Unit 2 - Chemistry

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 H 2 O.

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.

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 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

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

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 Alchemists in the middle ages were among the first to recognize that it would be convenient to represent chemical substances using symbols. In 1808, the English chemist, John Dalton, developed a system of symbols to represent many elements and compounds. –Scientists found Dalton’s system to difficult to use.

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) - CaCO 3 Sodium Chloride(salt) - NaCl Acetylsalicylic acid (aspirin) - C 9 H 8 O 4 Acetic acid (vinegar) - C 2 H 4 O 2 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.

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 (CO 2 )

Oxygen Atoms of oxygen can combine to form two different molecules: O 2 is oxygen gas. It makes up 21% of air. and O 3 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 CO 2 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 C 9 H 8 O 4 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? = 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 C 9 H 8 O 4 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 (atomic mass H) x 8 (1) x (atomic mass O) x 4 (16) x The atomic mass of one molecule of Aspirin is 180.

An Example - You do it! Theobromine (Chocolate) - C 7 H 8 N 4 O 2 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) - C 7 H 8 N 4 O 2 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? = 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 Example Theobromine (Chocolate) - C 7 H 8 N 4 O 2 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 (atomic mass O) x 2 (16) x The atomic mass of one molecule of chocolate is 180.

Homework Questions 1,2,4 on page 61

Inside the Atom We have spent a great deal of time discussing atoms but what do they look like? Atoms are “particles” that are comprised of smaller particles called “subatomic particles”. Electrons, protons, and neutrons are subatomic particles.

Inside the Atom - Protons Protons are positively charged particles. Protons have a relative mass of 1. Protons are located in the nucleus of the atom. Protons are significant because the number of protons in an atom determines what an atom is. –For example, any atom with one proton is an hydrogen atom. Any atom with 29 protons is a copper atom. The atomic number of an element indicates the number of protons in one atom of that element.

Inside the Atom - Protons Identify the element: 37 protons –rubidium 48 protons –cadmium 105 protons –dubnium

Inside the Atom- Electrons Electrons are negatively charged particles. Electrons have a relative mass of 1/2000 of a proton. Electrons travel in regions of space around the nucleus of the atom.

Inside the Atom- Neutrons Neutrons are neutral particles. Neutrons are neither positively nor negatively charged. Like protons, neutrons have a relative mass of 1. Like protons, neutrons are found in the nucleus of the atom. Experiments conducted by James Chadwick, in 1932, led to the discovery of the neutron.

Atomic Number The atomic number tells us the number of protons in one atom of the element. The atomic number also tells us the number of electrons in one atom of an element. The number of electrons is equal to the number of protons. Example: the atomic number of calcium is 20 therefore the number of protons is 20 and the number of electrons is also 20.

The Atomic Mass The atomic mass tells us the total number of protons and neutrons in one atom of the element. Therefore, if we know the atomic number and the atomic mass we can determine the number of neutrons. number of neutrons = atomic mass - atomic number Example: the atomic number of calcium is 20 and the atomic mass is 40. Therefore, the number of neutrons is = 20.

Sample Questions For each of the following elements, state the number of protons, electrons and neutrons in one atom. Sodium Selenium Fluorine Helium

Sample Questions Element Protons Electrons Neutrons Sodium Selenium Fluorine Helium 2 2 2

Standard Atomic Notation Scientists use a special system to communicate information about any atom. This system is known as the standard atomic notation. This system represents the numbers of subatomic particles. Examples: 35 CL 23 Na The top number is the atomic mass and the bottom number is the atomic number.

Standard Atomic Notation 35 CL 35 is the atomic mass, 17 is the atomic 17 number. The number of protons is 17, the number of electrons is 17 and the number of neutrons is Na 23 is the atomic mass, 11 is the atomic 11 number. The number of protons is 11, the number of electrons is 11 and the number of neutrons is 12.

Homework Questions 2 and 3 on page 89.

Organizing the Elements People often organize things to make them more useful. –Cupboards –Closets –Study notes for tests Up to the mid-1800s, scientists were busy discovering new elements. Then they tried to organize the elements alphabetically. But every time a new element was discovered, the whole list had to be changed.

Organizing the Elements Other methods of organization were considered but later discarded. –State (gas, solid, liquid) –Color –Taste John Dalton then found a quantity that could be measured for an element - its atomic mass. Several scientists then tried to arrange the known elements by their atomic masses. The best arrangement was produced by a Russian scientist, Dmitri Mendeleev.

Organizing the Elements Mendeleev began arranging the elements in order of increasing atomic mass and noticed that many elements shared common properties. These elements typically belonged to the same vertical column of his table. Mendeleev’s arrangement showed a regular pattern. Mendeleev’s periodic law states: If the elements are arranged according to their atomic mass, a pattern can be seen in which similar properties occur regularly.

Organizing the Elements Mendeleev’s periodic table was a major breakthrough in the understanding of the elements. However, it was discovered later on that using the atomic mass was not the proper way to organize the elements. The key was to use the atomic number or the number of protons. Therefore, a new law was born. The modern periodic law states : If the elements are arranged according to their atomic number, a pattern can be seen in which similar properties occur regularly.

Homework Questions 1, 2, 3, 4, 5 on page 108. Questions 1,2,3,4 on right side of page 109.

Groups of Elements The periodic table is useful since it organizes the elements according to similar properties. The set of elements in the same column in the table is called a chemical group and they share similar physical and chemical properties.