CIE AS Chemistry (9701) exams from 2022

Revision Notes

2.1.1 Period 3 Elements: Physical Properties

Properties of the Elements in Period 3

  • Elements in the periodic table are arranged in order of increasing atomic number and placed in vertical columns (groups) and horizontal rows (periods)
  • The elements across the periods show repeating patterns in chemical and physical properties
  • This is called periodicity

The-Periodic-Table-of-the-Elements, IGCSE & GCSE Chemistry revision notes

All elements are arranged in the order of increasing atomic number from left to right

Atomic radius

  • The atomic radius is the distance between the nucleus and the outermost electron of an atom
  • The atomic radius is measured by taking two atoms of the same element, measuring the distance between their nuclei and then halving this distance
  • In metals this is also called the metallic radius and in non-metals, the covalent radius

 

The Periodic Table - Atomic Radius, downloadable AS & A Level Chemistry revision notes

The atomic radius gives a measure of the size of atoms

Atomic radii of Period 3 elements table

The Periodic Table - Table 1_Properties of the Elements in Period 3, downloadable AS & A Level Chemistry revision notes

The Periodic Table - Atomic Radius Graph, downloadable AS & A Level Chemistry revision notes

The graph shows a decrease in atomic radii of Period 3 elements across the period

  • Across the period, the atomic radii decrease
  • This is because the number of protons (the nuclear charge) and the number of electrons increases by one every time you go an element to the right
  • The elements in a period all have the same number of shells (so the shielding effect is the same)
  • This means that as you go across the period the nucleus attracts the electrons more strongly pulling them closer to the nucleus
  • Because of this, the atomic radius (and thus the size of the atoms) decreases across the period

The Periodic Table - Atomic Radius 2, downloadable AS & A Level Chemistry revision notes

The diagram shows that across Period 3, the elements gain extra electrons in the same principal quantum shell

Ionic radius

  • The ionic radius is the distance between the nucleus and the outermost electron of an ion
  • Metals produce positively charged ions (cations) whereas nonmetals produce negatively charged ions (anions)
  • The cations have lost their valence electrons which causes them to be much smaller than their atoms
  • Because there are less electrons, this also means that there is less shielding of the outer electrons
  • Going across the period from Na+ to Si4+ the ions get smaller due to the increasing nuclear charge attracting the outer electrons in the second principal quantum shell nucleus (which has an increasing atomic number)
  • The anions are smaller than their original atoms because each atom has gained one or more electrons in their third principal quantum shell
  • This increases the repulsion between electrons while the nuclear charge is still the same
  • Going across P3- to Cl the ionic radii decreases as the nuclear charge increases across the period and less electrons are gained by the atoms (P gains 3 electrons, S 2 electrons and Cl 1 electron)

Ionic radii of ions of Period 3 elements table

The Periodic Table - Table 2_Properties of the Elements in Period 3, downloadable AS & A Level Chemistry revision notes

The Periodic Table - Ionic Radius Graph, downloadable AS & A Level Chemistry revision notes

Ions of Period 3 elements with increasing positive charge (metals) and increasing of outer electrons across the period

The Periodic Table - Ionic Radius, downloadable AS & A Level Chemistry revision notes

The diagram shows the electron configuration of the ions of Period 3 elements and their relative sizes

Melting point

Melting points of the elements across Period 3 table

The Periodic Table - Table 3_Properties of the Elements in Period 3, downloadable AS & A Level Chemistry revision notes

The Periodic Table - Melting Point Graph, downloadable AS & A Level Chemistry revision notes

Ions of Period 3 elements with increasing positive charge (metals) and increasing of outer electrons across the period

  • A general increase in melting point for the Period 3 elements up to silicon is observed
  • Silicon has the highest melting point
  • After the Si element the melting points of the elements decreases significantly

Electrical conductivity

  • Electrical conductivity refers to how well a substance can conduct electricity
  • Unlike the melting points, the electrical conductivity of the Period 3 elements shows a clear trend
  • Going across the period, the electrical conductivity of the elements decreases significantly

Trends in electrical conductivity across Period 3 table

The Periodic Table - Table 5_Properties of the Elements in Period 3, downloadable AS & A Level Chemistry revision notes

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