Chemistry- Unit 1- Periodicity

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  • Created by: FireDwarf
  • Created on: 27-10-13 14:52
What is the periodic table?
List of all the elements in order of increasing atomic number.
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Who discovered it? How?
Mendeleev, Left spaces for undiscovered elements and lined up elements with simular properites.
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What is a group?
Vertical- Simular Properties- same number of electrons in their outershell
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S block- get more reactive down the group To right right- they get more reactive up a group
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Horizontal- trends in properities
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How do we group the period 3 elements?
Na,Mg,Al / Si/P,S,Cl/Ar
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Metals, Giant structures
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Semi-conductor, semi-metal, 4 bonds (convalent)
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Non-metals, molecular structures
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Noble gas (atom)
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Describe the melting point as we move across period 3
Increases across the metals, with a large increase to Si, decrease in the non-metals but increase from p to s, decrease then from s to ar.
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Why the metals?
As you increase across the period, you increase the metallic bonding. More metallic bonding, more energy required to break these bonds, higher melting point
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Charge density, charg density increases from Na to Al and this causes larger attraction to the delocalised electrons
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what is charge density?
Ratio of ions charge to the mass.
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why Si large melting point?
4 convalent bonds- strong- require large amount of energy to break- high melting point
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Non metals?
Van der Walls- the strengh of these forces id dependant upon the size of the molecules and number of electrons. As we move across, the size of molecules change, causing changes in strengh of this force
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size of these molecules?
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How does the atomic radi change as we move across a period?
decreases- stronger ncuelar charge therefore pulling the electrons closer, decreasing radi
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Increases, more shells of electrons therefore increasing the distance between the outer electrons and the nucleus, increasing atomic radi.
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What is atomic radii?
Half the distance between the centeres of a pair of atoms
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Exceptions to the general first ionisation trend?
Al & S
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Why does Al and S not match the pattern?
Their 1st ionisation energy is lower then expected, it is lower then the previous element in the period.
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Why does Al not match?
It contains its outer electron in a higher energy shell then the previous element, which means it requires less energy to remove.
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Why does S not match?
It contains 2 electrons paired (3p4) compared to its previous element (3p3). If electrons are paired there is mutual repulsion and therefore it is easier to remove and requires less energy.
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How does the successive ionisation energies look?
General increase in energy needed.
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Closer to the nucleus on lower energy levels and therefore more energy required.
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How can we tell its group? How can we tell the element?
Look for a jump between ionisation energy, alot more energy is needed when you move up a shell (like the period) and look how many in the outer shell for group and then how many in each group for element.
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Card 2


Who discovered it? How?


Mendeleev, Left spaces for undiscovered elements and lined up elements with simular properites.

Card 3


What is a group?


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