Matter and Its Interactions
Matter is made of particles
All matter has mass and takes up space, and it is made of particles far too small to see. The particles are invisible, but their effects are not: sugar seems to vanish in water yet the water tastes sweet, a balloon gets heavier when you inflate it, and the smell of a candle crosses a room. Air is matter, so it has mass even though you cannot see it.
Conserving matter
In a closed system, the total mass before a change equals the total mass after. Traps appear when a gas escapes. Vinegar and baking soda in an open cup seems to lose mass, but the same reaction in a sealed bag or a balloon-topped bottle gives the same reading on a balance. Rusting and burning conserve matter too: the extra mass joins with oxygen from the air, or matter leaves as smoke and gas.
Identifying and combining materials
Materials are identified by properties such as density, magnetism, solubility, conductivity, melting point, hardness, and reaction to acid. A big piece and a small piece of the same metal have the same density but different mass, so “heavier” alone never identifies a material.
When two substances are mixed, the result may be a simple mixture that can be separated by filtering, sieving, evaporating, or using a magnet. Or a new substance may form, shown by a gas, a color change, a new smell, or heat. Heating and cooling that only change state - ice to water - are reversible and make no new substance.