EXTRA . HIGH LEVEL 1. PERIODIC TABLE. The periodic table is a table of the chemical elements in which the elements are arranged by order of atomic number . The elements are grouped in: a) Periods. There are seven rows in the periodic table called periods. They have been numbered from 1 to 7 . Each period indicates the last shell that is being filling up. b) Groups. There are 18 vertical columns in the periodic table called groups. They have been numbered from 1 to 18 ( in Arabic numerals ) from left to right. The periodic table is structured so that elements with the same type of valence electron configuration are arranged in columns. - The left-most columns include the alkali metals and the alkaline earth metals. In these elements the valence s orbitals are being filled (2) . - On the right hand side, the right-most block of six elements are those in which the valence p orbitals are being filled (6). These two groups comprise the representative elements. - In the middle is a block of ten columns that contain transition metals. These are elements in which d orbitals are being filled (10). - Below this group are two rows with 14 columns. These are commonly referred to Inner transition elements. In these columns the f orbitals are being filled (14) Important facts to remember: a) 2, 6, 10 and 14 are the number of electrons that can fill the s, p, d and f subshells (the l=0,1,2,3 azimuthal quantum number) b) The 1s subshell is the first s subshell, the 2p is the first p subshell (n=2, l=1), 3d is the first d subshell, and the 4f is the first f subshell

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2. PERIODIC PROPERTIES. The Modern Periodic Law states the chemical and physical properties of elements are a periodic function of their atomic numbers. The main periodic properties are: atomic radii, ionization energy ,electron affinity and electronegativity. 2.1. ATOMIC RADII. ( Radius ( singular), Radii ( plural)) The distance from the centre of the nucleus to the outermost shell of an atom is called the atomic radius of that atom. Practically, measurement of size of an isolated atom is difficult; therefore, it is measured when an atom is in company of another atom of same element. It is defined as one-half the distance between the nuclei of two atoms when they are linked to each other by a single covalent bond. a) Variation of atomic radii in a group. Atomic radii increase in a group from top to bottom. As we go down a group the number of shells increases and valence electrons from nucleus increases.

b) Variation of atomic radii in a period. Atomic radius generally decreases from left to right. In a period there is a gradual increase in the nuclear charge. Since valence electrons are added in the same shell, they are more strongly attracted towards nucleus. This gradually decreases atomic radii. In the case of noble (inert) gases there are exceptions and the atomic size of the elements may be greater than the other atoms of the period. There are a lot of valence electrons and there are a great repulsion among them.

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2.2 IONIZATION ENERGY It is the heat of reaction required to remove an electron from a neutral atom, for example, sodium: Na(g) →Na+ (g) + e If only one electron is removed, the ionization energy is known as the first ionization. If second electron is removed the ionization energy is called the second ionization energy. If third electron is removed the ionization energy is called the third ionization energy. Successive ionization energies of an atom increase rapidly as reduced electron-electron repulsion causes the electron shells to contract, thus binding the electrons even more tightly to the nucleus. a) Variation of ionization energy in a period. For any period, the ionization energy increases as the atomic number increases to reach the maximum value that for noble gases. Ionization potential increases across the period because of increase in nuclear charge due to which the atomic size decreases. Thus, more energy is required to pull away the electron from the outermost shell of the atom of smaller size. b) Variation of ionization energy in a group. They decrease as we move down the table because in each period the electron is being removed from a shell one step farther from the nucleus than in the atom immediately above it. Metals usually have low ionization potential whereas non-metals have high ionization potential.

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2.3. ELECTRON AFFINITY It is the amount of energy released when an electron is added to an isolated gaseous atom. Electron affinity is the ability of an atom to hold an additional electron. If the atom has more tendency to accept an electron then the energy released will be large and consequently the electron affinity will be high. Electron affinities can be positive or negative. a) Variation of electron affinity in a period. It increases from left to right across the period because of increase in nuclear charge and decrease in atomic size. This causes the incoming electron to experience a greater pull of the nucleus thus giving a higher electron affinity. The electron affinity of completely filled atoms is almost zero. An atom does not accept an electron in its outermost shell if it already has a stable configuration , as in the case of inert ( noble ) gases. b) Variation of electron affinity in a group. It decreased down the group because the number of shells increases i.e., the atomic size increases and the effective nuclear charge decreases. This causes the incoming electron not to experience much attraction of the nucleus thus giving a lower electron affinity.

