Group 1 Elements: The Alkali Metals
Nomenclature and Identity
Group name: The elements in Group 1 of the periodic table are called alkali metals. They got this name because when they react with water, they form alkaline (basic) solutions.
Member elements: This group includes six elements: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). All of them are metals and show similar properties because they are in the same group.
Electronic Configuration
Valence electron: All alkali metals have one electron in their outermost energy level, also called the valence shell. This single electron plays a big role in how the element reacts with other substances.
Ease of loss: Because there’s only one electron in the outer shell, it’s very easy for the atom to lose it during a chemical reaction. Losing this electron makes the atom more stable, forming a positively charged ion.
Chemical Reactivity
High reactivity: Alkali metals react very quickly and strongly with other substances, especially with oxygen in the air and water. Some of these reactions can even produce flames or explosions!
Not found pure: Since they react so easily, alkali metals are never found alone in nature. Instead, they are always part of compounds with other elements.
Trend in reactivity: As you go down the group from lithium to francium, the metals become more reactive. That’s because the outer electron is farther from the nucleus and easier to remove.
Physical Properties
Soft texture: These metals are so soft that you can actually cut them with a knife, which is unusual for metals.
Low melting/boiling points: Compared to other metals, alkali metals melt and boil at lower temperatures. This means they can turn into liquids or gases more easily.
Low density: Some alkali metals, like lithium, sodium, and potassium, are less dense than water, so they can float on it.
Good conductors: Even though they are soft, alkali metals can carry heat and electricity very well, which is a common feature of metals.
Silvery appearance: When you cut them open, they have a shiny, silvery surface. But this shiny look doesn’t last long because they quickly react with oxygen in the air and turn dull.
Increasing atomic size: As you move down the group, each element has more electron shells. This makes the atoms bigger in size from lithium at the top to francium at the bottom.
Reactions with Air, Oxygen, and Chlorine
Air reactions: When exposed to air, alkali metals quickly react with the oxygen and moisture. This forms substances like metal oxides and metal hydroxides.
Oxygen reactions: In pure oxygen, these metals form metal oxides such as lithium oxide (Li₂O), sodium oxide (Na₂O), and so on.
Chlorine reactions: Alkali metals also react with chlorine gas to produce white salts called metal chlorides. For example, sodium reacts with chlorine to form sodium chloride (NaCl), which is common table salt.
Exothermic nature: All these reactions release a lot of heat, which makes them exothermic. That’s why some of these reactions can look fiery or explosive.
Trends in Properties Down the Group
Reactivity trend: As you go down Group 1, the metals get more reactive. This is because it becomes easier for the atoms to lose their one valence electron.
Atomic size trend: The size of the atoms gets larger down the group because new electron shells are added as the atomic number increases.
Melting/boiling trend: The temperatures needed to melt or boil these metals go down as you move from lithium to francium. So the lower elements in the group melt and boil more easily.
Density trend: The density of alkali metals generally increases as you move down the group. This means the lower elements are heavier for their size.