TRENDS IN THE PERIODIC TABLE

Dmitri Mendeleev In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical classification schemes for elements known to date. The periodic table is base on the similarity of properties and reactivities exhibited by certain elements. Later, Henri Moseley ( England, ) established that each elements has a unique atomic number, which is how the current periodic table is organized.

The Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Horizontal rows = periods –There are 7 periods Vertical column = group (or family) –Similar physical & chemical prop. –Identified by number & letter (IA, IIA)

Across the Periodic Table Periods: Are arranged horizontally across the periodic table (rows 1-7)Periods: Are arranged horizontally across the periodic table (rows 1-7) These elements have the same number of valence shells.These elements have the same number of valence shells. 2nd Period 6th Period

Down the Periodic Table Family: Are arranged vertically down the periodic table (columns or group, or 1-8 A,B)Family: Are arranged vertically down the periodic table (columns or group, or 1-8 A,B) These elements have the same number electrons in the outer most shells, the valence shell.These elements have the same number electrons in the outer most shells, the valence shell. Alkali Family: 1 e- in the valence shell Alkali Family: 1 e- in the valence shell Halogen Family: 7 e- in the valence shell Halogen Family: 7 e- in the valence shell

All Periodic Trends Influenced by three factors: 1. Energy Level –Higher energy levels are further away from the nucleus. 2. Charge on nucleus (# protons) –More charge pulls electrons in closer. (+ and – attract each other) 3. Shielding effect

Shielding The electron on the outermost energy level has to look through all the other energy levels to see the nucleus. The inner electrons shield the outer electrons from the pull of the nucleus. This effect is known as electron shielding Second electron has same shielding, if it is in the same period

What do they influence?  Energy levels and Shielding have an effect on the GROUP (  )  Nuclear charge has an effect on a PERIOD (  )

Atomic Radius Average distance from the nucleus to the electron cloud. The electron cloud doesn’t have a definite edge. They get around this by measuring more than 1 atom at a time. © Prentice-Hall, Inc.

#1. Atomic Size - Group trends As we increase the atomic number (or go down a group)... each atom has another energy level, so the atoms get bigger. H Li Na K Rb

#1. Atomic Size - Period Trends Going from left to right across a period, the size gets smaller. Electrons are in the same energy level. But, there is more nuclear charge. Outermost electrons are pulled closer. NaMgAlSiPSClAr

Atomic Radius

Trends in Ionic Size: Cations Cations form by losing electrons. Cations are smaller than the atom they came from – not only do they lose electrons, they lose an entire energy level. The ionic radius decreases as the nuclear charge on the ion increases

Cation Group trends Each step down a group is adding an energy level Ions therefore get bigger as you go down, because of the additional energy level. Li 1+ Na 1+ K 1+ Rb 1+ Cs 1+

Ionic size: Anions Anions form by gaining electrons. Anions are bigger than the atom they came from – have the same energy level, but a greater area the nuclear charge needs to cover

Ion Period Trends Across the period from left to right, the nuclear charge increases - so they get smaller. Notice the energy level changes between anions and cations. Li 1+ Be 2+ B 3+ C 4+ N 3- O 2- F 1-

Ionization Energy Energy needed to remove an electron from a neutral atom Period - First ionization energy increases as you go from left to right across a period. Why? Group - ionization energy decreases as you go down a group. Why?

ELECTRON AFFINITY Energy change that occurs when an electron is added to an atoms outer level to form a negative ion Period - electron affinity (EA) increases from left to right across the periodic table Why? Group - electron affinity decreases down a group Why?

ELECTRONEGATIVITY a quantitative measure of the electron-attracting ability of an atom in a molecule Period - electronegativity across a period Group - electronegativity down a group The most electronegative element is fluorine. What is the least electronegative element?

Trends in the Periodic Table © Prentice-Hall, Inc.