GenChem reviewer

Atomic Radius

  • measure as distance from nucleaus to nucleaus and divided by 2

unit commonly used is pm

  • picometer = 10^-12m

example: iodine atomic radius is 140pm

How does atomic radius change across a period?

  • it is smaller to the right

  • why?

  • more protons in the nucleaus higher electrical force pulls electrons closer to nucleus

how does atomic radius change down a group?

  • it is larger down the group

  • why?

  • valence electrons are at higher energy levels and are not bound as tightly to the nucleus because they are screened or shielded (pushed away) by other electrons in inner levels

Ionization energy

  • is the amount of energy needed to remove an electron from a gaseous atom

Positive ion (cation) - removal of electron

negative ion (anion) - addition of electron

how does ionization energy change down a group?

  • ionization energy decreases as you move down a group

  • why?

  • the size of the atom increases

    • electron is further from the nucleaus

Ionic Size

  • metallic elements easily lose electrons

  • non-metals more readily gain electrons

Positive Ions

  • are always smaller than the neutral atom

Negative Ions

  • are always larger than the neutral atom

Ions size trands in periods

  • from left to right there is a decrease in size of positive ions

Ion size trends in columns

  • ion size increases as you move down a column for both positive and negative ions

Electron Affinity

  • the energy that an atom releases when it accepts an electron

  • electron affinity increases from left to right and decreases down a column

Electronegativity

  • the ability of an atom in a bond to pull on the electron. (Linus Pauling)

  • when electrons are shared by two atoms a covalent bond is formed

  • when the atoms are the same they pull on the electrons equally

  • when the atoms are different, the atoms pull on the electrons unevenly

Trends in Electronegativty

  • electronegativity generally decreases as you move down a group

  • electronegativity of the representative elements increases as you move across a period

Electronegativites of some elements

Fluorine 4.0

chlorine 3.0

oxygen 3.5

nitrogen 3.0

sulfur 2.5

carbon 2.5

hydrogen 2.1

sodium 0.9

cesium 0.7

NOTE:

  • most electronegative element is F

  • least electronegative stable element is Cs

Summary

  • in atomic radius, it is smaller to the right and larger down the group

  • in ionization energy, it is smaller down a group and increases from left to right

  • in ionic size, it increases as you move down a column for both cation and anion, but it decreases from left to right for cations

  • in electronegativity, when electrons are shared by two atoms, a covalent bond is formed

    • when the atoms are tha same, they pull on the electrons equally

    • when the atoms are different, the atoms pull om the electrons unevenly