Transcript 11.Chemical elements and their classification. S

Lection 11. Chemical
elements and their
classification. S-block of IA
group of elements. Hydrogen
PhD Falfushynska Halina
• Periodic Patterns
– The chemical behavior of elements is determined by
its electron configuration
– Energy levels are quantized so roughly correspond to
layers of electrons around the nucleus.
– A shell is all the electrons with the same value of n.
• n is a row in the periodic table.
– Each period begins with a new outer electron shell
– Each period ends with a completely filled outer shell
that has the maximum number of electrons for that
shell.
– The number identifying the A families identifies the
number of electrons in the outer shell, except helium
– The outer shell electrons are responsible for
chemical reactions.
– Group A elements are called representative
elements
– Group B elements are called transition elements.
• Chemical “Families”
– IA are called alkali metals because the react with water
to from an alkaline solution
– Group IIA are called the alkali earth metals because they
are reactive, but not as reactive as Group IA.
• They are also soft metals like Earth.
– Group VIIA are the halogens
• These need only one electron to fill their outer shell
• They are very reactive.
– Group VIIIA are the noble gases as they have completely
filled outer shells
• They are almost non reactive.
• Four chemical families of the
periodic table: the alkali metals
(IA), the alkaline earth metals
(IIA), halogens (VII), and the
noble gases (VIIIA).
Metal: Elements that are usually solids at room temperature.
Most elements are metals.
Non-Metal: Elements in the upper right corner of the periodic
Table. Their chemical and physical properties are different
from metals.
Metalloid: Elements that lie on a diagonal line between the
Metals and non-metals. Their chemical and physical
properties are intermediate between the two.
– Elements with 1, 2, or 3 electrons in their outer shell
tend to lose electrons to fill their outer shell and become
cations.
• These are the metals which always tend to lose electrons.
– Elements with 5 to 7 electrons in their outer shell tend
to gain electrons to fill their outer shell and become
anions.
• These are the nonmetals which always tend to gain electrons.
– Semiconductors (metalloids) occur at the dividing line
between metals and nonmetals.
How many protons, neutrons and electrons are found in an
atom of
133
55
Cs
Atomic number = protons and electrons
There are 55 protons and 55 electrons
Mass number = sum of protons and neutrons
133 – 55 = 78
There are 78 neutrons
Members of the s-Block Elements
IA IIA
Li
Be
Na
Mg
K
Ca
Rb
Sr
IA Alkali metals
Cs
Fr
Ba
Ra
IIA Alkaline Earth
metals
Physical Properties
• The alkali metals are soft, with low melting and boiling
temperatures.
• They have low densities - Li, Na and K are less dense than water.
• They have low standard enthalpies of melting and vaporization.
• They show relatively weak metallic bonding as only one electron is
available from each atom.
• Alkali metals colour flames.
• The ionic radii of the alkali metals are all much smaller than the
corresponding atomic radii. This is because the atom contains one
electron in an s level relatively far from the nucleus in a new
quantum shell, and when it is removed to form the ion the
remaining electrons are in levels closer to the nucleus.
• The metal thus obtained is 99% pure and is preserved by keeping it
wrapped in paraffin wax.
Metallic character
• High tendency to
lose e- to form
positive ions
• Metallic character
increases down both
groups
Electronegativity
• Low nuclear
attraction for
outer electrons
• Highly
electropositive
• Small
electronegativity
Group I
Li
1.0
Na
0.9
K
0.8
Rb
0.8
Cs
0.7
Fr
0.7
Predominantly ionic with fixed
oxidation state
Most electropositive metals.
Low first I.E. and extremely high second I.E.
Form predominantly ionic compounds with
non-metals by losing one electron.
Fixed oxidation state of +1.
Na+ Cl- (g)  Na (g) + Cl (g)
Na(g)  Na* (g)
[Ne]3s1 [Ne]3p1
Na*(g)  Na(g) + h
(589nm, yellow)
Flame test
Li deep red
Na yellow
K lilac
Rb bluish red
Cs blue
HCl(aq)
sample
Weak tendency to form complex
Complex formation is a common feature of d-block
element. e.g. Co(NH3)63+
:NH3
s-block metal ions have
no low energy vacant
orbital available for
bonding with lone pairs
of surrounding ligands,
they rarely form
complexes.
H3N:
:NH3
Co
H3N:
:NH3
:NH3
Atomic radii (nm)
Group I 1st I.E.
2nd I.E.
Li
0.152
Li
519
7300
Na
0.186
Na
494
4560
K
0.231
K
418
3070
Rb
0.244
Rb
402
2370
Cs
0.262
Cs
376
2420
Fr
0.270
Diagonal relationship of lithium with
magnesium on the basis of polarizing
power, electronegativity and covalent
nature
Ionization
Enthapy
Variation in Melting Points
1250
Note: The exceptionally high m.p. of calcium
is due to contribution of d-orbital participation
of metallic bonding.
