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Patterns of the Periodic Table
In Mendeleev's day no-one could explain why these patterns existed.
However, when scientists see patterns in nature like this, they know there must be underlying "r ules" or
"laws of nature" causing and controlling the patterns.
Perhaps Mendeleev's great contribution was not just the Periodic Table itself,
but the stimulus it gave other scientists to investigate the reasons behind the patterns.
Within 40 years Science had unravelled the secrets of atomic structure, the electron energy levels, and more.
At this sta e our task is to lear n s ome of th e atter ns.
Electrical Conductivity
As you go across any row ("period") of the table, you will
move through anumber of metals, then one or two semi-
metals, then into the non-metals.
Therefore, the conductivity will start out high, but r apidly
decrease as you encounter a semi-metal, and becomeextremely low at the non-metals.
r!, I
CLJ\ I i
llj~H~~tJTEI1:1
Boiling Points
follow a similar pattern to
Melting Points
Valencies are the same
down each group
Melting Point
You learned in topic 1 how melting point is determined by the
bonding within a substance.
At the left side of the table are the very active metals of d1e
Activity Series. They are also usually soft, and have relatively low
(for metals) melting points.
Moving to the right across a period you enter d1e "Transition
Block" containing typical hard, high melting point metals, held
strongly together by "metallic bonding".
Further right you hit d1e Semi-Metals. These often have very high
melting points because of their covalent lattice structure.
Then you enter d1e Non-Metals which have covalent molecular
structures and quite low mp's. At the far right column, each period
ends with an Inert Gas which are all s ingle-atom molecules, and
have d1elowest mp of each period.
This pattern repeats itself along each period.
Melting Points of ElementsI
I
I
I
Peaks are Transi ti on M etals
or Semi-Metals
Sketch Graph.ooo
N
Go~ooo... -
c-
oc..01
0 Na
c
Chemical Bonding, Valency & Reactivity
What you've already learnt about the Activity Series, Ionic and Covalent Bonding and Valency
will help you make sense of the following: ("" G 8 I Group nert ases
No chemical reactions,
no bonding
Activity of Non-Metals
Most active at top-right(FIuori ne)
Activity (generally)decreases downwardsand to the left.
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Atomic Radius
The s ize o f an atom is the distance across its outer electron shell.
You might think that the atoms along each period would be the same size,
because it's the same orbit being added to.
However, the increasing amount of positive charge in the nucleus pulls that
orbit inwards closer and closer to the centre.
1
0.1
~I
Li 0,1
0152~:
01
"IOJ
.~ 1
~I~Iu
Na .~: MQ AI Si P
O]lO 600------------------------------------~Radius decreasing across a periodCa197
o
Be112
o
K231
The Syllabus requires that you
produce a table and a graph of
the changes in a property
across a period,
and down a group
When you do, you can clearly see
how the Periodic Table got its
name.
"Periodic" means "recurring at
regular intervals".
This graph shows what aspreadsheet plot gives for the radii
of the first 37 elements.
o tice h ow the s ame g raphical
pattern keeps recurring ... it is a
periodic pattern.
The following diagramsare to scale and show therelative sizes of the first
20 elements
The numbers given are the atomic radii in picometres.
1 picometre = 1xl 0-12
metre
He50
oNe70
o o o o ooS102
Ar94
o o oDown each group the radius increases.
This is because, as you go down a group, you have added an entire
electron shell to the outside of the previous layer
Spreadsheet Plot of Atomic Radii0
aJ 0
m.....-Q)
E0 0u 0C. N.....,III
::J
"'00ro0a::
u
E0...-
0
Kr
Ar -----------~Ne ------------. Tfend
He _-------- Increasing up_------ down a gfO
20
Atomic Number
There are a number of irregularities and "glitches"
apparent on the graph. It is beyond the scope of
this course (and way beyond the K.ISS. Principle)
to attempt an explanation of these.
