Topic 3 - The periodic table Flashcards
What is the Atomic radius or Atomic Radii ?
the total distance from the nucleus of an atom to the outermost orbital of its electron.
Periodic Trends in Atomic Radii (groups/coulum)
the atomic radius tends to increase from top to bottom.
This trend results primarily from the increase in the principal energy number (n) of the outer electrons
Going down a group, the outer electrons have a greater probability of being further away from the nucleus causing the atom to increase in size.
Periodic Trends in Atomic Radii (period/row)
The atomic radius tends to decrease from left to right.
The major factor influencing this trend is the increase in Zeff across the row
Effective nuclear charge, Zeff is the net positive charge attracting an electron in an atom
The increasing effective nuclear charge steadily draws the valence electrons closer to the nucleus.
This causes the atomic radius to decrease.
when does the atomic radii increase?
down a group
what are the trends between zeff and atomic radii across a row?
atomic radii decreases
zeff increases
How to calculate Zeff?
Zeff = Z – S, where Z is the atomic number and S is the number of shielding electrons (number of electrons between the nucleous and the electron in question / number of non-valence electrons)
What is the effective nuclear charge (Zeff/Z*)?
is the net positive charge experienced by an electron in a multi electron atom. the term effective is used because the shielding effect of -ve charged electrons prevents higher orbital electrons from experiencing the full nuclear charge by repelling effect of inner layer electrons
what is considered to shield the valance electrons from the full electrostatic attraction of the nucleus.
the core electrons are generally closer to the nucleus than the valence electrons therefore they are considered to shield the valence electrons from full electrostatic attraction of the nucleus
What is electronegativity?
Electronegativity is the measure of the ability of an atom in a chemical compound to attract electrons from another compound.
Trends in electronegativity
Within each period (row) there is a steady increase in electronegativity from left to right of the periodic table.
why is there a steady increase in electronegativity from left to right of the periodic table
occurs due to nuclear charge. left -> right across a period the elements gain effective nuclear charge. This “positive charge experience” allows the atom to attract electrons thus making it more electronegative.
Periodic Trends in Electronegativity (groups/column)
down a group starting from top to bottom there is a decrease in electronegativity value.
why is there a decrease in electronegativity from top to bottom in a group?
the atomic radius gets larger to make room for the electrons, this creates less attraction between the the electrons and protons making it harder for the atom to attract electrons.
why is electronegativity used?
to estimate whether a given bond will be non-polar covalent, polar covalent or ionic.
electronegativity and bonding ……..
