Download Science 1st prep. 2nd term unit 1 lesson 2 During the chemical

Science 1st prep. 2nd term unit 1 lesson 2
Chemical compounds
The valency
During the chemical reaction, atoms try to reach the stable state. This is by:
1-Losing their outermost electrons (as in case of metals).
2-Gaining a number of electrons to fulfill the other shell by (8) electrons (as in case of nonmetals).
3-Sharing number of electrons to other different atoms (as in case of non-metals).
The valency
It is the number of electrons that an atom gained, lost or even shared during a chemical
reaction.
The outermost electronic of an atom determine its valiancy.
1
valency
Formed
Atomic
Number
Electronic configuration of some elements and their valences:
Element
Electronic
During chemical
configuration
reaction
K
L
M
Sodium (11Na23)
11
2
8
1
-loses one
electron
Chlorine (17Cl35)
17
2
8
7
-gain or shares
with one
electron
Oxygen (8O16)
8
2
6
gain or shares
with two
electron
Magnesium (12Mg24)
12
2
8
2
-loses two
electrons
Aluminium (13Al27)
13
2
8
3
-loses tree
electrons
Na+
Monovalent
Cl-
Monovalent
O- -
Divalent
Mg++
Divalent
Al+++
Trivalent
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
The valency of some metals:
Metal
Calcium Ca
Magnesium Mg
Iron 2 Fe
Lead Pb
Copper 2 Cu
Mercury Hg
valency
Metal
valency
Aluminum Al
Gold Au
Iron 3 Fe
Trivalent
Monovalent
Lithium Li
Potassium K
Sodium Na
Silver Ag
Copper 1 Cu
valency
Divalent
Metal
Note >>> some metallic elements have more than one valency such as:
Copper (Cu) which is monovalent and divalent.
Also , Iron (Fe) is divalent (( ferrous )) and trivalent (( Ferric )).
Sodium (Na) is monovalent, while aluminum (13Al) is trivalent?
Because sodium atom ( 2,8,1) losses one electrons from its outer level to be stable,
while oxygen (2,6 ) gains two electrons to fulfill its outer shell by (8) electrons.
The valency of some non metals:
Nonmetal
Hydrogen H
Chlorine Cl
Fluroine F
Bromine Br
Iodine I
valency
Monovalent
Sulphur S
Oxygen O
Divalent
Nitrogen N
Phosphorus P
trivalent
Nonmetal
valency
Sulphur S
Carbon C
Tetravalent
Nitrogen N
Phosphorus P
Pentavalent
Sulphur S
Hexavalent
Note >>> some nonmetal elements have more than one valency such as:
** Sulphur S is divalent, tetravalent and Hexavalent.
** Nitrogen N is trivalent and pentavalent.
** Phosphorus P is trivalent and pentavalent.
2
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
The valency of Nobel gases
The valiancy of noble gases is zero ?
because their outer electron shell is completely filled with electrons (have 8 electrons)
{except (2He) has 2 electrons}.
The atomic group
The valiancy of Atomic groups:
The atomic group (Radical)
It is a set of atoms of different elements joined together behave like one atom during a
chemiction , having a special valence electrons and cannot be existed solely
Valencies of some atomic groups (radicals)
Atomic group
valency
Atomic group
valency
Sulphate (SO4)
-2
Atomic group
valency
Phosphate
(PO4) –3
Trivalent
Carbonate (HCO3)
-2
Divalent
-
Monovalent
Hydroxide (OH)
Bicarbonate (HCO3)
Nitrate (NO3) Nitite (NO2) Ammonium(NH4) +
-
Question:
Mention an example for monovalent atomic group and trivalent atomic group?
What are the properties of atomic group?
Answer
(NO3)- is monovalent.
/
(PO4)
-3
is trivalent.
Atomic group has its own valency, behave like one atom during a chemical reaction and can not
be existed solely.
3
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
Chemical Formula
We can express the number of atoms and their types by chemical formula:
Chemical formula
It is a formula that represents the number and the type of the atoms in a molecule.
For example:
The chemical formula of sodium chloride (table salt) is NaCl.
This means that: this compound is composed of two atoms:
One atom of Sodium element.
One atoms of chlorine element.
The chemical formula of water is H2O.
This means that : This compound is composed of three
atoms
- One atom of Oxygen element .
-Tow atom of Hydrogen element .
How to write a chemical formula for a compound ?
We follow the following steps :
Steps
1 – Write the name of the compound
in words.
2 – Write the symbol of each
element or atomic group down to the
name .
3 – Write the valence down to each
symbol.
4 – Exchange their valences and
simplify them (shortened as much as
possible) .
5 – You don’t have to write the one
(1)
Calcium oxide
Sodium sulphate
Aluminum oxide
Ca O
Na
SO4
Al
O
2 2
1
2
2
2
Ca2 O2
Na2 (SO4)2
Al2 O3
Na2SO4
Al2O3
1 1
Ca O
4
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
*In case
of atomic groups if the number is not (1) Put the atomic group between brackets
and write the number right down to it.
