Chemical Change M4 Periodic Table: Chemical Change Slide 3 of 35 Learning objectives Key Concepts: –Combination, synthesis, decomposition, displacement,

Chemical ChangeChemical Change

M4 Periodic Table: Chemical Change Slide 3 of 35

Learning objectivesLearning objectives• Key Concepts:

– Combination, synthesis, decomposition, displacement, double displacement, precipitation, signs of reaction

– reaction, physical property, chemical property, element, compound, mixture, word equation, chemical equation,

– Word equation, chemical equation, reactant, product,

Learning objectivesLearning objectives

• Skills: – Identify diagrammatic representation for

element, compound and mixture – Distinguish between element, compound and

mixture – Distinguish between physical change and

chemical change – Identify a chemical reaction


Learning objectivesLearning objectives– Write word equations for simple combination

reactions between metals and non-metals given the names of the chemicals involved.

– Write chemical equations for simple combination reactions given the formula of the compounds

– Balance simple combination reactions given the formula of the chemicals involved using particle diagrams and the law of conservation of matter.

– Discuss signs of reaction (the four hints that indicate a chemical change)


Combination ReactionCombination Reaction• We will next start by considering a few variety of

interactions between elements which produce compounds. Whenever elements and/or compounds interact, they are said to have undergone a chemical reaction.

A chemical reaction produces a completely new substance or substances.

The most simple of these reactions is combination (or synthesis) reaction.

(When elements and/or compounds are just physical brought together, they form a mixture of course.)

Practice Question (7)

• Balance the following formulas– BaCl– NH4O– NaS– AuAg– Iron III Oxide


Combination ReactionCombination Reaction• Combination reactions are ones where two different

elements chemically combine to produce a single compound.

Element A + Element B Compound containing A and B

– A metal can combine with a non-metal to form a compound Metal + Nonmetal Compound containing

metal & nonmetal – Two non-metals can combine to form a compound.

Nonmetal A + Nonmetal B Compound containing nonmetal A & B

Combination ReactionCombination Reaction

• Two metals cannot combine to form compounds however. (They do mix to give alloys, which is a mixture and not a compound.)

• The physical and chemical properties of the compound are usually different from those of the elements it is made from.


Chemical EquationChemical Equation• You will study several different types of

chemical reactions and learn to represent them using words or formula of the substances involved.

The simplest way of representing a reaction is using the names of the chemical involved (called word equation).

A chemical equation is a chemical short-hand for a host of information

Chemical EquationChemical Equation

Sodium + oxygen Sodium oxide – Everything to the left of the arrow is referred to as

reactants and everything to the right product(s) – “” means produces or yields or gives or results

in – “+” on the left side means “reacts with” or

“combines with” – (If “+” appears on the right hand side it means

“and.”)


Representing ReactionsRepresenting Reactions• Here are some more examples of word

equations: Hydrogen + oxygen Water Coal (carbon) + oxygen Carbon dioxide Zinc + Iodine Zinc iodide Aluminum + Iodine Aluminum iodide Aluminum + bromine aluminum

bromide

Representing ReactionsRepresenting Reactions

• The other method of representing chemical reactions is to use the formula of the substances involved. – 2Na (s) + O2 (g) 2Na2O (s)

• Is this balanced?

– 2H2 (g) + O2 (g) 2H2O (l)– (Note hydrogen and oxygen and are diatomic

elements)



C (g) + O2 (g) CO2 (g) Zn (s) + 2I (s) ZnI2 (s) 2Al (s) + 6I (s) 2AlI3 (s) 2Al (s) + 6Br (l) 2AlBr3 (s)

• The equations above are referred to as chemical (or symbolic) equations.


• Notice a couple of things that’s different about a chemical equation compared to word equation:

– Chemical equation includes symbols in bracket next to the chemicals involved in the process

– Coefficients in front of the formula of the chemicals involved in the chemical process.


State SymbolsState Symbols• The symbols in brackets are referred to as the (physical)

state symbol. The state symbols indicate the physical state of the substances.

