periodic table

5/28/2018 Periodic Table

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CHEMICALPERIODICITY


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Learning Outcomes

describe qualitatively (and indicate the periodicity in) the variations

in atomic radius, ionic radius, melting point and electrical

conductivity of the elements

explain qualitatively the variation in atomic radius and ionic radius

interpret the variation in melting point and in electrical conductivity

in terms of the presence of simple molecular, giant molecular or

metallic bonding in the elements

explain the variation in first ionisation energy

describe the reactions, if any, of the elements with oxygen (to giveNa2O, MgO, Al 2O3, P4O10, SO2, SO3), chlorine (to give NaCl ,

MgCl 2, Al 2Cl 6, SiCl 4, PCl 5) and water (Na and Mg only)

state and explain the variation in oxidation number of the oxides

and chlorides in terms of their valance shell electrons


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Learning Outcomes

describe the reactions of the oxides with water [treatment of

peroxides and superoxides is not required]

describe and explain the acid/base behaviour of oxides and

hydroxides including, where relevant, amphoteric behaviour in

reaction with sodium hydroxide (only) and acids

describe and explain the reactions of the chlorides with water

suggest the types of chemical bonding present in chlorides and

oxides from observations of their chemical and physical properties

predict the characteristic properties of an element in a given group

by using knowledge of chemical periodicity

deduce the nature, possible position in the Periodic Table, and

identity of unknown elements from given information about

physical and chemical properties


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Periodic Table

Old periodic table (1869)

By Russian Mendeleev and German

Meyer

Elements arranged in order of atomic mass

Elements with similar chemical propertiesfell in the same column.


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The Periodic Law And The Periodic Table

Periodic law

law stating that many of the physical and chemical

properties of the elements tend to occur in asystematic manner with increasing atomic number.

Periodic table

is a tabular arrangement of the elements in order of

increasing atomic number such that elements

having similar chemical properties are positioned in

vertical column


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Period 3 Elements (Na Ar)

Period 3


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Trends In Atomic Size

Atomic Radius = half the distance between two

nuclei of a diatomic molecule.

}

Radius


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Trends in Atomic Size

Influenced by three factors:

1. Energy Level

2. Charge on nucleus

3. Shielding effect


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Periodic Trends

As you go across a period, the radiusgets smaller. This is caused by the increase in nuclear

charge and weak screening effect as

successive electrons are added to thesame quantum shell.

Na Mg Al Si P S Cl Ar


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Overall


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Trends in Ionization Energy

There is a general increase in first I.E.

as atomic number increases because:

a) The nuclear charge increases, due to

increase in number of protons and

electrons.

b) The radius of atom decreases with

increasing atomic number, hence more

energy required to remove outer

electrons.


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Trends in Ionization Energy

So IE generally increases from left to right.

Exceptions at full and 1/2 full orbitals.


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Trends in Ionic Size

Cations are smaller than their respective

atoms.

Anions are bigger than their respective atoms.


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Size of Isoelectronic ions

Iso- means the same

Iso electronic ions have the same

number of electronsAl3+ Mg2+ Na1+ Ne F1- O2- and N3-

all have 10 electrons

all have the configuration: 1s22s22p6


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Size of Isoelectronic ions

In an isoelectronic series (Na to Si) and (P to Cl),

ionic radius decreases as the proton number

increases.

This is because the same number of electrons areattracted more strongly by the increasing nuclear

charge.

Positive ions that have more protons would be

smaller.

Al3+

Mg2+

Na1+ NeF1- O

2- N3-


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Changes in melting points

To understand these changes we must

understand the nature of the bonding within the

elements.

Three types of structure occur as we crossperiod 3.

1) Metallic Structures, Na, Mg, Al

2) Giant Molecular, Si3) Molecular Structures, P4, S8, Cl2and Ar

P4< S8> Cl2> Ar


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Variation in Electrical Conductivity

Electrical conductivity is relatively high for

metals, lower for the metalloids and almost

negligible for non-metals.


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Chemical properties

Oxides

Most metallic elements, both metals and non-

metals, combine directly with oxygen. Metallic

elements form ionic oxides whilst non-metallicelements form covalently bonded oxides.

