CHEMISTRY UNIT2.1: Chemical Reactions

A physical reaction is a change in which no new substances are formed. o Examples include: melting an ice cube (it is still water – just in a different state) or tearing up a piece of

paper (it is still paper – just in a different shape). A chemical reaction is a change in matter that produces new substances with new properties.

o A chemical reaction also involves energy. Some chemical reactions store energy (breaking an ice pack), while others release energy in the form of heat (for instance, burning wood).

o Examples include: lighting a match, burning toast, or photosynthesis. o The chemical reaction for photosynthesis is: carbon dioxide + water → sugar + oxygeno Vinegar is produced when yeast and fruit sugars are combined. Vinegar is actually a dilute solution of a

chemical called acetic acid. o Dilute is a concentration that is reduced by being mixed with a liquid, such as water.

The substances that react together in a chemical reaction are called the reactants. The new substances that

are produced in a chemical reaction are called the products.

You can write a chemical reaction as such: reactants → products (the arrow indicates that a chemical change is taking place).

Examples to do together:a) Determine if the following are examples of physical changes (P) or chemical changes (C):

_____ Boiling water _____ Burning fire wood _____ Baking a cake_____ Making kool-aid _____ Painting a wall _____ Washing your clothes

b) List the reactants and the products. Write a proper chemical reaction for each example below.i) Nitrogen gas reacts with hydrogen gas to produce ammonia.

ii) Hydrogen gas reacts with oxygen gas to produce water.

iii) Lithium bromide is produced when lithium reacts with bromine gas.

Lab Safety HHPS (Hazardous Household Product Symbols) use different shapes and easy

to recognize icons to display some basic safety information about a product.

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o The four categories are: explosive, corrosive, flammable, and poison. o The shapes of the labels have specific meanings: If the shape of the label is an inverted triangle, it

indicates that the container is dangerous. If the shape of the label is an octagon, it indicates that the contents inside the container are dangerous.

o The label will also state one of three terms: caution (means temporary injury may be frequent;

death may occur with extreme exposure), danger (means may cause temporary or permanent injury

or death), or extreme danger (with means exposure to very low quantities may cause death or temporary or permanent injury).

This symbol means the container is dangerous. It can explode if heated or puncture causing flying bits of metal or plastic that can lead to serious injuries.

This symbol means the product inside the container is dangerous. The octagonal stop sign usually appears with one of three cautions.

Usually you will see the triangle with the explosive symbol inside it.

Examples include aerosol cans, such as hair spray or spray paint.

Product is corrosive and will burn skin, eyes, throat, or stomach. Examples include oven cleaner and toilet bowl cleaner.

Product is flammable and will catch fire easily if it is near heat, flames or sparks. Examples include gasoline and hair spray.

Product is poisonous and will cause illness or death if ingested. Examples include furniture polish and windshield washer fluid.

Workplaces, such as restaurants, repair shops, industrial plants, and schools, have many hazardous substances.

These hazards are indicated using WHMIS (Workplace Hazardous Materials Information System).

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CompressedGas

Flammable and Combustible Material

Corrosive Material Oxidizing Material

Dangerously Reactive Material

Poisonous andInfectious Material

Causing Other Toxic Effects

Poisonous andInfectious Material

Causing Immediate and Serious Toxic Effects

Biohazardous Infectious Material

These labels, and any pertinent information, such as steps for handling and storing the chemical, is found on the

MSDS (Material Safety Data Sheet) for any chemical.

2.2: Chemical Compounds All compounds are formed from two or more elements. The periodic table organizes all the elements in rows and columns. Each element has its own place in the periodic

table based on its properties and its atomic structure (the number of electrons, protons, and neutrons that an element has)

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Some trends of the periodic table:o Periods: represent a row on the periodic table. The period number represents the number of

electron shells in the atoms of an element. For example, lithium is in period 2, therefore it has 2 shells of electrons.

o Families or Groups: represent a column on the periodic table. Every element in the same group will have the same number of electrons in their last (valance) shell. For example, all elements in group 1 have 1 electron in their valance shell. All elements in the same group also share similar chemical and physical properties.

o Metals: are located on the left side of the periodic table (on the left side of the “staircase”). All metals (except for mercury) are malleable, shiny, conduct heat and electric current, and are solids at room temperature.