Such as: 1. Aluminum sulphate
Al
2. Magnesium hydroxide
SO4
Mg
3
2
Al 2(SO4)2
OH
2
1
Mg (OH)2
Exercise : write the chemical formula for each of the following molecules and mention
the number of forming elements and the number of atoms in each molecule?
1
2
3
4
5
– Hydrogen chloride.
– sodium Oxide
– Carbon dioxide.
– sodium hydroxide.
–Aluminium carbonate.
Compound
Chemical formula
1 – Hydrogen chloride.
H
Cl
1
2 – Sodium Oxide
1
HCl
Na
3 – Carbon dioxide
1
Na2O
C
4 – Sodium hydroxide
4
CO2
Na
5 – Aluminium carbonate.
O
No of atoms in the
molecule
1 + 1 = 2
No. of forming
elements.
2
1 +
2
2 = 3
2
O
1 + 2 = 3
2
OH
1 + 1 + 1 = 3
3
1
1
NaOH
Al
CO3
9 + 3 +2 = 14
3
2
3
2
Al2(CO3)3
5
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
Questions on lesson
Complete the following statements:
1 – the valency of metals may be …………………………. , ……………………….. or trivalent as their
outermost energy shells have 1 , 2 or 3 electrons.
2 – the valency is the number of electrons which ……………………. , …………………….. or shared by an
atom during chemical reaction.
3 – some metallic elements have more than one valency such as ……………… and ………………
4- the valency of iron is …………………. In ferrous chloride, while in ferric chloride is …………………
5- the valency of hydrogen H atom is ………………………. While the valency of oxygen 8O atom is
………………………………
6- some nonmetallic elements have more than one valency such as ………………., ………………. And
……………………………..
7- the valency of sulphur atom may be ………………………….., ………………………….. or ………………………..
8- phosphorus element has two valences which are ……………………… and …………………….
9- the valency of Nobel gases is ……………………….. as their outermost electron shell is
……………………. With electrons.
10- the atomic group is a set of atoms of different elements joined together acts as
……………………………………… during chemical reactions and has its own ………………………………….
11- ……………… and ………………. Are examples of monovalent atomic groups, while …………….. and
……………………….. are examples of divalent atomic groups.
12- the symbol of phosphate group is ……………….. and its valency is …………………………..
13- the difference between nitrate group and nitrite group is one ……………… atom.
14- the chemical formula of sodium carbonate is ………………………….. and it consists of ………….
Atoms of ……………………… different elements.
15- A compound has a chemical formula XO2, so the valency of X is ……………………………..
6
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
Complete the following table:
Compound
1 – Sodium carbonate
2- …………………………
3- Calcium Oxide
4- Aluminum hydroxide
Chemical formula
No of atoms in
the molecule
No of forming
elements
CuCO3
…………………..
7
………………..
Choose the correct answer:
1 – all the following elements are monovalent except ………………….
a. hydrogen
b. sodium
c. oxygen
d. chlorine
2– when an atom loses, gains or shares by one electron, its valency is ……………………
a. monovalent.
B. divalent
c. trivalent
d. tetravalent.
3- when a nonmetal gains or shares by two electrons, its valency will be ………………………….
a. monovalent.
b. divalent
c. trivalent.
d. tetravelnt.
4- all the following are nonmetals having more than one valency except ………………………
a. copper
b. phosphorus.
C. sulphur
d. nitrogen.
5- in trivalent elements, the outermost energy level contains ……………………. Electrons.
a. 3 or 5
b. 5 or 6
c. 7 or 1
d. 6 or 3
6- the valencyof argon 18 Ar is …………………………
a. trivalent
b. divalent
c. monovalent
d. zero.
7- the valency of copper in Cu2O is ………………………..
a. monovalent
b. divalent
c. trivalent
d. tetravalent.
8- the number of atoms equals the number of elements in the molecule of ………………………….
a. sodium hydroxide.
b. water
c. Calcium sulphate.
d. sodium nitrate.
9- the nitrate group is a ……………………… radical.
a. monovalent
b. divalent
c. trivalent
d. tetravalent.
10- the chemical formula indicates the ………………………… in the compound.
a. number of atoms
b. type of atoms
c. number of elements. d. all the previous.
11- element M form a compound M(OH)3 so, its valency is ………………………..
a. monovalent
b. divalent
c. trivalent
d. tetravalent.
12- each aluminum atom 13Al combines with ………………. Atoms of chlorine 17Cl to form aluminium
chloride molecule.
a.two
b. three
c. four
d. five.
7
Ms. Marim
Science 1st prep. 2nd term unit 1 lesson 2
Give reasons for :
1- both sodium 11Na and chlorine 17Cl are monovalent although they have different atomic
numbers?
…………………………………………………………………………………………………………………………………….
2- Potassium 19K is monovalent, while Oxygen 8O is divalent?
……………………………………………………………………………………………………………………………………
3- the chemical formula of sodium carbonate is Na2CO3?
……………………………………………………………………………………………………………………………………
4- the valency of nobel gases is Zero?
……………………………………………………………………………………………………………………………………
Write the names of the following compounds ?
1234-
CaSO4
H2SO4
CaCO3
CO2
8
Ms. Marim