1 Chemistry Notes Dr. Reeves Science Class (This was me when I had hair.)

Transcription

1 1 Chemistry Notes Dr. Reeves Science Class (This was me when I had hair.) Table of Contents Introduction Slide 5 Topics of Discussion Slide 6 Periodic Table Slide 10 Elements Slide 15 Chemical Formulas Slide 20 Elements Slide 24 Compounds Slide 25 Bonds Slide 26 Table of Contents (continued) Bonds, Covalent Slide 28 Bonds, Ionic Slide 30 Mixtures Slide 32 ph Scale Slide 37 Acids Slide 39 Bases Slide 41 Terms to know Slide 45 Table of Contents (continued) Catalyst Slide 47 Salts Slide 50 Chemical Equations Slide 51 Balancing Equations Slide 57 Practice Problems Slide 66 Answers Slide 67 References Slide 69 Introduction We will be covering all of the important AKS objectives you will need for High School. You will be tested over most of these AKS objectives. Some objectives will have labs, some will be demonstrated. The objectives we will cover are

2 2 Topics of Discussion Write chemical formulas for common chemical substances. Explain chemical activity of elements using the periodic table. Differentiate among elements, compounds and mixtures. Topics Continued Define an ion and describe its role in chemical bonding (ionic & covalent bonding). Describe the properties of acids and bases. List names, formulas, and uses of some acids and bases. Recognize common chemical symbols and formulas. Topics still continued Explain what a salt is and how salt forms. Demonstrate a knowledge of the Periodic Table of Elements. Describe the organization of the modern periodic table. Topics continued (last 4) Design and conduct an experiment to demonstrate the effect of temperature. Write and balance simple chemical equations. Illustrate how a catalyst slows down or speeds up a reaction. Devise a plan to separate a mixture. Periodic Table When you look at the picture you can see that the rows are different colors. Even though they skip some squares in between, all of the rows go left to right. Each of the rows are considered to be different PERIODS. The Periodic Table continues - Periods In the periodic table, elements have something in common if they are in the same row. All of the elements in a PERIOD have the same number of SHELLS. Periodic Table continued Every element in the top row (the first period) has one shell for its electrons. All of the elements in the second row (the second period) have two shells for their electrons. It goes down the periodic table like that.

3 3 The Periodic Table continues - Groups The periodic table has a special name for its columns also. When a column goes from top to bottom, its called a GROUP. The elements in a group have the same number of electrons in their outer shell. Periodic Table - Groups Every element in the first column (group one) has one electron is its outer shell. Every element on the second column (group two) has two electrons in the outer shell. Just keep counting the colored columns and you'll know how many electrons are in the outer shell. Transition Elements in the Periodic Table You'll notice that HYDROGEN can be in two groups, one and seven. Hydrogen is sometimes missing an electron, and sometimes it has an extra. Helium is different. It can only have two electrons in its outer shell, but it still get grouped with elements that have eight. Transition Elements in the Periodic Table The elements in between, with the gray color, are called TRANSITION elements. They are not in the main groups. Elements in the Table Each element has a name, a symbol, an atomic number, and an atomic mass. Some tables include the atomic weight. The letter is the symbol of the element. Elements in the Table The number on the left is the Atomic Number. This is the number of protons and electrons. Elements in the Table The number on the right gives the atomic mass. Chemical Formulas Some typical chemical formulas are: H 2 O for water NaCl for table salt C 2 H 6 O for Ethyl alcohol C 12 H 22 O 11 for table sugar

4 4 Letters and Numbers what does it all mean? The letters are symbols for the chemical elements. H is the symbol for Hydrogen. The numbers between the letters are subscripts and represent the number of atoms of the element that they follow in one molecule of the substance. So for example H 2 O has two atoms of Hydrogen and 1 atom of Oxygen for every molecule of water. This can also be interpreted as 2 moles of Hydrogen and 1 mole Oxygen in one mole of H 2 O. C 2 H 6 O has two atoms of Carbon, 6 atoms of Hydrogen, and 1 atom of Oxygen in every molecule of Ethyl Alcohol. The Mole? The mole interpretation is the more practical interpretation because we can not see single molecules and atoms for everyday work. So how many moles of carbon is in C 12 H 22 O 11 (table sugar)? Write the answer in your notes. Elements Elements are: Most basic of all matter Pure substances that have a set of unique properties Cannot be broken down or decomposed by chemical methods Compounds Compounds are pure substances having a unique set of properties that are produced when elemental substances chemically combine. Compounds are symbolized by a formula. Compounds are groups of two or more ELEMENTS bonded together. There are two main types of bonds which hold compounds together. Bonds What are these? A Bond is an electrical attraction between 2 atoms. There are 3 types of bonds. (Four if you count James.) 1 st an attraction between electrons of 1 atom for the positive nucleus of the other atom. 2 nd a repulsion between electrons of 1 atom for the other and

