Final answer:
The alkali metals, including lithium, sodium, potassium, rubidium, cesium, and francium, are placed in Group 1 because they all have similar properties. Hydrogen is also placed in Group 1 because it shares some similar properties with the alkali metals.
Step-by-step explanation:
The alkali metals, including lithium, sodium, potassium, rubidium, cesium, and francium, are placed in Group 1 of the periodic table because they all have similar properties. They are soft, shiny, and highly reactive metals. While hydrogen is not a metal, it is placed in Group 1 because it shares some similar properties, such as having one electron in its outer shell, like the alkali metals.