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Transcript of Ms. Eckersley Joel Darcie Katherine Chance Terrence Alex Bryce Danica Matt Taylor Terra Handouts...
Ms. Eckersley
Joel
Darcie Katherine
Chance
Terrence Alex
Bryce Danica
Matt
Taylor Terra
Handouts
Jordan
Emilia Maddie
James
Logan & Brayden
Sheldon
Ms. Eckersley
Cody Michael
John Ellen
Andrew Alex
Amy Jael
Kristin Kennedy
Ana Madison
Rebecca
Cierra Calla
Handouts
Mackenzie
Brandon Keegan
Brittany Sawyer
Renee Kae-Leigh
Unit 2: Chemistry in ActionLesson #1: A Bit of Review
Objectives: Describe the structure of an atom with its 3 subatomic particles Determine atomic number and atom mass of elements Define chemistry, matter, elements, atomic number, atomic mass, proton, neutron, electron, nucleus
Chemistry
Chemistry is the study of matter and the interactions/changes it undergoes
Some Definitions
Matter is anything that has mass and volume (occupies space)
Elements are pure substances whose atoms all have the same atomic number (same number of protons)
Atoms are the smallest part of an element that still retains all of the same properties of the element.
Atoms
Atoms are composed of 3 subatomic particles: 1) Protons – are found in the nucleus 2) Neutrons – are found in the nucleus 3) Electrons – are found in orbits
around the nucleus, called the electron cloud
Atoms
Subatomic Particle
Charge Mass Location
Recall the following information with respect to the parts of an atom:
Subatomic Particle
Charge Mass Location
Proton +1 1 a.m.u. NucleusNeutron 0 1 a.m.u. NucleusElectron -1 ~0 Electron
cloud
Recall the following information with respect to the parts of an atom:
Elements in the Periodic Table
The information about each element on the periodic table is arranged like this:
Atomic Number
The Atomic Number tells us the number of protons in the nucleus of an atom
In the example, an atom of fluorine has 9 protons in its nucleus
Atomic Mass
Almost all of the mass of an atom is found in the nucleus
Atomic Mass = # protons + # neutrons
Atomic mass is measured in atomic mass units (a.m.u.)
Atomic mass of fluorine is 19.00 a.m.u.
Example Problems
Determine the number of protons, neutrons, and electrons in neon:
Protons = ________ Neutrons = _________ Electrons = __________
Example Problems
Determine the number of protons, neutrons, and electrons in neon:
Protons = 10 Neutrons = 20 – 10 = 10 Electrons = # protons = 10
Example Problems
Determine the number of protons, neutrons, and electrons in aluminum:
Protons = ________ Neutrons = _________ Electrons = __________
Example Problems
Determine the number of protons, neutrons, and electrons in aluminum:
Protons = 13 Neutrons = 27 – 13 = 14 Electrons = # protons = 13
Unit 2: Chemistry in ActionLesson #2: The Periodic Table
Objectives: Describe the organization of the periodic table of elements • Metals, Non-metals,
Metalloids• Periods vs. families• Alkali metals, Alkaline
Earth metals, Chalcogens, Halogens, Noble gases
Relate an element’s position on the periodic table to its valence
The Elements Song: http://www.privatehand.com/flash/elements.htmlhttp://www.edu-cyberpg.com/IEC/elementsong.html
There’s antimony, arsenic, aluminum, selenium, And hydrogen and oxygen and nitrogen and rheniumAnd nickel, neodymium, neptunium, germanium, And iron, americium, ruthenium, uranium, Europium, zirconium, lutetium, vanadium And lanthanum and osmium and astatine and radium And gold, protactinium and indium and gallium And iodine and thorium and thulium and thallium.There’s yttrium, ytterbium, actinium, rubidium And boron, gadolinium, niobium, iridium And strontium and silicon and silver and samarium, And bismuth, bromine, lithium, beryllium and barium.There’s holmium and helium and hafnium and erbium And phosphorous and francium and fluorine and terbium
And manganese and mercury, molybdinum, magnesium, Dysprosium and scandium and cerium and cesium And lead, praseodymium, and platinum, plutonium, Palladium, promethium, potassium, polonium, Tantalum, technetium, titanium, tellurium, And cadmium and calcium and chromium and curium.There’s sulfur, californium and fermium, berkelium And also mendelevium, einsteinium and nobelium And argon, krypton, neon, radon, xenon, zinc and rhodium And chlorine, carbon, cobalt, copper, Tungsten, tin and sodium.These are the only ones of which the news has come to Harvard, And there may be many others but they haven’t been discovered.
