Arrangement of Elements

In the modern periodic table, the horizontal rows are called periods, and the vertical columns are called groups. The arrangement of elements is based on their structure and properties.  

Group 0 Elements

The elements in Group 0 are called noble gases. E.g. Helium, Neon, Argon

• Group 0 elements have an entire outer shell and are unreactive.
• They exist as single atoms and do not form molecules. 
• Their boiling points increase down the group.
• Group 0 is located on the far right of the periodic table.

Group 1 Elements

The elements in Group 1 are called alkali metals as they react with water to form an alkali. 

• When group 1 elements react with water, they form metal hydroxide (alkali) and hydrogen.
• They also react with chlorine and oxygen to form chlorides and oxides. E.g. Sodium, Potassium, Lithium.
• The elements in Group 1 have only one electron in their outermost shell and are very reactive.
• The reactivity of alkali metals increases down the group. This is because these atoms are more significant, resulting in the outermost electron being farther away from the nucleus. As a result, there are weaker electrostatic forces of attraction and more shielding between the nucleus and outer electron, which makes it easier to lose the electron.
• The melting and boiling points decrease as you move down the group.
  

Group 7 Elements

The elements in Group 7 are called halogens. These non-metallic elements exist as diatomic molecules consisting of pairs of atoms. E.g., fluorine, chlorine, bromine, and iodine.

• The reactivity decreases down the group. This happens because the atoms increase in size, and the outer shell is further away from the nucleus. Additionally, more shells are between the nucleus and the outer shell, which means the electrostatic attraction from the nucleus to the outer shell is weaker. As a result, it becomes harder to gain the one electron needed to fill the outer shell.
• Their melting and boiling points increase down the group.
• They have seven electrons in their outer shell.
• Group 7 elements readily combine with metals to form ionic compounds known as metal halides.
  

Displacement

A displacement reaction occurs when a more reactive element replaces a less reactive element in a compound. For example, when potassium chloride reacts with fluorine, the more reactive fluorine displaces the less reactive chlorine, forming potassium fluoride and releasing chlorine gas. These reactions can be used to investigate the reactivity of metals and extract metals from metal oxides.