Periodicity

= = = Periodic Classification of the Elements = = Variation in Physical properties =
 * = ﻿ =
 * 1A - Alkali metals
 * Lithium, Sodium, Potassium, Rubidium, Cesium, and Francium.
 * Hydrogen behaves as non-metals in contrast to other members of that group
 * has the ability to lose its valence electrons.
 * Very reactive
 * have low ionization energies and react with nonmetals to form ionic solids.
 * 2A - Alkaline earth metals
 * Two electrons in the outer shell
 * Low electron affinities
 * Low electronegativities
 * Readily form divalent cations.
 * 7A - Halogens
 * Seven valence electron
 * Exist at room temperature as a gas (F2 and Cl2), a liquid (Br2), and a solid (I2 and At)
 * Tend to gain one electron to form a halide
 * Are reactive, with fluorine being the most reactive of all nonmetals
 * 8A - Noble gases
 * Fairly nonreactive
 * Complete valence shell
 * High ionization energies
 * Very low electronegativities
 * Low boiling points (all gases at room temperature)
 * Representative Elements(Main group elements)-1A-7A. Every members of these groups has the same valence electron configuration.
 * d-Transition Elements - Group 3-12
 * After lanthanum(La), a group of 14 elements called the lanthanide series or lanthanides. The series of elements corresponds to the filling of the seven 4f orbitals.
 * After actinium(Ac), a group of 14 elements called the actinide series, or actinides. This series corresponds to the filling of the seven 5f orbitals.
 * **Effective Nuclear Charge**
 * Presence of shielding electrons reduces attraction between protons and outer electrons.
 * The repulsive force between electrons offset the attractive force by nucleus

Equation: Zeff = Z- σ Z = Actual nuclear charge (atomic number) σ = shielding constant (screen constant)


 * **Atomic Radius **
 * One half the distance between the two nuclei in two adjacent metal atoms
 * The larger the effective nuclear charge, the stronger the hold of the nucleus, th smaller the atomic radius
 * The atomic radius inreases with increasing atomic number in group elements
 * The atomic radius decreases with decreasing atomic number within period.


 * **Ionic Radius**
 * The Radius of a cation or an anion
 * If atom forms an anion, its size increases, because nuclear charge remains with additiona electron charges.
 * If atom forms a cation, it size decreases, because of reduction of electron- electron repulsion with same nuclear charges

 =Electronegativity = 
 * Electronegativity : ability of an atom to attract toward itself the electrons in a chemical bond.
 * Elements with widely different electronegativity forms ionic bond
 * Most electronegative elements are nonmetals. The least elements are akali and alkaline earth metals and aluminum.

= Ionization Energy = Na --> Na+ + e- Na+ --> Na2+ + e- Ex) Mg : I1 738 kJ/mol, I2 : 1450 kj/mol, I3 :7730 kj/mol - Ionizaion energy in each periods is increasing with atomic number - Ionization energy in each groups is decreasing with atomic number
 * Ionization Energy- The amount of energy or energy potential taking to detack one electron from an neutral atom
 * First Ionization Energy(T)- 496Kj/mol
 * Second Ionization Energy(I2)-4560kj/mol
 * The higher the ionization energy, it is harder to remove an electron.
 * Greater energy is necessary to remove remaining electrons.
 * The chart of Increase of Ionization Energy



