TRENDS IN THE PERIODIC TABLE

Dmitri Mendeleev In 1869 Mendeleev and Lothar Meyer (Germany) In 1869 Mendeleev and Lothar Meyer (Germany) published nearly identical classification schemes for published nearly identical classification schemes for elements known to date. The periodic table is base on elements known to date. The periodic table is base on the similarity of properties and reactivities exhibited by the similarity of properties and reactivities exhibited by certain elements. Later, Henri Moseley certain elements. Later, Henri Moseley ( England,1887-1915) established that each elements ( England,1887-1915) established that each elements has a unique atomic number, which is how the current has a unique atomic number, which is how the current periodic table is organized.periodic table is organized.

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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 Periods: Are arranged horizontally across the

periodic table (rows 1-7)periodic table (rows 1-7)• These elements have the same number of valence shells.These elements have the same number of valence shells.

1IA

18VIIIA

12

IIA13

IIIA14

IVA15VA

16VIA

17VIIA

2

33

IIIB4

IVB5

VB6

VIB7

VIIB8 9

VIIIB10 11

IB12IIB

4

5

6

7

2nd Period

6th Period

Down the Periodic Table•Family:Family: Are arranged vertically down the periodic table Are arranged vertically down the periodic table (columns or group, (columns or group, 1- 18 or 1-8 A,B)1- 18 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.

1IA

18VIIIA

12

IIA13

IIIA14

IVA15VA

16VIA

17VIIA

2

33

IIIB4

IVB5

VB6

VIB7

VIIB8 9

VIIIB10 11

IB12IIB

4

5

6

7

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.

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#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.

HLi

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.

Na Mg Al Si P S Cl Ar

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.

Li1+

Na1+

K1+

Rb1+

Cs1+

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.

Li1+

Be2+

B3+

C4+

N3-O2- F1-

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

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