Chemical Periodicity (HS 2) by Divani

1a) Atomic Size Across Period 3

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When going across Period 3, valence electrons increase sodium (Na) to Chlorine (Cl). However, the atomic radius decrease because the nuclear charge increase, the electrons cloud are pull closer towards nucleus.

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based on the graph,silicon shows the highest melting point than the rest of the elements in period 3.This is because silicon has a giant covalent structure.Thus the bonds that is present is called giant covalent bonds.

First Ionisation Energy across Period 3 (1 B)

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The first ionisation energy increases across period 3. Across period 3 Nuclear charge effect increases , attraction between protons and electrons increases, hence the first ionisation energy increases.

Magnesium: 1s² 2s² 2p⁶ 3s² ... and ... aluminium: 1s² 2s² 2p⁶ 3s² 3p1

First ionisation energy of Mg removed from fully filled 3s orbital.More stable. More energy needed.

Phosphorus: 1s² 2s² 2p⁶ 3s² 3p³ ... and ... sulphur: 1s² 2s² 2p⁶ 3s² 3p⁴

First ionisation energy of P removed from half filled 3p orbital.More stable. More energy needed.

2;.a)

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A giant covalent structure

Silicon has a giant covalent structure just like diamond. A tiny part of the structure looks like this:

2 b) Melting of phosphorous is lower than silicon because phosphorus exist as a rhombus structure at r.t.p. (P4) unlike silicon that has a giant covalent structure. More energy is required to break the strong covalent bonds in the giant structure compared to the rhombus structure of phosphorous.

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3. a) Period 3 : Na, Mg, Al - Metallic structure

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Na, Mg, Al - Metallic structure

Si - Giant Covalent Structure

P, S Cl, Ar - Simple Molecular Structure

1a) Atomic size across Period 3

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3.b)

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Electrical conductivity

None of these conducts electricity in the solid state, but electrolysis is possible if they are molten. They conduct electricity because of the presence of freely moving ions.

2 e)

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For an element to conduct electricity, it must contain electrons that are free to move. Since neither silicon nor sulphur contains free electrons, they cannot conduct electricity.

Characteristics of oxides across period 3

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Basic oxide: Na20, MgO

Amphoteric oxide: Al2O3

Acidic oxide: P4O10, SO2, SO3

2 d)

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Sulphur has a higher melting point and boiling point than the other two because

sulphur exists as S₈ molecules
chlorine exists as Cl₂ molecules ...
argon exists individual Ar atoms ...
the strength of the van der Waals’ forces decreases as the size of the molecule decreases
so the melting points and boiling points decrease in the order S₈ > Cl₂ > Ar

1c) Electronegativity across Period 3

2015-11-17 06:34:06 UTC

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Electronegativity increase across Period 3 because the size of atoms decrease, force to attract the electrons increase.

2 c) Melting point of phosphorus is lower than sulphur because sulphur exist in r.t.p as a molecule of 8 atoms (S8) unlike phosphorus which exist as P4

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1e) Electrical Conductivity from Sodium and Aluminium

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Electrical conductivity increases going acrossPeriod 3 from sodium to aluminium.

-the number of delocalised electrons increases

-there are more electrons which can move and carry charge

-so the electrical conductivity increases.