CHEM 217 Lecture Notes - Lecture 8: Wtwo, Alkaline Earth Metal, Periodic Trends
Unit 8 – periodic
properties
8. 1 N E R V E S I GN A L T R A N S M I S SI O N
movement/pumping of sodium and potassium is the basis for nerve signal transmission in brain and body
How do pumps/channels know which is which
oBoth are cations of group I metals (Na+, K+)
oPotassium lies below, has more p+ & e- than sodium
In this case, K has more p+ and e- and has a larger atomic radius 133pm vs 95pm for Na
Pumps and channels sensitive enough to distinguish
8. 2 M E ND E L E E V
8. 3 E L EC T RO N C O NF I G U R AT I O N, V A LE N C E EL E C TR O NS
Elements with similar properties are int eh same column – make connection between element’s
properties and electron configurations
As we move to the right across a row, orbitals filling in correct order
ow/ each subsequent row, te highest principal quantum # increases by 1
notice as you move down a column, the # of electrons in outermost principal energy level highest n value)
remains the same
Valence electrons are the important ones for chemical bonding
oFor main group elements, the valence electrons are those in the outermost principal energy level
For transition elements, we also count the outermost d electrons among valence
electrons even if they’re not in outermost principal energy level
Properties depend on valence – instrumental in bonding because held most loosely and
are easiest to lose or share
Same column = same # of valence electrons
Valence electrons are distinguished from core electrons
The core electrons are those in complete principal energy levels and those in complete d & f sublevels
oEx. silicon 1s2 2s2 2p6 3s2 3p2 - four valence electrons
oThose in the n=3 principal level and 10 core electrons
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ORBITAL BLOCKS IN THE PERIOD
Because of filling order of orbitals, table can be divided into blocks, representing filling of particular
sublevels
oFirst two columns on the left comprise the ‘s’ block w/outer electron configuration of ns1 (alkali
metals) and ns2 (alkaline earth metals)
oThe six columns on the right side of the periodic table comprise p block
Outer electron congigurations of
Ns2np1, ns2np2, ns2np3(pnictogens), ns2np4 (chalcogens), ns2np5 (halogens),
ns2np6 (noble gases)
The transition elements comprise the d block and the lanthanoids and actinoids comprise the f block
Notice the # of columns in a block is max # of electrons that can occupy that particular sublevel of that
block
oS block w/ 2 columns -> one s orbital holding max 2 electrons
oP block w/ 6 columns -> three p orbitals w/2 electrons each
oD block w/ 10 columns -> 5 d orbitals w/2 electrons each
oF block w/ 14 columns -> 7 orbitals w/ 2 electrons each
Note * the row# is equal to the # (or n value) of the highest principle level
Summarizing
oTable divisible into four blocks corresponding to the filling of the 4 quantum sublevels (s,p,d,f)
oRow # of a main group element is equal to the highest principal quantum number of that
element
WRITING ELECTRON CONFIGURATION FOR AN ELEMENT FROM ITS POSITION IN THE
TABLE
The D and f block elements
oConfigurations of these elements exhibit trends that differ
Orbitals fill as per image (d block)
Notice, the principal quantum # of the d orbital being filled across each row in
the transition series is equal to the row number minus 1
oEx. in fourth row, 3d orbitals fill
oIn fifth row, 4d orbitals fill
4s & 3d orbitals are extremely close to each other in energy and relative
ordering depends on exact species
Causes irregular behavior in the transition metals
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oEx. notice that in first transition series of the d block, the outer
configuration is 4s23dx w/two exceptions,
Cr is 4s13d5 and CU is 4s13d10
As we move across f block, the f orbitals fill
Note that for these leements, the principla quantum # of the f orbital being
filled across each row in the transition series is the row # minus two
oEx. in sixth row, 4f orbitals fill and in seventh row, 5f orbitals fill
In addition, within the inner transition series, the close energy spacing of the 5d
& 4f orbitals sometimes causes an electron to enter a 5d orbital instead of the
expected 4f orbital
8. 4 E X P L A NA T O R Y P O W E R O F T H E Q UA N TU M - M E C H A NIC A L
M O D E L
Chemical properties of elements are largely determined by the number of valence electrons they contain
oProperties are periodic because the number of valence electrons are periodic
Columns have same # of valence electrons
So similar chemical properties on columns
oOverall energy of atoms w/8 valence electrons (or two in the case of He) show that they are
particularly stable
When a quantum level is completely full, the overall energy of the electorns that occupy
that level is particularly low: those electrons cannot lower their energy by reacting with
other atoms or molecuels, so the corresponding atom is relatively inert/unreactive
Elements with electron configurations close to those of noble gases are the most reactive because they
can attain noble gas electron configuration by losing or gaining small number of electrons
oEx. alkali metals are among the most reactive because outer electron configuration (ns1) is one
electron beyond a noble gas configuration and readily react to loes the electron
This deoan’t mean that forming an ion with a noble gas configuration is in itself energetically favourable –
in fact, forming cation always requires energy but when the cation formed has a noble gas configuration,
the energy cost of forming the cation is often less than the energy payback that occurs when cation forms
ionic bonds with anions
On the right side of the table, halogens are among the most reactive non-metals because of their ns2np5
configuration – only one electron to gain for noble gas configuration.. tend to gain that 1 electron forming
1- ions
8. 5 P E RI O D T RE N D S IN TH E S I ZE O F A TO M S A N D E F FEC TIV E
NU C LE A R C HA R GE
We saw that the volume of atom primarily occupied by its electrons occupying atomic orbitals
Also saw orbitals don’t have definite boundaries but only represent statistical probability distribution for
where the electron is found. So how do we define size?
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Document Summary
1 n e r v e s i g n a l t r a n s m i s s i o n. Movement/pumping of sodium and potassium is the basis for nerve signal transmission in brain and body. How do pumps/channels know which is which o o. Both are cations of group i metals (na+, k+) Potassium lies below, has more p+ & e- than sodium. In this case, k has more p+ and e- and has a larger atomic radius 133pm vs 95pm for na. 2 m e n d e l e e v. 3 e l e c t r o n c o n f i g u r a t i o n , v a l e n c e e l e c t r o n s. Elements with similar properties are int eh same column make connection between element"s properties and electron configurations.
