Download - Chemistry Form 4 Lesson 14-1
-
Sir Antoine Lavoisier (1743 1794)
First to classify elements into groups
It is arranged into 4 different group as shown in table
In his table, elements are classified into metals and non-metals
It is not a good periodic table as substances such as heat, light
and sun were included in his grouping as these are not element
Still, his contribution towards the periodic table is treasured as
hes the 1st one to start grouping element
-
Johann W. Dobereiner ((1780 1849)
Invented a classifying method named triad where 3 elements are
grouped under the same category base on their relative mass.,
where the median is the average of the highest and lowest value
Weakness : The elements that can be categorized were very
limited.
Advantage : scientist begin to realize that there were relationship
between the elements with the same properties and the relative
mass of the elements involved.
-
John Newland (1837 1898)
Arrange the elements that were discovered during that time in a horizontal method in ascending order of their atomic masses. Each row consisted of 7 elements
He believed that elements with the same properties will repeat in every 8th elements in his periodic table. This pattern is similar to octave notes in the music score. That is why its called octaves law
Still, it is not enough as everything went wrong after the 17th elements (from H to Ca is true)
Still it is a very large contribution toward the modern periodic table as people now learned how to arrange the periodic table using atomic mass and its repeating theoriesmass and its repeating theories
-
Lothar Meyer (1830 1895)
Plotted a graph of atomic volume against atomic mass for all known
elements at that time.
Realize that elements with the same chemical properties occupied
the same relative positions on the curve.
Highlighted the pattern of the graph from the elements has a trend
in the tendencies of similarity of the substance
-
Dmitri Mendeleev (1834 1907)
Shown properties of elements changed periodically with atomic mass
He grouped elements with the same properties placed in the same vertical column
He also left some space for elements which is yet discovered at that time
Using the emptied space, the properties of the undiscovered element were predicted and it is later found similar to the properties predicted by him.
Separate elements which cannot be placed normally into his Separate elements which cannot be placed normally into his table as transition elements
His table are basis of todays Modern periodic table
-
J. G. Moseley (1887 1915)
Using X-Ray method to determine the position of elements in
Periodic Table. He then plotted a graph of square root of the
frequency of the X-ray from elements against proton
numbers. A straight line is obtained.
From the information, hes able to categorise the periodic
table similar to the Modern Periodic Table. He also
successfully proved Mendeleevs prediction of the empty
element.element.
His achievement had help in developing the Modern Periodic
Table today
-
A periodic table of partial ground-state electron configurations
-
Group 18 element (Noble Gas)
Our air consists of about 1% of noble gases. These gases are
inert(non-reactive) gases.
In the Modern periodic Table the Group 18s elements are
Helium Neon Argon
Krypton Xenon Radon
Below shows some physical properties of the elements
-
Element He Ne Ar Kr Xe Trend
Proton
number2 10 18 36 54
Atomic
radius
(nm)
0.050 0.070 0.094 0.109 0.130
Increase when goes down to
group. More shell is required when
more electron filling in, thus
causing the atomic radius to
increase.
Melting Monoatomic gases of noble gas Melting
point
(oC)
-270 -248 -189 -156 -112
Monoatomic gases of noble gas
have very weak Van Der Waals
forces between the atoms,
resulting the amount of heat
required to break the forces
between the atoms are little.
Generally, b.p and m.p increase
when goes down the group.
Boiling
point
(oC)
-269 -246 -186 -152 -107
Physical
stateGas Gas Gas Gas Gas
Since the boiling point is below
room temperature, so it exist as
gas
-
Element Proton numberElectron
arrangement
Helium (He) 2
Neon (Ne) 10
Argon (Ar) 18
Krypton (Kr) 36 2.8.18.8
2
2.8
2.8.8
Xenon (Xe) 54 2.8.18.18.8
From the electron arrangement, we can tell that, all the
Group 18 gases have achieved octet states. Thus, these
gases are very stable and unreactive. The octet
arrangement of the noble gas also allows them to exist as
monoatom, as they are already stable on its own.
Application of noble gas in our daily life
-
Helium
(He)
Use as weather balloon and airship
Use by divers where helium is mixed with oxygen gas to use in
ocean diving
Use by physicist in measuring low temperature thermometer.
Neon
(Ne) Use in commercial / advertisement boards.
Argon
(Ar)
Fill electrical bulbs
Support welding process (prevent air to react with the hot metal)(Ar) Support welding process (prevent air to react with the hot metal)
Krypton
(Kr)
Use in flash light in camera and DV
Use in laser to repair the retina of our eyes
Radon
(Rn) Kill cancerous cell
-
Group 1 elements
Group 1 are also known as alkali earth metal as it is an
alkali substance
The elements of Group 1 are
Lithium (Li) Sodium (Na) Potassium (K)
Rubidium (Rb) Caesium (Cs) Francium (Fr)
Below are some physical properties of Group 1 elements Below are some physical properties of Group 1 elements
-
Element
sLi Na K Rb Cs
Trend
Proton
number3 11 19 37 55
All alkali metals are grey soft solid
with shiny surface. Since its soft,
its easily to cut alkali metal
Atomic
radius
(nm)
0.15 0.19 0.23 0.25 0.26
Increase when goes down to
group. More shell is required
when more electron filling in, thus
causing the atomic radius to
increase.
