Chapter 2

Elements & Compounds

2.1 Models of Matter: The Particle Theory

• 2000 years ago a philosopher named Democritus suggested that matter was made up of tiny particles too small to be seen.

• If you keep cutting a substance into smaller pieces, you will eventually come to the smallest possible particles - the building blocks of matter. Think of Lego pieces.

The 4 Principles of the Particle Theory of Matter

• All matter is made up of tiny particles.• All particles of one substance are the same.

Different substances are made of different particles.

• The particles are always moving. The more energy the particles have, the faster they move.

• There are attractive forces between the particles. These forces are stronger when the particles are closer together.

Pure Substances and Mixtures

• There are two categories of substances:

– pure substances

– mixtures

Pure Substances

• Contains only one kind of particle.

• Examples: – aluminum foil only contains aluminum particles– sugar contains only sugar particles.

Mixture

• Contains at least two different pure substances.

• Examples:– Hot chocolate– Oreo cookie

How to Classify Mixtures

• When two pure substances are mixed together, they may mix smoothly or unevenly.

• If the substances mix well with one another, the mixture is called a solution.

• If the particles don’t mix well together then we have a heterogeneous mixture.

Classify the Following

• Salt and water – solution

• Pizza– heterogeneous mixture

• Garbage– heterogeneous mixture

• Air– solution

Elements and Compounds

• Elements are pure substances that cannot be broken down into simpler substances.– Elements are the building blocks of matter!!!

• Compounds are pure substances that contain two or more different elements in a fixed proportion. Example: water is H2O.

Atoms and Elements

• Scientists now call the particles in the particle theory atoms.

• Each element is made of only one kind of atom.

• How many kinds of atoms are there?– Since there are over 100 kinds of elements in

the periodic table, there are over 100 kinds of atoms.

Guess the Molecule

• I have 2 hydrogen atoms

• I have 1 oxygen atom

• I am water

Guess the Molecule• I have 10 hydrogen atoms• I have 2 oxygen atoms• I have 7 carbon atoms• I have 4 nitrogen atoms• I am desired in the morning but

avoid me in the evening• Cola drinks have me in

common• I am what makes coffee special• I am caffeine

Molecules

• Atoms join together in combinations.

• When two or more atoms join together, a molecule is formed.

• Molecules can contain two atoms or thousands of atoms.– Water molecules have 2 hydrogen atoms and 1 oxygen

atom– Methane gas molecules have one carbon atom and 4

hydrogen atoms– Acetic acid(vinegar) has 2 C, 2 O and 4 H

Guess the Molecule• I have 6 hydrogen atoms• I have 6 oxygen atoms• I have 6 carbon atoms• Everybody needs me• I will help keep colds away• You can get me by eating

oranges• I am vitamin C

Guess the Molecule• I have 8 hydrogen atoms• I have 4 oxygen atoms• I have 9 carbon atoms• I am used quite often by

teachers, usually in pairs• I am white in color• You need water when you use

me• I will make you feel better• I am aspirin

Assignment

• Complete “2.1 Worksheet” on classifying materials (it’s in the shared file). Copy the document into your science folder and then answer the questions on loose-leaf. Put your name and date on the sheet and hand in to teacher.

2.7 Chemical Symbols and Formulas

• All elements on the periodic table have symbols that are recognized world wide.

• It does not matter which country or language, the element Iron is always identified by “Fe” and Oxygen is “O”.

• The names are not always the same but the symbols are. Fe is iron in Canada, fer in France and Fier in Romania.

Chemical Symbols and Formulas• Today, a common set of symbols for elements is

accepted around the world. • A chemical symbol is an abbreviation of the

name of an element.• The names and symbols for elements come

from many sources.– Hydrogen comes from the Greek word for “water-

former.”– Mercury was named after a Roman God but the

symbol, Hg, comes from the Latin word Hydrargyrum for “liquid silver.”

Chemical Symbols and Formulas

• Single symbols are used to represent elements.

• Combinations of symbols are used to represent compounds. These combinations are called chemical formulas.

• The chemical formula indicates which elements are present and in what ratio.

