chemrevise.org 19/08/2013 Periodicity N Goalby chemrevise.org

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1 chemrevise.org 19/8/213 eriodicity Goalby chemrevise.org locks An s-block element will always have an electronic structure where the outer electron is filling a s-sublevel. kewise the outer electron of a p-block element will be in a p sublevel. 1 e block p block 2 e e d block 3 a l 4 a c Ti V r Mn e o i u Zn Ga Ge As e r r 5 Rb r Y Zr b Mo Tc Ru Rh d Ag d In n b Te I Xe 6 s a La f Ta W Re s Ir t Au g Tl b i o At Rn 7 r Ra Ac Rf Db g h s Mt Ds Rg n Uut l Uup Lv Uus Uuo f block e r d m m Eu Gd Tb Dy o Er Tm Yb Lu Th a U p u Am m k f Es m Md o Lr 1

2 chemrevise.org 19/8/213 eriodic Trends in roperties of Elements Various Elemental roperties change fairly smoothly going across a period. roperties include: Atomic and Ionic Radius Ionisation Energy Melting oints and oiling oints Density and onductivity Definition eriodicity is the pattern in the change in the properties of a row of elements. Repeated from one row to the next row EY Trends in Atomic Radius Atomic radii decrease as you move from left to right across a period. Atomic Radius pm Insert figures 7.6 Atomic umber EY 2

3 chemrevise.org 19/8/213 Relative atomic radii Atomic Radii decrease e Atomic Radii increases a Rb e a a Ga In Ge n As b e Te l r I e r Xe s Ra Tl b i o At Rn Atomic radii decrease as you move from left to right across a period, because the increased number of protons create more positive charge attraction for electrons in the same shell. Melting oints of Elements 1 e e e a l a c Ti V r Mn e o i u Zn Ga Ge As e r r Rb r Y Zr b Mo Tc Ru Rh d Ag d In n b Te I Xe s a La f Ta W Re s Ir t Au g Tl b i o At Rn M s tend to increase then decrease moving across periods ighest m.p. carbon, then W and area around it EY 3

4 chemrevise.org 19/8/213 Moving left to right in a period, melting points increase as the attractive forces change from metallic bonds with loosely held electrons to solids like carbon and silicon where the atoms are arranged in giant structures. Melting points then drop off sharply for non-metals, which have very weak forces of attraction. Melting points in periods 2+3 EY Melting points in periods 2+3 : metallic bonding melting point e a e atomic number Metallic bonding : strong bonding gets stronger the more electrons there are in the outer shell that are released to the sea of electrons. A smaller positive centre also makes the bonding stronger. igh energy is needed to break bonds. EY 4

5 chemrevise.org 19/8/213 melting point Melting points in periods 2+3 : Macromolecular e 1 5 e e atomic number and are Macromolecular: very strong covalent bonds between atoms high energy needed to break covalent bonds very high mp +bp EY melting point Melting points in periods 2+3 : simple molecular e 5 l atomic number Molecular (mple covalent l 2, 8, 4 ): weak van der waals between molecules, so little energy is needed to break them low mp+ bp 8 has a higher mp than 4 because it has more electrons ( 8 =128)( 4 =6) so has stronger v der w EY 5

6 chemrevise.org 19/8/213 Melting points in periods 2+3 : monoatomic melting point e e e atomic number The noble gases are monoatomic : weak van der waals between atoms so little energy is needed to break them leads to very low mp+ bp EY eriodicity in Ionisation Energy 25 e e 5 e l a a Atomic number The shape of the graph for periods two and three is similar. A repeating pattern across a period is called periodicity. 6

7 chemrevise.org 19/8/ e e e Atomic number There is a general trend across each period for the ionisation energy to increase. This is due to increasing number of protons in successive elements, which means the electrons are more strongly held to the nucleus. a l a 25 e e 2 15 l 1 e a 5 a Atomic number The noble gases are always at the maximum peak for each period, but there is a decrease in ionisation energy down the group. (true of all groups). This is because as one goes down the group the outer electrons become further from the nucleus and become more shielded from the nuclear pull. 7

8 chemrevise.org 19/8/ e e e a l a Atomic number There is a large drop each time between the group elements and the group1 elements. This is because the element in group 1 will have its outer electron in a new shell further from the nucleus and is more shielded. o the group 1 element is easier to remove and has a lower ionisation energy. otice the drop in ionisation energy down each group 25 e e irst Ionisation Energy Rb a Group umber X e r eriod 2 period 3 period 4 eriod 5 eriod 1 8

9 chemrevise.org 19/8/ e e e a l a There is a small drop between Atomic number e +, +. and are starting to fill a p sub shell, whereas e and have their outer electrons in the s sub shell. The electrons in the p subshell are slightly easier to remove because the 2p electrons are higher in energy. There is a small drop between e +, +. and are starting to fill a p sub shell, whereas e and have their outer electrons in the s sub shell. The electrons in the p subshell are slightly easier to remove because the 2p electrons are higher in energy. eryllium Electronic configuration : 1s 2 2s 2 oron Electronic configuration : 1s 2 2s 2 2p 1 2s 2p 2s 2p 1s 1s In addition, the 2s orbital shields the 2p orbital slightly 9

10 chemrevise.org 19/8/ e e 5 e l a a Atomic number There is a small drop between nitrogen and oxygen and also phosphorous and sulphur. When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove. or example with oxygen there are 4 p electrons and the 4th is starting to doubly fill the orbitals. itrogen Electronic configuration : 1s 2 2s 2 2p 3 xygen Electronic configuration : 1s 2 2s 2 2p 4 2s 2p 2s 2p 1s 1s Two electrons of opposite spin in same orbital 1

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