**Chemistry: Matter and Atoms**

**Review**

Scientific Method

Independent and dependent variables

Control

Hypothesis

Classifying Matter

Qalitative and Quantitative

Substance - matter with same fixed composition and properties

Pure(one kind of matter)

Heterogeneous and Homogenous mixtures

**Handling Numbers**

Scientific notation - used for extremly small and extremely large numbers

N x 10^n , where N is a number between 1 and 10. The n is a positive or negative whole number

Decimal moved right # (-)

Decimal moved left # (+)

**Accuracy and precision**

Accuracy - measure of how close your value is to the acutal value

Precision - how reproducibly you get the same answer

precision of a masuring tool is determined by the number of useful digits it give us = significant figures!!!!

Chemical Properties

Properties that can be observed only when there is a change in the composition of the substance

ability to react with another substance

Chemical change - change of one or more substances into another substance

Also Chemical Reaction - decompose, explosions, rust, oxidizing, tarnish, corrode, ferment, burn, rot

Physical

A change in matter that does not involve a change in the identity of the substance

boiling, freezing, melting, evaporating, dissolving, and crystallizing

Physical Properties - characteristics of a sample of matter that can be observed or measured without any change of identity

Solubility, melting point, color, density, electrical conductivity, physical state

Physical and Chemical Changes

Mixtures

Homogeneous = solution

Dissolved in water, Air, gasoline

Alloys - solid solutions that contain different metals(and sometimes nonmetals)

Aqueous solution - when the solvent is water

Substances

Elements - simplest form of matter and can not be broken down into simpler substances

Compounds

pure substance that can be broken down into elements

a combination of two or more different elements joined together in a fixed proportion

Physical properties

Don't involve changes is composition

Many are qualitative - blue solution, liquid, water is solid at 0C

Quantitative - iron has density of 7.86 g/ml, 35.7g of NaCl dissolved in 100mL of water

Volatile - substances that change to a gas easily at RT

Density - D = m/V

How can you measure density?

Extensive property - depends on how much matter is being considered

Intensive property - does not depend on how much matter is being considered

Atoms and energy

Law of conservation of mass - in a chemical change matter is neither created nor destroyed

Energy - the capacity to do work

Exothermic - reactions that give off energy in the form of heat

Some examples

Endothermic - reactions that absorb heat

photosynthesis

ice and salt

Chemical formula

**Measurement**

Macroscopic properties - direct measurements

Microscopic properties - indirectly measured at the atomic or molecular scale

SI Units

International system of units (or Frech for Systeme Internationale d'Unites)

All other units of measure can be derived from these

Mass and Weight

Mass - measure of the amount of matter in an object

Weight - the force that gravity exerts on an object

Chemist more interested in mass and use a balance measuring mass called weighing

SI units of mass = kg

We use gram because it is more convenient

1 kg = 1000g = 1 x 10^3 g

Volume

SI unit of length is meter(m)

Derived SI unit for volume is cubic meter (m^3)

Chemists usually work with smaller volumes

cubic centimeter (cm^3)

cubic decimeter (dm^3)

Liter - volume occupied by one cubic decimeter

1L = 1000mL

1L = 1000cm^3

1L = 1dm^3

1mL = 1cm^3

Density

Density = mass/volume

Intensive property - doesn't depend on quantity of mass percent- ratio will remain the same

SI-derived unit is kg/m^3

Awekward so we use g/cm^3 or just g/mL (more for liquids and solids)

g/L for gasses because they are less dense

Three temperature scales - Fahrenheit, Celsius, and kelvin

F most commonly used in US - normal freezing and boiling points of water - 32 F and 212 F

Celcius scale - freezing 0 C and boiling 100 C

Kelvin - SI unit base temp - absolute temp scale meaning 0 K is the lowes temp that can be obtained theoretically

Temperature Scales

MUY IMPORTANTE!!!!

Sig Figs

Any nonzero digit is significant.

Any zeros that are between nonzero digits are also significant.

All zeros to the right of all the nonzero numbers are not significant.

Zeros to the right of all the nonzero numbers are significant if you see a decimal actually written out

Counting numbers are considered to have infinite significant figures.

Examples - 100g 100.g 100. 0g 0.001- how many sig figs in each?

**Dimensional Analysis**

Procedure used to convert between units in solving chemistry

Also called factor-label method

1in = 2.52cm equal to 1in/2.54cm

Concersion factors equal 1 so can invert

Taking measurements

taking measurements from a scale write down all of the numbers on the screen

analog equipment write down the value you see and a guestimated number for the last digit

Math with sig figs

Addition and subtraction: Round your answer to the least precise decimal place of the value you’re doing a calculation with.

0.55g + 0.224g = 0.774g what should the answer be?

Multiplication and division: Find the number of significant figures for each number, and then write the answer so that it has the same sig figs as the least precise value.

1.000g/9mL = 0.1g/mL

**Useful tips for Dimensional Analysis**

Read question carefully. Write what you know and what you want to find(the goal unit).

Find appropriate equations that relate to the given info and the unknown - might have to look up many different conversions (it takes practice)

Check answer for correct sign, unit, and sig figs

Judge is number is reasonable

(Can also make a "ball-park estimate" to check)