5 5 Bonds - continued 3 rd The repulsion between the positive nuclei of the2 atoms. There are two main types of bonds which hold compounds together. There are COVALENT and IONIC/ELECTROVALENT compounds. Covalent compounds happen when the electrons are shared by the atoms. Ionic compounds happen when electrons are donated from one atom to another. Bond, Covalent Bond These are formed as a result of she sharing of 1 or more pairs of bonding elections. Each atom donates half of the electrons to be shared. Example of Bonds Let's look at Sodium Hydroxide (Na-OH)... You can see that on the left is the Sodium part and the right has the Oxygen/Hydrogen part. The bond which binds the Hydrogen to the Oxygen is covalent. The Sodium is bonded to the HYDROXIDE part of the compound with an ionic bond. This is a very good example of how there can be different types of bonds within one compound. Bond, Ionic / ELECTROVALENT Bond This type of bonding occurs when electrical attraction between 2 oppositely charged atoms or groups of atoms. Elements that are described as metalic tend to lose electrons. Elements that are described as nonmetalic tend to gain electrons. Mixtures A Mixture is the physical combination of 2 or more elements or compounds. Mixtures can be separated by using a difference in a physical property between the pure substance in the mixture. Mixture types There are 3 types of mixtures. Heterogeneous Homogeneous Colloids Heterogeneous These mixtures are not uniform in their distribution. A sampling of the mixture will not always show the same distribution of the components in the mixture.

6 6 Homogeneous These mixtures are uniform in their distribution. A sampling anywhere in the mixture would show the distribution was the same throughout the mixture. All solutions are homogeneous mixtures. Colloids These are classified as a heterogeneous mixture. These are mixtures whose components will not easily separate. These components are very small. Gravitational forces will not pull the components apart. ph Scale for Acids and Bases Scientists use something called the "ph" scale to measure how acidic or basic a liquid is. The scale goes from "0" to "14". Distilled water, which is neutral, is 7, right in the middle. ph Scale continued Most of the liquids you find every day have a ph near "7", either a little below, or a little above. When you start looking at the ph of chemicals, the numbers go to the extremes. If you ever go into a chemistry lab, you could find solutions with a ph of "1" and others with a ph of "14". Those chemicals are very dangerous. Acids All acids have certain physical and chemical properties when dissolved in water. Sour taste (never use taste to identify a chemical substance.) Color change, litmus paper changes from blue to red if an acid is present is one example. Acids - continued Acids react with active metals to form hydrogen gas and a metal compound. Acids are 0 to 6 on the ph scale. 0 is the strongest acid and 6 is the weakest acid. HCL (Hydrochloric Acid) H 2 SO 4 (Sulfuric Acid) Shampoo is a weak acid. Bases Bases are from 8" to "14 on the ph scale. Bases are usually taste bitter. Bases are slippery to the touch.

7 7 They can be poisonous and corrosive. Bases turn litmus paper from red to blue. How does this work? Acids are compounds which break into Hydrogen (H+) ions and another compound when placed in an aqueous (water) solution. Bases are compounds which break up into Hydroxide (OH-) ions and another compound when placed in an aqueous solution. But wait there s more If you have an IONIC compound and you put it in water it will break apart into two ions. If one of those ions is H+, then the solution is acidic. If one of the ions is OH- the solution is basic. So the ph scale is. a measure of the number of H+ ions in a solution. If there are a lot of H+ ions, the ph is very low. If there are a lot of OH- ions, that means the number of H+ ions is very low, so the ph is high. Terms to know ACID: A solution that has too many H+ ions. It comes from the latin word "acidus" which means "sharp". BASE: A solution that has too many OH- ions. Another word for base is ALKALI. AQUEOUS: A solution which is mainly water. STRONG ACID: An acid which has a very low ph (0-4). STRONG BASE: A base which has a very high ph (10-14). More Terms (You know you love em.) WEAK ACID: An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a ph close to 7 (3-6). WEAK BASE: A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a ph close to 7 (8-10). NEUTRAL: A solution which has a ph of 7. It is neither acidic nor basic. Catalyst (Say What?) A reaction has to have a certain amount of energy to happen. A catalyst lowers the amount of energy needed, so a reaction can happen easier. That energy is called the ACTIVATION ENERGY.

