how is matter classified? matter is classified using chemical and physical props

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