For example:

2Mg(s)+ O2(g) 2MgO(s)


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Chemical properties

Chlorides

There are a number of methods for preparing

chlorides. The direct preparation can be used

although the reaction can be vigorous.

For example:

2Al(s)+ 3Cl2(g) 2AlCl3(s)


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Chemical properties

Element Oxide Chloride

Na Na2O NaCl

Mg MgO MgCl2

Al Al2O3 AlCl3

Si SiO2 SiCl4

P P2O5 PCl3

S SO2 SCl2Cl Cl2O Cl2

The table below summarises the most common oxides

and chlorides of Period 3 elements.


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Oxidation Number

Oxides (Na to S)

The oxygen in the compound is always

the more electronegative element

(oxidation number -2).

The maximum oxidation number is thesame as the group number.

P and S show several oxidation numbers

(depends on the number of electrons

used for bonding).

Na in Na2O +1

Mg in MgO +2

Al in Al2O3 +3

Si in SiO2 +4

P in P4O10 +5

S in SO3 +6

S in SO2 +4


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Oxidation Number

Chlorides

Chlorine in the compound is

the more electronegative

element (has a negative

oxidation number -1)

In each case the oxidationnumber is the same as the

number of electrons in the

outer energy level of the atom

Na +1

Mg +2

Al +3

Si +4

P +5


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Reaction of oxides with water

The physical properties of these oxides depend on the type of bonding.

Na2O, Al2O3and MgO - high melting point.

MgO and Al2O3have a higher melting point than Na2O since the charges

are higher and the atomic radii smaller, resulting in a stronger electrostatic

attraction (forces) between the ions.

P4O10and SO3have a much lower melting points.

Element Formulae of oxide Structure of oxideMelting point of

oxide /C

Na Na2O Ionic 1275

Mg MgO Ionic 2852Al Al2O3 Mostly Ionic 2072

Si SiO2 Giant Covalent 1703

P P4O10 Simple Covalent 300

S SO3 Simple Covalent -10


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Acid-base properties of the

oxides of Period 3

Element Na Mg Al Si P S

Formulae

of oxideNa2O MgO Al2O3 SiO2 P4O10 SO2 SO3

Acid-base

characterof oxide Basic Basic Amphoteric Acidic Acidic Acidic

pH of

solution

when

dissolved

in water

12 - 14 8 - 9 7 (insoluble)7

(insoluble)2 - 4 2 - 4 13

The oxides therefore become more acidic on moving from left to right in

the periodic table

f C


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Reaction of Chlorides with

water NaCl and MgCl2are ionic chlorides - melting point is high.

AlCl3and SiCl4are molecular covalent chloride - melting points are thus

much lower than the ionic chlorides.

AlCl3actually exists in polymeric form in the solid state, which is

converted to a dimeric form in the gas phase. At high temperatures, itreverts to a simple molecular structure.

PCl5is ionic so its melting point is thus high. On heating, however, it

reverts to a simple covalent structure and sublimes.

R i f Chl id i h


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waterThe way in which chlorides react with water depends on the type of bonding

present in the chloride:

Ionic chlorides dissolve in water to give neutral solutions:

NaCl(s) Na+(aq) + Cl(aq) pH = 7

MgCl2(s) Mg2+(aq) + 2Cl(aq) pH = 7

Aluminium chloride reacts with water to give hydrated aluminium ions and

chloride ions. The hydrated aluminium ions undergo deprotonation to give

an acidic solution:

AlCl3(s) + 6H2O(l) [Al(H2O)6 ] (aq) + 3Cl(aq)

Al(H2O6)(aq) + H2O(l) [Al(H2O)5(OH)]2+(aq) + H3O

+(aq)

R ti f Chl id ith


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water

The other covalent chlorides react readily with water at room

temperature to form the oxide or hydroxide and HCl(g).

The HCl is formed as white misty fumes, and the observance

of these fumes is a good indication that the chloride is

covalent.

SiCl4(l) + 2H2O(l) SiO2(s) + 4HCl(g) pH = 1 - 2

PCl5(s) + 4H2O(l) H3PO4(aq) + 5HCl(g) pH = 1 - 2

periodic table

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