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Exercise 1: Ammonia NH3
NH3 ammonia is a gas injected into cultivated land to improve the development of green plants and help increase crop production. It is used in refrigeration systems, but any leak in the pipes of these appliances releases ammonia into the air, which irritates the eyes and causes poisoning.
1. Document 1 represents the Lewis structure of the ammonia molecule:
1.1. What is the valence of the hydrogen atom? 1.2. Specify the number of valence electrons of the nitrogen element. 1.3. Identify the type of bonds in this molecule.
2. Document 2 represents the charge of the electron cloud of each of the N and H atoms. - Copy and complete the following table:
Atoms Charge of nucleus Electronic configuration Position in the periodic table
3. The synthesis of ammonia is an oxidation-reduction reaction. This reaction is represented by the following equation: N2 + 3H2 2NH 3
3.1 - Choose from the oxidation numbers given below that which corresponds to the oxidation number of the nitrogen element in the NH3 ammonia molecule. a) o.n of (N) = 0 b) o.n of (N) = + I c) o.n of (N) = -III d) o.n of (N) = +III
3.2. Identify the species undergoing the reduction. 3.3. Extract from the text the harmful effects of NH3 ammonia on the human body.
Exercise 2: Calcium
Calcium plays an important role in bone formation. Too little calcium in the diet, especially during periods of bone growth, can lead to soft bones that break easily.
1. Calcium has four isotopes. The relative abundance of these varieties of atoms is shown in the table below: Calcium is located on the fourth row (period 4) and in the second column (group II) of the periodic table.
1.1. Determine the atomic number of the calcium element 1.2. Compare the composition of the nuclei of the four stable calcium isotopes. 1.3. Give the electronic configuration of the element located just above the calcium. 1.4. Draw from the text, the influence of a diet poor in calcium.
2. Fluorine is a yellowish gas of formula F2. Fluorine gas reacts with alkaline earth, it forms magnesium fluoride, calcium fluoride CaF2 ... etc).The fluorine atom has seven valence electrons.
2.2. Explain the formation of the bond in the calcium fluoride compound (CaF2). 2.3. Choose from the properties below those that represent this compound (CaF2).
Mass number (A) 40 42 43 44
Relative abundance (%) 96,941 0,647 0,135 2,086
Molecular compound - low melting points - non-electrolyte in aqueous solution - ionic compound - high melting points and electrolyte in aqueous solution.
Exercise 3: A Toxic Spot Remover
The 1,2-dichloroethene of molecular formula C2H2Cl2, is an efficient spot remover but it is toxic even in small quantity. So, it should not be inhaled.
1. A molecule of 1,2-dichloroethene consists of the three elements: carbon, hydrogen and chlorine,
which are represented respectively by the atomic symbols: C126 , H 1 1 and Cl
35 17 .
1.1. Write the electron configuration of each of these three atoms. 1.2. Copy and fill in the following table. (The relative charge of one proton= + 1)
2. Identify the type of the bond between the two carbon atoms in the adjacent molecule. 3. The molecules (C2H2Cl2) that enter the organism are not eliminated as they are, but
they are transformed in the liver into toxic product of formula C2H2O2Cl2. 3.1. Give the Lewis dot symbol of an oxygen atom, knowing that it has six valence electrons. 3.2. Specify the valence of an oxygen atom. 3.3. Write a Lewis structure of the molecule C2H2O2Cl2, where the bond between the two carbon atoms is single covalent bond. 3.4. Pick up why the molecules (C2H2Cl2) are toxic.
Exercise 4: Chemical Composition of Banana.
Banana contains compounds of potassium (k) and sodium (Na), it is a natural treatment for many diseases! Comparing to the apple, banana contains four times more proteins (which contain mainly the element nitrogen, three times more phosphorous and five times more vitamin A! Banana can be a good helper for persons who hope to stop smoking. Vitamins B6 and B12, as the potassium and the magnesium (Mg), help the body to recover from the effects of the absence of nicotine. Given: The electron configurations of: Mg: K2, L8, M2; P: K2, L8, M5; K: K2, L8, M8,N1 et N: K2, L5.
1. Identify among the given elements (Mg, P and N), those that belong to the same period (line) and those that belong to the same group (column).
