Chemical Properties
3.3.1
3.3.1
Discuss the similarities and differences
in the chemical properties of elements in
the same group.
 Q – What are chemical properties?

Chemical Properties

The chemical properties of an element are
largely determined by the number of
valence electrons.
 This explains why members of the same group
tend to have similar chemical properties.

We’ll start today with a quick review of the
groups and their properties…
Group 0: The Noble Gases
Colorless
gases
 Monoatomic
 Stable due to
their full outer
energy levels

Group 1: Alkali
Metals

Physical Properties:
 Soft, malleable - easily
cut with a knife
 Low densities
 Low melting points
 Good conductors of
electricity
Can you explain these
properties based on their
atomic structure?
Group 1: Alkali
Metals

Chemical Properties:
 VERY reactive (why?)
 tarnish rapidly when
exposed to air
 form ionic compounds
with non-metals
Alkali metals react with nonmetals to form ionic compounds

Alkali metals react readily with oxygen to form oxides.
 Write the balanced chemical equation for the reaction of lithium
with oxygen to form lithium oxide.

Alkali metals react readily with halogens to form halides.
 What would be the general balanced chemical equation for the
reaction of an alkali metal with a halogen?
 2 M + X2  2 MX
Try this reaction with sodium and chlorine… potassium and bromine… cesium and iodine …
Alkali metals in water


Alkali metals react readily with water to form hydrogen
and a metal hydroxide. This is why basic solutions used
to be called “alkaline”.
What would be the general balanced chemical equation
for the addition of an alkali metal to water?
 2 M + 2 H2O  2 MOH + H2
Try this reaction with lithium… sodium… potassium…
Alkali metals in water
The vigor of the reaction depends on the reactivity of the metal.
(Watch the demo and/or the videos below)
Li
Na
K another good one
Rb
Classic Newsreel: 20,000 Pounds of Sodium Exploding in a Lake
(scroll down the page to access this video)
Why?
Group 7: Halogens

Physical Properties:
 melting points increase as you go
down a period - @ room temp =
gas to liquid to solid
 Color in pure form (see right)
○ Different colors in water, in hexane
○ In water: Cl2 (aq) – pale green; Br2
– yel-org-br; I2 (aq) - brown
○ In hexane: Cl2 (aq) – pale green;
Br2 (aq) – org; I2 (aq) - violet
(aq)
Group 7: Halogens

Physical Properties:
 Diatomic molecules
 Very electronegative – with F2
being most EN
Group 7: Halogens

Chemical Properties:
 VERY reactive
 react with metals (to form ionic compounds - salts)
 reactivity decreases down the group
(a) Sodium metal (immersed in oil to prevent reaction with oxygen and moisture
in the air); (b) chlorine gas; (c) the reaction between sodium and chlorine; (d)
sodium chloride (common table salt)
Halides

Are the ionic salts formed by halogens and metals
 Halogen + metal  metal halide
 Remember some of these from earlier in this powerpoint?

The reactions that form them are generally fun to watch.
 The greater the difference in electro negativity, the more vigorous





the reaction.
Na + Cl
Na + Br
K + Br
K + Cl
H + Cl
Halides


are typically white solids
most are soluble in water except…
 Ag, Pb, & Hg
 The insoluble silver salts have characteristic colors that can be
used to identify the halides
○ Silver chloride
○ Silver bromide
○ Silver iodide
- white (rapidly darkens through purple to black)
- off-white / cream
- pale yellow
Halogens in displacement reactions

Normally we think of metals duking it out in single
replacement (displacement) reactions.
 Mg + 2 AgNO3  Mg(NO3)2 + 2 Ag

Halogens can also get in on the fun.
Cl2 (aq)  2 KCl (aq) + Br2 (aq)
which can be written as 2 Br- (aq) + Cl2 (aq)  2 Cl- (aq) + Br2 (aq)
 Br- and Cl2 are basically fighting for electrons
 Who wins? Why?
 2 KBr

(aq) +
We can determine the relative reactivity of halogens by
letting them try and take electrons from other halide
ions. (All in the Family Lab)
Halogens in displacement reactions

