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Science 2nd prep. 1st term Lesson 2 Graduation of the properties of Elements in the Modern periodic table we will study the graduation of some properities of the periodic table. 1-Atomic size 2-Electronegativity 3-Metallic and nonmetallic property ۞1-Atomic size property Think carefully with your colleagues in the co-operating group (fgure 1) and record : your observations on the following questions What do you observe for the graduation of the values of the atomic size of elements in relation ? to the increasing of the atomic number In periods ……………………………………… In groups •……………………………………… The atomic size evaluated in the bicometre = 1 / 1000000000000 »Bicometre = part of a million of a million of metre« From the previous, we conclude that 1- In period The atomic size of the same period decreases by the increase of their atomic numbers(G.R.?) 2- In group The atomic size of the same group increases by the increase of their atomic numbers(G.R.?) Due to The increase of the attraction force between positive nucleus and the electrons in the outermost energy level due to the increase of the number of the energy levels in the atoms 1 Science 2nd prep. 1st term 2-The electronegativity property observe and think carefully with your classmates and record your observations on the following questions: What do you observe for the graduation of values of the electronegativity of elements by increasing the atomic number ? • In periods.................................................................................... • In groups.................................................................................... Electronegativity values of some elements. electronegativity??! From the previous, we can conclude that : 1- In period By increasing the atomic number the electronegativity of elements of the same period increases 2- In group but it decreases in the same group. The electronegativity of fourine element is the highest value and equals 4 The polar compounds To understand the concept of the polarity of some chemical compounds, you can do the following activity Activity(3) Determination of the properties of the polar compounds. For the illustrated elements in it (Use fgure 2) • Oxygen and hydrogen in H2O molecule. • Nitrogen and hydrogen in NH3 molecule. ............................................................................ the electrons of the bond towards itself in : (A) Molecule of water H2O . (B) Molecule of ammonia NH3 . 2 Science 2nd prep. 1st term from the previous we can consider that : 1-The polar compound is a covalent compound, the electronegativity difference between its elements is relatively high. 2-Water molecule and ammmonia molecule are from examples of polar compounds The difference in electronegativity of the elements in the molecule has an important role in determining the type of link between the two chemical bonds 1 - link hydrogen atoms with oxygen atoms to form water molecule H2O The ability of the oxygen atom to attract e-covalent bonds (OH) is greater than the capacity of the hydrogen atom because the electronegativity of oxygen (3.5) is greater than Alsalbeh hydrogen (2.1) Water from the polar covalent compounds, because difference electronegativity 3.5-2.1 = 1.4 2 - Engagement nitrogen atom with three atoms of hydrogen to form ammonia molecule NH3 The ability of the nitrogen atom to attract e-covalent bonds (NH) is greater than the capacity of the hydrogen atom as the electronegativity of nitrogen (3) greater than Alsalbeh hydrogen (2.1) 3 Science 2nd prep. 1st term Ammonia compounds polar covalent because difference electronegativity 3-2.1 = 0.9 3 The metallic and nonmetallic property: – Elements are divided into 4 main kinds, which are : ☼ Metals. ☼ Nonmetals. ☼ Semimetals (Metalloids). Metals ☼ Inert gases. Nonmetals are characterized by that their outermost shells contain less than (4) electrons are characterized by that their outermost shells contain more than (4) electrons and less than(8) tend to lose these electrons during the chemical reaction To reach the nearest inert gas preceding them in the periodic table. tend to gain electrons during the chemical reaction. To reach the nearest inert gas next them in the periodic table, forming positive ions. forming negative ions Semimetals (Metalloids). They are the elements which have the properties of both metals and nonmetals. are characterized by that their outermost shells contain (3 to 6) electrons It is diffcult to identify semimetals by knowing their electronic confguration due to the difference of numbers of the electrons in theirvalencies shells as shown in the table: Activity Discovering the graduation of the metallic and nonmetallic properties in the periodic table. From the previous, we can conclude : 1- The period starts with strong metal, as the atomic number increases in the same period the metallic property decreases gradually until we reach semimetals and then nonmetals start appear and as the atomic number increases, the nonmetallic property increases until we reach the strongest nonmetal in group 7A. 4 Science 2nd prep. 1st term 2- Metallic property of the same group increases by the increase of the atomic number as we go from up to down (as in group 1A) due to the increase of the atomic size, while nonmetallic property decreases (as in group 7A) due to the decrease of electronegativity values. 5 Science 2nd prep. 1st term Questons on lesson 2 1 – in the same period,the element which has th highest electronegativity lies in group ……………… a. 1A b. 2A c.7A d. 0 2 – the electronegativity for 19K element is ……………… the electronegativity for 11Na element a. greater than b. smaller than c. equal to d. no correct answer 3 – the electonegativity of fluorine equals ………………. a. 2.1 b.4 c. 5 d. 6 4 – which of the following elements is a metallic element? ……………….. a. 12Mg b. 17Cl c. 8O d. 10 Ne 5 – An element (x) its atomic number is 13 so,the mumber of electrons in its ion is ……….. a. 8 b. 10 c. 11 d. 12 6 – all the following elements are metalloids except ……………. a. terllium. B. silicon. C. boron. D. bromine. 7 – each period in the periodic table starts with ………………… a. metal . b. metalloid c. nonmetal. D. inert gas. 8 - ………………. Is the least metallic element in group (1A) a. Na b. Cs c. K d. Li 9 – the nonmetallic property decreases gradually within group (7a) as we go from …………. a. left to right. B. right to left c. top to bottom. D. bottom to top. Complete the following statements: 1 – by increasing the atomic number, the values of atomic sizes …………….. in the periods of the periodic table. 2 – by increasing the atomic number in groups, the atomic size ……………… due to the increase of the mumber of …………… 6 Science 2nd prep. 1st term 3 – the element (8x) has ………. atomic size than element (6Y). 4 – by increasing the atomic number, the values of electronegativity ………. In the groups of the periodic table. 5 – the electronegativity in the modern periodic table increases from …………..to ……………. Inside the same period. 6 – in period (2) the electronegativity of oxygen (8O) is ………….. than that of mitrogen (7N). 7 – the polarity of water is ………………. Than that of ammonia as the difference in …………………. Between elements of water is ……………. Than that between elements of ammonia. 8 –the elements are classified into four main kinds which are metals, nonmetals, ………… and ………………….. 9 – the last level of metallic elements contains ………………… than four electrons , while that of nonmetallic elements contains ……….. than four electrons. 10 – the ………..ion carries a number of ……………… equals the mumber of lost electrons. 11 - ……………….. and ………………… are examples of metalloids. 12 – by increasing the atomic number within a period, the metallic property ……………., while the nonmetallic property …………… 7