2. Determine the relative charge of the electronic cloud of a magnesium atom. (Relative charge of one electron = -1)
Element Charge of the Nucleus
Column row Valence
3. Potassium of atomic number Z = 19, is found in the nature as mixture of three isotopes. The relative abundance of the atoms is shown in the following histogram.
Compare the composition of the nucleus of potassium isotopes.
4. Nitrogen (N) is the element that constitutes proteins and help plants to develop. 4.1.Give the Lewis dot symbol of nitrogen atom N. 4.2.Explain the formation of the bonds in nitrogen gas N2.
5. Tell, referring to the text why banana can be a good helper for persons who desire to stop smoking.
Exercise 5: Silicon
Silicon of symbol Si a metalloid used in fabrication of solar cells and transistors. It is prepared from pure sand.
1. The symbol of the nucleus of silicon atom is 2814 Si
In the following table, only one proposed answer for each question is correct. Write the number of each question then choose by justification the correct answer.
2. The silicon is found in nature as mixture of three isotopes. The relative abundance of these varieties of atoms is shown in the table below. Mass number A 28 29 30
Relative abundance (%) 90 6 4 Document 1
2.1.Compare the composition of nuclei of the three atoms of silicon. 2.2.What is the heaviest silicon isotope??? 2.3.Determine the charge of electronic cloud of the first two silicon isotopes. Deduce the one of the
third isotope. (Relative charge of 1 electron = -1) 3. Pick out from the text the uses of silicon.
Answers N Questions
a b c
The nucleus of this atom contains
14 protons and 28 neutrons
14 protons and14 neutrons
14 protons and 42 neutrons
2 The electron configuration of this atom is :
K2 L8 M4 K2 L6 M6 K2 L8 M8
3 The position of this element in the periodic table :
(groupe IV, période 4 ) (colonne 14, ligne 4 )
(groupe IV, période 3 ) (colonne 14, ligne 3 )
(groupe III, période 4)
| (colonne 13, ligne 4)
4 The valence of this atom is : 4 6 8
Atom Period (line ) Column
Exercise 6: Ethanol
Ethanol (C2H6O) is used as solvent for varnishes, perfumes, paintings ... It is also used as an antiseptic, an agent that reduces and prevents infection by eliminating the microorganisms that cause disease.
1. Referring to document 1: 1.1.Write the electron configuration of the 2 atoms: carbon and
hydrogen. 1.2.Deduce the atomic number of carbon element.
Document 1 2. Referring to document 2:
2.1. Show that this document represents an atom. 2.2. Give the symbol of oxygen nucleus atom. 2.3.Determine the position of oxygen in the periodic table.
3. Referring to document 1 and document 2: 3.1. Write the Lewis representation of each atom: carbon, hydrogen and oxygen. 3.2. Deduce the valence of each of the above atom.
4. Give the Lewis representation of the molecule C2H6O, such the bond between the two carbon atoms is single covalent bond.
Exercise 7: Magnesium oxide
Magnesium oxide is the oldest magnesium salts, described in a former medical dictionary has a high content of magnesium elementary 60.3%. But assimilation is bad enough as solubility. White powder, also called "chalk", magnesium oxide, or periclase is used as an active ingredient in many medicines, to regulate the levels of magnesium (Magnosol, Sympathyl ...) or fight against the stomach pain.
1. The histograms below show the constituents of the nucleus of each atom: magnesium and oxygen.
1.1.Reproduce and complete the table below:
Atomic number Mass number Electronic configuration
1.2.Write the Lewis representation of the atoms: oxygen and magnesium.
Carbon 2 14 (G:IV) Hydrogen 1 1(G:I)
1.3.Justify if the following statement are true.
The oxygen atom located on the line 2 (period 2) of the periodic table. Magnesium atom belongs to the column 2 (group 2) of the periodic table.
2. The magnesium metal (Mg) reacts with the oxygen (O2), to give the compound magnesium oxide MgO. - Explain the formation of bond in the compound of magnesium oxide.
3. List by referring to the text the importance of magnesium oxide.
Exercise 8: Minerals of milk
Minerals are chemical elements needed for the functioning of the human body. The following table shows the mass in mg of some chemical elements contained in 100 g of milk.
Symbol of element K Ca Cl P Na
Mass in mg 139 133 105 88 75
Given: 19 K : K 2 L8 M8 N1; ZCa : K
2 L8 M8 N2 ; 17Cl :K 2 L8 M7; 1