|Notes: 27 October
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Chemical Periodicity, cont.
- Period: the rows of elements showing a repeating pattern
of properties (e.g. Na - Ar).
- Group: a vertical column of elements on the table sharing
a family resemblance of properties (e.g. Li - Fr).
- Representative elements: the elements of the s-block and
p-block (blue and green on the table below).
- Transition metal elements: the elements of the d-block (yellow
in the table below).
- Inner-transition metal elements: The Lanthanides and Actinides
(not shown on the table below)
- IA = alkali metals;
- IIA = Alkaline earth metals;
- VIIA = Halogens (note the generic symbol of X standing for
- VIIIA = Noble gases (older = inert gases).
You should know the terminology above and memorize the
names and symbols for the elements shown in the table below.
Periodic Table of the Elements
Examples of Periodic Properties
Let's look at some of the elements and see what their properties
2 Na + 2 H2O Æ
2 Na+ + 2 OH- + H2
- Group IA, on the left side of the chart, is known as the
alkali metals because the react with water to produce
strong bases (a base is alkaline). Note that all of them are
soft (cut with a butter knife), low density (Li floats on oil,
Na and K float on water), very reactive metals. All of them react
with water with Li<Na<K<Rb<Cs. in each case the metal
gives its electron to water leaving hydroxide ion (OH-
a base) and hydrogen gas. For example with sodium:
2 Na + Cl2 Æ
- Group VIIA, on the right side of the chart, is known as the
halogens. The halogens form acids with water, are gases
at the top of the Periodic Chart and high vapor pressure liquids,
then solid going down; exist as diatomic molecules (X2),
and are very reactive towards metals. For example sodium reacts
violently with chlorine gas to give table salt (NaCl):
- Look at the elements of Period 3 (samples of Na - Cl, alkali
metals and halogens) Note how their properties change from metallic
- Combining ratios with hydrogen. 1 - 4 - 1: LiH, BeH2,
B3, C4, H3N, H2O,
- Group IA always +1
- Group IIA always +2
- Group IIIA commonly +3, Al always+3
- Group IV +4 or -4 (usually covalent)
- Group VA commonly -3
- Group VIA commonly -2
- Group VIIA commonly -1
- Metal oxides basic combined with water (e.g. NaOH, KOH),
non-metal oxides acidic combined with water (e.g. SO2
and water gives H2SO3, one of the important
acids in acid rain).
Trends: Note the trends for
- atomic size: decreases going from left -> right and from
bottom -> top; overall have diagonal, Cs (largest) -> F
- Size goes up with atomic number for any individual group.
- Size decreases irregularly as atomic number increases for
any given period (more charge pulls electrons in to nucleus,
but shielding reverses as subshells [s or p orbital sets] file.
- ionization energy: increases from left -> right and from
bottom -> top; overall have diagonal, Cs (lowest) -> F
- Ionization energy goes down with atomic number for any individual
- Ionization energy increases irregularly as atomic number
increases for any given period (more charge pulls electrons in
to nucleus, but shielding reverses as subshells [s or p orbital
- Note metallic vs. non-metallic elements"
- Groups IA, IIA, all B groups, diagonal from Al - Po gives
a divide between, with elements on line and next to line on right
Matter and Atoms
Why do we think atoms exist?
© R A Paselk
Last modified 27 October 2004