Chemistry TAKS Rotation

2011

I. Physical Change- a change in the physical properties of a substance.

A. This includes mostly phase changes. Ex. Ice to water II. Chemical Change- a change that alters the chemical

composition of a substance. A. If a chemical reaction occurs, a new substance will

be produced. B. A chemical equation uses the following format. Ex. H2 + O2 H2O Reactant + Reactant Product C. Reactant- what goes into a reaction D. Product- what is produced by the reaction

Physical vs. Chemical Changes

Physical Changes Chemical Changes

Melt Rust

Evaporate Corrode

Condensation/condensate Burn

Boiling Tarnish

Shred Produces

Dissolve Combust

Be sure to know the “terms” that can give you the answer to a physical/chemical change question…

These are a few of the common words that you might see in a TAKS question. Just by Knowing these key words you can identify the examples as physical or chemical changes. Ex. Which listed below is an example of a physical change. a. Burning a piece of paper- (chemical change)b. a piece of iron that rusts in the rain (chemical

change)c. Boiling a pan of water (physical change)d. A silver tea set that has tarnished (chemical

change)THE CORRECT ANSWER IS C!

I. Density- DEF- Measures how compact molecules are within a substance.

A. Formula: D=m/V where D= density measured in kg or g/mL or cm3

m= mass measured in kg or g V= volume measured In mL or cm3 II. Things to remember….. A. The density of water is 1.0 g/mL B. If an object is MORE dense than the liquid it is in…it will

sink. C. If an object is LESS dense than the liquid it is in….it will

float. D. The formula on the formula sheet is D=m/V however, be

prepared to rearrange the formula to be able to solve for m or V.

Density

I. Viscosity- DEF- a measure of a fluid’s resistance to flow.

Ex. Compare pancake syrup to water….which one will flow faster?

Water! SO…..water has a lower viscosity than pancake syrup. The longer something takes to flow, the greater the viscosity.

A. By increasing the temperature of a substance, you can DECREASE the viscosity.

Ex. Compare warm pancake syrup to cold pancake syrup

Viscosity

I. Buoyancy Force- DEF- Buoyant force is the upward force exerted by a fluid on an object.

II. Buoyancy- Buoyancy is the ability of a liquid (such as water) to support or hold up other liquids or objects.

A. This helps to explain how a large cruise ship floats even when the ship is more dense than the water it is in.

1. As the ship is pushing down (gravity), the water pushes up and supports the boat by this buoyancy force.

*** The TAKS tests loves to use the example of the boat in water so be sure you understand this concept!*

Buoyancy Force

This is about classification….. I. Elements- 1 type of matter that cannot be

separated by physical means Ex. Fe, N, Cl II. Compound- more than 1 type of matter that

cannot be separated by physical means Ex. NaCl III. Mixtures 1. Homogeneous- matter that CAN be separated

by physical means with uniform composition. Ex. Milk

2. Heterogeneous- matter that CAN be separated by physical means that does not have uniform composition. Ex. Chex mix

Elements, Compounds & Mixtures

Ex. Chicken noodle soup would be an example of a A. element B. compound C. homogeneous mixture D. heterogeneous mixture ???Think…..can the substance be separated? YES! So….is it a homogeneous mixture of a heterogeneous

mixture? (When you look at c.n. soup….does it look the same?

) **** TERM TO KNOW****** Alloy- a mixture of 2 or more metals

Know how to classify….

Quick Review I. Groups- vertical columns- 18 total 1. Group 1- most reactive metals, alkali metal 2. Group 2-alkaline earth metals 3. Group 17- Halogens, most reactive non-metals, 7

valence electrons 4. Group 18- noble gases, 8 valence electrons,

stable due to full octet, will NOT be involved in bonding

II. Metals vs Non-metals 1. Metals- left of staircase 2. Non-metals- right of staircase

The Periodic Table

3. Metals will Give AWAY electrons 4. Non metals will GAIN electrons. 5. Metalloids- elements that touch the staircase

on the periodic table. Have properties of both metals and non-metals.

III. WOAH important!!! A. All elements bond in order to have 8 valence

electrons. B. Elements in the same GROUP will have

similar chemical properties. *** If you are asked a question that deals with

elements having things in common….go with the GROUP answer 1st! (over picking a “next door neighbor” element).

I. Valence Electrons-DEF- atoms electrons in the outermost energy level/orbital.

Group 1-1 Group 2-2 Group 13-3, 14-4, 15-5, 16-6, 17-7, 18-8 II. Charges When elements transfer electrons (ionic bond- M + NM) in

order to be stable (have 8 valence electrons) they will GAIN or LOSE electrons. This causes them to have a charge (they will have MORE or LESS electrons compared to protons.)

More electrons than protons- negative charge Less electrons than protons- positive charge Group 18-0 charge since they wont gain or lose electrons.

Valence Electrons and Charges/Oxidation #’s

1. Which of these are composed of two or more different substances that are chemically combined in a definite ratio?

a. Compoundsb. Mixturesc. Elementsd. Solution2. Oxygen (O2) is an example of

a. An alloyb. A moleculec. A saltd. A mixture

Examples…..

I. An atom is made up of protons, neutrons and electrons.

II. Remember these 3 rules! 1. atomic #= # protons 2. # protons= # electrons 3. atomic mass= # protons + # neutrons

Structure of an Atom