Columns in the periodic table are called groups, while rows are called periods. Groups are organized in such a way that they have similar properties, one being that they have the same number of valence electrons.
But first, let's back up a little. What is a valence electron? We learned before that each element is defined by an exact number of electrons. These electrons are divided into energy levels. Each element in a period is in the same energy level. Once one energy level is filled, we move onto the next period on the table. Electrons fill from the lowest energy level to the highest.
For most elements, the highest energy level is not filled completely. The electrons in the highest energy level of an element are called valence electrons.
If we go back to our previous diagram of the atom, Boron has 3 electrons in its outermost shell, therefore it has 3 valence electrons. We will discuss more detail about energy levels and electrons later.
These are the electrons that usually define the properties of an element. Elements in the same group have the same number of valence electrons, hence they react in similar ways. This changes slightly in the transition metals, which we will learn more about later.
o All have relatively low boiling and melting points compared to most metals
o Very soft and can be easily cut through with a knife
o Reacts very quickly with water
o Low densities
o Has one valence electron
o Similar to Alkali Metals except slightly not as reactive
o Has two valence electrons
o Generally hard and dense
o Less reactive than the metals of Group 1 and 2
o Form colored compounds
o Good conductors of heat and energy
o Malleable
o High densities
o Generally hard and dense
o Less reactive than the metals of Group 1 and 2
o Form colored compounds
o Good conductors of heat and energy
o Malleable
o High densities
o Oxidizes rapidly in moist air
o Dissolves quickly in acids
o In room temperature, reaction with oxygen is very slow, but at 150-200 degree Celsius, they will ignite
o React with halogens upon heating
o All radioactive
o Oxidizes readily
o Very dense with distinctive structure
o As you move down the group, the elements become increasingly more metal-like, ending with Polonium which is essentially a metal
oHave six valence electrons
o Usually become ions with a 2- charge
o Highly reactive
o Can never be found alone as one atom in nature
o Reacts with metals to create salts
o Only group that includes elements that can exist in 3 states of matter at once in room temperature
o Have seven valence electrons
o Very unreactive/stable atom
o Has a complete valence electron shell
o Low boiling points
o No color, odor, or flavor under ordinary conditions
o Nonflammable