PSC Chap. 4 The Periodic Table

In modern periodic table, elements in the same column have similar properties.

John Newlands - Law of Octaves arranged first 16 elements in order of atomic mass found that similar properties were found every 8th element

Dmitri Mendeleev - invented the modern periodic system - basis of the modern periodic table arranged all known elements in order of atomic mass placed elements w/ similar properties in vertical columns

A couple of problems w/ Mendeleev's table Some elements did not fit into the right columns when put in order of atomic mass. If switched, they fit. -ex. Te and I, Co and Ni

A couple of problems w/ Mendeleev's table In order to put some elements in the right column, gaps had to be left in his table. He predicted elements would be discovered to fill the gaps Also correctly predicted properties of these undiscovered elements

Henry Mosely, using X-rays, discovered the atomic number of elements.

When elements in Mendeleev's table were placed in order of atomic number, they fell into the right columns.

Periodic Law - the physical and chemical properties of elements are a periodic function of their atomic numbers

Period or Series elements that form a horizontal row in the periodic table all elements in the same series have the same outer energy level

Group or Family elements that form a vertical column in the periodic table elements in the same group have similar electron configurations also have similar properties.

Periodic Table can be divided into 2 regions Metals - left side of table good conductors of electricity and heat shiny malleable groups 1-12 and some of groups 13-16 Nonmetals - right side of table poor conductors of electricity and heat dull brittle some of groups 14 -16 and all of groups 17 & 18

Metalloids Semiconductors (semi-metals) Have properties of both metals and nonmetals lie on dividing line used to make transistors and computer chips

Main-Group Elements Also called representative elements s and p block elements have consistent electron configurations

Group 1 Alkali Metals all end in s1 lose the outer e- to form +1 ions Very reactive metals React w/ water and oxygen soft

Group 2 Alkaline Earth Metals Active metals end in s2 lose 2 outer e-’s to form +2 ions not as soft as group 1 metals

Transition Metals d block elements not as reactive as groups 1 and 2 highest energy e-’s are in the d sublevel not as reactive as groups 1 and 2 have varied properties

Lanthanides and Actinides f block elements highest energy e-’s are in the f sublevel sometimes called rare earth elements or inner-transition elements Lanthanide series fills 4f sublevel shiny, reactive, irregular configurations

Lanthanides and Actinides Actinide series fills 5f sublevel radioactive

Group 16 Chalcogens Contains active nonmetals (top) to metalloids to less active metals end in s2p4 nonmetals gain 2 e-’s to form -2 ions

Group 17 Halogens Most reactive nonmetals react with metals to form salts end in s2p5 gain 1 e- to form -1 ions

Group 18 Noble Gases Mostly unreactive end in s2p6

Hydrogen In a class by itself Behaves unlike other elements because it has only 1 p+ and 1 e- Most common element in the universe

Properties of elements are determined by their electron configurations. Elements with similar properties have similar electron configurations.

Periodic Trends Atomic radii Reactivity

Atomic radius Atomic radius increases as you move down a group Add an energy level as you move down Atomic radius decreases as you move across a period Increased nuclear charge pulls e- cloud in tighter

Reactivity of Metals Metals tend to lose e-’s As you move down a group, reactivity of metals increases Atoms are bigger and e-’s are held less tightly As you move to the left, reactivity of metals increases atoms are bigger to the left

Reactivity of Metals The most active metal is in the lower left corner of the periodic table. Fr

Reactivity of Nonmetals Nonmetals tend to gain e-’s As you move up a group, reactivity of nonmetals increases Atoms are smaller and hold e-’s more tightly As you move to the right, reactivity of nonmetals increases (noble gases not considered) Atoms are smaller

Reactivity of Nonmetals The most active nonmetal is in the upper right corner of the periodic table. F

First Ionization Energy The attraction of an atom for e-’s determines the type of bond formed on a comp. Ionization Energy – energy required to remove an e- from an atom First Ionization Energy – energy required to remove the most loosely held e- in an atom (KJ/mole)

First Ionization Energy Ionization energies are periodic properties Tend to incr as Z incr in a period (left to right) Tend to decr as you move down a group Metals have low ioniz energies Nonmetals have high ioniz energies

First Ionization Energy As you go dn a column, outer level e-’s are farther from the nucleus \ held less tightly Also, there’s a decr in nuclear attraction betw outer e-’s & nucleus bec of other e-’s betw them Shielding Effect E-’s are held less tightly – less energy to remove them \ lower ionization energy

First Ionization Energy As you move across the table in a period, atoms get smaller bec of increased nuclear attraction E-’s held tighter, \ higher ionization energy

First Ionization Energy There are deviations from the expected as we move across the table Small decr betw Be (1s22s2) & B (1s22s22p1) Be – a 2s e- must be removed from a fairly stable atom B – a lone 2p e- must be removed Ion is more stable, \ takes less energy Small decr betw N(1s22s22p3) & O (1s22s22p4) N is more stable w/ ½-filled sublevel

Factors Affecting Ionization Energy Nuclear Charge (nuclear attraction) Shielding Effect Radius Sublevel