Compounds & Molecules
NaCl, salt
Buckyball, C60
Compounds & Molecules
• COMPOUNDS are a combination of 2 or
more elements in definite ratios by mass.
• The character of each element is lost when
forming a compound.
• MOLECULES are the smallest unit of a
compound that retains the characteristics of
the compound.
ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
ELEMENTS
THAT EXIST
AS
MOLECULES
Allotropes of C
ELEMENTS THAT EXIST AS
POLYATOMIC MOLECULES
S8 sulfur
molecules
White P4 and polymeric
red phosphorus
Molecular Compounds
Compounds without Ions
CO2 Carbon dioxide
CH4 methane
BCl3 boron trichloride
MOLECULAR FORMULAS
• Formula for glycine is C2H5NO2
• In one molecule there are
–2 C atoms
–5 H atoms
–1 N atom
–2 O atoms
STRUCTUAL FORMULAS
• Can also write glycine formula as
–H2NCH2COOH
to show atom ordering
• or in the form of a structural
H H O
H N C C O H
H
formula
MOLECULAR MODELING
H H O
H N C C O H
H
Ball & stick
Drawing of glycine
Space-filling
Naming Elements & Compounds
Chapter 2 & 3: Chemical Equations Handbook
molecules are
formed from
two or more
nonmetals.
CO2 Carbon dioxide
BCl3
boron trichloride
ammonium
chloride,
NH4Cl
Ionic
compounds
have a cation
and anion:
generally
involve a metal
and nonmetal,
NaCl
IONS AND IONIC COMPOUNDS
• IONS are atoms or groups of atoms with a positive
or negative charge.
• Taking away an electron from an atom gives a
CATION with a positive charge
• Adding an electron to an atom gives an ANION
with a negative charge.
Forming Cations & Anions
A CATION forms
when an atom
loses one or
more electrons.
Mg -->
Mg2+
+ 2 e-
An ANION forms
when an atom
gains one or
more electrons
F + e- --> F-
COMPOUNDS
FORMED
FROM IONS
CATION + ANION --->
COMPOUND
Na+ + Cl- --> NaCl
Are NEUTRAL.
Compounds have
EQUAL number of +
and - charges.
IONIC COMPOUNDS
NH4
+
Cl
ammonium chloride, NH4Cl
Properties of Ionic Compounds
Forming NaCl from Na and Cl2
• A metal atom can
transfer an
electron to a
nonmetal.
• The resulting
cation and anion
are attracted to
each other by
electrostatic
forces.
Electrostatic Forces
The oppositely charged ions in ionic compounds are
attracted to one another by ELECTROSTATIC
FORCES.
These forces are governed by COULOMB’S LAW.
Electrostatic Forces
COULOMB’S LAW
(charge on +)(charge on -)
Force of attraction =
(distance between ions)2
Direct relationship between charge and force:
charges increase, the force increases.
Inverse relationship between distance between
ions and force:
increase distance, decrease force.
Importance of Coulomb’s Law
NaCl, Na+ and Cl-,
m.p. 804 oC
MgO, Mg2+ and O2m.p. 2800 oC
PREDICTING ION CHARGES
In general
• metals (Mg) lose electrons ---> cations
• nonmetals (F) gain electrons ---> anions
METALS
M ---> n e- + Mn+
where n = periodic group
Na+
sodium ion
Mg2+
magnesium ion
Al3+
aluminum ion
Transition metals --> M2+ or M3+
are common
Fe2+
iron(II) ion
Fe3+
iron(III) ion
NONMETALS
NONMETAL + n e- ------> Xnwhere n = 8 - Group no.
Group 4A
Group 5A
Group 6A
Group 7A
C4-,carbide N3-, nitride O2-, oxide F-, fluoride
S2-, sulfide Cl-, chloride
Br-, bromide
I-, iodide
Charges on Common Ions
-4 -3 -2 -1
+1
+2
+3
By losing or gaining e-, atom has same
number of e-’s as nearest Group 8A atom.
Predicting Charges on Monatomic Ions
Binary Ionic Compounds
Mn2+ + O2- ----> MnO
manganese (II) oxide
Al3+ + S2- ----> Al2S3
aluminum sulfide
Ca2+ + 2 F- --->
Sn4+ + Cl- ----> SnCl4
Tin (IV) chloride or
Stannic chloride
CaF2
calcium fluoride
Practice Name & Formulas
Ultimate Equation Handbook
Only the binary compounds
• Exercise 2-1 pg. 10
• Exercise 3-2 pg 17
Homework:
Worksheets pgs 23-28
POLYATOMIC IONS
Groups of atoms with a charge.
MEMORIZE the names and formulas in
Table 3.1, page 89.
Polyatomic Ions
NH4+
ammonium ion
One of the few common
polyatomic cations
Polyatomic Ions
HNO3
nitric acid
NO3nitrate ion
Polyatomic Ions
CO32carbonate ion
HCO3bicarbonate ion
hydrogen carbonate
Polyatomic Ions
PO43phosphate ion
CH3CO2acetate ion
Polyatomic Ions
SO42sulfate ion
SO32sulfite ion
Polyatomic Ions
NO3nitrate ion
NO2nitrite ion
sheet pg #22
“ates”
Practice Name & Formulas
Ultimate Equation Handbook
Add the polyatomic compounds
• Exercise 2-1 pg. 10
• Exercise 3-2 pg 17
• Exercise 4-1 pg 20
• Exercise 4-3 pg 21
Homework:
Worksheets pgs 23-28 –poly
Pgs 29-33
Molecular & Ionic Compounds
Heme
NaCl