2.3.8. COMPOUNDS

Atoms in compounds are joined / bonded to
each other
 covalent bonds in molecules (H-Cl)
 or ions in ionic solids (Na+ Cl -)

Molecules: Definite, electrically neutral
group of covalently bonded atoms (H2O,
CH4, NH3)

So, molecular compounds made up of
molecules! Most organic compounds are
molecular. Also gases, liquids at R.T.
2.4.1. COMPOUNDS

Ionic: +vely or -vely charged atoms or
groups of atoms (Na+, NO3-, SO42-)

Ionic solids consists of ions, tend to be
high-melting solids.

Chemical formula: chemical symbols
for atoms in the compound
 Molecular
formula: chemical formula for
molecules showing members and types of
atoms in the molecule

Sugar(glucose): C12 H22 O11
11 O atoms -
12C, 22H, and
2.4.2. Compounds

BUT molecules have geometry and
specific arrangements of atoms
 Structural
formula:
e.g. Ethanol, C6H6O or CH3CH2OH
2.4.3. Compounds

Ball- and-stick model - shows geometry:
bond angles / length.

Space-filling model – computer graphics
from MO calculations
2.4.4. Compounds
Ionic Compounds
Consist of +ve and –ve ions held together
by electrostatic forces in a geometric array

Geometric array called crystal lattice

Example- (NaCl)
2.4.5. Compounds
Monatomic ions
Single atoms that have gained or lost electrons

For atoms: number e- = number p, charge=0

Loss of e-s leaves xs +ve charge cation
(Na  Na+ + e- ; Al  Al3+ + 3e-)
Gain of e-s causes xs -ve charge  anion
(Cl + e-  Cl- ; O + 2e-  O2-)


Metals typically form cations, non-metals form
anions.
CHEMISTRY DEPARTMENT
CHE 101 TUTORIAL 11 – 16 AUGUST
2008
Questions
Jones and Atkins – 4th Edition
1.7, 1.9, 1.11, 1.13, 1.15, 1.17, 1.19, 1.21,
1.31, 1.33
2.4.6. Compounds
Common ions related to group numbers:



Cations:- 1,2: M+, M2+
Anions: Grp17,-1(F-1, Cl-1); Grp16,-2(O-2,S2-)
Transition metals: Have multiple oxidation states
 e.g. Cu: Cu2+, Cu+, Cu3+; Pb; Sn, etc.
Polyatomic ions

Several atoms covalently bonded together as a
unit with a net positive and negative charge: NH4-,
SO42-
2.4.7. Ionic Compounds
The ammonium ion
Protons: 7 + (4x1) = 11
Electrons: 11-1 = 10
Net Charge: +1
2.4.8. Compounds
Ionic compounds must be electrically neutral, so ion
charges are used to “balance/write” formulas.
Ex. Write the formula for Cerium (III) sulfate
 Ce3+ combined with SO422(+3) + 3(-2) = 0, therefore Ce2(SO4)3
Note: Charges not written on actual formulas
Formular Unit:
Smallest unit of an ionic compound that contains the
same number of atoms as reflected in the formula
- NOT a molecule!!
2.5.1. Compounds
Formular Unit:
Smallest unit of an ionic compound that contains
the same number of atoms as reflected in the
formula - NOT a molecule!!
 empirical formula of an ionic compound. It is
used as an independent entity for stoichiometric
calculations

shows the kinds and numbers of atoms in the
smallest representative unit of a substance

is the lowest ratio of ions represented in an ionic
compound
e.g. NaCl and K2O (ionic ) or covalent networks such as
SiO2
2.5.2. Compounds
Ex. Calculate the ratio of atoms in mica,
KMg3 Si3 AlO10 (OH) 2.
Al: H: K: Mg: O: Si = 1: 2: 1: 3: 12: 3
Oxoanions
Polyatomic anions with oxygen atom(s) around
another central atom, CO32- carbonate, NO3- nitrate,
PO43- phosphate: see hand-out page
Mixture and Separation of Mixtures – Please
READ: pp 25-30 (4th edition), pp. 21-26 (3 rd edition)
3.5.3. Nomenclature (naming)…..
(See handout)
Common names vs systematic names = chemical
nomenclature
Cations
 Monatomic anion named as element plus “ion”,
e.g.
Na+; “sodium ion”
Al 3+; “aluminium ion”
Stock number (Roman numeral identifying the
oxidation state/charge) is included for elements
with more than one (common) ionic charge:
Co2+,Co3+,Co+; Cobalt (II),Cobalt (III) and Cobalt (I)

3.5.4. Nomenclature (naming)…..
Note: Stock numbers needed for transition metals
and heavier Grp 13-15 metals.
Anions

monatomic anion named by adding “ide” to
stem of element name plus “ion”
Cl- (Chlorine);
chloride ion
F- (fluorine);
fluoride ion
X- (halogen);
halide ion
O2- (oxygen)
N3- (nitrogen)
oxide ion;
nitride ion
3.5.5. Nomenclature (naming)…..
Oxoanions

anions with oxygen around central atom

named by adding “ate” to stem of name of
central atom
Examples
CO32- ; carbonate
Others?
SiO44-; Silicate
3.5.6. Nomenclature (naming)…..
What if two diferent oxoanions have same central
atom?


use “ate” for oxoanion with more O atoms
use “ite” for oxoanion with fewer O atoms
Ex: NO3- and NO2- named “nitrate” and
“nitrite”
SO42- and SO32- are sulfate and sulfite,
respectively
3.5.7. Nomenclature (naming)…..
There are cases of four oxoanions for same
central atoms (halogen). Then?

use prefix “hypo-” and “per-” for ion with
least and most O atoms, respectively

use “-ite” and “-ate” endings for ions with
2nd and 3rd least O atoms, respectively
3.5.8. Nomenclature (naming)…..
Ex
 ClO-,
hypochlorite

ClO2- ,
chlorite

ClO3-,
chlorate

ClO4-,
perchlorate
Exercise
Name the equivalent ions for the other
halogens
3.5.9. Nomenclature (naming)…..
Oxoacids

Molecular compounds


“Parents” / sources of oxoanions
Obtained by adding H+ to oxoanion
Names

The “-ite” oxoanion gives “-ous” acid

The “-ate” oxoanion gives the “-ic” acid
3.5.10. Nomenclature (naming)…..
Oxoanion
Oxoacid
ClO-, hypochlorite ion
HClO , Hypochlorous acid
ClO2-, chlorite ion
HClO2 , Chlorous acid
ClO3-, chlorate ion
HClO3 , Chloric acid
ClO4-, perchlorate ion
HClO4, perchloric acid