The intermolecular forces of Melting
point
(oC)
181 98 64 39 28
The intermolecular forces of
metal solid : metallic bonding;
Strength : how the free electrons
of metal are able to interact with
the nucleus of the atom. When
going down to group, metallic
bond decrease as the electrons
are getting further away from the
nucleus when the radius
gradually increase.
Boiling
point
(oC)
1347 890 774 689 677
-
Element Li Na K Rb Cs Trend
Proton
number3 11 19 37 55
Physical
stateSolid Solid Solid Solid Solid
Since the melting point of alkali
metal are all above room
temperature, so alkali metal exist
as solid.
Density
Even though alkali metals are
solid, some of them are actually Density
(g/cm3)0.53 0.86 0.97 1.53 1.88
solid, some of them are actually
less dense than water (Li, Na, K).
The mass / volume of Li, Na and
K are lower than 1.00Conducti
vity of
heat and
electricit
y
Good Good Good Good Good
Since its a metal usually it
conducts heat. As for electricity, it
has free mobile ion to move
around and conduct electricity.
-
Elements Lithium
(Li)
Sodium
(Na)
Potassium
(K)
Rubidium
(Rb)
Caesium
(Cs)
No. of
electrons3 11 19 37 55
Electron
arrangemen2.8.18.8.1 2.8.18.18.8.12.1 2.8.1 2.8.8.1
Reactive
Electroposi
tivity
Cation
formed
Reactivity increase when going down to Group 1
Electropositivity increase when going down to Group 1
Li+ Na+ K+ Rb+ Cs+
-
Since all Group 1 elements possessed the same number of
______________ so they exhibit similarity in terms of chemical
properties.
All Group 1 elements will ______ 1 electron away to achieve octet.
Reactiveness _______ as the electropositivity ________.
Electropositivity measures on how easy an atom release an
electron to become positively charges ion (cation). So, when
the distance between the outer-most electron and nucleus
increase, more ______ for the atom to release the outer-most
electron, thus it is more ____________
valance electron
donateincrease increase
easier
electropositiveelectron, thus it is more ____________electropositive
-
To study the chemical properties of Group 1 through
the reaction with water and oxygen.
Alkali metal become more reactive in their reaction
with water when goin down Group 1.
Type of alkali metal
Reactivity of alkali metal
Water and size of alkali metal
-
Lithium melted and
moved slowly at
random on the
surface of water
with plenty of fizz.
A colourless
solution is formed
Sodium melted
and moved rapidly
at random on the
surface of water
with hissing sound.
A colourless
solution is formed
Potassium melted
and moved very
fast at random on
the surface of
water and ignited
with a lilac flame,
gave out pop and solution is formed
which turn red
litmus red to blue
solution is formed
which turn red
litmus red to blue
gave out pop and
hissing sound. A
colourless solution
is formed which
turn red litmus red
to blue
-
2 Li (s) + 2 H2O (l) 2 LiOH (aq) + H2 (g)
2 Na (s) + 2 H2O (l) 2 NaOH (aq) + H2 (g)
2 K (s) + 2 H2O (l) 2 KOH (aq) + H2 (g)
This is due to the formation of the solution of metal hydroxide
which are alkaline
The reaction of potassium and sodium is too reactive, so its
too dangerous to be carried out by students
-
Alkali metal become more reactive in their reaction
with oxygen when going down Group 1.
Type of alkali metal
Reactivity of alkali metal
Oxygen gas and size of alkali Oxygen gas and size of alkali
metal
-
Lithium burned
slowly with red
flame. White fumes
which become a
white solid when
cooled to room
temperature, were
produced
Sodium burned
rapidly with a bright
yellow flame. White
fumes which
become a white
solid when cooled to
room temperature,
were produced
Potassium burned
very rapidly with a
lilac flame. White
fumes which
become a white
solid when cooled to
room temperature,
were produced
White solid
dissolved in water to
form colourless
solution that turned
red litmus paper to
blue colour.
White solid
dissolved in water to
form colourless
solution that turned
red litmus paper to
blue colour.
White solid
dissolved in water to
form colourless
solution that turned
red litmus paper to
blue colour.
-
4 Li (s) + O2 (l) 2 Li2O (s)
Li2O (s) + H2O (l) 2 LiOH (aq)
Yes, since all alkali metal has the same valence electron,
which is 1.
Lithium, sodium and potassium react similarly with oxygen. The
reactivity increase from Li , Na , K