= Electron Affinity = <span style="display: block; font-family: Arial,Helvetica,sans-serif;">X(g) + e- ======> X-(g) = Variation in Chemical Properties of the Representative Elements = Diagonal Relationships - similarities between pairs of elements in different groups and periods of periodic table Ex) Li, Be, B are similar to the elements located diagonally below in perioic table. This is because of closeness of charge densities <span style="display: block; font-family: Arial,Helvetica,sans-serif;">exists as monatomic species which is called as noble gas. Its atoms have completely filled valence shells which <span style="display: block; font-family: Arial,Helvetica,sans-serif;">gives great stability. It has highest ionizaton electron and have no tendency to accept extra electron. It is also called <span style="display: block; font-family: Arial,Helvetica,sans-serif;">as inert gas depending on whether they produce acids or bases when dissolved in water. Some oxides are amphoteric which have both acidic and basic properties. Ex)Al2O﻿3
 * Electron affinity is the energy change associated with the addition of an electron to a gaseous form.
 * Electron affinity generally become more negative from left to right across the period.
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif;"><span style="font-family: Arial,Helvetica,sans-serif;">Neutral atom + electron ==> negative atom [[image:AffinityTable.gif]]
 * **Hydrogen (1s) -** Can be unipositive ion(H+) or hydride ion(H-). Usually, ionic hydride reacts with water to produce hydrogens
 * **Group 1A Elements -** Called as Alkali metals, with low ionization energy. It reacts with water to produce hydrogen gas and metal hydroxide. It form different kinds of oxides due to stability of oxide
 * **Group 2A Elements -** Called as Alkaline earth metals. Only Ca, Sr, Ba are reactive enough to react with water. Also, the reactivity with oxygen increases from top to bottom. Ca, Sr, Ba can also react with aqueous acid.
 * **Group 3A Elements -** Metalloid(Boron) and metals. They form unipostive and tripositive ions. Moving down the group, the more likely unipositive ion forms. It also forms molecular compounds
 * **Group 4A Elements -** Nonmetal (Carbon), metalloids, metals. The metallic elements do not react with water but acids to produce hydrogen gas. It forms compounds with +2 and +4 oxidation states.
 * <span style="display: block; font-family: Arial,Helvetica,sans-serif;">**Group 5A Elements -** <span style="font-family: Arial,Helvetica,sans-serif;">nonmetals(nitrogen and phosphorus), metalloids, metal(bismuth). Elemental nitrogen is diatomic gas. Phosphorus exists as P4 Molecules.
 * **Group 6A Elements -** nonmetals (Oxygen, Sulfur and selenium), metalloids. Oxygen is diatomic gas. Sulfur and selenium have molecular formulas. It forms molecular compounds with nonmetals such as SO2, SO3, H2S**.**
 * **Group 7A Elements -** called as halogens. They have great reactivity such as high ionization energy and large electron affinity. It reacts to from moleular compounds or hydrogn halides. ex) HF, HCL, HBr
 * **<span style="display: block; font-family: Arial,Helvetica,sans-serif;">Group 8A Elements - **
 * **<span style="display: block; font-family: Arial,Helvetica,sans-serif;">Oxides Across a Period ****:**Oxygen is likely to react with 1A, 2A ionis that have low ionization energies. Most oxides can be acidic or basic

= <span style="font-family: Arial,Helvetica,sans-serif; font-size: 150%;">AP Questions related to Periodicity = 1-4 a) Ca b)S c)Fe d)N e)Cs
 * 1) One of the above elements is a transition metal - c) Feis in d orbital
 * 2) One of the above elements forms a polyatomic anion where it has an oxidation number +6. - b) because S is in 6A group
 * 3) Which of the above has the smallest atomic radius? -d) Because of Atomic size trend direction
 * 4) Which o the above is the least electronegative?-e) Because of the periodic table trend shown above.

5. Which of the following has exactly 3 valence electrons ? -d) a) Carbon b)Nitrogen c)Hydrogen d)Boron e)Beryllium Boron because of its two 2s electron and one 2p electron.

6. Which of the following lists the element in order of decreasing atomic radius (largest atomic radius first)? - a) a) K ,Ca, C, F b) F, O, Al, Na c)Rb, Cs, Ba, Ra d)Si, Ge, As, Sb e) Li, Be, Na, C Because of the trend shown above 7. Which of the ions below has the largest ionic radius? e) a) Li+ b)Be+2 c)F- d)Cl- e)Br- Because of the trend shown above 8. Which of the following group of elements are expected to have highest ionization energy? e) a) Alkali metals b)Alkaline earth c) Transition metals d) Halogens e) Noble gases Because the trend shown above 9. For the isoelectric series S2-, CI-, Ar, K+, Se3+, which species requires the least energy to remove an outer electron? a) a) S2- b) CI- c) Ar d)K+ e) Se3+ (-) ions means larger radius, which means S2- has the greatest radius, and due to greatest radius it is easier for S2- to lose electron. 10. All of the following statements concerning the alkali metals are true EXCEPT : a) a) They are strong oxidizing agents b) They form ions with +1 oxidation state. c)As the atomic numbers of alkali metals increase, the electronegativity decreases. d)As the atomic numbers of alkali metals increase, their first ionization energy decreases. e) They form ions that are soluble in water Because Na is Na+ and e- so NA can be both oxidizing and reducing agent, therefore a is not always true. SOURCES : []