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How is Matter Classified? • Matter is classified using chemical and
physical props.
Pure Substances • a sample of matter that has definite chemical
and physical properties • Elements • Compounds
ATOM • the basic unit of matter • all matter is composed of atoms
ELEMENTS • simplest substances from which more
complex substs. are made • ea. elem. contains single type of atom • 111 diff. elements discovered to date • represented by symbols – usually one or two
letters
1st letter is always capitalized, second letter is always sm. case
• most symbols come from their names • some symbols come from Latin or Greek names • some elem. named in honor of person or place they
were discovered • ea. elem. has its own unique set of chem. and
physical props.
Small number of elements make up most common substs.
• H is most common element • Living things are made primarily of C, H, O,
and N
MOLECULE • neutral group of atoms held together by
covalent bonds • two or more atoms combined in a definite ratio • atoms may be of the same or different elements
Elements may exist as single atoms or as molecules
• Helium gas consists of single atoms (monatomic gas) • Nitrogen gas consists of molecules
• Ea. molec. consists of two nitrogen atoms (diatomic gas)
7 diatomic gases are elements: • Bromine • Iodine • Nitrogen
• Chlorine • Hydrogen • Oxygen • Fluorine
ALLOTROPES • one of a number of different molecular or
crystalline forms of an element • diff. forms of the same element • Oxygen consists of 2 allotropes – O2 and O3
(ozone) • Carbon has many allotropes
• most common are graphite and diamond
• Allotropes have different properties
COMPOUND • the product that results when two or more
different elements are chemically combined
Two types of compounds: • Ionic compounds – consist of positively and
negatively charged ions • ION – an atom or group of atoms w/ an electrical
charge • Covalent compounds – made of neutral
molecules
ACID • a class of compounds whose water solns. taste
sour, turn blue litmus paper red, and react with bases to form salts (ionic compounds)
pH • a numerical scale used to express acidity • 0 to 14 • 7 is neutral
• comps. w/ pH less than 7 are acids • comps. w/ pH greater than 7 are bases
BASE • a class of compounds that taste bitter, feel
slippery in water soln., turn red litmus to blue, and react with acids to form salts
ORGANIC COMPOUNDS • covalent compounds containing carbon
(except carbonates and oxides)
INORGANIC COMPOUNDS • compounds outside the organic family of
compounds
Compounds are represented by formulas
• molecular formula - C12H22O11 (sugar) • ionic formula – NaCl (table salt) • shows numbers of atoms of ea. elem. present in
compound
Structural Formulas • show the exact number of atoms present in a
molecule and how these atoms are bonded to one another • lines represent the bonds betw. atoms
MIXTURE • a collection of 2 or more pure substs.
physically mixed together • proportions can vary • properties can vary
ALLOY • solid mixture (usually mixture of metals)
Two diff. classifications of mixtures:
HOMOGENEOUS MIXTURE • a mixture containing substs. that are uniformly
distributed • solution
• salt water • koolaid • tea • brass (alloy)
• all regions are identical in composition & properties
HETEROGENEOUS MIXTURE • a mixture containing substs. that are not
uniformly distributed • some regions have different properties than other
regions • dirt • granite • choc. chip ice cream • veg. soup • ice water
How mixtures differ from compounds:
• Props. of mixtures reflect props. of components. Props. of compounds do not • reflect. props. of elems. that compose it.
• Comps. have definite composition. Composition of mixtures can vary.
Most mixtures can be separated by physical means. Some mixtures
may need to be separated by chemical means.
• react one component so it can be removed easier
All compounds must be separated by chemical means
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