We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them...

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Water

Transcript of We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them...

Page 1: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Water

Page 2: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

What about molecules?

• We have been studying about elements just by themselves such as oxygen and hydrogen. • If you put them together you have a

molecule of water (H2O).

• A cup of water contains millions of molecules of H2O.

Page 3: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Chemical Formulas

Page 4: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

What is a chemical formula?• Chemical, or molecular, formulas are a concise

way of expressing information about the atoms that constitute a particular chemical compound.

• Wait…what?

• It is an expression which states the number and type of atoms present in a molecule of a substance.

Page 5: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Do you know what the chemical formulas are for the following substances?

Page 6: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Carbon dioxide

Page 7: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Sodium chloride or salt

Page 8: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Magnesium sulfate (AKA Epsom salt)

MgSO4

Page 9: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

For something more complicated….Glucose or sugar

Page 10: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Subscripts

Page 11: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Definition• A subscript is used to represent the number of

each atom being represented. • If only one atom is represented, there is no

subscript.• In the formula for water, what is the subscript?• There is only one atom of Oxygen, so it does not

have a subscript.

H2OH2OH = HydrogenO = Oxygen

Page 12: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Some exceptions exist

• Usually the subscript just multiplies or shows the number of atoms of a single element. If the subscript exists outside of a set of parenthesis then it will multiply the atoms of all of the elements inside the parenthesis.

• How many of each atom are there now?• Answer: Nitrogen-1, Carbon-3, Hydrogen-9

N(CH3)

3

N = NitrogenC = CarbonH = Hydrogen

Page 13: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Here are some molecules…

Page 14: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

• In this image the Carbon atom is blue and the Oxygen atom is red.• Write the chemical formula for this

molecule.Answer: CO

This substance is carbon monoxide

Page 15: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

• In this image the Carbon atom is black and the Oxygen atoms are red.

• Write the chemical formula for this molecule.

Answer: CO3

This substance is carbonate

Page 16: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

• In this image Hydrogen atoms are white and Nitrogen atom is red.

• Write the chemical formula for this molecule.

Answer: NH3

This substance is ammonia

Page 17: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

• In this image blue represents Nitrogen atoms, red represents Oxygen atoms, white represents Hydrogen atoms and black represents Carbon atoms.

• Write the chemical formula for this molecule.

Answer: C8H10N4O2

This substance is caffeine

Page 18: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Coefficient

Page 19: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

7H2

O

Definition• Coefficients appear on the left side of a chemical

formula.• They are used to multiply all the atoms in a

compound• In the following formula, which is the coefficient?• Earlier we learned that the subscript 2 meant that

there were two Hydrogen atoms. The coefficient 7 means there are 7 times more.

• How many Hydrogen atoms do we have? • How many Oxygen atoms?

7H2

O

Page 20: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Chemical Equations

Page 21: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Chemical Equations• representation of chemical reaction in

equation: a representation, using chemical symbols in a form resembling a mathematical equation, of the process involved in a chemical reaction

• This is an example of a chemical equation. The components on the left combine together to yield (represented by the arrow) the component on the right.

2H2+O22H2O

Page 22: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Parts to a chemical equation

Page 23: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

•2H2+O22H2O

Reactant Produ

ct

Yields

Page 24: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Law of conservation of mass

Page 25: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

• Atoms are neither created, nor destroyed, during any chemical reaction.

• This means that the same number of atoms that are present after a reaction are the same number of atoms that are present before a reaction.

• There is only a rearrangement

Page 26: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Balancing chemical equations

Page 27: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Subscripts are never changed when balancing an equation

Page 28: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Step 1• Write out your “un-balanced” equation using

formulas of reactants and products.

CH4+O2CO2+H2O

Page 29: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Step 2• Count up the atoms in the products and reactants.• How many carbons, hydrogens, and oxygens are

on each side? Are they equal?

CH4+O2CO2+H2O

C=1H=4O=2

C=1H=2O=3

They are NOT equal

Page 30: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Step 3• Since our carbons are ok we will not mess with

those now.• However, we have half the number of hydrogens

in the products than we do in the reactants.• What do we need to add? Where do we add it?

CH4+O2CO2+H2OCH4+O2CO2+2H2

O C=1H=4O=2

C=1H=4O=4

They are still NOT equal

Page 31: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Step 4• Now we have half the number of Oxygens.• What do we need to add? Where do we need to

add it? Is everything equal now?

CH4+O2CO2+2H2OCH4+2O2CO2+2H2

O C=1H=4O=4

C=1H=4O=4

They ARE now balanced

Page 32: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Practice Time

Page 33: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

H2+O2H2O2H2+O22H2O

Page 34: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Fe+Cl2FeCl32Fe+3Cl22FeCl3

Page 35: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Cu+AgNO3Cu(NO3)2+AgCu+2AgNO3Cu(NO3)2+2Ag

Page 36: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Zn+HClZnCl2+H2

Zn+2HClZnCl2+H2

Page 37: We have been studying about elements just by themselves such as oxygen and hydrogen. If you put them together you have a molecule of water (H 2 O). A.

Pb(NO3)2+AlCl3PbCl2+Al(NO3)3

3Pb(NO3)2+2AlCl33PbCl2+2Al(NO3)3