2.4. ELECTRONEGATIVITY. It is a measure of an atom's ability to hold electrons. It is the ability of an atom in a molecule to attract electrons to itself. The general trend of Electronegativity in the periodic table is :

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ACTIVITIES 1) Arrange each of the following quartet of four chemical species in the order of increasing the radius. (a) Ar, Cl- , K+ , S2- (b) C, Al, F, Si (c) Na, Mg, Ar, P (d) I- , Ba2+ , Cs+ , Xe 2) Choose the smallest one from each group of atoms or ions. (1) Li, Na, K (2) P, Sb, As (3) S, Cl, Ar 3) Fill in the blanks with appropriate words. Decreases increases minimum

increases

smaller

(4) O+, O, O -

decreases

increases

a. The force of attraction between nucleus and valence electrons _______________ in a period. b. Atomic radii of elements _______________ in a period from left to right. c. Radius of cation is _______________ than that of the neutral atom of the same element d. Electronegativity _______________ in a period from left to right and_______________ in a group from top to bottom. e. Metallic character of elements _______________ from top to bottom in a group. f. Ionization energy of the 1st element in a period is _______________ in the entire period. 4) Three atoms have the electron configurations shown below. (1) 1s2 2s2 2p6 (2) 1s2 2s2 2p6 3s1 (3) 1s2 2s2 2p6 3s2 Which of the three atoms has the highest 1st ionization energy? Propose which atom may have the highest 2nd ionization energy? 5) The 2nd ionization energies are defined as the energy required to remove the second electron from the atom. The 3rd and 4th ionization energy is defined in a similar manner. Select from among elements X, Y and Z the one that will most clearly exhibit the properties (a), (b) and (c) given below. (a) to form a monovalent ionic compound with chlorine. (b) to form a covalent bond with chlorine. (c) To have the oxidation number of +2 in most cases.

6) Filled and half-filled subshells show a small increase in stability in the same way that filled shells show increased stability. So, when trying to remove an electron from one of these filled or half-filled subshells, a slightly higher ionization energy is found. Example 1: Which element has a higher ionization energy, Be or B?

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Example 2: Which element has a higher ionization energy, N or O?

Example 3: Which element has a higher ionization energy, Zn or Ga?

7) Which element has a higher electron affinity, N or C ?

8) Considera las configuraciones electrónicas de estas tres especies: A2+: 1s2 2s2p6 ; B: 1s2 2s2p6 ; C–: 1s2 2s2p6 a) ¿Tendrán el mismo radio atómico? ¿Por qué? b) ¿Cuál de las tres especies tendrá el mayor radio? c) ¿Cúal de los tres elementos A, B y C presentará la energía de ionización más elevada? d) ¿Y cuál el valor más alto de la afinidad electrónica? 9) Dos elementos, X e Y, tienen, respectivamente, las siguiente configuraciones electrónicas: 2 2 6 2 6 10 2 2 2 6 2 6 10 2 4 X: 1s 2s p 3s p d 4s ; Y: 1s 2s p 3s p d 4s p . a) Indica si son elementos representativos, de transición o de transición interna. b) Señala el grupo y el período al cual pertenecen. c) Justifica cual de los dos tendrá mayor energía de ionización. 10) Se tienen dos elementos de números atómicos 11 y 17 respectivamente. Explicar de forma razonada: a) Su nombre, símbolo y el tipo de elemento que es cada uno (representativo, de transición, etc.) b) Su situación en el sistema periódico. 6

c) El número de electrones que tiene cada uno en su última capa. d) Cuál es el gas noble más próximo a cada uno de ellos. e) Qué elemento les precede. Escribe los símbolos de todos los elementos químicos que aparezcan.

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ACTIVITIES. ANSWERS 1) Solution: (a) K+ < Cl- < S2- < Ar (c) P < Mg < Na < Ar

(b) F < C < Si < Al (d) Ba2+ < Cs+ < I- < Xe

2) Solution: (1) Li

(3) Cl

(2) P

(4) O+

3) Fill in the blanks with appropriate words. Solution: Decreases

increases

minimum

increases

smaller

decreases

increases

a. The force of attraction between nucleus and valence electrons increases in a period. b. Atomic radii of elements decreases in a period from left to right. c. Radius of cation is smaller than that of the neutral atom of the same element d. Electronegativity increases in a period from left to right and decreases in a group from top to bottom. e. Metallic character of elements increases from top to bottom in a group. f. Ionization energy of the 1st element in a period is minimum in the entire period. 4) Atom (1) has the closed electron shell, and should have the highest ionization energy. Atoms (2) and (3) are sodium and magnesium, respectively. The second electron to be removed is a 2p electron for Na but a 3s electron for Mg. You can surmise that the outer electron is easer to remove as compared with the inner electron. 5) X belongs probably to an alkaline metal group since both 1st and 2nd ionization energies are small. You can surmize Y is a group 13 element and Z a group 1 element. (a) Z (b) Y (c) X 6)

