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