. CHAPTER 2: CHEMISTRY

Composition of Matter 2-1

Matter EVERYTHING IS MADE OF MATTER Matter: anything that occupies space and has mass Mass: quantity of matter an object has Mass is NOT the same as weight Weight: the pull of gravity on an object

Elements Pure substances that cannot be broken down chemically into simpler kinds of matter About 100 elements Only 30 crucial to living things Almost 90% mass of all living things made from combinations of only 4 elements! Oxygen (O) Carbon (C) Hydrogen (H) Nitrogen (N)

What we are made of…..

Elements Each element has chemical symbols Consists of 1 or 2 letters Most cases symbol derives from first letters in name of element Some come from Latin words for elements Example: Symbol for sodium = Na from word natrium (Latin) Atomic Number Atomic Mass Element Symbol Element Name

Atoms Simplest particle of an element that has all the properties of that element So small cannot be observed Scientists therefore make models describing the structure/properties of atoms Two main parts: Nucleus Electron shell

Nucleus Central core of atom Made up of two particles: PROTONS NEUTRONS Positively charged Neutral + 0

Electrons High-energy particles with little mass. Move around nucleus at very high speed Move within different energy levels Electrons in outermost energy levels have the most energy Each energy level can hold a certain number of electrons First energy level holds 2 Second energy level holds 8

Electron orbits: Example Carbon

Compounds Pure substance made up of atoms of two or more elements The amount of atoms in the compound are fixed Example: Water, H2O indicates that atoms always combine in a proportion of two hydrogen atoms to one oxygen atom Physical and chemical properties of a compound differ from the physical and chemical properties of individual elements that compose it

How do elements form compounds? Most atoms are not stable as individual atoms Depends on the number and arrangement of electrons in the atoms of elements Atoms are stable when the outermost energy level is filled Most atoms are not stable in their natural state  therefore tend to react with other atoms  in ways that make the atoms more stable (atoms react to make themselves more stable) These reactions = chemical reactions

Chemical Reactions What does a chemical reaction consist of? chemical bonds are broken Atoms are rearranged New chemical bonds—attachments—are formed

Chemical Vs. Physical Change This is only a change in the state of the matter: Solid  liquid; Solid gas Gas solid; Gas liquid Liquid solid; Liquid  gas This is a change in the composition of matter

Why do atoms form bonds? TO BECOME MORE STABLE Ionic Bonds Forms when atoms gain or lose electrons -Has 7e- -Wants 8e- -Has 3e- -Wants 2e- Why do atoms form bonds? TO BECOME MORE STABLE

Why do atoms form bonds? TO BECOME MORE STABLE Covalent Bonds Forms when two atoms share one or more electrons -Hydrogen has 1e- in the outer electron shell -oxygen has 6e- in the outer electron shell -hydrogen wants 2e- -oxygen wants 8e- -they share to make each other happy Why do atoms form bonds? TO BECOME MORE STABLE

Ionic or Covalent Bond? Metals Nonmetals Ionic: metal + nonmetal Ex. NaCl Covalent: nonmetal + nonmetal Ex. HCl

Review Questions Define element, atom, compound, molecule. How are particles arranged in the atom? How can we predict which elements are stable under natural conditions and which elements tend to undergo chemical reactions? How does an ionic bond differ from a covalent bond? Neon seldom, if ever, combines with other elements to form compounds. Why is this so? In the early 1900’s, hydrogen gas was used to inflate airships. After one large airship crashed and caught on fire, helium gas began to be used to inflate airships. Why was helium preferred over hydrogen?

Review Questions: Answers Define element, atom, compound, molecule. Elements are substances that cannot be broken down chemically into simpler chemical substances. An atom is the simplest part of an element that retains all of the properties of the element. A compound is a pure substance made up of two or more elements. A molecule is the simplest part of a substance that retains all of the properties of the substance and that can exist in a free state. How are particles arranged in the atom? Protons and neutrons make up the nucleus of the atom. Electrons move around the nucleus

Review Questions: Answers How can we predict which elements are stable under natural conditions and which elements tend to undergo chemical reactions? Stable elements have filled outermost energy levels. Elements with unfilled outmost energy levels tend to be reactive How does an ionic bond differ from a covalent bond? In an ionic bond, ions with opposite electrical charges attract each other. In a covalent bond, the atoms share pairs of electrons Neon seldom, if ever, combines with other elements to form compounds. Why is this so? Neon has the maximum number of electrons that its outermost energy levels can hold. Thus, neon is stable and tends not to react with other atoms. In the early 1900’s, hydrogen gas was used to inflate airships. After one large airship crashed and caught on fire, helium gas began to be used to inflate airships. Why was helium preferred over hydrogen? Hydrogen is very reactive, while helium is relatively unreactive.

ENERGY Ch. 2-2

Energy & Matter The ability to do work or cause change. Energy cannot be destroyed or created Energy can be converted into another form Ex. Light bulb: electrical energy  radiant energy (light)  thermal energy (heat)

States of Matter All atoms & molecules in any substance are in constant motion Rate which atoms or molecules move determines the state it is in: Solid Liquid Gas

States of Matter Solid Liquid Gas Definite shape Definite volume Not compressible Tightly packed particles Liquid Indefinite shape Medium packed particles Gas Indefinite volume Compressible Loosely packed particles Solid Liquid Gas

Chemical Reactions CO2 + H2O  H2CO3 Living things undergo thousands of chem. Rxns during lifetime Consist of: Reactants: left side of equation Products: right side of equation CO2 + H2O  H2CO3 REACTANTS PRODUCTS

