lecture1 - 1 Introduction: Matter and Measurement 1.1 The...

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1 1 Introduction: Matter and Measurement 1.1 The Study of Chemistry 1. What is Chemistry? Chemistry is the study of the composition, structure, properties, and changes of matter at molecular level . Matter is anything in the universe that has mass and occupies space. Matter is described by its properties. A Property is any characteristic that allows us to recognize a particular type of matter and to distinguish it from other types. 2. Why Chemistry?
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2 1.2 Classifications of Matter 1. Three (physical) States of Matter A Gas (also known as vapor) takes the volume of the container A liquid has fixed volume but takes the shape of container A solid has a fixed volume and shape 2. Pure Substances A pure substance is a matter that has distinct properties and a composition that does not vary from sample to sample. There are two kind of pure substances: elements and compounds A. Elements: The simplest pure substance is an element, which cannot be further broken down into simpler substances. Each element is composed of one and only one kind of atom. Elements are denoted by one or two letter symbols, of which the first letters are always capitalized. (*only the first letters) All the 117 currently known elements and their symbols are listed in Periodic Table. The abundances of elements vary widely. Oxygen is the most abundant one in the Earth’s crust and human’s body.
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3 B. Compounds : A compound is a pure substance that contains two or more atoms. • The composition of any given compound, regardless of its souces, is the same. E.g., the composition of water: 11% H and 89% O by mass. (Why sea water and lake water taste so different?) Law of constant composition (or Law of difinite composition ): The elemental composition of a pure compound (either by the # of atoms or by mass) is always the same. • Keep in mind: the properties of a compound is totally different from those of the make-up atoms. E.g., H 2 +O 2 H 2 O • Most pure substances are compounds. (Q: How can you approve H 2 O is a compound not an element?)
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3. Mixtures : Two or more pure substances mix together to form a mixture . – The substances making up a mixture are called the components of the mixture. – Each component in a mixture maintains its own chemical properties . – Mixtures may have variable composition. – Mixture can be either homogeneous or heterogeneous. Homogeneous mixtures are called solutions. Solutions can be gas (air), liquid (seawater) or solid (white gold ring). Q: Why sea water and lake water taste so different? classification of matter Matter Uniform throughout? Heterogeneous Homogeneous Have a variable composition? Pure Substance Solution (Homogeneous Solution) Be separated into simpler substances? Element
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lecture1 - 1 Introduction: Matter and Measurement 1.1 The...

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