Be
1000
Ca
Sr
750
Ba
Mg
500
250
Li
Na
10
K
20
Rb
30
40
Cs
50
60
Occurrence and Extraction
• These elements are too reactive to be found free in
nature. Sodium occurs mainly as NaCI (salt) in seawater and dried-up sea beds. Potassium is more widely
distributed in minerals such as sylvite, KCI, but is also
extracted from sea-water. The alkali metals are so
reactive they cannot be displaced by another element,
so are isolated by electrolysis of their molten salts.
Electrolysis of Lithium chloride
• A mixture of dry lithium chloride (55%) and potassium
chloride (45%) is fused and electrolysed in an electrolytic
cell shown in the figure.
• Potassium chloride is added to increase the conductivity
of lithium chloride and to lower the fusion temperature.
The cell is operated at a temperature of about 723 K and
voltage of 8-9 volts is applied.
• At cathode: Li+ + e- → Li
• At anode : 2CI- - 2e- → CI2
Basic oxides, hydroxides
Hydroxides
Reaction with water:
Li2O
LiOH
Oxide: O2- + H2O  2OHPeroxide: O22- + 2H2O  H2O2 +
2OHSuperoxide: 2O2- + 2H2O 
2OH- + H2O2 + O2
Na2O,
NaOH
Na2O2
K2O2, KO2 KOH
Rb2O2,
RbO2
Cs2O2,
CsO2
RbOH
Strength increase
Oxide
.. .. 2:O:O:
.. ..
. .:O:.O:
.. ..
CsOH
Peroxide ion
Super oxide
Experimentally and theoretically proved that alkali metals can
form covalent diatonic molecule M2. Alkali metals containing
approximately 1% of M2. Li2 molecule can exist and does exist,
because the binding effect dominates the effect of break and the
energy of Li-Li is quite large (25.8 kcal / mol).
Among the heteronuclear alkali-metal fermionic species, LiNa is
the least reactive, whereas LiCs is the most reactive. For the
bosonic species, LiK is the most reactive in zero field, but all
species considered, LiNa, LiK, LiRb, LiCs, and KRb, share a
universal reaction rate once a sufficiently high electric field is
applied. (Phys. Rev. A 84, 062703 (2011)).
Reactions with oxygen
S-block elements reacts readily
with oxygen.
they have to be stored under
liquid paraffin
to prevent contact with the
atmosphere.
Formed by
S-block elements are strong
reducing agents.
Their reducing power increases
down both groups.
(As the atomic size increases, it
becomes easier to
remove the outermost electron)
Normal
Oxide
Peroxide
Superoxide
Li
Na
K, Rb, Cs
Reaction with water
M(s)  M+(aq) + eH2O(l) + e-  OH-(aq) + ½ H2(g)
Although lithium has highly negative Eo, it only
reacts slowly with water. This illustrates the
importance of the role of kinetic factors in
determining the rate of a chemical reaction.
Reaction with
hydrogen
All the IA elements
react directly with
hydrogen.
2Na(s) + H2(g) 
2NaH(s)
The reactivity
increases down the
group.
The hydrides are ionic.
The spontaneously inflammable silicone
hydride reacts with the oxygen of the air.
SiH4 + 2 O2==> SiO2 + 2 H2O
Reaction with chlorine
All the s-block metals react directly
with chlorine to produce chloride.
2Na(s) + Cl2(g)  2NaCl(s)
All group I chlorides are ionic.
Reactions of
chlorides
All group I chlorides are
ionic and readily
soluble in water. No
hydrolysis occurs.
Reactions of oxides and hydroxides
1. All group I oxides reacts with water to form
hydroxides
Oxide: O2- + H2O  2OHPeroxide: O22- + 2H2O  H2O2 + 2OHSuperoxide: 2O2- + 2H2O  2OH- + H2O2 + O2
2. All group I oxides/hydroxides are basic and the
basicity increases down the group.
Reactions of hydrides
They all react readily with water to give the
metal hydroxide and hydrogen due to the
strong basic property of the hydride ion, H:H:-(s)+ H2O(l)  H2(g)+ OH-(aq)
Hydride ions are also good reducing agent.
They can be used to prepare complex hydrides
such as LiAlH4 and NaBH4 which are used to
reduce C=O in organic chemistry.
Solvay process
The Solvay process results in soda ash (sodium carbonate (Na2CO3)) from brine
(NaCl) and from limestone (as a source of calcium carbonate (CaCO3)). The
overall process is: 2 NaCl + CaCO3 → Na2CO3 + CaCl2
1. In the first step in the process, CO2 passes through a concentrated aqueous
solution of NaCl and ammonia (NH3).
NaCl + CO2 + NH3 + H2O → NaHCO3 + NH4Cl (I)
2. The CaCO3 in the limestone is partially converted to quicklime CaO and CO2:
CaCO3 → CO2 + CaO (II)
3. The sodium bicarbonate (NaHCO3) that precipitates out in reaction (I) is filtered
out from the hot NH4Cl solution, and the solution is then reacted with the CaO left
over from heating the limestone in step (II).