8 8 Catalyst Catalysts are used to make very difficult reactions happen. They help very large molecules combine. If you look at the graph, you will notice that when the activation energy is lower, the products can combine easier. So the forward and reverse reactions are both speeded up. So a Catalyst speeds up the reaction buy lowering the amount of energy needed for the reaction to occur. Salts When acids react chemically with bases, they form a class of compounds called salts. Water is also produced. The reaction is called a Neutralization The properties of the acid and the base are lost as two neutral substances. Salt and water are formed. Chemical Equations Putting formulas together. Chemical equations give information in two major areas. 1 st they tell us what substances are reacting (those being used up) and what substances are products (those being made). 2 nd the coefficients of a balanced equations tell us in what ratio the substances react or are produced. Chemical Equations (Reactants & Products, what s what?) The reactants are on the left side of the equation. 2 H 2 +O 2 2 H 2 O So the hydrogen and oxygen molecules are the reactants. The products are on the right side of the equation. 2 H 2 + O 2 2 H 2 O So water is the product. Chemical Equations (Arrow, what arrow?) The arrow means produces or yields. 2 H 2 + O 2 2 H 2 O There can be one, two, three, or more substances on either side of the arrow. Ca(H 2PO 4 ) 2 +CaSO 4 +HF Ca 10 F 2 (PO 4 ) 6 + H 2 SO 4 Chemical Equations (What about those big numbers in front?) Coefficients are the numbers in front of the formulas. 2 H 2 + O 2 2 H 2 O Coefficients give two very important pieces of information about the equation

9 9 1 st the number of molecules (or atoms) involved in the reaction is given. 2 nd the number of moles of each substance involved in the reaction is given. Chemical Equations (What about those big numbers in front? Part II) So the coefficients of an equation tell us how many moles of each reaction are involved as well as how many moles of each product get produced. Chemical Equations (What about those little numbers behind?) Subscripts are the small numbers located just behind the element symbols. 2 H 2 + O 2 2 H 2 O The subscripts identify what kind of molecules react! Balancing Chemical Equations (background) When matter undergoes a chemical change, it follows the Law of Conservation of Mass which states atoms are neither created or destroyed during any chemical reaction. What this means is that the atoms rearrange themselves during a chemical reaction. Balancing Chemical Equations (steps) Determine what the reactants and products are. Balance the equation by adding coefficients to the appropriate molecules so that the number of each type of atom are equal on both sides of the equation. One important note: DO NOT CHANGE SUBSCRIPTS WHEN BALANCING EQUATIONS. Balancing Chemical Equations (pratice) It is an unbalanced equation H 2 + O 2 H 2 O (sometimes also called a skeleton equation). This means that there are UNEQUAL numbers of at least one atom on each side of the arrow. There are two atoms of hydrogen on each side, BUT there are two atoms of oxygen on the left side and only one on the right side. Balancing Chemical Equations (practice continued) H 2 + O 2 H 2 O (Remember this: A balanced equation MUST have EQUAL numbers of EACH type of atom on BOTH sides of the arrow.) An equation is balanced by changing coefficients in a somewhat trial-and-error fashion. It is important to note that only the coefficients can be changed, NEVER change a subscript. The coefficient times the subscript gives the total number of atoms.

10 10 Balancing Chemical Equations (practice continued) H 2 + O 2 H 2 O The hydrogen is balanced, but the oxygens are not. We have to get both balanced. We put a two in front of the water H 2 + O 2 2 H 2 O and this balances the oxygen. Balancing Chemical Equations (practice continued) H 2 + O 2 2 H 2 O However, this causes the hydrogen to become unbalanced. To fix this, we place a two in front of the hydrogen on the left side. 2 H 2 + O 2 2 H 2 O This balances the equation. Balancing Chemical Equations (Tips) Two things you CANNOT do when balancing an equation. You cannot change a subscript. You cannot place a coefficient in the middle of a formula. The coefficient goes at the beginning of a formula, not in the middle, as in: H 2 + O 2 H 2 2O Balancing Chemical Equations (Tips) There is another thing you should avoid. Make sure that your final set of coefficients are all whole numbers with no common factors other than one. For example, this equation is balanced: 4 H O 2 4 H 2 O all the coefficients have the common factor of two. Balancing Chemical Equations (Tips) 4 H O 2 4 H 2 O The equation correctly balanced, but it is not the BEST answer. The best answer has all common factors greater than one removed. Balance these. H 2 + Cl 2 HCl O 2 O 3 Zn + HCl ZnCl2 + H 2 KClO 3 KCl + O 2 S 8 + F 2 SF 6 Fe + O 2 Fe2O 3 C 2 H 6 + O 2 CO 2 + H 2 O

11 11 Answers H 2 + Cl 2 2 HCl 3 O 2 2 O 3 Zn + HCl ZnCl 2 + H 2 KClO 3 KCl + O 2 S8 + F 2 SF 6 Fe + O 2 Fe2O 3 C 2 H 6 + O 2 CO 2 + H 2 O That s it. You may need to review certain sections. If you don t understand some of this, ask questions. Study your notes. References Andrew Rader Studios, Chem4Kids. [Online] Available Johnson, Porter, Science and Mathematics Initiative for Learning Enhancement. [Online] Available. 1March 1997 Park, John, L. ChemTeam. A Tutorial for High School. [Online] Available