Periodicity

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  • Created by: kudzi.c
  • Created on: 09-12-14 14:31

Introduction

Periodic table arranged by increasing atomic number.

Period - horizontal row of elements in Periodic Table. Elements show trends in properties across a period.

Group - vertical column, elements in a group have similar chemical properties*.

Periodicity - a regular periodic variation of properties of elements with atomic number and position in the periodic table.

Trends down a group can also affect trends across a period.

*Elements in the same group react in a similar way because they have similar electron configurations.

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First Ionisation Energy & Atomic Radii

Trend across period is a general increase in first ionisation energies.

  • Atomic radii decreases (because inc. nuclear charge pulls electrons in)
  • Nuclear charge increases
  • Shielding by inner electrons remains the same.

Increased nuclear charge is the most important factor, as more energy is required to remove a single electron.

Sharp decrease in first I.E. is due to addition of a new shell which leads to increased electron shielding by inner electrons and increased distance of the outermost shell from the nucleus.

Trend down a group is a general decrease in I.E.

  • Atomic radii increases
  • Shielding by inner electrons increases
  • Nuclear charge increases. (ouwieghed by other factors)

Attraction between nucleus and other electrons decreases down a group so less energy needed to remove an electron. Increased distance and shielding are the most important factors.

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Boiling & Melting Points

Trend across periods 2 and 3

Groups 1 - 4. General increase in boiling points.

Groups 4 - 5. Sharp decrease in boiling point.

Groups 5 - 0. Comparatively low boiling points.

Between group 4 and 5, elements go from giant metallic structures to simple molecular structures. The forces also change from metallic bonding to van der Waals forces, which are much easier to break.

Mpts & bpts of metals in period 3 increase across period because there is an increase in ionic charge and number of delocalised outershell electrons. This increases the electrostatic attraction increaing melting and boiling points.

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Periods 2 & 3

Electron Configuration - going across Period 2 the number of electrons increases, changing the electron configuration, the pattern is repeated across Period 3 except instead of 2s and 2p subshells, Period 3 has 3s and 3p subshells.

Atomic Radii - decreases across both periods. Elements in Period 3 have greater atomic radii than the corresponding elements in Period 2.

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