Example 1: I1(Be) > I1(B)

It's harder to ionize an electron from beryllium than boron because beryllium has a filled "s" subshell. Example 2: I1(N) > I1(O) Nitrogen has a half-filled "2p" subshell so it is harder to ionize an electron from nitrogen than oxygen. Example 3: I1(Zn) > I1(Ga) It's harder to ionize an electron from Zn than boron because Zn has a filled "d" subshell. 7) Since a half-filled "p" subshell is more stable, carbon has a greater affinity for an electron than nitrogen. 8) Solution: a) Aunque las tres especies tienen configuraciones isoelectrónicas, no son el mismo elemento. La primera es un ion dipositivo, formado a partir de la cesión de dos electrones del elemento neutro A, que será el magnesio (Z = 12). B es el neón (Z = 10). Por último, la última especie iónica procede del elemento C que ha ganado un electrón, por lo que su número atómico será 9, es decir, se trata del flúor. Teniendo en cuenta esto, obviamente la respuesta es negativa, ya que el radio atómico depende de la atracción que ejerza el núcleo (valor de Z) sobre la última capa electrónica.

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b) Según lo expuesto anteriormente, y puesto que hay que descartar a B (recuérdese la definición de radio atómico) nos encontramos con que las dos especies que quedan, A 2+ y C–, tienen igual número de capas electrónicas, pero al tener C menor valor de Z que A, la atracción sobre el nivel electrónico más externo (que es para ambos el mismo, el segundo) será menos intensa en el caso de C–, por lo que su radio será mayor. c) Recordando cómo varía la energía de ionización en el sistema periódico, será B (el neón) el elemento de mayor energía de ionización. (Luego sería C, el flúor, y, por último, A, el magnesio). d) Para esta propiedad periódica no se debe contar con B, ya que al ser un gas noble, no tiene “afinidad” por tomar (o ceder) electrones. Por tanto, será C el elemento de mayor valor. 9) Solution: a) Teniendo en cuenta qué es un elemento representativo, qué es uno de transición y qué uno de transición interna, X será un elemento de transición (pertenece a un grupo titulado con la letra B, e Y un elemento representativo (marcados en el S.P. con la letra A). b) X pertenece al período cuarto y al grupo IIB, grupo 12 en la nueva notación propuesta por la I.U.P.A.C., mientras que Y está en el cuarto período, y en el grupo VIA. c) Teniendo en cuenta cómo varía la energía de ionización dentro del S.P., al estar ambos en el mismo grupo pero Y más hacia la derecha, será este elemento el de mayor energía de ionización (mayor valor de Z, e igual número de capas electrónicas). 12) Solution: a) Los elementos de números atómicos (Z) 11 y 17 corresponden, respectivamente al sodio y al cloro. Ambos son elementos representativos; el sodio es un metal alcalino y el cloro, un halógeno. b) El sodio se encuentra en el grupo IA (grupo 1 según las nuevas recomendaciones de la IUPAC), período 3º, y el cloro está situado en el grupo VIIA (grupo 17) y también el el tercer período. c) Puesto que ambos son elementos representativos, el número de electrones que tienen en su última capa coincide con el grupo; por tanto, el sodio tendrá un electrón y el cloro siete. d) En el caso del sodio, el gas noble más próximo es el neón, Ne; para el cloro, será el argón, Ar. e) El elemento anterior al sodio (Z =11) es el neón, Ne. En el caso del cloro (Z = 16), el elemento que le precede es el azufre, S.

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LINKS 1) http://www.mikeblaber.org/oldwine/chm1045/notes/Struct/EPeriod/Struct09.htm 2) http://www.colorado.edu/physics/2000/periodic_table/index.html 3) http://www.chem1.com/acad/webtext/atoms/atpt-6.html 4) http://www.tutorvista.com/content/science/science-ii/periodic-classification-elements/trends.php 5) http://www.grandinetti.org/Teaching/Chem121/Lectures/IonizationEnergy

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