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Chemistry: Matter and Atoms
Transcript of Chemistry: Matter and Atoms
Chemistry: Matter and Atoms
Independent and dependent variables
Qalitative and Quantitative
Substance - matter with same fixed composition and properties
Pure(one kind of matter)
Heterogeneous and Homogenous mixtures
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!!!!
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
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
Homogeneous = solution
Dissolved in water, Air, gasoline
Alloys - solid solutions that contain different metals(and sometimes nonmetals)
Aqueous solution - when the solvent is water
Elements - simplest form of matter and can not be broken down into simpler substances
pure substance that can be broken down into elements
a combination of two or more different elements joined together in a fixed proportion
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
Endothermic - reactions that absorb heat
ice and salt
Macroscopic properties - direct measurements
Microscopic properties - indirectly measured at the atomic or molecular scale
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
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 = 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
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?
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 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)