– s = Solid – l = liquid – g = gas – aq = aqueous (dissolved in water, in other words in

solution) • You should by now know the physical states of most of the

elements and be able to supply the state symbol for any element that appears in an equation.


State SymbolsState Symbols• As far as compounds go all compounds of metals are solid. Compounds formed by the combination two non-metals

however, can be solid, liquid or gas. – However, most of those that you will have to work with and be

able to recognize are gaseous. – Water of course is liquid. – But, carbon dioxide (CO2) and carbon monoxide (CO), both

oxides of carbons are gaseous. – Both sulfur dioxide (SO2) and sulfur trioxide (SO3) are gaseous as

well. – Hydrogen sulfide (H2S) is also gaseous. – All halides of hydrogen (hydrogen chloride, HCl, hydrogen

bromide, HBr, and hydrogen iodide, HI) are gaseous as well.


CoefficientsCoefficients• Coefficients in front of the formula are

required to conform to the law of conservation of matter. That is, since matter cannot be destroyed or created, atoms and molecules cannot be destroyed or created in a chemical process. The number of atoms at the end of a chemical process must be equal to the number of atoms in the beginning. For simple combination reaction, you can balance them by drawing (or imagining) particle diagrams.


Combination ReactionCombination Reaction• So a reaction between sodium and oxygen can be visualized

as follows: Na + O2 Na2O

• What that means is that to form one unit of the compound sodium oxide, two sodium atoms are needed to combine with one atom of oxygen. – Each formula can be made to represent one fundamental

particle. – Na represents 1 atoms of sodium, and O2 represents 1

moleculeof oxygen (which is 2 atoms). • Notice, as written, the equation shows the loss/destruction

of one oxygen atom and creation of one sodium atom!

+


Combination ReactionCombination Reaction• Since oxygen atoms travel around in pairs (Diatomic), we

must end up with two oxygen atoms in the number of units of the compound produced.

+

• So, in the equation a molecule of oxygen is shown to produce two units of sodium oxide. Accounting for the number of oxygen atoms has meant the creation of sodium atoms.


Combination Reaction: Balancing Combination Reaction: Balancing EquationEquation

• The creation of 3 sodium atoms, which we can balance by adding three more sodium atoms to the left.

+

• Giving us the balanced equation: 4Na + O2 2Na2O

• A chemical equation must be balanced so as to not contradict the law of conservation of matter.


Combination Reaction: Balancing Combination Reaction: Balancing EquationEquation

• A reaction between zinc and iodine can be visualized as follows: Zn + I2 ZnI2 +

• Draw balanced diagrams to represent the following reaction: Al + I2 AlI3


Practice QuestionPractice Question• Draw balanced diagrams to represent the following reaction:

Al + O2 Al2O3


Combination Reaction: Metal + Combination Reaction: Metal + NonmetalNonmetal

• In the lab you observed some dramatic combination reaction, one of which was that between zinc and iodine. Zinc + Iodine Zinc iodide

• When a metal (such as zinc) and non-metal (such as iodine) combine to form a compound, the name of the compound is derived by writing the name of the metal first followed by the name of the non-metal whose last syllable is replaced by an –ide ending. – Iodine therefore becomes iodide.

• Hence the name of a compound of zinc and iodine is zinc iodide.

You also observed a reaction between aluminum and iodine. The word equation for that looks like this:

Aluminum + Iodine Aluminum iodide



• So, names of all compounds formed by the combination of a metal and iodine have the format: name of metal followed by iodide.

As a matter of fact, compounds containing iodine and a metal are referred to as iodides. – That is, zinc iodide, aluminum iodide, sodium iodide, magnesium

iodide are examples of iodides. • You also observed some reactions between oxygen and other

elements. Sodium + oxygen sodium oxide Magnesium + oxygen magnesium oxide

• In other words, compounds of consisting of an element and oxygen are referred to as oxides.