Chemical Formulas - examples• Calcium Carbonate(chalk) - CaCO3

• Sodium Chloride(salt) - NaCl• Acetylsalicylic acid (aspirin) - C9H8O4

• Acetic acid (vinegar) - C2H4O2

• Special notes: – Each symbol in a formula represents an element.

– If only one atom of an element is present in the compound, no subscript is used.

– If more than one atom of an element is used, then the symbol is followed by a number indicating how many atoms are used. This is called the subscript.

Homework

• Answer questions 1,2,3,4,5 on page 59.

2.8 Atoms, Molecules, and the Atmosphere

• Every person on the planet earth needs air to breathe. But, have you ever wondered what air is made up of?

• Take a minute and write down what you think makes up air.

• Now, write down the corresponding percentages for each component of air.

Atoms, Molecules, and the Atmosphere

• Here are the actual components of air:– Oxygen – Nitrogen – Argon (Ar)

– Carbon Dioxide (CO2)

Oxygen• Atoms of oxygen can combine to form two

different molecules:

• O2 is oxygen gas. It makes up 21% of air.

• and O3 is ozone. It is formed naturally in the

upper layers of the atmosphere.

• Ozone is important since it absorbs most of the ultraviolet radiation from the Sun.

• The ozone layer is being destroyed by CFCs or chlorofluorocarbons.

Nitrogen

• Nitrogen makes up 78.02% of the atmosphere.

• It is not very reactive, which means we can inhale it without causing chemical changes in our lungs.

• We do not want to inhale nitrogen dioxide since it is a very toxic gas.

Argon

• Argon gas is completely harmless.

• Almost all of the argon in the atmosphere has leaked out from inside the Earth.

• Argon is used for filling electric light bulbs and fluorescent tubes.

• Argon and other gases make up 0.94% of the atmosphere.

Carbon Dioxide CO2

• When fossil fuels burn, the two main products are carbon dioxide and water.

• Carbon dioxide is used by plants.

• Carbon dioxide makes up 0.03% of the atmosphere.

Carbon Monoxide (CO)

• Produced during combustion when there is a lack of oxygen. For example, if you use a propane barbecue indoors, or if you run an automobile inside a closed garage.

• The CO molecule is similar to the oxygen molecule in that when carbon monoxide enters the lungs, the body’s red blood cells treats it the same as oxygen and carries it throughout the body. The cells of the body are then starved of the oxygen they need and you could die.

Answering Questions about Various Molecules

By looking at the chemical formula of a molecule we can answer a variety of questions such as:

• Which elements are required to construct the molecule?• How many atoms, in total, are required to construct the

molecule?• How many atoms, of each element, are required to

construct the molecule?• What is the ratio of each type of atom in the molecule?• What is the mass of each molecule?

An Example

C9H8O4 or Aspirin

• Which elements are required to construct the molecule?

C = Carbon H = Hydrogen O = Oxygen• How many atoms, in total, are required to construct the

molecule?

9 + 8 + 4 = 21 total atoms in one molecule of Aspirin• How many atoms, of each element, are required to

construct the molecule?

9 Carbon, 8 Hydrogen and 4 Oxygen atoms are required to construct one molecule of Aspirin.

An Example

C9H8O4 or Aspirin

• What is the ratio of each type of atom in the molecule?

9/21 is Carbon 8/21 is Hydrogen 4/21 is Oxygen • What is the mass of each molecule?

Mass of one molecule of aspirin is calculated as follows: (atomic mass C) x 9 (12) x 9 108

(atomic mass H) x 8 (1) x 8 8

+ (atomic mass O) x 4 (16) x 4 64

180

The atomic mass of one molecule of Aspirin is 180.

An Example - You do it!

Theobromine (Chocolate) - C7H8N4O2

• Which elements are required to construct the molecule?• How many atoms, in total, are required to construct the

molecule?• How many atoms, of each element, are required to

construct the molecule?• What is the ratio of each type of atom in the molecule? • What is the mass of each molecule?

An Example - You do it!

Theobromine (Chocolate) - C7H8N4O2

• Which elements are required to construct the molecule?

C = Carbon H = Hydrogen N = Nitrogen O = Oxygen • How many atoms, in total, are required to construct the

molecule?

7 + 8 + 4 + 2 = 21 total atoms in one molecule of Chocolate• How many atoms, of each element, are required to

construct the molecule?