2 NH4Cl + CaO → 2 NH3 + CaCl2 + H2O (III)
CaO makes a strong basic solution. The NH3 from reaction
(III) is recycled back to the initial brine solution of reaction (I).
The NaHCO3 precipitate from reaction (I) is then converted to
the final product, Na2CO3, by calcination (160 - 230 C),
producing water and carbon dioxide as byproducts:
2 NaHCO3 → Na2CO3 + H2O + CO2 (IV)
Thermal Stability of
carbonates and hydroxides
Thermal stability refers to decomposition of the compound on
heating. Increased thermal stability means a higher temperature
is needed to decompose the compound.
Li2CO3  Li2O + CO2 ( at 700oC)
All other group I carbonates are stable at ~800oC
All group I hydroxides are stable except LiOH
at Bunsen temperature (lies between 750-950 degrees Celsius).
Uses of s-block compounds
• Sodium carbonate
– Manufacture of glass
– Water softening
– Paper industry
• Sodium hydrocarbonate
– Baking powder
– Soft drink
Alkali metals in farmacy
• Lithium stearate is mixed with oils to make all-purpose and hightemperature lubricants
• Lithium carbonate has a sedative effect. It is highly effective in
preventing attacks of depression or mania, by stabilising your
chemistry.
• Potassium bromide, KBr, was used as an antaphrodisiac
• Potassium permanganate, KMnO4, is an important oxidizing,
antiseptic and antidote agent
• Baking soda (NaHCO3) due to its extremely basic is an especially
good antacid and is used in products such as Alka-Seltzer.
Important: Children under the age of 6 should not take any
antacid medicines unless prescribed by a doctor.
• Drinking soda with a medicine pill make it dissolve faster once it
is swallowed .
Alkali metals Poisoning
• External exposure to large amounts of Cs-137 can
cause burns, acute radiation sickness and even
death. Exposure to Cs-137 can increase the risk
for cancer because of exposure to high-energy
gamma radiation. Internal exposure to Cs-137,
through ingestion or inhalation, allows the
radioactive material to be distributed in the soft
tissues, especially muscle tissue, exposing these
tissues to the beta particles and gamma radiation
and increasing cancer risk.
Alkali metals analysis
• Na+ + [Sb(OH)6]  Na[Sb(OH)6] – white
crystalline precipitate
• Na+ + Zn(CH3COO)2 + 3UO2(CH3COO)2 + CH3COO–
+ 9H2O 
NaCH3COOZn(CH3COO)23UO2(CH3COO)29H2O
– green-yellow precipitate
• KCl + NaHC4H4O6  KHC4H4O6 + NaCl – white
crystalline precipitate
• 2K+ + Na+ + [Co(NO2)6]3–  K2Na[Co(NO2)6] –
yellow precipitate;
Hydrogen is the simplest of all
elements
Production of hydrogen
As the reaction between a metal and acid produces hydrogen, we
can place this reaction in a flask that is connected to a delivery
tube, that will allow hydrogen to pass through it ending up in a
water trough, hydrogen will try to escape by bubbling up into the
glass jar
Extraction of Hydrogen
• Zn + 2HCl  ZnCl2 + H2
• Al + NaOH + 3H2O  Na[Al(OH)4] + 3/2 H2
• 2Na + 2H2O  2NaOH + H2
• СaH2 + 2H2O  2Ca(OH)2 + H2
• С + 2H2O  СO + H2
Properties of hydrogen
•
•
•
•
•
•
Colorless: - can’t be see
Odorless: - has no small
Tasteless: - doesn’t have a taste
Gas: - found in gas state, not liquid, or solid
Lightest gas: - least density, lighter then air
Explosive: - H2 + O2
H2O + energy
reactants combine causing an explosion
Chemical properties of Hydrogen
• Hydrogen is slightly more soluble in organic
solvents than in water.
• It does not usually react with other chemicals
at room temperature.
• Hydrogen reacts with oxygen:
• 2Н2 + О2  2Н2О; Н2 + hν  2Н; Н2 + О2  2ОН
• ОН + Н2  Н2О + Н
• Hydrogen is a good reducing agent: CuO + H2  Cu + Н2О
• Hydrogen also forms ionic bonds with some metals,
creating a compound called a hydride: Ca + H2  CaH2
• Hydrogen reacts with non-metals: 3Н2 + N2  2NH3; H2 +
Cl2  2HCl
Group 1A – The alkali metals
Some facts…
1) These metals all have ___
electron in their outer shell
2) Reactivity increases as you go _______ the group. This is
because the electrons are further away from the _______
every time a _____ is added, so they are given up more easily.
3) They all react with water to form an alkali (hence their
name) and __________, e.g:
Potassium + water
2K(s)
+
2H2O(l)
potassium hydroxide + hydrogen
2KOH(aq)
+
Words – down, one, shell, hydrogen, nucleus
H2(g)