The Periodic Table
The periodic table can be divided into 3 main sections: 1) Metals▪ Found on the left side of the table▪ Left of the zigzag line▪ Most are shiny (have luster) & are solids at
room temp.▪ Most are good conductors of electricity▪ Many are malleable and ductile
The Periodic Table
The periodic table can be divided into 3 main sections: 2) Non-metals▪ Found on the right side of the periodic
table▪ Always right of the zigzag line▪ Most are gases or dull brittle solids at
room temp.▪ Most are poor conductors of heat &
electricity
The Periodic Table
The periodic table can be divided into 3 main sections: 3) Metalloids▪ Found near the zigzag line▪ Have properties of metals & non-metals
The Periodic Table - Periods
The periodic table can also be divided up into periods and families
Periods are horizontal rows on the table
Periods show energy levels of the electrons
There are 7 periods in total Each period is numbered starting from
the top of the periodic table E.g. Period 1 contains hydrogen &
helium
12
345
67
The Periodic Table – FamilIes (Groups)
Families are vertical columns on the periodic table
The tall columns are numbered IA-VIIIA, and the short columns are numbered IB-VIIIB
Sometimes they are numbered 1-18 Families often contain elements
with similar properties
IA
IIA
IIIB IVB VB VIB VIIB VIIIB IB IIB
IIIA IVA VA VIA VIIA
VIIIA
Family IA – Alkali Metals
This group contains extremely reactive metals
They have only 1 valence electron
Family IIA – Alkaline Earth Metals
This group contains reactive metals
They contain 2 valence electrons
Family VIA – Chalcogens
This group contains the oxygen family
This group contains mainly non-metals
They contain 6 valence electrons
Family VIIA – Halogens
This group contains non-metals Halogens are gases or liquids at
room temp. They contain 7 valence electrons They are the most reactive of the
non-metals
Family VIIIA – Noble (Inert) Gases
This group contains non-metals Noble Gases are gases at room
temp. They contain 8 valence electrons
(except He – 2) They are the do not react with
other elements
Assignment: Alien Periodic Table
Use you knowledge of Earth’s periodic table to help you arrange the aliens’ elements onto a blank periodic table.
Each alien symbol should be located in the same position that earth’s corresponding element symbol would be located.
Use the clues in the handout to help you
Chemistry in Action
Topic #3: Bohr Models
Draw Bohr models of elements, showing valence electrons
http://www.teachertube.com/viewVideo.php?title=Explosive_Alkali_Metals&video_id=58932
Drawing Atoms (Bohr Models)
To draw a diagram of a particular atom, we need to know the atomic number and atomic mass of that atom
These numbers allow us to find the number of protons, electrons, and neutrons
Creating Bohr Models
1) Draw a circle to represent a nucleus
2) Fill the circle with the number of protons & neutrons
3) Electrons fill the rings/orbits/shells or “energy levels” surrounding the nucleus
Each shell is capable of holding a specific number of electrons
Electron Configuration
Each shell can hold a specific number of electrons: Shell 1: 2 Shell 2: 8 Shell 3: 8 Shell 4: 18
Drawing Bohr Models
Example: Draw a Bohr model for nitrogen (atomic number = 7; atomic mass = 14.00)
Drawing Bohr Models
Example: Draw a Bohr model for sodium (atomic number 11; atomic mass = 23.0)
Drawing Bohr Models
Identify the following element based on its Bohr model:
P = 10
N = 10
Electron Configuration - Advanced
Note: This information will not be for marks on a test (it may be for bonus).