• You also observed some reactions between other metals and non-metals: zinc + sulfur zinc sulfide iron + sulfur iron sulfide

• In general then: Metal + non-metal metal and name of non-metal with –ide

ending



• Hydrogen becomes hydride. Nitrogen becomes nitride. Oxygen becomes oxide. Fluorine becomes fluoride. Phosphorus becomes phosphide. Sulfur becomes sulfide. Chlorine becomes chloride. Bromine becomes bromide.


Combination Reaction: Non-metal + non-Combination Reaction: Non-metal + non-metalmetal

• So what do you call a compound of hydrogen and oxygen combined together? Hydrogen + oxygen hydrogen oxide?

• Not really, though that would make sense. You all know it’s called water.


Combination ReactionCombination Reaction• The names and the products of a reaction between two non-

metals are not as easy to figure out and determine.

++

• hydrogen (gas) + oxygen (gas) water

• Other reactions were: carbon + oxgyen carbon dioxide

++

– This is the reaction that takes place when coal burns.



Nitrogen + oxygen nitrogen oxide – This reaction can take place in the engine of a car.

nitrogen + hydrogen nitrogen + hydrogen ammonia ammonia

++

hydrogen + fluorine hydrogen + fluorine hydrogen fluoride hydrogen fluoride

++



hydrogen + chlorine hydrogen chloride

hydrogen + bromine hydrogen bromide

hydrogen + iodine hydrogen iodide sulfur + oxygen sulfur dioxide

• But notice that as long as the compound is made of two different elements, their names end in –ide.


• A compound is different from a mixture in that the atoms in a compound are chemically bonded together, and that’s why the physical and chemical properties of the compound is markedly different from the elements from which it is made.

• In the next several slides we will look at properties of some elements and the compounds they form.

Practice Problem (33)

• The next few slides show how compounds have different properties then the elements the are made of, they are examples, you do not need to learn them

• Write the balanced chemical equation for each in one box on your assignment sheet


Formation of WaterFormation of Water• Element: Hydrogen, symbol: H,

formula: H2

Properties: • an odorless molecular gas room

temperature • transparent, clear, light passes

through it • chemically reactive - very reactive

when a small spark is provided

Element: Oxygen, symbol: O; formula: Element: Oxygen, symbol: O; formula: OO2 2

Properties: Properties:

• an an odorlessodorless molecular molecular gas gas at at room temperature room temperature

• transparenttransparent, clear, light passes , clear, light passes through it through it

• chemically reactive - very chemically reactive - very reactive when heatedreactive when heated

Compound: Water, HCompound: Water, H22O O


• An An odorlessodorless liquidliquid at room temperature at room temperature

• transparenttransparent, clear, light passes through it , clear, light passes through it

• not vernot veryy chemicall chemicallyy reactive reactive, the compound is stable, the compound is stable


Formation of AmmoniaFormation of Ammonia• Element: Hydrogen, H; symbol:

H, formula: H2

Properties: • an odorless molecular gas room

temperature • transparent, clear, light passes

through it • chemically reactive - very reactive

when a small spark is provided

Element: Nitrogen, N; Element: Nitrogen, N; symbol: N, formula: N2


• A A odorlessodorless molecular molecular gas gas at at room temperature room temperature



Compound: Ammonia, NHCompound: Ammonia, NH33

Properties: Properties: • a characteristic a characteristic pungent smelling pungent smelling gasgas at room temperature at room temperature


• A relatively reactive compoundA relatively reactive compound


Carbon dioxideCarbon dioxide• Element: Carbon, symbol: C;

formula: C.

