1

Chemical CompoundsChemical Compounds

Chapter 3Chapter 3

Jons J. Berzelius 1779-1848.Accurately determinedatomic weights, used infuture Periodic Table. Originated modern chemical formulas, including “K” and “Na” for potassium and sodium.

2

Molecules and Chemical FormulasMolecules and Chemical Formulas

Molecules and Molecular CompoundsMolecules and Molecular Compounds

Molecules are assemblies of two or more atoms bonded together.

Each molecule has a chemical formula.The chemical formula indicates:

which atoms are found in the molecule, andin what proportion they are found.

Compounds formed from molecules are molecular compounds.

3

Molecular formulasgive the actual numbers and types of atoms in a molecule.Examples:

Molecules and Molecular CompoundsMolecules and Molecular CompoundsMolecular and Empirical Molecular and Empirical FormulasFormulas

H2O, CO2, CO, CH4, H2O2, O2, O3, and C2H4.

Empirical formulasgive the relative numbers and types of atoms in a molecule.That is, they give the lowest whole number ratio of atoms in a molecule.

Examples: H2O, CO2, CO, CH4, HO, CH2.

4

Picturing MoleculesPicturing Molecules

Molecules occupy three dimensional space. However, we often represent them in two dimensions.

The structural formula gives the connectivity between individual atoms in the molecule.

The structural formula may or may not be used to show the three dimensional shape of the molecule.

Molecules and Molecular CompoundsMolecules and Molecular Compounds

5

Picturing MoleculesPicturing Molecules

Molecules and Molecular CompoundsMolecules and Molecular Compounds

6

Different representations of methane (CH4)

7

When an atom or molecule loses electrons, it becomes positively charged.

Ions and Ionic CompoundsIons and Ionic Compounds

•For example, when Na loses an electron, it becomes Na+. Positively charged ions are called cations.

8

When an atom or molecule gains electrons, it becomes negatively charged.

Ions and Ionic CompoundsIons and Ionic Compounds

For example when Cl gains an electron it becomes Cl.Negatively charged ions are called anions.An atom or molecule can lose more than one electron.

9

12p+ 12 e- lose 2 e-

12p+ 10 e-

Ions and Ionic CompoundsWhen an atom or molecule loses two electrons, itbecomes doubly positively charged.

For example, when Mg loses two electrons, it becomes Mg2+

Mg atom Mg2+ ion “magnesium atom” “magnesium ion”

10

16 p+ 16 e- gain 2 e-

16p+ 18 e-

Ions and Ionic CompoundsWhen an atom or molecule gains two electrons, itbecomes doubly negatively charged.

For example, when S gains 2 electrons, it becomes S2-

S atom S2- ion“sulfur atom” “sulfide ion”

11

Predicting Ionic ChargePredicting Ionic ChargeThe number of electrons an atom gains or loses is related to its position on the periodic table.

Ions and Ionic CompoundsIons and Ionic Compounds

whereas non-metals tend to form anions.

Metals tend to form cations

12

Ions and Ionic CompoundsIons and Ionic CompoundsWhat ions do the main group elements (the “A” elements) form? It depends on their grouping.

Group IA elements (H, Li, Na..) form 1+ ions (H+,Li+, Na+…)Group IIA elements (Be, Mg, Ca)form 2+ ions (Be2+, Mg2+…)Group IIIA elements (B, Al, Ga) form 3+ ions (B3+, Al3+, …)

Group VA elements (N, P…) form 3- ions (N3-, P3-)Group VIA elements (O, S,..) form 2- ions (O2-, S2-…)Group VIIA elements (F, Cl, Br.) form 1- ions (F-, Cl-, Br-….)

Group VIIIA elements do not form ions.Neither does Group IVA.

13

Ions and Ionic CompoundsIons and Ionic Compounds

Na .

Ionic CompoundsIonic Compounds The majority of chemistry involves the transfer of electrons between species.

Example:To form NaCl, the neutral sodium atom, Na, must lose an electron to become a cation: Na+

.Na+

11 p+

11 e-

11 p+

10 e-

14

whereas non-metals tend to form anions.

The electron cannot be lost entirely, so it is transferred to a chlorine atom, Cl, which then becomes an anion: Cl-.

Ions and Ionic CompoundsIons and Ionic CompoundsIonic CompoundsIonic Compounds

The Na+ and Cl- ions are attracted to form an ionic NaCl lattice which crystallizes.

Cl

.Cl-

17 p+

17 e-17 p+

18 e-

(from Na atom)

15

Important: note that there are no easily identified NaCl molecules in the ionic lattice. Therefore, we cannot use molecular formulas to describe ionic substances.

