2. Compounds are combinations of two or more different elements bound in fixed proportions. B The building blocks of matter are atoms, ions, and molecules. 1. An atom is the smallest unit of matter that exhibits the characteristics of an element. a. Each atom consists of subatomic particles. They are the positively charged protons, uncharged neutrons, and negatively charged electrons. b.Each atom contains a nucleus of the subatomic particles. 1)Each element has an atomic number that is equal to the number of protons in the nucleus of its atom. 2)The mass number of an atom is the total number of neutrons and protons in its nucleus. 3)Isotopes are forms of an element that have the same atomic number, but different mass numbers. 2. An ion is an electrically charged atom or combinations of atoms. a. The charge of an ion is noted by superscript beside the symbol for that atom. 3. A molecule is a combination of two or more atoms/ions of elements held together by chemical bonds. C Chemical formulas are a type of shorthand to show the type and number of atoms/ions in a compound. 1. Each element in the compound is represented by a symbol (e.g., H = hydrogen, N = nitrogen). 2. Subscripts show the number of atoms/ions in the compound. D Organic compounds contain carbon atoms combined with one another and with various other atoms. Only methane (CH 4 ) has only one carbon atom. 1. Hydrocarbons: compounds of carbon and hydrogen atoms. 2. Chlorinated hydrocarbons: compounds of carbon, hydrogen, and chlorine atoms. 3. Simple carbohydrates: specific types of compounds of carbon, hydrogen, and oxygen atoms. 4. All compounds without the combination of carbon atoms and other elements’ atoms are inorganic compounds. 2-3 How Can Matter Change? Chapter 2 11
A Matter undergoes physical, chemical, and nuclear changes. 1. Physical change is a change that does not alter a samples chemical composition, but chemical changes reorder the arrangement of atoms, ions, or molecules in the sample. B The law of conservation of matter: 1. We can never destroy the atoms involved in a physical or chemical change; just rearrange them in different patterns or combinations. C The law of conservation of matter states that no atoms are created/destroyed during a physical or chemical change. The same is true for energy. 1. Atoms are rearranged into different patterns/combinations. 2. Atoms can have physical or chemical changes but they are never created/destroyed.
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