Classifying Matter

Consider…

• Consider for a moment your dresser in your room.

• Mentally draw out your dresser, label all drawers….

• Your clothes tend to be organized into specific drawers. We find that it is easier to find a common thing between them and place them in the same drawer.

• Matter can be sorted in a similar fashion, where we put things in organized “drawers”.

Pure Substances

• a substance that contains only one type of matter. This may be broken into elements and compounds (like single socks and pairs, they both go in the sock drawer).

Pure Substances

• Element a group of one type of atom

Ex. Carbon in your pencil (C)

Oxygen in a diving tank (O2)

• Compounds a group of chemically bonded atoms that are different

Ex. Water in a jar (H2O)

Carbon dioxide in air (CO2)

** Atoms will always bond in the same ratio constant composition… H2O always has 2 hydrogen atoms and 1 oxygen atom

Mixtures

• If the matter is not pure it is called a mixture. Mixtures can be combinations of solids, liquids and gases.

Ex. Pop water, sugar, carbon dioxide

liquid, solid, gas

• Mixtures can be broken into 2 groups Homogeneous, and Heterogeneous mixtures

Homogeneous Mixtures and Solutions• are mixtures with only one visible phase that is you can only see one component.

• Ex. Cherry Kool-Aid the crystals are dissolved into the water and the solution appears as a single red liquid.

Solutions – a note…

• **A solution has two components

• a solute, which is the substance that is being dissolved

• And…

• the solvent, which is the substance that is dissolving the solute.

• In the Kool-Aid example, the crystals are the solute and water is the solvent.

Heterogeneous Mixtures

• have more than one visible phase.

Ex. Salad dressing –can see the oil and vinegar phases

• Heterogeneous mixtures can be broken down further into suspensions, colloids, or emulsions –they seem like one phase but will settle out if given time

Suspension

• the small particles are barely visible with the eye, and if left undisturbed the suspended particles will eventually settle out.

• Many of the products in your fridge that instruct you to shake well before use are suspensions; the shaking causes the particles to become suspended.

• For example if tomato juice is left for a long period of time, it will develop two layers as the tomato settles to the bottom.

Colloids

• contain suspended particles that are so small they do not settle out.

• Example: In fog the water droplets are not small enough to be dissolved by the air, and they are not large enough to fall as rain droplets.

Emulsions

• a type of colloid in which tiny liquid droplets are mixed into another liquid.

• Milk is an example of an emulsion in which drops of cream are mixed with water.

• ** In order to tell the difference between a solution and a colloid, you could shine a light through the solution; if the light is scattered it is a colloid. This is called the Tyndall Effect

Pure Substancecontains only one type of matter

MixturesCombination of matter

(s, l, g or combo)

Compounds1 or more type of atoms

combined chemically.

Elements1 type of atom

Matter

HomogeneousOne phase: looks the same

throughout.

HeterogeneousTwo phases: has two or more

visible parts.

Suspension

Colloid

Emulsion

Classifying Matter Task

• Complete the questions in the worksheet.

Models of the Atom

a Historical Perspective

Aristotle

Early Greek Theories• 400 BCE - Democritus thought matter

could not be divided indefinitely. This lead to the idea of the smallest indivisible unit of matter… ατομος (the atom!!)

• 350 BCE - Aristotle modified an earlier

theory that matter was made of four

“elements”: earth, fire, water, air.

• Aristotle was wrong. However, his

theory persisted for 2000 years.

Democritus fire

air

water

earth

John Dalton• 1800 -Dalton proposed a modern atomic model

based on experimentation not on pure reason.

• All matter is made of atoms.

• Atoms of an element are identical.

• Each element has different atoms.

• Atoms of different elements combine

in constant ratios to form compounds.

• Atoms are rearranged in reactions.

• His ideas account for the law of conservation of

mass (atoms are neither created nor destroyed

– only rearranged) and the law of constant

composition (elements combine in fixed ratios).

Adding Electrons to the Model

1) Dalton’s “Billiard ball” model (1800-1900)Atoms are solid and indivisible.

2) Thompson “Plum pudding” model (1900)

Negative electrons in a positive framework.

3) The Rutherford model (around 1910)Atoms are mostly empty space.Negative electrons orbit a positive nucleus.

Materials, when rubbed, can develop a charge difference. This electricity is called “cathode rays” when passed through an evacuated tube. These rays have a small mass and are negative.Thompson noted that these negative subatomic particles were a fundamental part of all atoms.

Ernest Rutherford • Rutherford shot alpha () particles at gold foil.

Most particles passed through.

So, atoms are mostly empty.

Some positive -particles

deflected or bounced back!

Thus, a “nucleus” is positive &

holds most of an atom’s mass.

Radioactive substance path of invisible

-particles

Lead block

Zinc sulfide screen Thin gold foil

Böhr’s model

There are 2 types of spectra: continuous spectra & line spectra. It’s when electrons fall back down that they release a photon. These jumps down from “shell” to “shell” account for the line spectra seen in gas discharge tubes (through spectroscopes).

• Electrons orbit the nucleus in “shells”• Electrons can be bumped up to a higher shell if hit by an electron or a photon of light.