Science 2nd prep 1st term revision
Attempts of elements Classification
1 – Mendeleev's eriodic table:
Elements are calssified in an ascending order according to their atomic weights.
2 – Moseley's periodic table:
Elements are calssified in an acending order according to their atomic numbers.
3 – Modern periodic table:
Elements are classified in an ascending order according to
- their atomic number.
- the way of filling the energy sublevels with electrons.
Modern periodic table18 vertical groups. / 7 Horizontal periods .
s-block / p-block / d-block / f- block
Graduation of the properties of elements in modern periodic table.
1 – Atomic size
In periods
Atomic size decrease from left to right
In groups
Atomic size increase from up to down.
2 – Electronegativity
In periods
Electronegativity increase from left to right
In groups
Electronegativity decrease from up to down.
Electronegtivity / Element2.5 / C
3 / N
3.5 / O
4 / F
2.1 / H
* if the electronegtivity between two elements of a compound is more than 1.7, the bond between them is an ionic bond, but if it is less than 1.7, the bond is a covalent bond.
Ex.
The electonegtivity in NaCl = 3 – 0.9 = 2.1 > ioinic bond
Ex.
The electonegtivity in H2O = 3.5 – 2.1 = 1.4 > polar compound
Ex.
The electronegtivity in H2 = 2.1 – 2.1 = 0 > non-polar compound.
Polar compound
They are covalent compounds in which the difference in electronegativity between their elements is relatively high
.
3 – Metallic and non- metallic property:
Elements classified into four main kinds:
1- Metals 2 – Nonmetal 3 – metalloids (semimetals) 4 – Nobel gases.
Metals tend to lose their outermost electrons and change into positive ions.
Non- metals tend to gain electrons and change into negative ions
Graduation of metallic and nonmetallic property:
In periods:
Metallic property decrease from left to right, while non-metallity property increase.
In groups:
Metallic property increase from up to down while non metallity propery decrease.
Chemical properties of metals
1 – Reaction of metal with dilute acids:
Mg + HCL MgCl2 + H2 ↑ (( Hydrogen evolved ))
2 – Reaction of metal with Oxygen:
Mg + H2O Mg(OH)2 (( Magnesium hydroxide )) ( Basic oxides )
Basic oxides
They are metallic oxids, some of them dissolve in water forming alkaline solutions.
3 – Reaction of metal with water:
Metals / Reaction with waterK and Na / React instantly
Ca and Mg / React very slowly
Zn and Fe / React with hot water
Cu and Ag / Don't react .
Chemical activity series:
It is a series in which metals are arranged ina a descending order according to ttheir chemical activity.
Chemical properties of nonmetals
1 – Reaction of nonmetal with dilute acids:
Nonmetals don't react with dilute acids like sulpher and carbon.
2 – Reaction of nonmetal with Oxygen:
C + O2 CO2 ( Carbon dioxide )
CO2 + H2O H2CO3 ( Carbonic aicd ) ( Acidic oxide )
Acidic oxide
They are nonmetallic oxides which dissolve in water forming acidic solutions.
Basic oxides / Acidic oxidesMetal oxide / Non metal oxide
Reaction of metal with oxygen / Reaction of nonmetal with oxygen
Some dissolve in water give alkalis / Dissolve in water give acids.
Turn litmus paper into blue / Turn litmus paper into red
Example : Na2O , MgO / Example : CO2 , SO2
Main groups in the modern periodic table:
1 – Alkali metals ( group (1 A )
- good conductor of heat and electricity.
- Have low density.
- They are mono-valent.
- Form positive ion.
- They are active metals.
2 – Alkaline earth metals ( group 2A )
- good conductor of heat and electricity
- have higher density than Alkali.
- They are di-valent.
- Form positive ion
- Less active metals than Alkali group.
3 – Halogens ( group 7 A )
- located in right side of table
- mono-valent
- form negative ion
- they are diatomic molecule ex: Cl2 , Br2 , F2
- they may be liquid , solid and gas
- they are active elements.
- React with metals forming salts ex: KBr , NaCl
- Each element replace element below it in its salt solution.
