intro and background: accuracy vs. precision€¦ · 2 math with sig figs • multiplication and...

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INTROANDBACKGROUND:Measurement,Uncertainty,Ma<er,

Periodicity,andNomenclature

Accuracyvs.PrecisionACCURACY

Closeness to the true value

PRECISION How close a series of measurements are to each other

*Tools with MORE numbers after the decimal = MORE precise

WHEN MAKING MEASUREMENTS, IT’S GOOD TO HAVE BOTH!!

Accuracyvs.Precision %ErrorCompare a measurement to its accepted value

% ERROR

EXPERIMENTAL VALUE

ACCEPTED VALUE

ACCEPTED VALUE

100

•  EXAMPLE: Sally found the mass of a 34.0 g sample to be 32.7 g.

What is the % error in her measurements?

3.82%

SignificantFigures

“SIG FIGS”

All the numbers that are certain in a measurement, including one that is uncertain

•  RULES: 1) All non zero digits are significant 2) Zeros between other sig figs count

Ex: 1002 3) Zeros at the end before an implied decimal point don’t count (if it’s there then they do)

Ex: 12400 / 400.

4) When a number is smaller than one, zeros before the first S.F. don’t count

Ex: 0.045 5) Zeros after a decimal do count (once you have a S.F.)

Ex: 45.8300

RoundingwithSigFigs•  If digit to the right is LESS than 5… LEAVE IT BE!!

(Ex: 56.43 with 3 Sig Figs would be 56.4) •  If digit to the right is GREATER than 5… ROUND UP!!

(Ex: 67.39 with 3 Sig Figs would be 67.4) •  If digit to the right EQUALS 5… GO FOR EVEN #s!!

(Ex: 94.65 with 3 Sig Figs would be 94.6, while 94.75 with 3 Sig Figs would be 94.8)

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MathwithSigFigs•  Multiplication and Division:

Count SIG FIGS in each and use the LEAST amount in the answer!

Ex: 3.052 X 2.10 X 0.75 = 4.8069

CORRECT SIG FIGS = 4.8

•  Addition and Subtraction:

Count DECIMAL PLACES in each and use the LEAST amount in the answer!

Ex: 3.45645 mL – 2.43 mL = 1.02645 mL

CORRECT SIG FIGS = 1.03 mL

SigFigPracKce•  How many sig figs are in these numbers?

1) 91,600 2) 0.003005 •  Calculate and round using the appropriate rule:

3) 0.04216 + 0.0004134 = 4) (5.610) x (34.908) x (2.30) =

Prefixes

Positive exponents are LARGER than the base unit, while negative are SMALLER!!

M (mega) = 106

k (kilo) = 103

D (deka) = 102

d (deci) = 10-1

c (centi) = 10-2

m (milli) = 10-3

µ (micro) = 10-6

n (nano) = 10-9

Ex: 1 km = 1,000 m (KILO is

LARGER!)

Ex: 1,000 mm = 1 m

(MILLI is SMALLER!)

TemperatureConversions•  Equations to know:

-FAHRENHEIT TO CELSIUS C = .56 X (F – 32)

-CELSIUS TO FAHRENHEIT

F = ( 1.8 X C ) + 32 -CELSIUS TO KELVIN

K = C + 273

•  EXAMPLE:

What is -14 °C expressed in Kelvin?

Know the reverse as

well!

ConversionFactors•  Amounts can be expressed in different EQUAL ways

SOME COMMON CONVERSIONS:

1 in = 2.54 cm 1 ft = 12 in 1 yd = 3 ft 1 mi = 5280 ft 1 m = 10 dm 1 m = 100 cm

1 m = 1000 mm 1000 m = 1 km 1 g = 10 dg 1 g = 100 cg 1 g = 1000 mg 1000 g = 1 kg

1 mL = 1 cm3 1000 mL = 1 L 1 min = 60 s 1 hr = 60 min 1 day = 24 hr 365 days = 1 yr

DimensionalAnalysis•  EXAMPLE:

What is 5 km expressed in meters?

5 km X 1000 m 1 km

= 5,000 m

•  In order to cancel a unit, one must be on the “top” and the other must be on the “bottom” (immediately write the top unit on the bottom for the conversion factor)!!

