetals gain

enough e- to fill their valence level and become anions.

Always crisscross valences and reduce to

determine the formulas of ionic compounds Do not use prefixes in the names. Ions form a crystalline lattice.

Summing up: Covalent

Covalent bonding occurs when two nonmetals share electrons to fill their valence energy level.

Never use valence to determine the formula there isn’t any valence. Since the two atoms share electrons, they do not take on a charge.

Always use prefixes in the names. Atoms combine to form individual molecules.