AP BIO CH.2 - I Matter consists of chemical elements in...

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I. Matter consists of chemical elements in pure form and in combinations called compounds A. Elements and Compounds 1) Matter is anything that takes up space and has mass 2) An element is a substance that can’t be broken down to other substance by chemical reactions. 3) A compound is a substance consisting of two or more different elements combined in a fixed ratio. It has characteristics different from those of its elements. B. Essential Elements of Life 1) Trace elements are those required by an organism in only minute quantities. Some trace elements are needed by all forms of life, others are required only by certain species. 2) An iodine deficiency in the diet causes the thyroid gland to grow to abnormal size, a condition called goiter. II. An element’s properties depend on the structure of its atoms A. Subatomic Particles 1) The atom is the smallest unit having the properties of its element, these tiny bits of matter are composed of even smaller called subatomic particles. 2) Neutron and Proton are packed together tightly to form a dense core, or atomic nucleus, at the center of the atom. 3) Electron and protons are electrically charged. Each electron has one unit of negative charge, each proton has one unit of positive charge. B. Atomic Number and Atomic Mass 1) Atomic number is the number of protons, which unique to the element. It’s written as a subscript to the left of the symbol for the element. 2) Mass number is the sum of protons plus neutrons in the nucleus of an atom. It’s written as a superscript to the left of an element’s symbol.
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