b
The table has seven rows and 18 columns. Each row represents one period; the period number of an element
indicates how many of its energy levels house electrons. Sodium, for instance, sits in the third period, which
means a sodium atom typically has electrons in the first three energy levels. Moving down the table, periods
are longer because it takes more electrons to fill the larger and more complex outer levels.
The columns of the table represent groups, or families, of elements. The elements in a group often look and
behave similarly, because they have the same number of electrons in their outermost shell — the face they
show to the world. Group 18 elements, on the far-right side of the table, for example, have completely full
outer shells and rarely participate in chemical reactions.
DOWN A GROUP- Electrons are further from nucleus (more shielding) less controlled by nucleus
ACROSS A PERIOD-More electron are being added to the same shell: so tighter control
Metal reactivity increases down a group (easier to lose e-)
Non-metals are also more likely to react in a way as to hold on to e-
Group A- elements are sometimes called the
representative elements because they exhibit the
full range of chemical properties
Group B - these are the transition elements - elements
that are filling their d orbitals and display a range of
stable and reactive cation states