K + Br2 KBr
Cl2 + KBr KCl + Br2
Properties of elements and their uses:
Element / Its usesSodium Na / Transfere heat inside nuclear reactor
Cobalt 60Co / In food preservation, as it emits gamma rays.
Silicon Si / In manufacture of electronic devices.
Liquified nitrogen / In preservation of eye cornea ( boiling point - 196 º )
Importance of water
- it is essential in all vital processes.
- Transportation in rivers and oceans.
- Generate electricity.
Source of water
- rivers, oceans and seas
- rains
- wells
- springs
the importance of water internationally:
- Agricultural field
- Industrial field
- Personal field
Structure of water
One oxygen atom and two hydrogen atoms tied by two single covalent bonds
Having angle between them equal 104.5 º
Hydrogen bond
It is a weak electrostatic attraction forece that arises between the molecules of polar compounds.
Properties of Water
A. physical properties / B. chemical propertyies1 – water exists in three states / 1- water has weak ionization
2 – good polar solvent / 2 –water resist decomposition.
3 –boils at 100ºC and freezes at 0ºC / 3 – water has neutral effect.
4 – water density decrease on freezing
5 – water has high latent heat.
6 – water has high specific heat.
Water pollution:
It is the addition of any substance to the water which causes continuous gradual change in water properties and affecting the health and the life of living creatures.
Water pollutions can be divided into
Artificial pollutants / Natural pollutants1 - Biological / Mixing animal and human wastes with water / Belharzia, typhoid and hepatitis. / - Volcanic eruptions.
- Death of living creatures.
- Lightning accompanying thunder storms.
2 – Chemical / Factories discharge residues and sewage / Lead cause death of brain cells
Mercury cause blindness
Arsenic cause liver cancer.
3 – Thermal / Increasing water temperature. / Death of marine creatures.
4 – Radiant / Dumping atomic wastes
Leakage of radioactive materials. / Cause cancer.
Cause genetic mutations.
Protection of water from pollution:
- preventing of getting rid of sewage and wastes of factories in rivers or canals.
- Developing purification water stations.
- Disinfection of water tanks.
- Don't store tap water in plastic bottles.
- Spreading environmental awareness.
Atmosphere
The Earth is surrounded by a gas envelope that rotates with it about its axis, and extends 1000 km above sea level.
Atmospheric Pressure.
The weight of air column of an atmosphere height on a unit area is called air pressure or atmospheric Pressure
It is measured by a unit called a bar. The bar equals 1000 millibar (mbar).
Normal atmospheric pressure at sea level equals 1013.25 millibar.
Change of atmospheric pressure with change in height above sea level
Notice it was found that:
A- 50% of atmosphere mass occurs in the area between sea level and 3 km high. Meanwhile
B-90% of its mass is concentrated in the frst 16 km above sea level.
What is the effect of the height decrease of an atmospheric air column on its weight?
The air pressure Increase from sea level to increase the length (weight) column of air.
What is the effect of rising up above sea level on the air density?
The air pressure decrease from sea level to increase the length (weight) column of air.
Altimeter in airplanes is used to determine the elevation of the navigation based on the atmospheric pressure at this level.
Life application
Barometer to determine today’s weather.
Atomspheric pressure maps:
in atmospheric pressure maps, points of eual pressure are joined by curved lines known as Isobar.
Advantages and disadvantages of lower and higher areas in Egypt.
Areas / Characteristics / Advantages / DisadvantagesHigher areas like :
- mokattam hill
- el haram hill
- Sinai hill / Consist of limestone rock that are susceptible to erosion. / _ clean air
_ away form crosdedness. / Have difficult roads to go up and down.
Lower areas like:
- siwa oasis.
- Kattara depression
- Wadi el natroun.
- Ewainat oasis. / Sea level is higher than earth's level. / Suitable for life in the middle of deserts. / _ the rise of sea level affects the design of buildings.
_ Formation of salt depositions affect agriculture.
Atmospheric envelope is divided into several layers according to the changes in the atmospheric pressure and temperature
There is a region between each two successive layers.