Ions and Ionic CompoundsIons and Ionic Compounds

16

Ionic CompoundsIonic Compounds Consider the formation of Mg3N2:Mg loses two electrons to become Mg2+

Nitrogen gains three electrons to become N3-.For a neutral species, the number of electrons lost and gained must be equal.However, Mg can only lose electrons in twos and N can only accept electrons in threes.Therefore, Mg needs to lose 6 electrons (2 3) and N gain those 6 electrons (3 2).

Ions and Ionic CompoundsIons and Ionic Compounds

17

Ionic CompoundsIonic Compounds I.e., 3Mg atoms need to form 3Mg2+ ions (total 3x2+ charges) and 2 N atoms need to form 2N3- ions (total 2x3- charges).Therefore, the formula is Mg3N2.

Ions and Ionic CompoundsIons and Ionic Compounds

Mg N

N3-Mg2+

3 2Be careful! what’s the ionic compound formed between magnesium and oxygen?)

MgO

18

Naming of compounds, nomenclature, is divided into organic compounds (those containing C) and inorganic compounds (the rest of the periodic table)

Naming Inorganic CompoundsNaming Inorganic CompoundsNames and Formulas of Ionic CompoundsNames and Formulas of Ionic Compounds

Cations formed from a metal have the same name as the metal.

Example: Na+ = sodium ion.

If the metal can form more than one cation, then the charge is indicated in parentheses in the name.

Examples: Cu+ = copper(I); Cu2+ = copper(II).

19

Hydrogen ion H+ Cupric ion Co2+

Lithium ion Li+ Cuprous ion Cu+

Sodium ion Na+ Ferric ion Fe3+

Potassium ion K+ Ferrous ion Fe2+

Silver ion Ag+ Manganous ion Mn2+

Magnesium ion Mg2+ Mercurous ion Hg22+

Calcium ion Ca2+ Mercuric ion Hg2+

Strontium ion Sr2+ Nickelous ion Ni2+

Barium ion Ba2+ Plumbous ion Pb2+

Zinc ion Zn2+ Stannous ion Sn2+

Cadmium ion Cd2+ Stannic ion Sn4+

Aluminum ion Al3+ Chromic ion Cr3+

20

Monoatomic anions (with only one atom) are called ide.Example: Cl is chloride ion.Exceptions: hydroxide (OH), cyanide (CN), peroxide (O2

2).

Polyatomic anions (with many atoms) containing oxygen end in -ate or -ite. (The one with more oxygen is called -ate.)

Examples: NO3- is nitrate, NO2

- is nitrite.

Naming Inorganic CompoundsNaming Inorganic CompoundsNames and Formulas of Ionic CompoundsNames and Formulas of Ionic Compounds

21

Naming Inorganic CompoundsNaming Inorganic Compounds

nitrate NO3- hydroxide OH-

nitrite NO2- phosphate PO4

3-

carbonate CO32- ammonium NH4

+

sulfate SO42- perchlorate ClO4

-

sulfite SO32- chlorate ClO3

-

cyanide CN - chlorite ClO2-

chromate CrO4-2 hypochlorite ClO -

dichromate Cr2O72- carbonate CO3

2-

permanganate MnO4-

bicarbonate (or hydrogen carbonate) HCO3-

22

Hydride H - oxide O2-

fluoride F - peroxide O22-

chloride Cl - sulfide S2-

bromide Br - nitride N3-

iodide I -

Monoatomic ions

23

Names and Formulas of Binary Molecular CompoundsNames and Formulas of Binary Molecular Compounds

Binary molecular compounds have two elements.The most metallic element is usually written first (i.e., the one to the farthest left on the periodic table). Exception: NH3.If both elements are in the same group, the lower one is written first.Greek prefixes are used to indicate the number of atoms.

mono 1di 2tri 3tetra 4penta 5hexa 6hepta 7octa 8nona 9deca 10

Name: NO2

SO3

N2O4

P2O5

CCl4

CO

CO2

Nitrogen dioxideSulfur trioxide

Dinitrogen tetroxide

Diphosphorus pentoxideCarbon tetrachlorideCarbon monoxideCarbon dioxide

24

Naming Organic CompoundsNaming Organic Compounds

Name, formula, bp oC Name, formula, bp oC

Methane CH4 -162 Methyl alcohol CH3OH, 66

Ethane C2H6 -89 Ethyl alcohol C2H5OH, 98

Propane C3H8 -42 Propyl alcohol C3H7OH, 97

Butane C4H10 0 Isopropyl alcohol

Pentane C5H12 36 CH3-CH(OH)-CH3, 82

Hexane C6H14 69 [Propyl alcohol and isopropyl

Heptane C7H16 98 alcohol are isomers]

Octane C8H18 126

Nonane C9H20 151

Decane C10H22 174