Energy Transfer 1. We take in food 2. Sugars undergo series of chemical rxns 3. Sugar & substances are broken down to carbon dioxide & water (cellular respiration) 4. During this process, energy is released for use by body Exergonic Reactions: release of energy Endergonic Reactions: absorption of energy

Activation Energy In order for exergonic & endergonic reactions to begin, energy must be added to the reactants The amount of energy needed to start a chemical reaction = activation energy Catalysts reduce the amount of activation energy needed to begin a reaction Enzymes: crucial catalyst for living things We have thousands, each made for specific reactions

Activation Energy Diagram

Reduction-Oxidation Reactions Many chemical rxns that help transfer energy in living things involve the transfer of electrons These known as reduction-oxidation rxns OR redox rxns Oxidation rxns: reactant loses one or more electrons becoming more positively charged Reduction rxns: reactants gain one or more electrons becoming more negatively charged Always occur together OILRIG: Oxidation Is Loss Reduction Is Gain (of electrons)

Example: Redox Reaction Formation of NaCl: Sodium Chloride Sodium atom loses electron to achieve stability when it forms ionic bond  sodium atom undergoes oxidation When a chlorine atom gains an electron  undergoes reduction Na + Cl  NaCl

Review Questions What are the three states of matter? How can a substance be changed from a liquid to a gas? State the difference between endergonic and exergonic reactions Explain how a catalyst affects a reaction Why does a reduction reaction always accompany an oxidation reaction Living things need a constant supply of energy, even though many of the chemical reactions they undergo release energy. Why is this true?

Review Questions: Answers What are the three states of matter? Matter can exist as a solid, liquid or gas How can a substance be changed from a liquid to a gas? A substance can be changed from a liquid into a gas by heating State the difference between endergonic and exergonic reactions: Endergonic reactions involve a net absorption of free energy. Exergonic reactions involve a net release of free energy. Explain how a catalyst affects a reaction: A catalyst lowers the amount of activation energy that is required for a chemical reaction to begin. Why does a reduction reaction always accompany an oxidation reaction? If an atom is oxidized (loses electrons), then another atom must be reduced (accept those electrons that have been lost). Living things need a constant supply of energy, even though many of the chemical reactions they undergo release energy. Why is this true? Even exergonic reactions need a small amount of energy—activation energy—to begin.

SOLUTIONS Ch. 2-3

Describing Solutions Mixture which one or more substances are uniformly distributed in another substance. Solute: substance dissolved in the solution Solvent: substance in which the solute is dissolved EXAMPLE: sugar water Sugar = solute Water = solvent Concentration of solution is measurement of the amount of solute dissolved in fixed amount of solution The more solute dissolved, the greater the concentration of solution Aqueous solutions: water is solvent Crucial for living things

Mixture Two main kinds: Homogeneous: uniformly mixed throughout Ex. Sugar water Heterogeneous: not uniformly mixed throughout Ex. Oil & vinegar salad dressing

Acids & Bases One of the most important aspects of a living system is the degree of its acidity or alkalinity Alkaline = Base

Acids If the number of hydronium (H3O+) ions in solution is greater than the number of hydroxide (OH-) ions in solution = acid Ex. of Acidic solutions: Orange juice, Vinegar Ex. of common acid: hydrochloric acid (HCl) How does it affect our everyday lives? Sulfur dioxide (SO2): produced by burning fossil fuels, reacts with water in the atmosphere to produce acid rain Acid rain: can make lakes too acidic to support life

Bases If the number of hydroxide (OH-) ions in solution is greater than the number of hydronium (H3O+) ions in solution = basic Ex. of common basic solutions: Cleaning agents Soaps Ex. of common base: sodium hydroxide (NaOH)

Neutral If the number of hydronium ions equals the number of hydroxide ions in solution Example: Pure water **Hydronium ion = H3O+ **Hydroxide ion = OH-

pH Scale Scale for comparing the relative concentrations of hydronium ions and hydroxide ions in a solution pH of 0-7 = Acidic pH of 0 is VERY acidic pH of 8-14 = Basic pH of 14 is VERY basic pH of 7 = Neutral pH of solution is measured with Litmus Paper

pH Scale A solution with a pH of 3 compared to a solution with a pH of 5 pH of 3 is 100X more acidic than pH of 5 pH of 3 is 10X more acidic than pH of 4 pH of 1 is 1000X more acidic than pH of 4 pH of 13 is 10X more basic than pH of 12 **there is a 10X difference between each number in the pH scale

What does the pH scale look like? 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 BASE ACID NEUTRAL

Buffers Chemical substances that neutralize small amounts of either an acid or base added to a solution We have complex buffering systems keeping our body fluids at safe levels Ex. Stomach acid & urine are acidic Ex. Intestinal fluid & blood are basic

Review Questions What is a solution? Describe the dissociation of water. What pH value is neutral? Define acid and base. What is a buffer? The active ingredient in aspirin is acetylsalicylic acid. Why would doctors recommend buffered aspirin for some people, especially those who have a “sensitive” stomach?

Review Questions: Answers What is a solution? A solution is a mixture in which one or more substances are uniformly distributed in another substance Describe the dissociation of water: The oxygen atom of one water molecule removes the hydrogen atom of another water molecule. This results in one hydronium ion (H3O+) and one hydroxide ion (OH-) What pH value is neutral? A pH value of 7 is neutral. Define acid and base: An acid is a solution that contains more hydronium ions than hydroxide ions. A base contains more hydroxide ions than hydronium ions. What is a buffer? A buffer is a chemical substance that neutralizes small amounts of acids or bases added to a solution. The active ingredient in aspirin is acetylsalicylic acid. Why would doctors recommend buffered aspirin for some people, especially those who have a “sensitive” stomach? The buffer reduces the acidity of the aspirin and thus is less irritating to the stomach.