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Highest Value Inert gases
..._....., Fluorine ~ot included
'21 I I r-1,~ 1 1; :::::::::__ ._ EI .. V 1 I , Io. ( J.' ectronegatlvlty a ues r..--.!-....~.."'-"-T-"-'''['-'-''~-''-j
~: ~~ ~~ of selected elements 1~~1~~':~~::~';~~Or._j~IL_:..J..~_~-------------t-t- -1- [3.0! i...1 I r 1r. (values decrease to left) -,r---T-_ -+-~--+l~ ,0.81 ! I" I 2 8\
-0 1 I' -----{ t---,-.- ..t-+-l'
l-",-1- :1-..-1'.----.1.---1~--f- -1-.- -:..l .._~
VlI 0.8 Ii : I ' i j, I !2.5 i~:ro~)--lr--1----:-- ..I..--.. --- ---+-- -"II--r+-+-1+1;:;1--,~tr;:;-~-'-lr--r-'-+-,-- _+_~ L....JL.J..~L---,--_..1..._J
L__1.._..!I '--_L-.I _..I-_ J
keep it simple science
Ionization Energy
The meaning of tlle "1st Ionization Energy" was explained
previously in relation to the Activity Series of Metals.
+A (g)
where "A" stands for any atom
in the gas state
Any atom can lose an electron if enough energy is
supplied... even atoms which do not normally lose
electrons.
The Periodic Trend in 1st Ionization Energy
You should remember that the very active metals are the
ones with low 1st ionization energies. They easilylose their
outer electron(s) and so react readily.
Explanations:
1st I.E. increases to the right because each atom across a
period has more and more (+ve) nuclear charge attractingand holding electrons in the orbit concerned. Therefore, it
requires more energy to remove an electron.
1st I.E. decreases down each group because, at each step
down, anextra whole layer of electrons has been added to the
outside of tlle atom. The outer shell is further away from the
nucleus, and is partially "shielded" from nuclear attraction by
the layers of electrons underneath it. Therefore, it becomes
easier and easier to remove an electron.
Electronegativityis avalue assigned to each element to describe tlle
power of an atom to attract electrons to itself.
Atoms with a tendency to gain electrons and
form negative ions have high values.
Atoms with a tendency to lose electrons easily
Qow 1st I.E.) and form (+ve) ions have very low
values.
Once again, there is a pattern in these values in
the Periodic Table.
Northmead High School SL#603217
Successive Ionization Energies
Having added the energy o f 1st I.E. an d r emoved an
electron from any atom, it is then possible to add more
energy and remove a2nd electron, and a 3rd, and s o on.
A(g)
+1st I.E. A (g) + e
2nd I.E. A + ----.. A+2 + e
(g) (g)
3rd I.E. A+2 ~ A+3 + e
(g) (g)
...and so on,
according to how many electrons
the atom has
Once the f irst electr on is removed, tl1e remaining electrons
are pulled in t ighter to the nucleus. Each one experiences
increased force of attraction, so it requires more energy to
remove the next electron.
Once the entire outer orbit has been stripped away,the next
ionization must remove an electron from an underlying
orbit, which requires ahuge increase in the next ionization
energy. This results in an interesting pattern:
Patterns in Successive Ionization Energy Data
(values shown are energy measurements)
Successive Elements on Period 3
Element Electron 1st 2nd 3rd 4th
Config. I.E. I.E. I.E. I.E.
Sodium 2.8.1 0.5 4.5 6.9 9.6
Magnesium 2.8.2 0.7 1.4 7.7 10.5
Aluminium 2.8.3 0.6 1.8 2.8 11.6
Notice how the values "jump" (underlined data) as the next
ionization has t o remo ve an electron from the next lower
orbit.
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As early as 1830, the German a) .
noticed patterns in the properties of the elements. In 1860,
the English scientist b) proposed a
"Law of c) " d es cr ibing the
repeating pattern of properties.
It was the Russian d) who invented
the e) , in more or less its
modern form. He realized that there were probably many
elements that had not f ) ,
so he g) in his table for later
additions . By s tudying the details of k no wn elements, he
w as able to h) very precisely the
properties of the missing elements.
Sure enough when discovered, the missing elements were
found to have properties i) .
Conductivity, which generally j) to
the right, as you go from metals to k) .
and .
Melting Points: tend to l) to about the
mid dle of each p eriod, then m)............................. The
highest value is usually a n) metal or
o ne of the 0) elements. The
lowest value on each period is always the
p)................................ gas member on the extreme
g) (right/left)
Valencies are r) down each vertical
group. Bonding follows the pattern of the main categories
of elements. s) form t) .
bonds when they lose electrons and become u) .
ions. The Semi-metal elements form only v) .
bonds. The Non-metals can bond w) .
or can x) electrons to form y) .
l0ns.
Chemical Reactivity is different for metals and n on -
metals. The most ac tive metals are located at the lef t
z)................................... (top/bottom) of the table.