o Group 1 metals are called Alkali Metals which are the most reactive metals. Their reactivity increases as you move down the group. The most reactive metal is cesium (Cs).

o Group 2 metals are called Alkaline Earth Metals which are the 2nd most reactive metals.

o Metalloids: elements that have properties of both metals and non-metals. They are found at the “staircase” on the periodic table. For example, boron, silicon, and arsenic.

o Non-metals: are located on the right side of the periodic table (on the right side of the “staircase”). All non-metals are non-malleable, do not conduct heat or electric current, are dull and brittle, and can be solids, liquids, or gases at room temperature.

o The most reactive non-metals are in group 17, called halogens. Their outermost electron shell is one electron short of being full. Their reactivity decreases as you go down the group. The most reactive halogen is fluorine (F).

o Noble Gases: are located in group 18 on the periodic table. They have a full outer electron shell (8 electrons), which makes them unreactive. They are also called “inert gases” since they do not react with other elements.

o Hydrogen: it is located in group 1 and period 1. Hydrogen is unique because it only has 1 electron in its only shell. It can behave like the group 1 metals, since it only has one electron in its outer shell. However, it can behave like the group 17 non-metals, since it needs only one electron to complete its outer shell.

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You can determine the number of protons, electrons, and neutrons by looking at an element’s atomic mass and its atomic number.

Remember that protons are positively charged and are found inside the atom’s nucleus. Neutrons are neutrally charged and also found inside the atom’s nucleus. Together, the protons and neutrons make up the atomic mass of the atom.

Electrons are negatively charged and are found in shells (or orbits) that surround an atom’s nucleus. Electrons are very small in comparison to protons or neutrons. We say that their mass is equal to zero.

An atom is neutral if it has the same number of protons as electrons. All elements are neutral yet unstable since they all have outer (valence) shells that are not full. Only noble gases (in group #18) are stable since they are the only elements that have a full valence shell of electrons.

All other elements need to gain or lose electrons in order to have a full valence shell. This is what gives

the atom an overall charge. It would now be considered an ion which is an atom with an overall electrical charge (either positive or negative).

Since METALS always have 1, 2, or 3 electrons in their valence shell, it is easier to LOSE these electrons to a non-metal and have a full inside shell. Since the metal LOSES electrons, it now has more protons than electrons. This is what gives all metals a POSITIVE CHARGE. A positively charged ion

is called a cation. Since NON-METALS always have 5, 6, or 7 electrons in their valence shell, it is easier to GAIN extra

electrons from a metal and have a full shell. Since the non-metal GAINS electrons, it now has more electrons than protons. This is what gives all non-metals a NEGATIVE CHARGE. A negatively

charged ion is called an anion. The ATOMIC NUMBER is the number of protons that the element has. And, remember that in a neutral

element, the number of electrons equals the number of protons (this is what makes it neutral since the positive charge cancels out the negative charge).

The ATOMIC MASS is the number of protons + the number of neutrons in the atom’s nucleus.

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Examples to do together:Name Symbol Atomic

MassAtomic Number

Number of

Protons

Number of

Electrons

Number of

Neutrons

Metal or Non-

metal?

Does it gain or

lose electrons?

Type of Ion formed?

NitrogenCa

74.98

18Barium

We can draw a Bohr diagram to represent the number of protons, neutrons, and electrons that an element has. Remember that the first shell can hold a maximum of 2 electrons, and each shell after this can hold a maximum of 8 electrons. You cannot move to the next shell unless the inside shell is full with its maximum number of electrons.

Examples to do together:a) Lithium b) Oxygen

d) Aluminum e) Chlorine

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Chemical Formulas The short form for a chemical compound is called a chemical formula. A chemical formula is a

group of letters and subscript numbers that represent the make-up of a chemical compound. The letters are the chemical symbols. They tell you which elements are in the compound. The subscript numbers tell you how many atoms of these elements are in the compound. For example: H2O is the chemical formula for water. It tells us that that there are 2 hydrogen atoms and

1 oxygen atom. We do not write the subscript number of 1 since it is already assumed by the chemical symbol.

