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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