Generally, activity decreases aa) and to tile
ab) The Inert Gases show no chemical
activity. Apart from them, the most active non-metals are
located on the r ig ht ac) (top/bottom)
of the table. Activity generally decreases as you move
ad) and .
WHEN COMPLETED, WORKSHEETS
BECOME SECTION SUMMARIES
Atomic Radius ae) across a period
because each successive element h as af ) .
(more/less) positive charge in the ag) to
attract the electron shell and pull it inwards. As yo u g o
down a group the radius ah) as each new
electron shell is added.
First ai) Energies aj) .
across a period, as the increasing amount of nuclear chargemakes it more and more difficult to ak) .
an electron. The values al) down a
group because each extra shell of electrons is am) .
(more/less ) s trongly held than the previous.
Successive Ionization Ener gies measure the energy
required to an)............................ another, subsequent
electron from an atom. T he energy required to remove the
next electron is always ao) .
(higher/lower). When the next electron happens to b e in
the next lower shell, the value ap) .
by a huge amount.
ag) is a value which describesthe power of an atom to ar) electrons.
The element with the highest value is as) ,
and values decrease as you move to the at) .
and asyou move au) the Periodic Table.
1. a) Write equations to represent the 1st, 2nd, 3rd & 4th
ionisations for a calcium atom.
b) Between which two o f these successive ionisations
would you expect a h uge increase in the required energy?
2. On each of the following Periodic Table diagrams label
the arrows with the word "increasing" or "decreasing" tocorrectly describe the trend in the direction shown.
a) Atomic
Radius
r;
I;o""P), (right)I}-t-~ - - - - - - - - ,
;;)(d?~J~:HffillE!b) Electro-
negativity
Also indicate
("H"&"L") the
position of
elements with
highest &lowest values.
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207.2grams of
Lead
, contains.; ,. 6.022 x 1023 39.95 grams of
,. Lead atoms Argon
1~'(~1 39.95 207.2 l...- ..J 6.~~~t:i~;23 12.01grams ofI
_~~". C b1 1 " ~ . Argon atoms ar on
mo e, 1 mole.... 1 mole,. contains
= 12.01grams' = 39.95 grams"" = 207.2 grams .,...,. "'" 6.022 x 1023', _--_... ,., .; Carbon atoms
E AC H OF T HE SE HAS H~ SAME NUMBER OF ATOMS ". ".
... ~'" e
. 16 .,. .."Copyright 2005-2006
"......... ~----........_-_ ..... - ....
Quantities in Chemical Calculations
Atoms, molecules and ions always react with each other in
fixed, whole-number ratios. That's why balancing an
equation is so important... it actually brings the equation
into line with what is happening at the particle level.
For example, when hydrogen and oxygen react to form
water, the balanced equation is
This is a t r ue description of what is happening to the
molecules:
enCD
m
2 Moleculesof H20
However, when we carry out chemical reactions in the
laboratory or in Chemical Industry, we cannot see or count
the molecules. Instead, we measure the mass or volume of
substances.
To measure out the correct numbers of particles for a
reaction we need a simple w ay to convert masses and
volumes to numbers of molecules, and vice-versa. That's
the purpose of
The Mole
1 mole of a ny element or compound contains exactly the
same number of particles.
1 mole of each substance has a different mass, because the
atoms and molecules allweigh differently.
The really clever and convenient thing about the mole is its
link to the Periodic Table and the "Atomic Weights" shown.
6
CCarbon
18
AtArgon
82
PhLead
Defining the Mole
For technical reasons, the "atomic standard" used to
compare the masses of all atoms is the carbon atom,
which contains
6protons
6 neutrons
6 electrons
Since this is the standard of comparison, the formal
definition of the mole is:
"the number of atoms contained inexactly 12 grams of carbon-12"
Note: In Topic 1 it was pointed out that the Mass
Number for any atom is a whole number. It has still not
been explained why the ' 'Atomic Weights" in the
Periodic Table are mostly not whole numbers.
This WILL be explained in a later topic.
If you cannot wait, go find out about "Isotopes".
Avogadro's Number
Just how many atoms are in 1 mole?
Obviously, it is a very large number. We now know that it
is about 6,000 billion trillion.
Avogadro's Number
6.022 X 1023
particles in 1 mole of anything
This number is named in honour of an Italian scientist
who you will learn about s oon.
