In simple terms just by looking at them, and doing an electrical conductivity test you can tell the following.
the metals are shiny and conduct electricity. The non-metals which are gases or liquids are easy to distinguish. The solid non metals such as sulfur are not shiny and do not conduct electricity. (graphite conducts electricity but is soft and not that shiny). The metalloids look a bit like metals but are very poor conductors of electricity.
Determination of some physical and chemical properties is necessary.
All elements are either metal or non-metal or metalloids.
Scandium is a metal.
gold
To find out whether a substance is a metal, its electrical conductivity, and the acid-base character of its oxides are researched.
Fluoride is neither, it is an ion that cannot exist on its own as a substance because it is electrically charged. Fluorine is a non-metal.
All elements are either metal or non-metal or metalloids.
Scandium is a metal.
gold
An ionic substance, or a salt
diamond
No, because non metal atoms do not enter an excited state.
To find out whether a substance is a metal, its electrical conductivity, and the acid-base character of its oxides are researched.
Fluoride is neither, it is an ion that cannot exist on its own as a substance because it is electrically charged. Fluorine is a non-metal.
Lignite is a non-metallic substance.
CO2 It is a non metal + a non metal the rest are ionic bonds ie metal + non metal
An element that is not a metal is a non-metal (e.g. carbon) or inert gas (e.g. Argon).
You get copper sulphide, because a metal and a non-metal are reacting.