In these regions, the temperature remains consatant.
1 – Tropopause
Is the region between troposphere and stratosphere
2 – Stratopause
Is the region between stratosphere and mesosphere.
3 – Mesopause
Is the region between mesosphere and thermosphere.
1-It extends 13 km above sea level to the tropopause.
2-As we go up, the temperature decreases by a rate of 6.5 ºC per 1 km
Exercise
If the temperature at the base of Mount Everest is 20.6 ºC, how much is the temperature at its top if the mountain height is 8862 m?
Solution:
Height (km) =8.862 km
The decrease in temperature = height (Km) v 6.5 = 6.5 × 8.862=57.603 ºC
Temperature at the top = temperature at the base – decrease in temperatur
=57.603 - 20.6= -37.003 ºC
1-It extends from tropopause (13 km above sea level) to the stratopause (50 km) with thickness of 37 km.
2- temperature is constant and measure (– 60º C), then increases gradually until it reaches 0º C at the end of the layer.
4-It contains ozone layer
5-. The air moves in this part horizontally, making it suitable for fying planes
1-It is extended from the stratopause (50 km above sea level) to the mesopause with thickness of about 35 km.
2-Temperature decreases with height rate until reaches (– 90º C) at its end.
3-This layer is much vacuumed as it contains only a limited amount of helium and hydrogen gases.
4-Meteors are formed in this layer and burnt due to friction with air molecules
Mesosphere layer is highly rarefied?
Because it contains limited quantities of helium and hydrogen gases only.
it is the hottest layer of the atmosphere.
1-It extends from the mesopause to 675 km with a thickness of about 590 km.
2-Temperatures reaches about 1200º C.
3-Its upper part contains charged ions. extends until 700 km above sea level known as ionosphere.
Ionosphere layer
- Ionosphere plays an important role in wireless communication as it refects radio waves transmitted by radio stations.
Van-Allen belts:
They are two magnetic belts surrounding ionosphere and play an important role in scattering of harmful charged cosmic radiations.
Aurora phenomenon:
It is a phenomenon that appears as brightly coloured light curtains seen from the both poles of the earth.
Exosphere layer:
This is the area where satellites float around the Earth and transmit weather condition information and TV prvograms.
Exosphere:
It is a region in which the atmospheric envelope is inserted with outer space.
Ionosphere is very important in wireless communications?
Because it reflects radio waves transmitted by radio stations and communication centers.
The harmful charged cosmic radioations are scattered away from the earth before entering ionosphere layers?
Due to the presence of Van-Allen belts.
Comparison between the layers of atmospheric envelope
Points / Troposphere / Stratosphere / Mesosphere / ThermosphereThickness: / 13 kilometers / 37 km / 35 km / 590 km
Temperature / - 60 at its top / -60 to 0 ºC / -90 at its top / 1200 ºC at its top
Pressure: / 100 mb / 1 mb / 0.01 mb
It contains: / 75% of atmospheric mass.
99% of atmospheric water vapour / Most of ozone gas / Limited quantities
of helium and
hydrogen only / Charged ions in its
upper part.
Air movement: / Vertically / Horizontally
Since the mid 20th century, erosion of the Ozone Layer depletion and global warming phenomena have been the most serious threats
Position of ozone layer
- located at height 20 : 40 Km above sea level
Structure of ozone layer
·
O2 O + O
O + O2 O3
Thickness of ozone layer.
is located at a height between 20:40 km above sea level with thickness of 20 km
- Dobson was taken as a measuring unite of ozone layer degree.
- natural degree of ozone is 300 Dobson (( defined as 3 mm thickness. ))
- 100 Dobson = 1 mm thickness.
Importance of Ozone Layer
We should know the types of UV rays first:
Types of UV raysNear ultraviolet / Medium ultraviolet / Far ultraviolet
(UV – A ) / (UV – B ) / (UV – C )
- 100% of far ultraviolet rays don't penetrate ozone layer
- 95 % of medium ultraviolet rays don't penetrate ozone layre.