In reality, electrons are found in sub-shells within the shells.
Sub-shells include: s, p, d, and f
Electron Configuration - Advanced
Energy Levels
1st 2nd 3rd 4th 5th 6th 7th
Orbitals
"s" 2 2 2 2 2 2 2
"p" 6 6 6 6 6 6
"d" 10 10 10 10 10
f" 14 14 14 14
Total 2 8 18 32 50 72 98
Electron Configuration - Example
An electron configuration table is a type of code that describes how many electrons are in each energy level of an atom and how the electrons are arranged in each energy level.
Example: The electron configuration of hydrogen is 1s1
1 s 1Number of electrons in the sub shellName of
the sub-shell
Energy Level
Electron Configuration - Example
Example: Electron configuration of carbon:
1s2
2s2 2p2
Carbon has 2 electrons in the s sub-shell
of the 1st energy level Carbon has 2 electrons in the s sub-shell
of the 2nd energy level and 2 electrons in the p sub-shell of the 2nd energy level
Electron Configuration: Example
What is the electron configuration of fluorine (atomic number 9)?
The Bohr Game
You need: A partner Clean hands
Each group needs: A Bohr model template A non-permanent marker A damp piece of paper towel 20 jujubes
Chemistry in Action
Topic #4: Lewis Dot Diagrams
Objectives: To be able to draw Lewis Dot Diagrams for the first 20 elements To be able to relate the number of valence electrons to an elements position on the periodic table
Lewis Dot Diagrams
A Lewis dot diagram is a graphic method to represent an element and its valence electrons.
In Lewis dot diagrams, dots are placed around the outside of an element to illustrate the valence electrons
Lewis Dot Diagrams
Each dot represents one valence electron in the outermost shell of the atom
Rules for Drawing Lewis Dot Diagrams
1) The first 2 dots areput on opposite sides.2) A maximum of 2 dots go on each side.
The Octet Rule
The octet rule states that atoms with eight electrons in their valence shell will be stable
The exception to this rule is hydrogen and helium, which are stable with 2 valence electrons.
Lewis Structures & the Periodic Table Notice any patterns?
Patterns
All elements in the same family have the same number of valence electrons
Elements in the same family have very similar Lewis Dot Diagrams.
Alkali Metals
Alkali metals all have one valence electron
Alkaline Earth Metals
Alkaline earth metals all have two valence electrons
Chalcogens
Chalcogens have 6 valence electrons
Halogens
Halogens have 7 valence electrons
Noble Gases
Noble Gases have full valence shells
Most have 8 valence electrons (Helium has 2)
Examples:
Draw Bohr and Lewis Dot Diagrams for the following element: Helium (atomic number 2)
Examples:
Draw Bohr and Lewis Dot Diagrams for the following element: Potassium (atomic number 19)
Examples:
Draw Bohr and Lewis Dot Diagrams for the following element: Carbon (Atomic number 6)
Examples:
Draw Bohr and Lewis Dot Diagrams for the following element: Phosphorus (Atomic number 15)
Ions
Atoms are generally in their most stable form when they are filled to a maximum number of 8 electrons (2 for hydrogen or helium).
Atoms will often gain or lose electrons to reach this stable form
Atoms that gain or lose electrons are called ions or charged particles
Ions
Since protons are stuck in the nucleus, a transfer of electrons must occur for an ion to form
Atoms will form ions when they are gaining or losing electrons to their outer shell.
Monatomic vs. Polyatomic Ions
Ions that are formed from only one atom are called monatomic ions.
