Matter – Properties & Changes (Physical & Chemical) E42 – E57

Physical Properties of Matter Marbles, bicycles, and trees are all made of matter, they have mass and take up space. Rainbows and sound are not made of matter. Marbles, bicycles, and trees are very different objects. They have different physical properties. Physical properties – properties that can be observed or measured without changing an object, or any of the materials it is made of, into something else.

cont. Every substance has physical properties that can be used to identify it. Some properties can change – mass and size. Other properties never change – color, smell, attraction to magnets, and melting and boiling points. Whether you have a tiny iron pin or a huge iron beam, the iron will be the same color, attracted to magnets and will have to same melting and boiling points.

Observable Physical Property Texture – how the surface feels; rough, smooth, waxy or powdery. Malleability – the ability of a substance to be bent without breaking. Ductility – the ability of a substance to be pulled into thin threads without breaking. Brittle is the opposite of being malleable or ductile. Buoyancy – the ability to float on a liquid or rise in a gas.

Measurable Physical Properties Mass & Volume: These are physical properties that can be measured. They vary depending on the amount of the substance. Density – the amount of mass that fits in a given volume. Use the formula mass ÷ volume.

Density of Common Substances SubstanceDensity (g/cm 3 )Buoyancy Helium floats in pure water Air0.001floats in pure water Wood0.5floats in pure water Olive Oil0.9floats in pure water Pure water1.0 Diamond3.5sinks in pure water Lead11.3sinks in pure water Mercury13.6sinks in pure water

Physical Change When a substance goes through physical change, the physical properties may change, but it does not become a different substance. Cutting up a sheet of paper into hundreds of pieces, digging a hole in the ground, or an eroding cliff, where rocks fall into the ocean. The atomic structure has stayed the same. Rolling, bending and shaping does not change it. (malleability and ductility) The changes are in shape, size and number.

Chemical Reactions In chemical change, new substances have been formed. A cracked open egg vs. a cooked egg. The cooked egg changes color, a good indication of a chemical change. The atomic structure of the egg has been rearranged due to the cooking process.

Chemical Changes They require absorbing energy or releasing energy. A reaction that absorbs energy is endothermic. A reaction that releases energy is exothermic. Much of the energy in everyday life comes from burning substances such as wood, oil, coal, gasoline, and natural gas. The chemical changes in the burning produce our energy.

cont. Changes can produce light, sound, smoke, a new color, or a new smell, but the true test for whether or not a chemical change has occurred, is whether or not a new substance was formed.

Chemical Properties The properties of a substance determine what kind of change it can go through. Combustibility – the ability to burn; wood, paper, charcoal. Their atoms rearrange when they come into contact with new atoms. Reactivity – they explode when exposed to air or water. The atoms in the first column of the periodic table are very reactive metals. Stability – go through chemical changes very slowly. They rarely react with anything at all. Atoms in the far right column of the periodic table have stability. They are called Noble Gases.

Types of Reactions Combustion (exothermic) – when they combine with oxygen; they burn and give off heat and light. They become much more complex substances. Decomposition – a substance is broken down into simpler substances. Double Replacement – when they exchange ions with each other to make a new substance.

Preventing Chemical Change Helium (Noble Gas) surrounding history documents; Declaration of Independence Modern books are printed on paper with no acids – replaced with bases Dim lights Using paint as a seal on metal to prevent corrosion and weakening Refrigeration and freezing food - slows growth of bacteria Preservatives added to food, plastics, oil and gasoline