Chapter 4: Periodicity
4.2, 4.3, 4.4

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  • Created on: 10-12-14 19:27

4.2 Trends In properties of elements of period 3

Elements in group 1,2,3 (Sodium, Magnesium, Aluminium)
-Are metals. they have giant structures and lose their outer electrnons to form ionic compounds 
Elements in group 4 (Silicon)
-Giant structures has 4 outer electrons to form 4 covalent bonds, semi-metal, some metallic properties  
Elements in group 5,6,7 (Phosphurus, sulfur, chlorine) 
-Non-metals, accept electrons to for ionic compunds, share electrons to form covalent compounds
Elements in group 8 (Argon)
-Is a noble gas, full outer shell, unreactive
Trends in Melting and Boiling points
-Giant structures(on left) tend to have high melting and boiling points 
-Molecular or atomic structues (on right) tend to have low melting and boiling points 
Melting points of metals increase from Na to Al because the strength of metallic bonding, more electrons join the delocalised sea of electrons that holds the metallic lattice together. 
Melting points of non-metals with molecular structures depend on size of the vaan der waal forces between molecules. this depends on the number of electrons in the molecule and how closely th e molecules can pack together 
Silicon has higher melting point due to its giant structure 

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4.3 More Trends In properties of elements of P-3

Atomic Radii
-Are taken to be half the distance betweeen the centres of a pair of atoms, this is to be because there is no point at which the electron cloud denisity drops to zer
-Atomic Radii can differ and it depends on the type of bonding, Covalent, metallic, ionic, Vaan der waal.
-Covalent radius most commonly used as a a measure of the size of the atom
-Even metals can form covalent molecules in the gas phase
Noble gases do not bond covalently with on another, they do not have a covalent radii
The graph shows:
-Atomic radius is a periodic property beacuse it decreases across each period amd there is a jump when we start the next period
-Atoms get larger as we down a group 
Why the radius of atoms decrease along the period
-Across a period there is an increase in protons in the nucleus and electrons to the Outer main level 
This increases the nuclear charge and it pulls the electrons closer as there are no extra shells added for sheilding, so shielding stays the same so Atom raius decreases as you go across a period 
Why the radii of atoms increase down a group.
-As we go down a group each element gains one extra main level of electrons
-As we go down a group shielding increases, outermost electron further away from nucleus, radius increases.

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4.3 More Trends In P-3 continued

First Ionisation energy 
-The first ionsiation energy is the energy required to remove one mole of electrons from a mole of isolated gaseous atoms. 
-First ionisation energy generally increases across a period 
-Alkali metals have lowest values
-First ionisation energy decreases down a group 
Why the first ionisation energy increases across a period 
-As we go across a period, number of protons increase, shielding stay the same, so the higher the nuclear charge the greater the hold so harder it is to remove a electron.
Why the FIE energy decreases down a group
-Shielding increases which leads to a increasing distance from the nucleus and therefore is easier to remove 
-Electrons get easier to remove as we go down as they get further away from teh nucleus 
Why there is a drop in ionisation energy from one period to the next
-This is becasue we start a new main level and there is an increase in the atomic radius as the outer most electron is further away and is therefore lesss strongly attracted and easier to remove.  

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4.4 A closer look at IE

Elements Of Period 3 shows:
-FIE actually drops between group 2 and 3, Al has a lower FIE than Mg
-IE drops slightly between group 5, P, and group 6, S.
The drop in FIE between groups 2 and 3  
-The electron arrangement in the P sub-Shell is already in a higher energy level than the S-electron, so takes less energy to remove it 
Drops in FIE between group 5 and 6 
-An electron pair will be easier to remove in their orbital as it will be repelling each other in the sulfur
-P has no paired electrons as each electron is in a different orbital
-S has a paired electron in a orbitl so it is easier to remove due to the repulsion. 
Successive IE
-Removing one electron after another gets harder and more energy is required
-This is beacause there is a greater nucear hold to overcome and it has to remove electrons which are closer to the nucleus
-There is a gradual increase and thena  sharp increase when beginning to remove another shells/main levels electrons  

906, 1763, 14,564, 21,013
-this element is in group 2 as there is a big jump in IE after the 2 IE 

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