Periodic Table Class #2 OB: Trends of the periodic table. (atomic mass + atomic size) Trend: A general pattern or tendency; consistent and repetitive On the periodic table there are many periodically repeating patterns. The table itself is arranged in order of increasing atomic number (which is the number of electrons = the number of protons. There are group trends (that follow a pattern going down groups). There are period trends (that follow a pattern going across periods). We’ll start to examine these patterns now.

The first and simplest trend is atomic mass. To determine the group trend for atomic mass we’ll look at atomic mass of four elements in two different groups. Let’s do group 2 and group 16: Group 2 Atommass Be Mg Ca Sr Group 16 Atommass O S Se Te

It should be clear that going down these and all the groups of the periodic table, that the atomic mass gets larger (because the atoms get larger. Group 2 Atommass Be9 amu Mg24 amu Ca40 amu Sr88 amu Group 16 Atommass O16 amu S33 amu Se79 amu Te128 amu To state this properly: The group trend for atomic mass is increasing.

This time let’s do the period trend for atomic mass, we’ll examine period 3 and 4. Remember, whenever possible, use 4 atoms in a row to measure a trend. atomsNaMgAlSi masses atomsKCaScTi masses

This time let’s do the period trend for atomic mass, we’ll examine period 3 and 4. Remember, whenever possible, use 4 atoms in a row to measure a trend. atomsNaMgAlSi masses23 amu24 amu27 amu28 amu atomsKCaScTi masses39 amu40 amu45 amu48 amu How can we state this trend???

The period trend for atomic mass in increasing. When ever you state a trend, it’s always as a complete sentence. Start with: “The period trend…” or “The group trend…” Then, state the trend itself… Finish with increasing or decreasing. It’s easy, the rules are clear. Memorize the way to do this, but not the actual trends. The trends are right on the table to figure out every time you need them. Always use 4 atoms in a row to measure a trend.

Trend #2 Atom Size (atomic radius in picometers) How big is a picometer? A meter is a basic unit of length in the metric system. A picometer is 1 x of one meter, or: One picometer = 1 pm = m That’s one trillionth of one meter. With a “T” - a Trillionth! Really, really tiny, but NOT ZERO.

Using four atoms in a row from groups 1 and 17, determine the group trend for atomic size, and state it in one sentence in proper form. Group 17 Atomradius F Cl Br I Group 1 Atomradius Li Na K Rb Group trend for atomic radius:

Using four atoms in a row from groups 1 and 17, determine the group trend for atomic size, and state it in one sentence in proper form. Group 17 Atomradius F60. pm Cl100. pm Br117. pm I136 pm Group 1 Atomradius Li130. pm Na160. pm K200. pm Rb215 pm The group trend for atomic radius is increasing.

Because each time you go lower in the group, the atoms are adding orbitals. Each period number increase is an increase of orbital number. Why is the group trend for atomic radius size increasing? (write this down!)

This time we’ll look over the period trend for atomic radius using the first 4 atoms of period 4 and of period 5. Period 4 Atoms KCaScTi Radius in pm Period 5 Atoms RbSrYZr Radius in pm

Period 4 Atoms KCaScTi Radius in pm Period 5 Atoms RbSrYZr Radius in pm The period trend for atomic radius is decreasing!

How could the atomic radius decrease as you go across the period? What do these atoms have changing that could affect that? Let’s look at period 4 to start: Atom:RbSrYZr # of orbitals 4444 # protons Radius in pm

Going across a period, each atom has the SAME NUMBER OF ORBITALS for the electrons, but each successive atom has ONE MORE PROTON, pulling harder and harder on those negative electrons in this 4th orbital. The nucleus becomes increasingly more positive, the inward pull on the electrons becomes greater and greater, making the atomic radius shrink.

The Trend for Atom Size, in picture form.

What happens with the atomic sizes of Co, Ni, Cu and Zn? Look at those atomic radii now. Atom: CoNiCuZn Atomic radius in pm

Atom: CoNiCuZn Atomic radius in pm If the period trend for atomic radius is decreasing, how can copper be bigger than cobalt nickel? How can zinc be bigger than cobalt and nickel? Trends are patterns that are regular and predictable, but not the law. These are exceptions to the trend. You already know a few another “exceptions to a trend”, The AlPo dog food exception to the metalloid “rule”.