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الثلاثاء، 26 مارس، 2013

كيمياء لغات - الباب الثانى | Trends the metallic and non-metallic properties


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كيمياء لغات - الباب الثانى | Trends the metallic and non-metallic properties

01 Trends The Metallic and non metallic Properties



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كيمياء لغات - الباب الثانى | Trends the metallic and non-metallic properties
5) Trends the metallic and non-metallic properties
*Berzelius classified elements into metals and non-metals
Points of comparison Metals Non-metals
1) No. of electrons in the valence level. less than half the maximum (Less than 4 ) more than half the maximum (more than 4)
2) Position in the periodic table. at the beginning of periods. at the end of periods.
3) Atomic radius. relatively large. relatively small.
4) Ionization potential. relatively small. relatively large.
5) Electron affinity. relatively small. relatively large.
6) Electronegativity. relatively small. relatively large.
7) Losing or gaining electrons. atom loses electrons of the valence shell to reach the stable structure of nearest noble gas. atom accept electrons of the valence shell to reach the stable structure of the nearest noble gas.
8) Kind of ions. the ions are (+ve) (Electro positive elements) the ions are (-ve) (Electro negative elements)
9) Electric conductivity high electric conductivity bad electric conductivity
Metalloids:- Elements have the metallic appearance of metals but the most properties of non-metals at the same time.
Properties of metalloids: -
1) Their valency shell is nearly half filled.
2) Electronegativity is intermediate between metals and non-metals .
3) Their electrical conductivity is less than metals but more than
non-metals , so they are called semiconductors
4) They have important uses in electric instruments such as
semiconductors and are known as transistors .
Ex:- ( Boron – Silicon – Germanium )
G.R.F
1) Metals are good conductors of electricity
Because: - They have free valence electrons (easily transferred).
2) Non-metal are bad conductors of electricity or insulators .
Because: -Their valence electrons difficult transferred(strongly bounded).
3) Metals have small values for ionization energy and electron affinity.
Because: - Metals have relatively large atomic radius.
(found at the beginning of periods)
4) Non-metals have a high values of ionization energy and electron affinity.
Because: - Non-metals have relatively small atomic radius
( found at the end of periods )
5) Metals are called electropositive elements while non-metals are called electronegative elements.
Because: - Metals tend to lose electrons forming ( + ve ions ).
but non-metals tend to gain electrons forming ( -ve ions ).
Variation of metallic and non-metallic properties in the periods:-
* Begin with a strong metal finish with a strong non-metal
* Between them, metalloids are present so metallic property decreases from left to right across the periods .and non –metallic property increases.
In groups: * The metallic property increases and non-metallic property
decreases from up to down.
G.R.F 1- Caesium has the most metallic properties
but flourine has the most non-metallic properties
*Because Caesium lies at the bottom on the left hand side of the periodic table So its atom lose the valence electron easily .but fluorine lies at the top right so it gains electron to complete its outer level.
* The strongest metal lies at the bottom of the left hand side of the
periodic table but the strongest non-metal lies at the top of right
hand side of the periodic table. Group 7A [ Halogens ]
6- Trends the acidic and basic properties
• Compare between acidic oxides and basic oxides
Acidic oxides Basic oxides
They are non-metallic oxides such as
CO2 , SO2 , P2 O5 , SO3 G.R.F They are metallic oxides such as
Na2O ,CaO , K2O , CuO, , MgO G.R.F
They dissolve in water forming acids Some dissolves in water forming alkalis
CO2 + H2O H2CO3 carbonic acid
SO3 + H2O H2SO4 sulphuric acid Na2O + H2O 2NaOH sod. hydroxide
K2O + H2O 2KOH
They can’t react with acids They can’t react with alkalis
They react with alkalis forming salt and water .
CO2 + 2NaOH Na2 CO3 + H2O They react with acid to forming salt and water .
Na2O + 2HCl 2NaCl + H2O
MgO + H2SO4 MgSO4 + H2O
* Alkali :- Water soluble basic oxide
Amphoteric oxides
Def * They are oxides which reacts with acid as a basic and react with base as acidic forming salt and water.
For example: (Al2 O3 , SnO , ZnO , Sb2O3 )
Aluminium oxide , Tin oxide , Zinc oxide ,Antimony oxide
*In the periods :Acidic property in oxides increases and basic property
decreases when atomic number increases from left to right.
* In the group 1A :-
Basic property increases from up to down due to
increasing atomic size of element while the charge remains constant
Explaining :-
*Acids and alkalis are considered hydroxy compounds
*They have the fromula MOH
*They are ionized by two different methods
1-It may be ionized giving OH- and considered base
MOH ( base ) M+ + OH-
2-It may be ionized giving H+ and considered an acid.
HMO ( acid) MO¬¬- + H+
M+
Repulsion force attraction force
H+ O-
attraction force
* When attraction force between M+ and O- greater than attraction
force between O- and H+ it is ionized giving H+
* When attraction force between H+ and O- greater than attraction
force between O- and M+ it is ionized giving OH-
*When the two attraction forces are equals it is ionized as acid or as
base depending on medium of reaction.
[ reacts with acid as base and with base as acid ]
*The above attraction force depends on atom of element according to
its size and its electric charge
* in alkali metals as Na
It is characterized by a large size and has one positive charge
[ small attraction force] so attraction force with O- decreases but attraction force between O- and H+ increases so it is ionized into OH-
* in Non-metals as Chlorine [ from left to right ]
It is characterized by a small size and has more charges
so attraction force with O- increases but attraction force between O- and H+ decreases so it is ionized into H+


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