Final answer:
Metals have a higher density than water due to their closely packed atoms with higher atomic masses. However, a steel needle can float on water due to water's surface tension, which holds it up like a skin when it is laid carefully across the surface.
Step-by-step explanation:
The density of a metal is greater than the density of water because metals are made up of atoms that have a higher atomic mass and are packed closely together, resulting in a higher mass per unit volume. Despite being denser, a steel needle or paper clip can float on the surface of still water due to the surface tension of water. At the molecular level, the cohesion between water molecules creates a sort of 'skin' at the surface, which is strong enough to support small objects that are carefully placed on it without breaking this surface layer.
Furthermore, objects that have a density less than water float, while denser objects like metals typically sink. However, the shape of an object can influence buoyancy too. A lump of clay sinks in water, but shaped into a boat, it floats because it displaces more water and experiences greater buoyant force, according to Archimedes' Principle. This concept does not directly apply to the floating needle example but illustrates how shapes can affect floating and sinking.