REMEMBER… THE UNITS ARE YOUR FRIENDS!!

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DimensionalAnalysis•  MORE EXAMPLES:

a)  3.48 g to kg

b)  12.3 L to mL

c)  66 mm to km

d)  1.130 days to s

0.00348 kg

12,300 mL

0.000066 km

97,630 s

DensityRelationship of mass to volume

D = Mass / Volume •  Units are g / mL or g / cm3 •  INTENSIVE PROPERTY: amount of the substance does not affect it

•  If density is given, mass or volume could be determined…

M = D x V V = M / D

PracKce

A piece of wood has a mass of 11.2 g and a volume of 23 mL. What is the density?

Mercury metal is poured into a graduated cylinder that holds 22.5 mL. The mercury used to fill the

cylinder weighs 0.3060 kg. Calculate the density (in g/cm3) of mercury.

PracKce

A piece of wood has a density of 0.82 g/mL and a volume of 0.031 L. What is the mass of the wood in mg?

Aluminum has a density of 2.70 g/cm3. What is the mass (in kg) of a cube with a side of 6.78 cm?

HowDoesSomethingFloat?•  Lower density items FLOAT on higher density items… ice is less dense than water! •  Most wood is less dense than water •  Helium is less dense than air •  A ship is less dense than water

Ma<erAnything that has mass and takes

up space

THREE STATES OF MATTER

•  SOLID: definite shape, definite volume, high density, not easily compressed, slow moving particles

•  LIQUID: indefinite shape, flows but has a definite volume, not easily compressed

•  GAS: indefinite shape, indefinite volume (takes the shape of the container), low density, easily compressed, fast moving particles (VAPOR = gaseous state that is liquid or solid)

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DescribingMa<erINTENSIVE PROPERTY

EXTENSIVE PROPERTY

Depends on the type of matter, NOT the amount

Depends on the amount of matter present

EX: Hardness, density, color, melting point

EX: Mass, volume, weight

TypesofProperKes•  PHYSICAL PROPERTY: quality observed or measured WITHOUT changing the substance’s composition

EX: state, color, melting point, density •  CHEMICAL PROPERTY: observed only if the substance undergoes a chemical change

EX: ability to oxidize (rust), flammability, ability to ferment

TypesofChanges

•  PHYSICAL CHANGE: properties of the material may change, but NOT the composition (REVERSIBLE)

EX: cutting, melting, boiling, freezing, crushing •  CHEMICAL CHANGE: the composition of the matter always changes (IRREVERSIBLE)

EX: cooking food, photosynthesis, rusting

MixturePhysical blend of two or more components

TWO TYPES:

•  HOMOGENEOUS è uniform composition throughout

•  HETEROGENEOUS è NOT uniform in composition

SoluKonHomogeneous mixture in which one substance

is dissolved in another

•  SOLUTE: substance that is dissolved •  SOLVENT: substance doing the dissolving

Solution Solute Solvent

Lemonade

Soda pop

Ocean water

•  INSOLUBLE: does NOT dissolve •  SOLUBLE: does dissolve

SUGAR

SUGAR

SALT

WATER

WATER

WATER

SeparaKngMixtures•  Differences in PHYSICAL properties can be used to separate mixtures

1) DECANT: pour off one layer leaving behind another layer of a mixture (density)

2) FILTRATION: separates a solid from the liquid

3) MAGNET: removes substances that are magnetized (ex: iron filings) 4) CHROMATOGRAPHY: separates colors

5) DISTILLATION: uses a difference in boiling points of two substances to separate them

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DisKllaKonApparatus PureSubstanceComposition does NOT vary

TWO TYPES:

•  ELEMENT è simplest form of matter that has a unique set of properties

(Ex: hydrogen, oxygen, gold, lead)

•  COMPOUND è contains two or more elements CHEMICALLY combined in a fixed proportion

(Ex: water, carbon dioxide, sugars)

ReacKonLawsLAW OF CONSERVATION OF ENERGY

Energy can neither be created nor destroyed… only changed from one form to another!

LAW OF CONSERVATION OF MASS Mass can neither be created nor destroyed… Total mass in the universe is constant!

