Dmitri Mendeleev, a Russian chemist was not the first
to study the relationship between atoms.
However, he was the first to create a working model of the
relationships. His Periodic Table of the
Elements even had predictive powers. Germanium
(Ge), gallium (Ga) and scandium (Sc) were undiscovered when he created the
table, but he left spaces for them. Unfortunately,
there were a few errors – although he placed iodine and tellurium in the
correct positions, he assumed that tellurium’s atomic mass must have been
incorrect – it was not.
‘If the elements are arranged according
to their atomic mass, a pattern can be seen in which similar properties occur
regularly.’
Mendeleev's journey to create the Periodic Table is fascinating.
Looking for more Periodic Table goodness? Check this out!
Modern Periodic Table
During
the time Medeleev created his periodic table, isotopes were unknown. Upon their discovery, chemists realized that it
is better to organize the table in a slightly different manner, thus, clearing
up the iodine/tellurium conundrum.
‘If the elements are arranged according
to their atomic number, a pattern can be seen in which similar properties occur
regularly.’
Periodic Table
On
a periodic table, label the following:
- periods
- families/groups
- group numbers (1 to 18)
- period numbers (1 to 7)
- alkali metals, alkaline earth metals, transition metals, boron group, carbon group, pnicogens, chalcogens, halogens, noble gases, lanthanides, actinides
- staircase
- location of metals, non-metals, metalloids
Metals, Non-metals & Metalloids
- metals – malleable, ductile, conductive, shiny (ex. Na, Pb, Hg)
- non-metals – brittle, non-conductive, dull (ex. N, S, Ar)
- metalloids – have properties of both metals and non-metals (ex. Te, Si, Te)
Organization of the Elements
There
are many different ways that the elements could be grouped. Below are a few possibilities:
- by state – most are solid, 11 are gases, 2 are liquids
- by colour/appearance – most are silvery and shiny or coloured and shiny (metals); all gases are colourless, except F and Cl
- by metals/non-metals – there are 4 times as many metals as non-metals (recall properties of each); some elements have properties of both (metalloids)
- by atomic mass – Mendeleev’s Periodic Table (caused problems)
- by atomic number – Modern Periodic Table (fixed the earlier problems)
-
by
reactivity – there are trends in reactivity in families (notice that the metal and non-metal trends for increasing reactivity are opposite to each other; also notice that the Noble Gas family is shaded to indicate that they are basically unreactive)
Check out the reactivity trends within the alkali metals and alkaline earth metals.
Now go on to the Ionization Energy lesson.
Homework
Review
p. 30 # 3, 4, 7, 8, 12
Which element is the most
reactive? Circle the correct
element in each set below.
(a)
Li, Cs,
K
(b)
N, Sb, P
(c)
Cl, P, Ar, S
(d)
Co, Cs,
Na, Be
(e)
Mg, Ba,
Ca
Which element is the least
reactive? Circle the correct
element in each set below.
(a)
P, Ar,
Cl
(b)
Te, O, Se
(c)
Al, Na, Mg
(d)
As, Kr,
Br, Se
(e)
Cs, Li,
Ca, Ba
