Fisica

Properties of matter (chapter 2)
2.1 Classifying matter
A pure substance is matter that always has the same composition. Some examples are table salt and table sugar . Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. Substances are classify as elements or compounds.
An element is a substance that cannot be broken down intosimpler substances, there are only about 100 elements. And atom is the smallest particle of an element. An element has a fixed composition because it contains only one type of atom. Chemists use symbols to represent elements, each symbol has either one or two letters.
A compound is a substance that is made from two or more substances and can be broken down into those simpler substances. Alwayscontains two or more elements joined in a fixed proportion.
Mixtures tend to retain some of the properties of their individual substances. The properties of a mixture can vary because the composition of a mixture is not fixed. There are 2 types of mixtures:
1. Heterogeneous mixture: the parts of this mixture are noticeably different from one another.
2. Homogeneous mixture: the substances are soevenly distributed that it is difficult to distinguish one substance in the mixture from another.
Based on the size of its largest particles, a mixture can be classified as a solution, a suspension or a colloid
a) Solutions: when substances dissolve and form a homogeneous mixture
b) Suspensions: is a heterogeneous mixture that separates into layers over time
c) Colloids: contains someparticles that are intermediate in size between the small particles in the solution and the larger particles in a suspensions.
2.2 Physical properties
A physical property is any characteristic of a meterial that can be observed or measured without changing the composition of the substances in the material. Some examples are viscosity, conductivity, malleability, hardness, mealting point, boiling pointand density.
*Viscosity is the tendency of a liquid to keep from flowing ( is resistance to flowing). Usually decreases when it is heated.
*Conductivity is the material's ability to allow heat to flow. Materials that have a high conductivity are called conductors.
*Malleability is the ability of a solid to be hammered without shattering. One example is gold.
*Hardness
*Melting point isthe temperature at which a substance changes from solid to liquid
*Boiling point is the temperature at which a substance boils
Density is used to test the purity of a substance. Is the ratio of the mass of a substance to its volume
Physical properties are used to identify a material, to choose a material for a specific purpose or to separate the substances in a mixture. Some commonseparation methods are filtration and distillation.
Filtration: process that separates materials based on the size of their particles
Distillation: process that separates the substances in a solution based on their boiling points.
A physical change occurs when some of the properties of a material change but the substances in the material remain the same , some can be reversed.
2.3 Chemicalproperties
A chemical property is any ability to produce a change in the composition of matter. Chemical properties can be observed only when the substances in a sample of matter are changing into different substances. Two examples are:
Flammability: material'sability to burn in the presence of oxygen. Sometimes is not a desirable property.
Reactivity: property that describes how readily a substancecombines chemically with other substances.
A chemical change occurs when a substance reacts and form one or more substances. Three common types of evidence for a chemical change are a change in color, the production of a gas and the formation of a precipitate (precipitate is any solid that forms and separates from a liquid mixture. When matter undergoes a chemical change the composition of...