Examples to try together:a) CH4 b) Ca3(PO4)2 c) 2Mg3N2

d) NH3 e) 3LiSO3 f) Al2(SO4)3

Ionic Compounds Ionic compounds are formed when a metal gives a non-metal its valence electrons. The positively charged metal

bonds with the negatively charged non-metal. This forms an ionic bond between a metal and a non-metal. The ionic bond is formed by the transfer of electrons between the metal to the non-metal.

Ionic compounds are always: solids are room temperature; have a very high melting point; and they conduct electricity when they are melted or dissolved in water.

Examples of ionic compounds include: NaCl (Sodium chloride; which is known as table salt); CaCl2 (Calcium chloride; which is known as road salt); and CaO (Calcium oxide; which is known as lime used in plaster).

Rules for writing and naming ionic compounds: Always write the metal first, and the non-metal second. Write the symbol for both the metal and the non-metal. Look at the charge for each of the elements. Write this charge number above its chemical symbol. Now, use the “criss-cross” method to create each element’s subscript number. This means that the charge

number of the metal will become the subscript number of the non-metal; and the charge number of the non-metal becomes the subscript number of the metal.

Remember that we do not write a subscript of “1”, and if necessary, always reduce subscripts. For example, Ca2S2 can be reduced to Ca1S1 and since we do not write the subscript of 1, it becomes CaS.

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Finally, when you name the ionic compound, you write the name of the metal first, then the name of the non-metal second. Change the ending of the non-metal’s name to “-ide”, For example, CaS would be named calcium sulfide.

Examples to do together:i) Give the names and chemical formulas for the following examples:a) Calcium and Nitrogen b) Lithium and Fluorine c) Aluminum and Sulfur

ii) Give the chemical formulas for the following examples:d) Beryllium chloride e) Rubidium iodide f) Sodium oxide

iii) Give the names for the following examples:g) K3P h) CaF2 i) BaBr2

Multivalent Metals Some metals have more than one possible charge. In order to know which charge number to use, we indicate the

charge with a Roman numeral (I, II, III, or IV). For example: Copper can have a charge of 1+ or 2+. If we want to use Cu2+ we would indicate it as Copper (II) When writing the name for an ionic compound that includes a multivalent metal, always put the Roman numeral

in the name. Multivalent metals include:

Chromium (2+ or 3+) Manganese (2+, 3+, or 4+) Iron (3+ or 2+)Nickel (2+ or 3+) Rhodium (3+ or 4+) Palladium (2+ or 4+)Tin (2+ or 4+) Platinum (2+ or 4+) Gold (1+ or 3+)Mercury (1+ or 2+) Lead (2+ or 4+)

Examples to do together:i) Give both the names and chemical formulas for the following examples:a) Tin (IV) and sulfur b) Gold (I) and nitrogen c) Mercury (II) and chlorine

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ii) Give the names for the following examples:d) Ni3N2 e) FeP f) PbO2 g) HgBr2

iii) Give the chemical formulas for the following examples:h) Copper (II) oxide i) Gold (I) sulfide j) Tin (III) chloride

Polyatomic Ions Some ions have more than one type of atom. These ions are known as polyatomic ions, and the entire polyatomic

ion carries a specific charge. The polyatomic ions include:

NH4+ (Ammonium) PO4

3- (Phosphate) PO33- (Phosphite)

SO42- (Sulfate) SO3

2- (Sulfite) CO32- (Carbonate) ClO3

- (Chlorate)NO3

- (Nitrate) NO2- (Nitrite) HCO3

- (Bicarbonate) OH- (Hydroxide)

Examples to do together:i) Give the names and chemical formulas for the following examples:a) Calcium and nitrate b) Cesium and phosphite c) Barium and sulfate

ii) Give the names for the following examples:d) K3PO4 e) Al2(SO3)3 f) Mg(OH)2

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iii) Give the chemical formulas for the following examples:g) Rubidium carbonate h) Sodium bicarbonate i) Gallium nitrite

Molecular Compounds Molecular compounds are formed between two non-metals. A covalent bond is formed between the two non-

metals as they share their valence electrons in order to fill each of their valence shells. Molecular compounds can be solids, liquids, or gases at room temperature; they have lower melting points than

ionic compounds; and they do not conduct electric current when they are melted or dissolved in water. Examples of molecular compounds include: CH4 (Methane); CO2 (Carbon dioxide); and H2O (Water).