PeriodicLaw

•  MOSELEY (1913) developed the Modern Periodic Table

•  Arranged elements in order of increasing atomic number

Properties of elements repeat when placed in order of INCREASING atomic number

ReadingtheTable•  PERIOD: Row on the Periodic Table / Energy level •  GROUP: Column (families) with similar physical and chemical properties

Three classes of elements on the Periodic Table…

MetalsFound on the left hand side and middle

of the table

•  About 80% of elements are in this class

•  High luster (shiny)

•  Good conductors of heat and electricity

•  Typically solids at room temperature (except Hg)

•  DUCTILE: can be drawn into wires

•  MALLEABLE: hammered into thin sheets

•  High density and melting point

•  Form cations (+)

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Metals NonmetalsFound on the right hand side of the

table

•  No luster

•  Poor conductors of heat and electricity

•  Most (not all) are gases at room temp

•  Low density and melting point

•  Not malleable or ductile

•  Brittle

•  Tend to form anions (-)

Nonmetals MetalloidsFound along the “staircase” on

the table

•  Have properties of both metals and nonmetals

•  Ex: B, Si, Ge, As, Sb, Te, Po, and At

•  Ion formation depends on their group

Arsenic Poisoning (from H2O)

Metalloids PeriodicTableGroups

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WhyAreFamiliesSimilar?

Each family has the same number of VALENCE ELECTRONS (outermost

electrons of an atom) which determines an element’s properties… All want

EIGHT!!

IonsCharged (+ or -) atoms

•  Atoms in their elemental state are NEUTRAL (protons and electrons are EQUAL)

•  Atoms can gain or lose electrons giving them a charge

•  Ions have DIFFERENT number of protons and electrons

CaKonsPositively (+) charged ions

•  Atoms that LOSE electrons become cations (loss of negatively charged particles)

•  Formed from Metals

•  Number of electrons lost determines the charge (1+, 2+, etc.)

BOINK!

BOINK!

MAGNESIUM

Mg 2+

AnionsNegatively (-) charged ions

•  Atoms that GAIN electrons become anions (more negatively charged particles)

•  Formed from Nonmetals

•  Number of electrons gained determines the charge (1-, 2-, etc.)

CHLORINE

Cl 1-

WhatDeterminestheCharge?

LOCATION on the Periodic Table and VALENCE ELECTRONS!!

1+ 2+ 3+ 3- 2- 1-

WhatDeterminestheCharge?

Atoms want EIGHT electrons in their outer or highest energy level to be stable… They want to be like a NOBLE GAS! So they GAIN

or LOSE electrons to accomplish this... Whichever is EASIER!!!!

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FactorsInfluencingTrends1)   Electron Energy Level: distance

from the nucleus

2)   Effective Nuclear Charge (Zeff): # of protons influences the pull on the electrons

3)   Shielding Effect: valence electrons are “shielded” from the pull / charge of the nucleus by all the electrons in between

+

AtomicRadiusHalf the distance between the nuclei of two atoms

of the same element (aka ATOMIC SIZE)

•  Trend: INCREASES down a column and DECREASES going across a row

AtomicRadius

WHY DOES IT FOLLOW THIS TREND?

As you go down a column, the number of e- and energy levels increase… so the radius INCREASES!

H Li

Na

K

Rb

•  Group:

Half the distance between the nuclei of two atoms of the same element (aka ATOMIC SIZE)

AtomicRadius


As you go across a row, all e- are in the same energy level and the nuclear charge is larger, causing the outer e- to be held tighter… so it DECREASES!

•  Row:

Na Mg Al Si P S Cl Ar

Half the distance between the nuclei of two atoms of the same element (aka ATOMIC SIZE)

AtomicRadiusHalf the distance between the nuclei of two atoms

of the same element (aka ATOMIC SIZE)

IonicRadiusHalf the distance between two ions

•  Trend: INCREASES down a column and DECREASES going across a row for cations and anions, but cations are SMALLER and anions are LARGER

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As you go down a column, the number of e- and energy levels increase… so the radius INCREASES!