Sometimes ions can be formed from molecules or groups of atoms. These are called polyatomic ions. NH4
+ ammonium is a positive polyatomic ion
NO3- nitrate is a negative polyatomic
ion
Anions and Cations
Gain electrons = negative charge = anions
Lose electrons = positive charge = cations
E.g. Chloride anion E.g. Sodium cation
Chlorine accepts an extra Sodium donates an
electron from a cation electron to an anion
Na+
Examples
If Chlorine gains an electron, it becomes a negative ion with a charge -1This is written Cl-
Cl Cl
Examples
If Oxygen gains two electrons, it becomes a negative ion with a charge of -2
This is written O2- not O-2
If Lithium loses an electron, it becomes a positive ion with a charge of +1
This is written Li+
How Elements Combine
Atoms will form bonds in order to find a stable electron configuration (8 valence electrons). To do this, they will:
Share Electrons Covalent Bond
Gain ElectronsLose Electrons
Ionic Bond
Electronegativities
We can tell what type of bond will form between 2 atoms by looking at the difference between their electronegativities
Electronegativity (En) is a chemical property that describes the tendency for an element to attract electrons to itself.
Covalent Bonds
Covalent bonds occur between 2 non-metals
Atoms share electrons The difference in electronegativity is
less than 1.8
E.g. H2O, O2
We will study covalent bonds more in depth in a couple of days...
Ionic Bonds
Ionic bonds form between metals and non-metals
They occur when the difference in electronegativity (En) is greater than 1.8
Electrons are lost or gained
E.g. NaCl, MgBr2
Ionic Compounds: Lewis Dot Diagrams
Opposites attract! When one atom donates an electron
and another atom accepts an electron to fill their valence shells, the positive and negative ions stick together to form an ionic bond.
Na+
Ionic Compounds – The Cris-Cross Method
1) Write the chemical symbols for each of the atoms involved
2) Calculate the combining capacity for each atom (ion) involved
3) Cris-cross the combining capacities and write the formula
4) Put the formula in lowest terms
Example – Binary Compound
Combine Magnesium and Oxygen to make Magnesium Oxide
1) Chemical Symbols: Mg and O2) Combining Capacities Mg2+ and O2-
3) Criss Cross : Mg2+ O2- Mg2O2
4) Put in Lowest Terms MgO
Example: Binary Compounds
Combine Magnesium and Bromine to make Magnesium Bromide
Example: Binary Compounds
Combine Sodium and Chlorine to make Sodium Chloride
Example: Compounds – Polyatomic Example
Combine Ammonium and Iodine to create Ammonium Iodide
Example: Compounds – Polyatomic Example
Combine Calcium and Phosphate to make Calcium Phosphate.
Example: Compounds – Multiple Valence Example
Combine Lead (II) and Sulfate to make Lead (II) Sulfate
Chemistry in Action
Topic #6: Naming Ionic Compounds
Objectives: Be able to determine the name of an ionic compound by looking at its formula Be able to discuss why it is important to have a standard system of naming
The IUPAC System of Naming Compounds
IUPAC is the International Union of Pure and Applied Chemistry
The goal of IUPAC is to ensure that spoken and written chemicals are unambiguous.
Each chemical name should refer to a specific substance.
Why is Naming Important? Dihydrogen Monoxide FAQ Dihydrogen Monoxide (DHMO) is a colorless and
odorless chemical compound, also referred to by some as Dihydrogen Oxide, Hydrogen Hydroxide, Hydronium Hydroxide, or simply Hydric acid. Its basis is the highly reactive hydroxyl radical, a species shown to mutate DNA, denature proteins, disrupt cell membranes, and chemically alter critical neurotransmitters. The atomic components of DHMO are found in a number of caustic, explosive and poisonous compoundssuch as Sulfuric Acid, Nitroglycerine and Ethyl Alcohol.