Results? : A halogen higher in group 17 will displace a
lower halogen from its salts.
In a reaction…
 F2 would displace Cl , Br, I
 Cl2 would displace Br and I
but would NOT displace F
 Br2 would displace I,
but would NOT displace F or Cl
 I2 would NOT displace F nor Cl nor Br
most reactive
least reactive
Group 7: Halogens

More Chemical Properties:
 react in water to form acidic
solutions
 resulting acids can act as
oxidants – (donate oxygen)
○ bleaching property
○ toxic to microbes
 used as disinfectants & in water
treatment
3.3.2

Discuss the changes in nature, from
ionic to covalent and from basic to
acidic, of the oxides across period 3.
 What is an oxide?
 What is the nature of bonding of the
elements in period 3 with oxygen?
 What is a base? What is an acid?
Oxides of Period 3 elements
Na
Mg
Al
Si
P
S
Cl
Ar
Na2O
Na2O2
MgO
Al2O3
SiO2
P2O5
P2O3
P4O10
P4O6
SO3
SO2
Cl2O7
ClO2
Cl2O
----
Ionic Bonding
Highly
Polar
Covalent
Basic
Amphoteric
Polar Covalent
Weakly
acidic
Acidic
Bases and Acids

Simple definitions:
 Bases produce OH- ions when put in water.
○ Bases can neutralize acids, forming salt and water.
 Acids produce H+ ions when put in water.
○ Acids can neutralize bases, forming salt and water.
Reactions of Period 3 Oxides
REACTION with WATER
 Na2O (s) + H2O (l)  2 NaOH

MgO (s) + H2O (l)  Mg(OH)2

Al2O3 (s)

SiO2 (s)
(aq)
(aq)
+ H2O (l)  No Reaction
+ H2O (l)  No Reaction
(very difficult to break up giant covalent structure)
REACTION with WATER cont.

P4O6 (s) + 6 H2O (l)
 4 H3PO3

P4O10 (s) + 6 H2O (l)
 4 H3PO4

SO2 (g) + H2O (l)
 H2SO3

SO3 (g) + H2O (l)
 H2SO4
Cl2O7 (s) + H2O (l)
 2 HClO4

(aq)
phosphorous acid
(aq)
phosphoric acid
(aq)
sulfurous acid
(aq)
sulfuric acid
(aq)
chloric acid

Cl2O (s) + H2O (l)
 2 HOCl (aq)
hypochlorous acid
Reactions of Period 3 Oxides
REACTION with acids / bases

Na2O (s) + 2 HCl (aq)
 NaCl (aq) + H2O (l)

MgO (s) + 2 HCl (aq)
 MgCl2 (aq) + H2O (l)

Al2O3 (s) + 6 HCl (aq)

Al2O3 (s) + 2 NaOH (aq) + 3 H2O (l)
 2 AlCl3 (aq) + 3 H2O (l)
 2 NaAl(OH)4 (aq)

SiO2 (s) + 2 NaOH (aq)

2 Na2SiO3
(aq)
+ H2O (l)
REACTION with acids & bases cont.

P4O6 (s)
(or H3PO3

P4O10 (s) + 12 NaOH (aq)
SO2 (g) + 2 NaOH (aq)

Cl2O7
(or HClO4

(aq)
(aq)
(aq)
(aq)
 4 Na3PO4 (aq) + 3 H2O (l)
 Na2SO3 (aq) + H2O (l)
- sulfurous acid)
SO3 (g) + 2 NaOH (aq)
(or H2SO4
 4 Na2HPO3 (aq) + 2 H2O (l)
- phosphoric acid)
(aq)
(or H3SO3

+ 8 NaOH (aq)
- phosphorous acid)
(aq)
(or H3PO4

(aq)
 Na2SO4 (aq) + H2O (l)
- sulfuric acid)
+ 2 NaOH (aq)
 2 NaClO4 (aq) + H2O (l)
- chloric acid)
Cl2O (s) + 2 NaOH (aq)
(or HOCl (aq) - hypochlorous acid )
 2 NaOCl (aq) + H2O (l)
Homework – Section 3.3
Read the text… if you haven’t already.
 Do Exercise 3.3 # 1-10

Due on __________.