•  Group:



Cations are SMALLER because as e- are lost nuclear charge increases and holds tighter, while anions are LARGER because as e- are added nuclear charge decreases and does not hold as tight… but each type still DECREASES as go across!

•  Row:


IonizaKonEnergyAmount of energy required to remove a

valence electron from an atom

•  Trend: DECREASES down a column and INCREASES going across a row




As you go down a column, more energy levels are added and the valence e- are more “shielded” from the pull of the nucleus, making it easier to pull off an e-… so it DECREASES!

•  Group:




As you go across a row, the nuclear charge gets greater (holds e- tighter) and the orbital gets closer to being full which adds stability, making it harder to pull off an e-… so it INCREASES!

•  Row:



•  Watch for EXCEPTIONS like Be / B, N / O, etc.... WHY do they occur?

•  To remove a second e-, even MORE energy is required (gets harder to steal) so I.E. INCREASES with each electron removed!

•  Number of valence e- can also be seen… look for jumps in energy (Ex: Be)

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ElectronegaKvityAbility of an atom to attract electrons

when the atom is in a compound





As you go down a column, more energy levels are added, making the valence e- farther from the nucleus and not held as “tightly” due to shielding… so it DECREASES!

•  Group:




As you go across a row, metals are more likely to give up e- to form cations, while nonmetals want more e- to be stable, forming anions … so it INCREASES!

•  Row:

ElectronAffinityAmount of energy released when an

electron is added



Think in terms of electronegativity… the stronger the attraction to an e-, the more energy is released!

Metallic/ReacKvity

•  As you go down a group, the metallic character INCREASES as well as the reactivity of the elements •  Exception: Halogens… As you go down the family reactivity DECREASES! Therefore, the most reactive element in the halogen family is Fluorine!!

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IonicBondTRANSFER of electrons between atoms forming opposite charges which attract to each other

•  Each atom achieves a noble gas configuration (full valence shell)

•  Usually between a METAL and a NONMETAL

•  Formula Unit: lowest whole-number ratio of ions in an ionic compound (ex: NaCl or MgCl2)

NamingIonicCompounds•  To name an IONIC compound, ask yourself this question first…

Is the METAL in the compound MULTI-CHARGED? (in the d-block including Pb

and Sn, but NOT Zn or Ag)

NamingIonicCompounds•  EXCEPTIONS:

-All transition metals (d-block) are multi-charged except Ag is always Ag1+ and Zn is always Zn2+ so no Roman numerals are needed

-Pb and Sn behave like transition metals

NamingIonicCompounds•  If the answer is NO…

1) Name the cation (metal) first… remember it keeps its name

2) Then name the anion (nonmetal)… ending in -ide

•  EXAMPLE:

Name the following compound: AlBr3

Aluminum bromide

NamingIonicCompounds•  If the answer is YES…

1) Criss-cross the SUBSCRIPTS and make them the charges (metals = “+” / nonmetals = “-”)

2) Check the charge on the anion (-) and see if it is correct… if it is NOT, multiply the “-” charge by a # to get the correct charge and then multiply the “+” charge by the same #

3) Write the name of the metal with its charge in parentheses as a Roman numeral [I, II, III, IV] followed by the nonmetal with an “ide” ending

NamingIonicCompounds•  EXAMPLES:

Name the following compound: Fe2O3

IRON IS A MULTI-CHARGE METAL!!

Fe2O3 Iron (III) oxide =Fe3+O2-

Name the following compound: ZnCl2

Make sure charge on anion is correct!!

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NamingIonicCompounds•  If the compound has a POLYATOMIC ION:

1) Follow all previous rules, but the polyatomic ions get to keep their name

•  EXAMPLES: Name the following compound: KNO3

Name the following compound: NH4Cl

NamingIonicCompounds•  If the compound is a HYDRATE (contains water)…

1) Follow all previous rules

2) Attach the correct PREFIX to the word “hydrate” to indicate the amount of water molecules present… put this right after the name

PREFIX NUMBER PREFIX NUMBERMono 1 Hexa 6Di 2 Hepta 7Tri 3 Octa 8

Tetra 4 Nona 9Penta 5 Deca 10

NamingIonicCompounds

•  EXAMPLES: Name the following compound: CuSO4 • 5H2O

Name the following compound: Pb(ClO4)2 • 3H2O

IonicCompoundFormulas•  Rules for writing formulas…

1) Write the SYMBOL of each element or ion from the name (cation is always written first followed by the anion)

2) Determine the CHARGE on each…

-Multi-Charged: it’s in the ( )

-Polyatomic: keeps its charge

-Otherwise: get from the table

3) Criss-cross the charges and make them SUBSCRIPTS… simplify (reduce), if possible

IonicCompoundFormulas

•  EXAMPLE:

Write the formula for calcium chloride.