Naming Binary Ionic Compounds
Rules:1) The cation (positive ion) comes first2) The anion (negative ion) comes second3) The cation takes the element name4) The anion takes the elements name, but ends with “ide”
Examples: Binary Ionic Compounds
Example: NaCl Cation = Sodium Anion = Chlorine Chloride
Name: Sodium Chloride
Examples: Binary Ionic Compounds
Example: MgBr2
Cation = Magnesium Anion = Bromine Bromide
Name: Magnesium Bromide
Examples: Binary Ionic Compounds
Example: AlCl3
Example: SiO2
Naming Binary Ionic Compounds with Multiple Valences
Elements with more than one combining capacity need to be identified
Roman numerals after the cation are used to indicate the combining capacity
To determine what the oxidation number is, you must first determine what the combining capacity is.
Example: Ionic Compounds with Multiple Valences
Example: PbCl4
First, determine the charge of chlorine 1-
Second, determine what the charge of lead has to be to balance the chlorine 4+
Use the roman numeral to indicate the charge:
Lead (IV) chloride
Example: Ionic Compounds with Multiple Valences
Name: CoBr3
Charge of bromine = 3- The charge of cobalt must be 3+ to
balance
Cobalt (III) bromide
Example: Ionic Compounds with Multiple Valences
Name: PbO2
Charge of oxygen = 2- There are 2 oxygen atoms that we
must account for: 2 x 2- = 4-
Lead (IV) oxide
Example: Ionic Compounds with Multiple Valences
Name: FeS
Example: Ionic Compounds with Multiple Valences
Name: SnBr2
Example: Ionic Compounds with Multiple Valences
Name: Cr2O3
Naming Polyatomic Ionic Compounds
To name polyatomic ionic compounds, use the names off the back side of the periodic table.
Example: Naming Polyatomic Compounds
Name : AlPO4
Cation = Aluminum Anion = Phosphate
Name: Aluminum phosphate
Example: Naming Polyatomic Compounds
Name : Ba(CN)2 Cation = Barium Anion = cynanide
Barium cyanide
Example: Naming Polyatomic Compounds
Name NH4NO3
Cation = Ammonium Anion = Nitrate
Name: Ammonium nitrate
Example: Naming Polyatomic Compounds
Name KNO2
Example: Naming Polyatomic Compounds
Name CaCO3
Example: Naming Polyatomic Compounds
Name Pb(OH)2
Chemistry in Action
Topic #7 – Covalent Compounds
Objectives: Be able to differentiate between ionic and covalent bonds Be able to show electron sharing of electrons in covalent bonds Be able to name covalent compounds Be able to write the formula for covalent compounds
Ionic Recap
Up until now, we have discussed ionic compounds
In ionic compounds, one element donates an electron to another, so both have complete valence shells
K Cl [K][ Cl ]+ -
Ionic Recap
In ionic bonds, the difference in electronegativity is greater than 1.8
Ionic bonds are formed between a metal and a nonmetal
Covalent Bonds
Covalent bonds are formed when atoms share electrons
They occur between two non-metals
The difference in electronegativity is less than 1.8
Electron Sharing in Covalent Bonds
In a covalent bond, electrons are shared.
Structures are drawn to show the sharing
OHH
• All atoms involved now think that they have complete outer shells• The electrons go around both atoms
Short-hand Form
Rather than drawing all electrons, we can draw a line to show the sharing of electrons
OHH
Example
Example: Oxygen shares 2 sets of electrons
OO
O O• Sharing 2 sets of electrons is shown by a double line.
Try this one...
CO2
Try this one...