Rules for writing and naming molecular compounds:

To determine which non-metal to write first, always write the non-metal that has the lower group number first. For example, if you combined carbon and oxygen, you would write carbon first since it is group #14 and oxygen is in group #16.

Use the criss-cross method to determine each non-metal’s subscript number. Remember to not write the subscript number “1”. For molecular compounds, you do not reduce any subscript numbers. Leave it as is. When naming a molecular compound, you must add a prefix in front of each non-metal’s name. This

prefix is determined by the non-metal’s subscript number. If the first non-metal has an assumed subscript number of “1”, you do not use a prefix. For example: CO2 is named carbon dioxide; Si3P4 is named trisilicon tetraphosphide.

Change the ending of the 2nd non-metal to “-ide”. The prefixes are:

1 = mono- 2 = di- 3 = tri- 4 = tetra 5 = penta

Some molecular compounds have special name:

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H2O (water) CH4 (methane) NH3 (ammonia) H2O2 (hydrogen peroxide)

Some molecular compounds are known as diatomic molecules. These are always gases. They include: H2 O2 N2 Cl2 F2 Br2 I2

Examples to do together:i) Give the name and chemical formula for the following examples:a) Carbon and Sulfur b) Nitrogen and Chlorine c) Arsenic and Iodine

ii) Give the names for the following examples:d) Si3N4 e) CH4 f) NBr3 g) Cl2

iii) Give the chemical formulas for the following examples:h) Ammonia i) Diphosphorus trisulfide j) Dicarbon tetraselenide k) Oxygen gas

Structural diagrams are diagrams used to demonstrate the covalent bonds formed within a molecular compound. Each “stick” in the diagram represents one bond that is formed when two non-metals share an electron.

Examples to do together:a) H2O b) NH3 c) CH4 d) CO2

2.3: Chemical Reactions There are different forms of evidence that a chemical reaction has occurred:

o There is a change in energy (a temperature change – increasing or decreasing; light or heat being produced).

o There is a change in colour11

o A gas is formed (bubbles are formed)o There is a new odour producedo A precipitate is formed (a solid substance within a liquid)

There are 3 ways in which a chemical reaction can be expressed:o A chemical equation is an equation that uses chemical symbols to represent reactants and

products in a chemical reaction.o A word equation is when you use words for the reactants and the products.

Example: oxygen gas + hydrogen gas → watero A skeleton equation is when you replace the words with the chemical formulas.

Example: O2 + H2 → H2Oo A balanced equation is when you use coefficients to balance the number of atoms in the

reactants with the number of atoms in the products. It follows the Law of Conservation of Mass. Example: 2O2 + H2 → 2H2O

The Law of Conservation of Mass states that during a chemical reaction, the total mass and number of atoms of the reactants equals the total mass and number of atoms of the products.

Examples to do together:a) Sodium reacts with nitrogen gas to produce sodium nitride.

b) Magnesium chloride reacts with lithium phosphide to produce magnesium phosphide and lithium chloride.

c) Calcium hydroxide reacts with Potassium phosphite to produce calcium phosphite and potassium hydroxide.

d) Barium oxide reacts with bromine gas to produce barium bromide and oxygen gas.

There are 4 types of chemical reactions:Type of Reaction Representation of the

ReactionExample of the Reaction

Synthesis(two or more reactants combine

to produce a new product)

A + B → AB hydrogen gas + oxygen gas → waterH2 + O2 → H2O

Decomposition(one compound breaks down into two or more simpler compounds

AB → A + B water → hydrogen gas + oxygen gasH2O → H2 + O2

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or elements)Single Displacement

(one element takes the place of another element in a compound to produce a new single element and

a new compound)

A + BC → AC + B(if A is a metal)

OR

D + BC → BD + C(if D is a non-metal)

copper + silver nitrate → copper (II) nitrate + silverCu + AgNO3 → Cu(NO3)2 + Ag

aluminum bromide + oxygen gas → aluminum oxide + bromine gas

AlBr3 + O2 → Al2O3 + Br2

Double Displacement(two compounds react to form

two new compounds in which the metals change places)

AB + CD → AD + CB calcium hydroxide + lithium nitrate→ calcium nitrate + lithium hydroxide

