Periodic Trends


Aim: How to use the periodic table to understand trends and patterns that occur.


Materials Needed: periodic table (Chemistry periodic table, wall size. This should contain atomic number, atomic masses, s,p, d, f blocks,  and element symbols, etc.  A junior high school level periodic table will not suffice.) If teacher does not have such a periodic table, wall size, teacher can use transparancies or data projector but to use the data projector teacher has to find an image of desired periodic table, then make it an electronic image) Sketch pad, colored pencils, markers

Student Activity: Honors Project: special project. (up to 2 days)

Notes:

1. These are general periodic trends of elements. There are
many exceptions to these general rules.

2. Period:a row of elements on the
periodic table. Remember that sentences are written in rows and end with
a period.
Groups: a column of elements on
the periodic table. Remember that group is spelled group and groups go
up and down.

3. Atomic radius is simply the radius of the atom, an indication of the
atom’s size

    atomic radius decreases
    as you go from left to right across a period.

      Stronger attractive forces in atoms
      (as you go from left to right) between the opposite charges in the nucleus
      and electron cloud cause the atom to be ‘sucked’ together a little tighter.

    atomic radius increases as
    you go down a group.

       There is a significant jump in the
      size of the nucleus (protons + neutrons) each time you move from period
      to period down a group. Additionally, new energy levels of elections clouds
      are added to the atom as you move from period to period down a group, making
      the each atom significantly more massive, both is mass and volume.

4. electronegativity is an atom’s ‘desire’ to grab another atom’s electrons.
electronegativity increases
as you go from left to right across a period.Elements on the left of the period
table have 1 -2 valence electrons and would rather give those few valence
electrons away (to achieve the octet in a lower energy level) than grab
another atom’s electrons. As a result, they have low electronegativity.
Elements on the right side of the period table only need a few electrons
to complete the octet, so they have strong desire to grab another atom’s
electrons.electronegativity decreases
as you go down a group.

5. Ionization Energy: The energy required to remove the most loosely bound electron from an atom in the gaseous state.
across a period, ionization energy increases
down a group ionization energy decreases.

6. Diagonal Rule:

Reactivity
refers to how likely or vigorously an atom is to react with other substances.
This is usually determined by how easily electrons can be removed (ionization
energy) and how badly they want to take other atom’s electrons (electronegativity)
because it is the transfer/interaction of electrons that is the basis of
chemical reactions.

    Metals

      reactivity decreases as
      you go from left to right across a period.

       reactivity increases as
      you go down a group

        The farther to the left and down
        the periodic chart you go, the easier it is for electrons to be given or
        taken away, resulting in higher reactivity.

    Non-metals

      – reactivity increases as
      you go from the left to the right across a period.

      – reactivity decreases as
      you go down the group.

        The farther right and up you go on
        the periodic table, the higher the electronegativity, resulting in a more
        vigorous exchange of electron.

7. Ionic Radius is not the same as atomic radius: Metals – the atomic radius of a metal is generally larger than the
ionic radius of the same element.

       Generally, metals loose electrons
      to achieve the octet. This creates a larger positive charge in the nucleus
      than the negative charge in the electron cloud, causing the electron cloud
      to be drawn a little closer to the nucleus as an ion.

    Non-metals – the atomic radius of a non-metal is generally smaller than
    the ionic radius of the same element.

      Generally, non-metals loose electrons
      to achieve the octet. This creates a larger negative charge in the electron
      cloud than positive charge in the nucleus, causing the electron cloud to
      ‘puff out’ a little bit as an ion.

8. Melting points: Metals – the melting point for metals generally decreases as you go
down a group.

Non-metals – the melting point for non-metals generally increases as
you go down a group.

9. Electron configurations(representative elements): Same group= same # valence electrons
Same period= same principle energy level

Homework: periodic table work packet or periodic table vocabulary words

1