3.1 The Periodic Table

Syllabus

What does this mean?

History

The IB doesn’t often ask questions about Science History directly.

But they could, so you should be familiar with the general ideas.

Johann Dobereiner

· Noticed groups of three elements with similar properties.

· He called them Triads.

· He noticed that the Atomic Weight of the “middle element” was approximately the average weight of the other two.

John Newlands

· Placed elements in order of weight and noticed properties repeated every eighth element.

· Called this the Law of Octaves

· But the law breaks down after the first few Periods

Dimitri Mendeleev

· Placed elements in order of weight and repeating properties

· Left gaps in table for undiscovered elements

· Predicted properties of undiscovered elements accurately

Mendeleev - Gandalf in disguise

Henry Moseley

· Put elements in order of Atomic Number, correcting some problems with Mendeleev’s table.

The Modern Periodic Table

Elements in a Group should share chemical properties – react similarly

British textbooks tend to label the Groups on the Periodic Table 1-8 (or 1-7 then 0).

This tells you how many electrons are in the outside shell.

But it ignores the entire d-block (or Transition Metals) in the middle.

The IB prefer Group 1-18

They also expect you to know the common names for some groups

Group 1 = ______________________________________

Group 2 = ______________________________________

Group 15 (5) = __________________________________

Group 16 (6) = __________________________________

Group 17 (7) = __________________________________

Group 18 (8) = __________________________________

The Modern Table #2

Elements in a Period do not share chemical properties.

In fact, chemical properties in every period slowly change from metals on the left side of the table to non-metals on the right, with semi-metals (metalloids) between)

But elements in same period have the same number of shells or energy levels.

Rb and Xe have 5 shells, for example.

Metals, Non-metals, Metalloids.

British students would/should have a working knowledge of the different properties of metals and non-metals from Year 8 onwards.

Blocks on the Periodic Table.

You’ll rarely deal with any elements with Atomic Numbers beyond 50.

So most elements are either Main-Group elements (s-block and p-block) or Transition Elements (d-block).

s, p d, and f are the names of the sub-levels (or sub-shells) within energy levels from Topic 2

f-block elements exist but are mainly man-made, so we usually tuck them out of the way at the foot of the table

But that’s only because putting them in a more realistic place makes the table rather unwieldy.

The top row of the f-block are Lanthanoids (starting with Lanthanum)

The bottom row of the f-block are Actinoids (starting with Actinium)

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