Post on 17-Sep-2020
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.