7 Carbon, 8 Hydrogen, 4 Nitrogen and 2 Oxygen atoms are required to construct one molecule of Chocolate.

An ExampleTheobromine (Chocolate) - C7H8N4O2

• What is the ratio of each type of atom in the molecule? 7/21 is Carbon 8/21 is Hydrogen 4/21 is Nitrogen and

2/21 is Oxygen• What is the mass of each molecule?Mass of one molecule of chocolate is calculated as follows: (atomic mass C) x 7 (12) x 7 84 (atomic mass H) x 8 (1) x 8 8 (atomic mass N) x 4 (14) x 4 56 + (atomic mass O) x 2 (16) x 2 32 180

The atomic mass of one molecule of chocolate is 180.

Assignment

• Do the “Counting Atoms” worksheet that’s in the shared file– For the molecules containing calcium,

aluminum and chromium calculate the atomic mass also.

• Hand in the worksheet and then move on.

• Questions 1, 2 and 4 on page 61

2.7 Counting 2.7 Counting AtomsAtoms

Rules for Counting Atoms1. The symbol of an element represents one

atom of that element.

Example: Na – 1 atom of Sodium

2. The subscript number indicates the number of atoms for that element.

Examples: H2 – 2 atoms of Hydrogen

H2SO4 – 2 atoms of Hydrogen

1 atom of Sulfur 4 atoms of Oxygen

3. A subscript outside a bracket multiplies to all the elements inside the brackets.

Examples: Mg3(PO4)2 – 3 atoms of Mg

1×2 = 2 atoms of P 4×2 = 8 atoms of O

Ca4(SO4)3 - 4 atoms of Ca

1×3 = 3 atoms of S4×3 = 12 atoms of O

4. A coefficient is a number written in front of a chemical formula. The coefficient indicates the number of molecules of that compound. A coefficient multiplies the number of atoms of each element in the formula.

Examples:

2H2O = H2O + H2O = 4 atoms of H and 2 atoms of O

3CuSO4 = CuSO4 + CuSO4 + CuSO4 = 3 atoms of Cu

3 atoms of S 12 atoms of O

4Pb(NO3)2 = Pb(NO3)2 + Pb(NO3)2 + Pb(NO3)2 + Pb(NO3)2 =4 atoms of Pb1×2×4 = 8 atoms of N3×2×*4 = 24 atoms of O

2.10 Names & Formulas for Compounds

• We’ve been looking at chemical formulas and calculating numbers of atoms, but how do you know how to put these elements together to form compounds?

• There are 5 basic rules that you follow to write out a chemical formula:

How Elements Combine

• 1: metals combine with nonmetals a lot of the time

• 2: write the name of the metal element first and then the name of the nonmetal

• 3: change the ending on the nonmetal to “ide”• 4: look up the “combining capacity” of the

elements involved• 5: atoms will combine so that each element is at

full capacity

Combining Capacity

• Combining capacity is basically how many connections an atom can make to other atoms

• For example if the metal sodium joins with a nonmetal such as bromine, they each have a combining capacity of 1 so the compound created would be NaBr (1 atom of each because each element can make one bond)

combining capacity of some metals

• Aluminum • Barium• Calcium• Magnesium• Potassium• Silver• Sodium• zinc

• 3• 2• 2• 2• 1• 1• 1• 2

combining capacity of some nonmetals

• Bromine• Chlorine• Fluorine• Iodine• Oxygen• sulfur

• 1 (bromide)• 1 (chloride)• 1(fluoride)• 1 (iodide)• 2 (oxide)• 2 (sulfide)

Assignment

• Look over the example of ball & hook diagrams on p. 65 of the text– Start ball & hook diagrams by drawing the

metal first and it’s hooks, then attach the nonmetal element to it

– Using these examples and info. in your notes and text, do the following questions

– 3 & 4 p. 65

Assignment

• Do “Naming Ionic Compounds” worksheet (it’s in the shared file and notes are provided on the sheet)

Chapter 2 Review Questions

• P. 76 & 77 # 2, 3, 4, 8, 10 and 11

• Study chapter 2 notes and prepare for quiz tomorrow!