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Calculating Mole Quantities
You need to be able to calculate mole quantities in terms of
both mass and number of particles.
Molar Mass
The "Molar Mass" of any chemical species is the mass (in
grams) of 1 mole of the substance.
You need to add up all the Atomic Weights
of all the atoms given in the formula.
Examples:
Name
Argon
Sodium
Formula
Ar
Na
Molar Mass (g)
39.95
22.99
Oxygen
CWorine
(16.00 x 2)
(35.4 5 x 2)
32.00
70.90
Water
Carbon Dioxide
Sodium chloride
H20 (1.008x2 + 16.00)
CO2 (12.01 + (16.00x2)NaCl (22.99 + 35.45)
18.016
44.01
58.44
Number of Moles in a Given Mass
When you weigh a chemical sample you then need to be
able to calculate how many moles this contains.
No. of moles = mass of substance vou havemolar mass
n= m
MM
Example Calculations
1. How many moles in a) 5.23g of magnesium?
b) 96.7g of water?
a) n = --ill..-
MM
5.23 = 0.215 mol24.31
b) n = -- ill..- _96_.7 _
MM (2x1.008 + 16.00)= 96.7/18.016= 5.37 mol
2. What mass is needed if you want to have 1.50 molesof s alt (sodium cWoride)?
n = --ill..-
M:M
so m = n x M M = -1.50 x (22.99 + 35.45)= 1.50 x 58.44
= 87.7 g
Northmead High School SL#603217
Moles and Numbers of Particles
Since one mole of any substance contains Avogadro's
Number of particles:
No. of moles = No. of particles you haveAvogadro's Number
Example Calculations
1. How many moles are present in a sample of lead
containing 7.88 x 1024
atoms?
7.88xl024
---23
6.022xlO
= 13.1 mol
2. a) How many atoms of lead are needed to make
0.0250 mole?
b) What would be the mass of this quantity?
Solutiona)n=~
NA
b) m = n x M1vl= 0.0250 x 207.2 (molar mass of Pb)= 5.18 g
23so N = n x NA = 0.0250 x 6.022x10
= 1.51 x 1022 atoms
Mole Quantities in Chemical Equations
When you consider an equation like
CD
C()
m2 Molecules
of H20
However, the number of molecules reacting is really just a
ratio. The actual numbers migh t b e
or, (let's use Avagadro's number)
(2 x NA) H2 + NA 02 --.- (2 x NA) H20
The Balancing Coefficients in a Chemical Equation
May be Interpreted as Mole Ratios
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Comparing Mass Changes
When Metals Burn
Atoms always react in simple whole-number mole ratios,
but atoms have different masses, and compounds have
various formulas, so the result is that chemicals do NOT
react in simple ratios by mass.
That's why we need the mole... we measure quantities by
their mass, b ut this mak es no s en se u ntil moles are
calculated.
The syllabus requires that you should consider the mass
changes involved when various' metals combine with
oxygen to form their oxide compound.
The following table shows the mass changes for ;lOOg of
the metal in each case:
100g of Formula Mass 0z Mass of
Metal of oxide n eeded( g) O xide fo rmed
Lithium Liz 115 215
Iron FeZ
03
43 143
Zinc ZnO 49 149
Lead PbOz 15 115
Empirical Formulas vMolecular Formulas
Y ou are r emin ded that a molecular formula really does
describe the atoms present in a molecule.
The molecular compound methane,
has formula CH4
, because that's
exactly what each molecule contains ...
1 carbon atom and 4 hydrogen atoms.
Lattice structures, either ionic or covalent
are NOT molecular.
Example: sodium chloride, NaCl
The formula does NOT
describe a molecule, but only
gives the simplest ratio between
the bonded atoms ... this is an empirical formula.
On the previous page was an example of how formulas are
determined by analysing the mass composition of a
compound.
You should note that this metho d can o nly produce an
empirical formula. (In fact, the w or d "empirical" means
something determined by experiment, not by theory.)
If a molecular compound, with molecular formula XzY6
was analysed by mass measurements, its empirical formula
would be calculated t o be :>"''Y3
... simplest ratio of atoms.
Northmead High School SL#603217
A Little History ...
How the Mole was Invented
The "mole" a s a m easure of chemical quantities, is a
mathematically convenient device (a "trick") to help
chemical calculations.
