Composition of Matter Elements, Compound, & Mixtures Chapter 21.4 & 21.5 P 361-363.

Composition of Matter

Elements, Compound, & Mixtures

Chapter 21.4 & 21.5

P 361-363

Pure Substances• Have you ever looked at a picture

and couldn’t tell whether it was a painting or copy? Did you go up and touch it?

• The properties of materials can be used to classify them into categories.

Pure Substances• Materials are either pure substances or a

mixture of substances.

• Pure substances are either an element or compound

Elements• Remember:

– An atom is the smallest piece of matter that still retains the properties of the element.

• All substances are made from atoms.

• If all the atoms in a substance are alike, it is called an element.

Elements• The graphite in your pencil is an

example of an element. – All the atoms in the graphite are carbon

atoms• The copper covering on a penny is

an example of an element.– All the atoms that make up the covering

are copper atoms.• The zinc in the middle of a penny is

an example of an element. – All the atoms that make up your penny

center are made of the element zinc.

Elements

• There are 90 elements found in nature• Over 20 have been made in laboratories

– These are usually unstable and don’t last long

•Some elements you might recognize in your everyday life.

Copper pot or pan

Elements

• How many atoms are bound together in an element is shown by an elemental formula.– Many elements have the basic

unit of one individual atom.• The elemental formula for these

elements is the chemical symbol found on the periodic table

• Example: Gold’s elemental formula is Au

Elements

• Some elements are found in basic units of two or more.– Example: Oxygen’s elemental formula

is O2

• The subscript 2 shows that there are two atoms of oxygen in each molecule of Oxygen

Compounds• Two or more elements can combine to

form a compound• These elements combine in a fixed

proportion – Example: water is a compound in which 2

hydrogen atoms combine with 1 oxygen atom

• Can you imagine putting an explosive silvery metal and a greenish-yellow, poisonous gas on your food??

Compounds

• You may have if you dashed some table salt on your food today!

• Salt is a compound made up of the 2 elements sodium and chlorine

• Like salt, compounds usually look different from the elements in them

Compounds

• A compound is represented by its chemical formula.– The chemical formula is made from the

symbols of the elements that make the compound up.

– Sodium Chloride’s chemical formula is NaCl

• Na is the symbol for Sodium• Cl is the symbol for Chlorine• We will learn how to write these formulas

later.

Mixtures

• Who enjoys eating pizza and pop for lunch?

• If so, then you enjoy 2 foods that are classified as mixtures

• A mixture, such as pizza or pop, is a material made up of two or more substances that can be easily separated by physical means.

Mixtures

Heterogeneous Mixtures:• Unlike compounds, mixtures aren’t

always made of the same proportions of the substances that make them up.

• Remember that pizza? The chef doesn’t measure out precisely how much of each topping is sprinkled on. Plus, you can easily see most of the toppings on the pizza

• A mixture in which different materials can be seen easily is called a heterogeneous mixture

• Other examples: granite, dry soups, concrete

Suspensions• A suspension is a mixture that will

separate if left undisturbed– The particles can be seen “suspended”

in the suspension• Example: Sand in water – the sand does not

dissolve in water– The sand is able to separate from the water

over time.– The sand can “settle”

– Particles are large• Light can not be shown through a

suspension– Suspensions “scatter” light

Mixtures

Homogeneous Mixtures:• Remember that pop? It’s an example

of a homogeneous mixture• A homogeneous mixture contains 2

or more substances blended evenly throughout

• There are three special types of Mixtures:– Solutions, Suspensions, and Colloids

Solutions• Solutions are mixtures that do not

separate if left undisturbed.– The particles are dissolved into the

liquid.• Example: Salt Water- when salt is

dissolved in water the water and salt will not separate if left undisturbed.

• The salt does not “settle”– The salt is the solute– The Water is the solvent

• Particles are small

• Light can be shined right through a solution– Does not scatter light

Colloids• A colloid is a type of mixture that

never settles

• Its particles are larger than those in solutions but not heavy enough to settle

• Examples: Milk, paint, fog

ColloidsDetecting Colloids:• To tell for certain if a liquid is a colloid, pass a

beam of light through it• A light beam is invisible as it passes through a

colloid, but can be seen when passing through a solution

• This occurs because the particles in a colloid are large enough to scatter light

• The scattering of light by colloidal particles is called the Tyndall effect

• Can you think of any other colloids?

Element, Compound, Mixture

Properties of Matter

Section 2

p. 526-533

Physical properties• Physical properties are

observations that you make without changing the identity of the substances that make up the material

• For instance, you can stretch a rubber band or bend a piece of wire

• The ability to stretch or bend are physical properties

• Some other physical properties are color, shape, size, melting point, and boiling point

Physical Properties

• Appearance:• How would you describe a tennis

ball? (shape, color, state of matter)• How would you describe a soft

drink? (color, state of matter, taste)

• You could also measure its volume and temperature—these are all physical properties

Physical Properties• Behavior:• Some physical properties

describe the behavior of a substance

• For instance, objects containing iron (I.e. safety pins) are attracted by a magnet

• Remember that soft drink? If you were to knock it over, it would spread onto the table and floor—the ability to flow is a physical property of liquids

Physical Propertiesto Separate

• Have you ever licked the icing from the middle of a sandwich cookie?

• If so, then you’re using physical properties to identify the icing and separate it from the rest of the cookie

• You can use other physical properties to separate such as using a sifter to separate poppy seeds from sunflower seeds

• Or sand from iron fillings by using a magnet

Physical Change

• If you break a piece of gum, you change some of its physical properties—shape and size

• However, you haven’t changed the identity of the materials that make up the gum

• Each piece still tastes and chews the same

Physical Change

• A physical changephysical change is any change in size, shape, or state of matter

• These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change!

Physical Change

So, does a change in state mean that a new substance has formed?

Physical Change to Separate• In some parts of the world, water is

very scarce, many such areas lie near the sea

• They obtain their drinking water by using the physical property of boiling point to separate the the salt from the water

• This process is called distillation• In distillation, you use an apparatus

to vaporize and condense liquid, leaving the solid material behind

Chemical Properties

• Have you ever seen the warning labels on paint thinners and lighter fluids that read “FLAMMABLE”

• Flammability is a chemical property

• Burning produces new substances during a chemical change

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