Properties: • a solid (powder) at room

temperature

• black coloured, absorbs all light, none passes through

• chemically reactive when heated slightly

Element: Oxygen, O;Element: Oxygen, O; symbol: O; symbol: O; formula: Oformula: O2 2


• a a gas gas at room temperature at room temperature



Compound: Carbon dioxide, COCompound: Carbon dioxide, CO22

Properties: Properties: • a a gasgas at room temperature at room temperature


• not vernot veryy chemicall chemicallyy reactive reactive, the compound is stable, the compound is stable


Sulfur DioxideSulfur Dioxide• Element: Sulfur, symbol: S;

formula: S. Properties:

– a solid at room temperature – yellow coloured – insoluble in water – chemically reactive when

heated slightly

Element: Oxygen, O; symbol: O; Element: Oxygen, O; symbol: O; formula: Oformula: O2 2


• a a gas gas at room temperature at room temperature



Compound: Sulfur dioxide, SOCompound: Sulfur dioxide, SO22

Properties: Properties: • a a gasgas at room temperature at room temperature


• readily dissolves in waterreadily dissolves in water


Sodium oxideSodium oxide• Element: Sodium,

symbol: Na; formula: Na. Properties:

– a solid at room temperature

– silver coloured – very reactive (hence

stored under oil)

Element: Oxygen, O;Element: Oxygen, O; symbol: O; symbol: O; formula: Oformula: O22

Properties: Properties: • a a gas gas at room temperature at room temperature • transparenttransparent, clear, light passes , clear, light passes

through it through it • chemically reactive - very chemically reactive - very

reactive when heatedreactive when heated

Compound: Compound: Sodium oxide, Na oxide, Na22OO

Properties: Properties: • a gray a gray solidsolid at room temperature at room temperature • hygroscopic hygroscopic • readily dissolves in waterreadily dissolves in water


Compound and mixtureCompound and mixture• A mixture on the other hand retains the properties

of the elements and/or compound it is made of. – For example sea water is a mixture and it

retains the saltiness of salt and fluidity of water. – Vinegar is a mixture of acetic acid and water – Air is a mixture of different gases (nitrogen,

oxygen, argon and a few others). – Alloys are mixtures of two or more metals. Steel

is an alloy of iron, chromium and nickel; bronze: copper & tin etc.


Signs of reactionSigns of reaction• When you observed combination reactions, you would have

noted the following signs of reaction– change in color and/or – production of a solid where there was no solid or

a different colored solid from that already present in the mixture, and/or

– Bubbling or evolution of a gas that is colored or has an odor, and/or

– Change in energy--either production of energy in the form of sound energy (explosion) or generating heat energy (increasing temperature) or using up heat energy (decreasing temperature).


Why do elements react with one Why do elements react with one another?another?

• Elements react with each other because they are energetically unstable.

Atoms of noble gases are energetically stable while the rest of the elements in the periodic table are not. – Atoms of noble gases are energetically stable

because their valence shells contain the maximum number of electrons that they can accommodate.

• So, atoms of other elements try to attain a similar electronic structure as those of noble gases and they do so by reacting with other elements.

Atoms of other elements achieve the same electronic structure as a noble gas by either losing electrons, or gaining electrons or sharing electrons between themselves.


Metal atoms lose electronsMetal atoms lose electrons• Metal atoms in general achieve noble gas structure by losing

their valence electrons.

Na

Sodium atom Sodium atom after losing 1 electron

Na

Mg

Magnesium atomMagnesium atom after losing 2 electrons

Mg


Nonmetal atoms either gains Nonmetal atoms either gains electronselectrons

• Non-metal atoms when reacting with metals achieve noble gas structure by gaining electrons.

O

Oxygen atomOxygen atom after gaining 2 electrons

O

F

Fluorine atomFluorine atom after gaining 1 electron

F


……or share electronsor share electrons• Non-metal atoms when reacting with other non-metal atoms,

they achieve noble gas structure by sharing electrons between themselves.

Chlorine atom Hydrogen & chlorine atoms sharing 2 electrons between them.

H Cl+ H Cl

Hydrogen atom

• We will have more to say about metals losing electrons, non-metals either gaining electrons or sharing electron when we look at other chemical reactions and bonding.

Documents

Chemical Change M4 Periodic Table: Chemical Change Slide 3 of 35 Learning objectives Key Concepts: –Combination, synthesis, decomposition, displacement,