Gay-Lussac's Law
Joseph Gay-Lussac wa s a French sc ie nt ist wi th an
unfortunat e name, bymodern standards. He lived 200 years
ago, and was very interested in flight using balloons, so he
investigated the way gases react chemically.
After a series of clever experiments, in which the volumes
of reacting gases were measured, in 1808 he propo sed the
"Law of Combining Volumes":
When measured
at constant temperature and pressure,
the volumes of gases in a chemical reaction
show simple, whole-number ratios
to each other.
The volume of a gas is easily changed by temperatur e and
pressure, so it is very important that the volumes are all
measured at the same conditions.
Hydrogen(g) + Chlorine(g)~ Hydrogen chloride(g)1 litre 1 litre 2 litres
Hydrogen(g) + Oxygen(g)2 litres 1 litre
. W ater (g) (vapour)
2 litres
Hydrogen(g) + Nitrogen(g) --.. Ammonia(g)3 litres 1 litre 2 litr es
Notice that in every case, t hat the volumes are alwaysi n a
simple, whole number ratio to each other.
Now con sider the balanced equ ation s fo r these thr ee
example reactions:
The mol e ra ti os a re t he same as the vo lume r atios
discovered by Gay-Lussac!
enter .Avogadro!
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Avogadro's HypothesisThe Italian, Amadeo Avogadro (1776-1856) was trained in
Law, but became very interested in Science.
In 1811, he noticed the similarity between Gay-Lussac's
Law (an empirical "law" based on experiment) and the
concept that atoms must combine in simple, whole number
ratios to form compounds.
Equal Volumes of all Gases
Contain Equal Numbers of Molecules
(when measured at the same conditions
of temperature and pressure)
Prior to Avogadro, it was assumed that the the reaction
involved single atoms, like this:
Hydrogen{g) + Chlorine(g) ~ Hydroge n chloride (g)1 volume : 1 volume 2 volumes
Now, reasoned Avogadro, gases react in simple, whole-
number volume ratios because each litre of gas has the
same number o f molecules in it. Therefore, to get the
volume ratios shown above, each hydrogen molecule, and
each chlorine molecule, must have 2 atoms!
i.e. Hydrogen is H2(g) and Chlorine is Cl2(g)' and the correct
equation is
Then, for the same reaction, scientists could measure the
masses of these gases as well as volumes. This showed that
chlorine atoms must be about 35 times heavier than
hydrogen ... chemists were on the way to figuring out the
relative atomic weights of elements, and being able to
calculate chemical quantities.
Although he did not invent the concept of the mole, we
name the number of particles in 1 mole i n Avogadro's
honour ...
Northmead High School SL#603217
Molar Volume of a GasIf 1 mole of any chemical species contains the same
number of particles (Avogadro' s Number) AND if equal
volumes of gases contain equal number of particles
(Avogadro'S Hypothesis), then it follows that
1 mole of any gas must occupy the same volume,
if measured at the same temperature and pressure.
This volume is the "Molar Volume" and is the same for
every gas. It is measured at the standard set of conditions
known as Standard Laboratory Conditions (SLC); 25C
and 1 standard atmosphere of pressure.
Mole Calculations Involving GasesThis additional knowledge opens up the opportunity to
carry out quantity calculations which involve mass and
volumes of gases.
Example Problems1.
If 15.65g of calcium carbonate (CaC03) was completely
decomposed by heat, what volume of carbon dioxide
gas would be produced (if measured at SLC)?
Solution
Always begin with the balanced equation for the reaction.
CaC03(s) . CO2(g) + CaO(s)mole ratio = 1 : 1 : 1
Moles of CaC03: n =..J.!L = 15.65 = 0.1564 molj\1},,f 100,09
Mole ratio is 1 :1, so moles of CO2
formed = 0.1564
~
:. Volume of CO2 = 0.1564 x 24.8...... Molar Vol.
= 3.88 L (at SLC) of all gasesat S LC
2.
What volume of hydrogen g as ( at S LC) wo uld be
produced if 10.00g of lithium metal was reacted with
sulfuric acid?
Solution
2 Li(s) +2 :
. H2(g) + Li2SO4(aq)1 1
Moles of lithium: n = ..J.!L = 10.00 = 1.441 mol
MM 6.941
Mole ratio is 2:1, so moles of H2
= 1/2 X 1.441=0.7204
:. Volume of Hz = 0.7204 x 24.8
= 17.9 L (at SLC)