Ca(OH)2 + LiNO3 → Ca(NO3)2 + LiOH

Examples to do together:i) Determine the type of reaction that each of the following examples is depicting. Then, balance each chemical equation.a) _____ NaOH + _____ Ca(NO3)2 → _____ NaNO3 + _____ Ca(OH)2

Type of Reaction: __________________________________

b) _____ Al2O3 → _____ Al + _____ O2

Type of Reaction: __________________________________

c) _____ BeBr2 + _____ Li → _____ LiBr + _____ BeType of Reaction: __________________________________

d) _____ Ba + _____ PO4 → _____ Ba3(PO4)2

Type of Reaction: __________________________________

ii) Determine the type of reaction that is occurring, create the products for the chemical reaction and then balance the chemical equation.a) _____ ZnSO4 + _____ K → _______________________________

Type of Reaction: _______________________________________

b) _____ NH3 → _____________________________________________Type of Reaction: _______________________________________

c) _____ Be + _____ NO3 → __________________________________Type of Reaction: ______________________________________

d) _____ CaSO4 + _____ Al(OH)3 → ___________________________Type of Reaction: _______________________________________

2.4: Acids and Bases

An acid is a compound that tastes sour, corrodes metals and tissues, and turns blue litmus paper red. Acids have a higher concentration of H+ ions and have a pH value between 0 – 6.

o Examples of acids include: lemons, grapefruits, vinegar, apples, and yogurt.

A base is a compound that tastes bitter, has a slippery texture, corrodes tissues, and turns red litmus paper blue. Bases have a higher concentration of OH- ions and have a pH value between 8 - 14.

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o Examples of bases include: eggplant, unsweetened chocolate, bitter melon, tonic water, and most cleaning products.

Property Acids BasesTaste Tastes sour Tastes bitter

Texture Has no characteristic texture Has a slippery textureConductivity Conducts electric current when

dissolved in waterConducts electric current when

dissolved in waterCorrosion Corrodes living and once-living tissue,

as well as metalsCorrodes living and once-living

tissueChemical reaction with metals Are reactive with metals Are not reactive with metals

Chemical reaction with litmus paper Turns blue litmus paper red Turns red litmus paper blueChemical reaction with each other Loses many of their properties when

they react with bases.Loses many of their properties

when they react with acids.

One way to identify acids and bases is to use an acid-base indicator. An acid-base indicator is a substance that changes colour when added to an acid or a base. For

example, litmus paper. Another way to identify acids and bases is to use numbers. For this, we use the pH scale which is a scale

from 0-14 that describes how acidic or basic a substance is. o Acids have a pH value of 0-6. The lower the pH value, the stronger the acid. Therefore, an acid with a

pH of 0 is very strong, while an acid with a pH of 6 is very weak. The stronger the acid, the higher the concentration of H+ ions present in the solution.

o Bases have a pH value of 8-14. The higher the pH value, the stronger the base. Therefore, a base with a pH of 14 is very strong, while a base with a pH of 8 is very weak. The stronger the base, the higher the concentration of OH- ions present in the solution.

o A solution with a pH of 7 is considered to be neutral. Examples of neutral substances are salt and pure water.

o Every pH value actually indicates a 10x increase in the strength of a solution. For example, an acid with a pH of 4 is 10x more acidic than an acid with a pH of 5. Another example is an acid with a pH of 3 is 1000x more acidic than an acid with a pH of 6.

The chemical reaction between an acid and a base is a double displacement reaction. Specifically, it is known as

a neutralization reaction.o The hydrogen ions (H+) from the acid combine with the hydroxide ions (OH-) to produce water (H2O).

Then, the metal from the base combines with the non-metal from the acid to produce a salt.

o Example: HCl (aq) + NaOH (aq) → H2O + NaCl acid + base → water + salt

o Example: H3PO4 + Mg(OH)2 → ________________________

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o Example: H2SO3 + Al(OH)3 → _________________________

An example of a neutralization reaction is one that takes place in your body. Your stomach produces a powerful acid to kill germs that might be in your food when you eat. This acid is neutralized by a strong base in your small intestine. If your stomach produces too much acid, you may feel pain around the area of your chest and throat. This is called acid reflux, or heartburn.

An antacid is a base that is used to neutralize the acid from your stomach. That is why you chew an antacid (for example, Tums or Rolaids) to treat your acid reflex (heartburn).

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