Ca2+ Cl-

CaCl22+=2-

IonicCompoundFormulas•  If POLYATOMIC IONS are present…


2) Treat polyatomic ions as a whole… put in parentheses when subscripts are used

Fe(OH)3

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IonicCompoundFormulas•  If the compound is a HYDRATE (contains water)…


2) Use the PREFIX in front of “hydrate” to indicate the number of water molecules... Write this after the name by adding “• #H2O”

•  EXAMPLE:

Write the formula for iron (III) chloride hexahydrate.

CovalentBondSHARING of electrons between atoms to

satisfy the octet rule

•  Involves two NONMETALS

•  Known as covalent or molecular compounds

•  MOLECULE: group of atoms joined by a covalent bond

•  DIATOMIC MOLECULES: elements that cannot exist as single atoms

Ex: H2, N2, O2, F2, Cl2, Br2, and I2

NamingCovalentCompounds•  Naming a covalent / molecular compound:

1) Write the name of the first element

2) Change the ending of the second element to –ide

3) Add correct PREFIXES to each to indicate the number of atoms (no mono on FIRST element)

PREFIX NUMBER PREFIX NUMBERMono 1 Hexa 6Di 2 Hepta 7Tri 3 Octa 8

Tetra 4 Nona 9Penta 5 Deca 10

CovalentCompoundFormulas•  Rules for writing covalent / molecular formulas:

1) Write each element symbol from the name

2) Use PREFIX in the name to determine the subscript for each element… DO NOT SIMPLIFY!!!

•  EXAMPLE:

Write the formula for dinitrogen pentoxide.

HydrocarbonsCompounds made of carbon and hydrogen

•  Organic compounds… Three groups we will look at: Alkanes, Alkenes, and Alkynes

•  Named with PREFIXES based on the number of carbon atoms present:

PREFIX #OFC PREFIX #OFCMeth 1 Hex 6Eth 2 Hept 7Prop 3 Oct 8But 4 Non 9Pent 5 Dec 10

Alkanes•  Have the generic formula: CnH2n+2

•  Contains all single bonds

•  Naming: Use the correct prefix with –ane ending

•  Formula: Prefix determines how many carbons… Do the math to determine the number of hydrogens

•  EXAMPLES: Name the following compound: C3H8

Write the formula for butane.

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Alkenes•  Have the generic formula: CnH2n

•  Contains one double bond

•  Naming: Use the correct prefix with –ene ending



Write the formula for decene.

Alkynes•  Have the generic formula: CnH2n-2

•  Contains one triple bond

•  Naming: Use the correct prefix with –yne ending



Write the formula for octyne.

NamingAcids•  Rules for naming acids:

1) Hydrogen atom connected to anion (-) that ends in –ide then it is named…

•  hydro- root of the element- ic acid

•  EXAMPLES:

HCl H2S


2) Hydrogen atom connected to a polyatomic ion ending with –ite then it is named…

•  (root of the polyatomic ion)- ous acid

•  EXAMPLES:

HClO2 HNO2


3) Hydrogen atom connected to a polyatomic ion ending with –ate then it is named…

•  (root of the polyatomic ion)- ic acid

•  EXAMPLES:

HClO3 H2SO4

AcidFormulas•  Rules for writing formulas of acids:

1) Hydrogen (H+) usually written first

2) Name indicates the anion (-) in the formula

3) Write the charges for each symbol and criss-cross to get subscripts

•  EXAMPLE:

Sulfurous acid

intro and background: accuracy vs. precision€¦ · 2 math with sig figs • multiplication and...

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