Cl2
Two Types of Covalent Bonds
There are 2 types of covalent bonds that you need to know for this class: 1) Non-polar covalent 2) Polar covalent
1) Non-polar Covalent Bonds
Non-polar covalent bonds occur when there is equal sharing of electrons
The electrons spend the same amount of time in the orbit of both elements
Electronegativity difference is less than 0.5
Examples: (I Have No Bright Or Clever Friends) I2 H2 N2
Br2 O2 Cl2 F2
1) Non-polar Covalent Bonds
Rules for naming non-polar covalent bonds: The compound takes the same name as
the element:
E.g. Cl2 = chlorine
2) Polar Covalent Bonds
Polar covalent bonds occur when there is unequal sharing of electrons
The electrons spend more time orbiting one element than the other
Electronegativity difference is between 0.5 and 1.8
2) Polar Covalent Bonds
Rules for naming polar covalent bonds:1) The element on the left side of the periodic table is listed first (exception: when there is carbon and hydrogen – carbon goes first)2) Use prefixes to show the number of each element in the compound3) The second element ends in “ide”
Prefixes for Polar Covalent Compounds
1 – mono (only for the 2nd element) 2 – di 3 – tri 4 – tetra 5 – penta 6 - hexa
Examples: Polar Covalent Compounds
Write formulae for the following:
Dihydrogen monoxide =
Phosphorus heptachloride =
Sulfur hexachloride =
Examples: Polar Covalent Compounds
Write the names of the following formulae:
CO2 =
N2O5 =
PCl5 =
Chemistry in MotionTopic #8: Chemical Reactions
Objectives: Be able to describe the Law of Conservation of Mass Be able to solve problems about the Law of Conservation of Mass Be able to write word equations and skeleton equations
Chemical Reactions
A chemical reaction is a process that involves the rearrangement of the molecular structure of a substance
Reactant 1 + Reactant 2 Product (Read “Reactant 1 reacts with
Reactant 2 to produce products”)
Law of Conservation of Mass
During a chemical reaction, the total mass of the reactants is always equal to the total mass of the products.
Matter is never destroyed or created.
Word Equations
Word equations summarize what’s happening in a chemical reaction.
Example: When magnesium reacted with oxygen, magnesium oxide was formed.
Magnesium + Oxygen Magnesium oxide
Try this one:
It was found that copper (II) sulfide was formed when copper reacted with sulfur.
Using Word Equations to Solve Conservation of Mass Problems
We can use word equations to help us solve conservation of mass problems.
Example: How many grams of sodium are needed to combine with 35.5 grams of chlorine to make 58.5 grams of sodium chloride?
Using Word Equations to Solve Conservation of Mass Problems
Example: How many grams of sodium are needed to combine with 35.5 grams of chlorine to make 58.5 grams of sodium chloride?
Step 1: Write a word equation Step 2: Write all known masses Step 3: Solve for the unknown mass
Try this one:
When 72 grams of water is decomposed, 8 grams of hydrogen is made along with some oxygen. What mass of oxygen is made?
Skeleton Equations
Chemical symbols and formulas contain more information about substances and how they react.
To develop a skeleton equation, you start by replacing words with chemical symbols and formulas.
Skeleton Equations
Skeleton equations summarize a chemical reaction in symbolic form.
They are not complete or accurate, however because it may violate the law of conservation of mass.
Skeleton Equations
Write the skeleton equation for the following reaction: Sodium combines with chlorine to make sodium chloride
Step 1: Write the word equation Step 2: Replace words with chemical
symbols
Try this one...
Potassium nitrate is mixed with sodium iodide and it reacts to form sodium nitrate and potassium iodide
State of Substances
Often, it is useful to know the state of the chemicals that are involved in the reaction.
You can add this information to a chemical equation by inserting an abbreviation in brackets after each chemical formula
Abbreviations for States
State Abbreviation
Examples (at Room Temp)
Solid (s) Iron: Fe(s)
Salt: NaCl(s)
Liquid (l) Water: H2O(l)
Gas (g) Helium: He(g)
Aqueous Solution(Dissolved in water)
(aq) Salt solution: NaCl(aq)
Example
Write the skeleton equation for:A solid piece of sodium was mixed
with water to form an aqueous solution of sodium hydroxide and hydrogen gas.
Chemistry in Motion
Topic #9: Balancing Chemical Equations
Objectives: Be able to determine the number of atoms of each element on the reactants side and the products side of chemical equations. Be able to determine whether or not an equation is balanced
The Law of Conservation of Mass
According to the law of conservation of mass, the mass of the products will always be equal to the mass of the reactants.
