chemistry chapters 2-8 chapter 2: properties of matter

CHEMISTRYCHEMISTRY

Chapters Chapters 2-82-8

CHAPTER 2:CHAPTER 2:PROPERTIES OF MATTERPROPERTIES OF MATTER

04/20/23 Chapter 2 Properties of Matter 2

CLASSIFYING MATTER Matter - Anything that takes up space and

has mass

Based on their compositions, materials can be

divided into pure substances and mixtures.


PURE SUBSTANCES (BOX 1) pure substance (or simply a substance) -

matter that always has exactly the same composition

Fixed, uniform composition every sample has same properties.

Can be classified into 2 categories:

elements and compounds


ELEMENTS (BOX 2) Millions of known substances, but only about

100 elements.

Element - substance that CANNOT be broken down into simpler substances

Only 1 type of atom fixed composition

No 2 elements contain

same type of atom


ELEMENTS At room temperature (20°C, 68°F, 300K)

most are solids

some are gases

(i.e. oxygen & nitrogen)

only 2 are liquids,

bromine and mercury


ELEMENTS 1813, Jons Berzelius suggested

use of symbols to represent elements.

Helps scientists to communicate without confusion


ELEMENTS 1 or 2 letters: 1st capitalized, 2nd not

Some based on Latin names

Symbol for gold is Au because Latin name for gold is aurum

Sometimes name gives clue to properties

hydrogen from Greek words hydro (water) and genes (forming)


COMPOUNDS (BOX 3) compound - substance that is made from two

or more simpler substances and CAN be broken down into those simpler substances

Simpler substances are

either elements or compounds.


COMPOUNDS (BOX 3) Always contains 2 or more elements joined in a

fixed proportion.

Properties of a compound differ from those of the substances from which they are made.


COMPOUNDS (BOX 3) Example: Water (H2O)



Compound of 2 elements hydrogen (H) and oxygen (O)

H H

O



H2 & O2 both gases at room temperature

H2 can fuel a fire & O2 can keep a fire burning

H2O does not burn or help other substances burn.

Water decomposes into its component elements, hydrogen & oxygen, when direct electrical current is passed through it. Volume of hydrogen (right) is twice the volume of oxygen (left).


Example: silicon dioxide (SiO2)

Always 2 O atoms for each silicon (Si) atom

O colorless gas Si gray solid

Compound found in most light-colored grains of sand

COMPOUNDS

SiO2 is a colorless, transparent solid


MIXTURES - (Box 4) Matter that doesn’t always have the same

composition

Tend to retain some of properties of their individual substances.


MIXTURES (Box 4) The properties of a mixture can vary because

the composition of a mixture is not fixed.


MIXTURES (Box 4)

No matter how well you stir, substances that make up mixture will not be evenly distributed.

Can be classified by how well parts are distributed throughout mixture. Homogeneous Heterogeneous


homogeneous mixture - substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another

Appears to contain only one type of substance

Example: swimming pool water:

H2O + substances that dissolve in water

MIXTURES: HOMOGENEOUS (BOX 5)


Greek words hetero (“different”) and genus (“kind”)

heterogeneous mixture - parts of the mixture are noticeably different from one another

MIXTURES: HETEROGENEOUS (BOX 6)


MIXTURES: HOMOGENEOUS & HETEROGENEOUS


Stainless steel serving spoon is a homogeneous mixture of iron, chromium, and nickel. It is difficult to distinguish one substance from another.

MIXTURES: HOMOGENEOUS


Sand is a heterogeneous

mixture. It is not the

same throughout.

MIXTURES: HETEROGENEOUS


Matter

mixturespure

substances

compoundselements homogeneous heterogeneous

Anything that takes up space & has mass


Matter

mixturespure substances

compoundselements homogeneous heterogeneous

Anything that takes up space & has mass

Matter that always has exactly the same composition

substances that CAN’T be

broken down into simpler substances.

Matter that doesn’t always have the same composition

substances made from 2 or more simpler substances &

CAN be broken down.

even distribution difficult to

distinguish one substance in the

mixture from another.

parts of the mixture are noticeably

different from one another.


ELEMENTS, COMPOUNDS, AND MIXTURES

(a)an element(hydrogen)

(b)a compound

(water)

(c)a mixture(H & O)

(d)a mixture(H & O)

Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 68

hydrogenatoms hydrogen

atoms

oxygen atoms


Chart Examining Some Components of Air

Nitrogen consists of molecules consisting of two atoms of nitrogen:

Oxygen consists of molecules consisting of two atoms of oxygen:

Water consists of molecules consisting of twohydrogen atoms and one oxygen atom:

Argon consists of individual argon atoms:

Carbon dioxide consists of molecules consistingof two oxygen atoms and one carbon atom:

Neon consists of individual neon atoms:

Helium consists of individual helium atoms:

N2

O2

H2O

Ar

CO2

Ne

He

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 35


The size of the particles in a mixture has an effect on the properties of that mixture.

Key Concept: Based on the size of its largest particles, a

mixture can be classified as a solution, a suspension, or a colloid.

SOLUTIONS, SUSPENSIONS, AND COLLOIDS


Solution - mixture that forms when substances dissolve and form a homogeneous mixture

Example: Sugar dissolved in water

Spoonful of sugar in a glass of hot water & stir, the sugar dissolves in the water homogeneous mixture of sugar & water.

SOLUTIONS


Properties of liquid solutions: Particles small so… do not separate into distinct layers over time. none of the substances in the solution are

trapped in the filter. can see through because light passes through

them without being scattered in all directions.

Particles in a solution are too small to settle out of the solution, be trapped by a filter, or scatter light.

SOLUTIONS


Suspension - heterogeneous mixture that separates into layers over time

Examples: sand mixed with water

SUSPENSIONS


Properties of a suspension: Because suspended particles are large… suspended particles settle out of mixture

(form layers) can use a filter to separate out suspended

particles can scatter more light in all directions (cloudy)

SUSPENSIONS


Colloid - contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension

i.e.: homogenized milk, fog (water droplets in air)

COLLOIDS


Properties of a colloid: does not separate into layers can’t use a filter to separate the parts scatters light (cloudy, opaque)

COLLOIDS

Key Concepts for Solutions, Suspensions & Colloids

Properties of liquid solutions: Particles small so… Particles will not separate into layers over

time.

None of the substances in the solution can be trapped in a filter.

Can see through the solution because light passes through them without being scattered in all directions.



Properties of a suspension: Because suspended particles are large… Suspended particles settle out of a mixture

(Parts WILL separate).

CAN use a filter to separate out suspended particles.

Can scatter more light in all directions (cloudy)



Properties of a colloid: Does NOT separate into layers.

Can not use a filter to separate the parts.

Scatters light (cloudy, opaque). The light will be reflected by the larger particles in a colloid.


chemistry chapters 2-8 chapter 2: properties of matter

Documents