The Periodic Law Concept Mendeleev (1869): Elements showed recurring properties according to increasing mass Moseley: The nuclear charge increased by 1 for each element in the periodic table H = 1 He = 10 Li = 3 Be = 4 B = 5 C = 6 N = 7 O = 8 F = 9 Ne = 10 Na= 11 Mg = 12 Al = 13 Si =14 P = 15 S = 16 Cl = 17 Ar = 18 The Periodic Law: The properties of elements recur in a repeating pattern when arranged according to increased atomic number.

Groups and Periods of Elements Vertical column is called Group Horizontal row is called Period Total number of groups: 18 Total number of Periods: 7 US System group numbers are roman numbers IA to VIIA, IIIB-VIII, IB and IIB IUPAC numbering: 1-18 Group IA or 1: elements are called Alkali metals Group IIA or 2: elements are called Alkaline earth metals Group VIIA or 17: elements are called halogens Group VIIIA or 18: elements are called noble gases (unreactive gases)

Periodic Table-Elements Representative elements: These elements found in A groups. The behavior of these elements is predictable (MgO) Transition Elements: They are found in Group B in the middle of table. The properties are unpredictable (FeO, Fe2O3) Inner Transition Elements: They are found beneath the main portion of the periodic table. These two series are placed below the main portion to avoid the unreadable width of table. The first series elements are called Lanthanides and are considered the part of 6 th period. The Second series elements are called Actinides and are part of 7 th period

Periodic Trends Atomic Radius: Distance from nucleus to the outer most electrons (Energy level) The radii decrease from bottom to top in a group and decrease from left right in period Metallic Character: The metallic character decreases from left to right in a period. The metallic character decreases from bottom to top in a group Ex: Lithium is a metal and Nitrogen, Oxygen and Fluorine and Neon are gases

Atomic Radius

Predicting Physical Properties Predict the missing values Element Atomic Radius Density Melting point Ca nm 1.54 g/ml ? Sr nm ? 769 o C Ba ? 3.65 g/ml 725 o C (0.217nm) (2.63 g/ml) (839 o C) ElementAtomic Radius (nm) Density (g/ml at 20 o C Melting Point ( o C) Atomic Mass (amu) Li Na K Rb Ca

Predicting Chemical Properties The chemical reactivity of an element can be expected from other element in the same group Mg + O 2 MgO The same reactivity can be observed in Ca, Sr and Ba Practice Exercise: K 2 O, CaO, Ga 2 O 3, GeO 2 Predict the formulas of Rb, Sr, In, Pb

Blocks of Elements s Block elements p Block element d block elements f block elements

Electron Configuration/Condensed Electron configuration Period and group number will help to write condensed configuration of an element Exercise: Co, Zn, Se Predict the number of d electrons in Platinum using the table

Valence Electrons Subject: Only representative elements In a chemical reaction, only outer most electrons participate. These electrons are called valence electrons. The valence electrons are farthest from the nucleus and more available to react with another atom Group number indicates the number of valence electrons in an element (atom)

Electron Dot formulas/Lewis structures Expression of valence electrons in an atom with dots Lewis Structure: Symbol of an element surrounded by valence electrons Guidelines: 1) Write the symbol 2) A dot represents one electron. Place 2 dots on each side of the atom for eight valence electrons. For odd numbers (ex: one valence electron), place one dot on any side of the symbol 3) The group number indicates the number of valence electrons Exercise: Si, Xe, K, I

Ionization Energy ‘Amount of energy required to remove an electron from a neutral atom in the gaseous state’ Ionization energy Atom Ion + + e - 1) Atoms lose electron to get nearest noble gas configuration. 2) Alkali metal have lowest ionization energy 3) Noble gases have the highest ionization energy 4) Ionization energy decreases in a group from top and increases in period from left to right

Ionization trend in table

Ionization energy Base on trend predict the relative ionization energy 1) Li and Na 2) O and F 3) Na and Mg 4) O and S 5) Mg and O

Ionic Charges Metal tend to lose electrons and nonmetals tend to gain electrons. The positive charge on a metal is equal to the valence electrons. Na: Valence electron= 1 and Charge = 1+

Ionic Charges

Electron Configuration of Ions Electron configuration of ions is similar to its parental atom with the loss valence electrons Exercise: Mn 2+ Fe3+ Se 2- Cd 2+