Reactants Products
The Law of Conservation of Mass
In normal chemical reactions, there will be the same number of atoms of an element on the products side and the reactants side.
Balanced Equations
Is the following equation balanced? E.g. Fe + S FeS
Tips:
1) Make a T-table out of the equation.
Fe + S FeS
Tips:
2) List all the elements.
Fe + S FeS
Fe Fe
S S
Tips:
3) List the number of atoms of each element on each side.
Fe + S FeS
Fe = 1 Fe = 1
S = 1 S = 1
Tips:
4) Form a conclusion.Fe + S FeS
Fe = 1 Fe = 1
S = 1 S = 1
There are equal numbers of atoms of each element on each side, so the equation is balanced
Is the following equation balanced? 2H2 + O2 2H2O
Unbalanced Equations
Are the following equations balanced?
K + Cl2 KCl
HgO Hg + O2
Try these...
Ca + H2O Ca(OH)2 + H2
N2 + H2 NH3
4Al + 3O2 2Al2O3
Try it!
For the rest of the week, we will be learning how to balance the equations if they are unbalanced.
Try it for yourself!
Chemistry in Action
Topic #10 – Balancing Chemical Equations Part 2
Objectives: Be able to balance chemical equations Describe why we never change the subscripts in chemical equations
Unbalanced Chemical Equations
A chemical equation is unbalanced if the number of atoms of each element on the products side is not equal to the number of atoms of each element on the reactants side.
Example: H2 + O2 H2OH = 2O = 2
H = 2O = 1
NEVER CHANGE THE SUBSCRIPTS
You can’t just add atoms at random to each side – you have to work with the molecules
This means we can’t change the subscripts of a molecule, we can just change the number of molecules on each side.
Example
Example: H2 + O2 H2O
Can we just change the equation to:H2 + O2 H2O2?
NO!!!
H = 2O = 2
H = 2O = 1
Never Change the Subscripts!!
H2O is not the same as H2O2
If we change the subscripts, we also change the type of product or reactant.
H
H
OH
HO O
Water Peroxide
Example
Example: H2 + O2 H2O
So instead we change the number of molecules of the compound.
H = 2O = 2
H = 2O = 1
Example
Example: H2 + O2 2H2O
If we have 2 molecules of water on the products side, now the oxygens are balanced – but what about the hydrogens?
H = 2O = 2
H = 2 4O = 1 2
Example
Example: 2H2 + O2 2H2O
If we have 2 molecules of hydrogen on the reactants side, now the equation is balanced.
H = 2 4O = 2
H = 2 4O = 1 2
Example
Example: 2H2 + O2 2H2O
If we have 2 molecules of hydrogen on the reactants side, now the equation is balanced.
H
H
OH
H
OH H
H H
O
O
Process for Balancing Chemical Equations
1) Draw boxes around the compounds. Never change anything in the box.
2) Make a list of the elements and the numbers of atoms of each element
3) Write numbers in front of each box until there is the same number of atoms of each element in the products and reactants. Whenever you change a number, make
sure to update your table
Try this one…
KCl K + Cl2
Try this one…
Fe + Cl2 FeCl3
Tips for Getting the Answer FasterMINOH = Me Know Chemistry
It won’t always work, but try this order for faster results.
M = Metals – Balance metals such as Fe or Na first
I = Ions – Look for polyatomic ions to balance next (more on this tomorrow)
N = Non-metals – Balance non-metals such as Cl or N next
O = Oxygen H = Hydrogen – save them for last
Example:
S8 + O2 SO3
S = 8O = 2
S = 1O = 3
Example:
C7H16 + O2 CO2 + H2O
C = 7H = 16O = 2
C = 1H = 2O = 3
Tricky Example:
C2H4O2 + O2 CO2 + H2OC = 2H = 4O = 4
C = 1H = 2O = 3