Welcome to Chemistry 101, an introduction to Chemistry. Chemistry 101 will touch on the important topics of first year chemistry and beyond. These Chemistry 101 topics that will be discussed below are matter, atoms, molecules, states of matter, solutions, acids and bases, oxidation-reduction reactions, rates of reactions and equilibrium, thermochemistry and stoichiometry.
Chemistry 101 - Matter
Chemistry 101 begins with the introduction of matter, as chemistry is the study of matter. The atomic theory teaches that matter is made up of pure substances known as atoms and molecules. Atoms are single elemental particles, such as gold, silver and potassium. Molecules are chemical combinations of two or more atoms, such as water (H2O), oxygen (O2) and carbon dioxide (CO2). Matter may also be composed of mixtures of substances, such as a glass of orange juice. A glass of juice is a mixture of many different atoms and compounds, which are NOT chemically combined. Because they are not chemically combined, they can be separated by physical means. For instance, water a pure substance, can be removed from orange juice, which is what juice manufacturers do to make concentrate.
Chemistry 101 - Atoms
Chemistry 101 introduces the concept of atoms as the basic units of matter. Atoms are not the smallest units of matter, however. Rather, atoms consist of protons and neutrons, which are housed in the nucleus of an atom, and electrons, which surround the nucleus. Protons are positively charged, electrons are negatively charged, and neutrons possess no charge. Atoms differ from one another because of the number of protons present in their nuclei. For instance, atoms with only one proton in the nucleus are all hydrogen atoms. Atoms with 12 protons in the nucleus are all carbon atoms. Atoms are neutral particles, which mean they do not carry a charge. Therefore, atoms have equal numbers of protons and electrons. As stated previously, an atom's identity is determined by the number of protons in its nucleus. Its chemical properties - in other words, what it reacts with - is determined by the number of electrons in its outermost energy level. Elements are made up of one type of atom. For example, a sample of the element gold is made up of far more than a trillion gold atoms. Elements are organized in a Periodic Table. They are organized in the table horizontally by an increasing number of protons and vertically, by recurring chemical properties. Elements in the same vertical column, also known as group, possess similar chemical properties.
Chemistry 101 - Molecules
Chemistry 101 defines molecules as combinations of more than one atom chemically bonded together. The type of bonds that are formed between atoms is determined by their chemical properties, which are ultimately determined by the number of electrons in their outermost energy levels. Atoms form bonds to fill their outermost energy levels with electrons. Molecules have full outermost energy levels. Noble gases, which are nonreactive gases such as helium and neon, do not form molecules because they already have full outermost energy levels. The strength of the bonds that atoms form together determines the resulting molecule's physical properties, such as state of matter - whether solid, liquid or gas - and melting and boiling points.
Chemistry 101 - States of Matter
Chemistry 101 describes the three states of matter in which atoms and molecules exist - solid, liquid and gas. Solids have tighter and more compact molecular structures than liquids, which have closer molecular structures than gases. Gas molecules exist very far apart from each other and interact as little as possible with each other. They do interact with each other, as predicted by Kinetic Molecular Theory, which says they travel in straight lines, randomly colliding with each other. Gases expand in volume with increasing heat, and decreasing pressure, and decrease in volume, with decreasing heat and increasing pressure.
Chemistry 101 - Solutions
Chemistry 101 defines a solution as a homogeneous mixture of two or more substances that exists in a single phase, such as the liquid phase. The solute is the substance that exists in the lesser amount, and the solvent in the greater amount. For example, in a solution of salt water, salt is the solute and water is the solvent. Solutions in which water is the solvent are known as aqueous solutions. Solutions follow the saying, "like dissolves like," meaning that solutes and solvents with similar polarity - positive and negative regions - will dissolve in each other, whereas solutes and solvents in which one is polar and one is nonpolar will NOT dissolve in each other. Oil and water don't mix because oil is nonpolar, lacking positive and negative regions, and water is polar.
Chemistry 101 - Chemical Reactions
Chemistry 101 not only describes atoms and molecules, but most importantly, the reactions they undergo. Chemical reactions are interactions between pure substances - either atoms or molecules -- that result in the rearranging of atoms and molecules. It is important to note that atoms are never lost in chemical reactions. They are only rearranged. An example of a chemical reaction is the rusting of iron. Iron reacts with oxygen in the air to produce iron oxide.
4Fe(s) + 3O2(g) --> 2Fe2O3(s)
Notice that there are 4 atoms of pure solid iron on the reactant (left) side of the equation ("s" stands for solid). These 4 iron atoms react with 3 oxygen gas molecules (oxygen exists in nature as two oxygen atoms bonded together) to form 2 molecules of Iron (III) oxide. The same number of iron and oxygen atoms exists on both sides of the equation, but they are now rearranged. Rearranging atoms to make new molecules completely changes their properties. Whereas iron is a metal, iron (III) oxide is a reddish powdery substance.
Chemistry 101 - Acids and Bases
In Chemistry 101, acids are defined as molecules that contribute hydrogen ions to solution. A hydrogen ion is a hydrogen atom that has lost its only electron. The stronger an acid the more hydrogen ions are donated to solution. The measure of hydrogen ion concentration is known as pH. pH is the negative logarithm of hydrogen ion concentration. The smaller the pH, the MORE hydrogen ions in solution. The larger the pH, the fewer hydrogen ions that exist in solution. Bases are molecules that take up hydrogen ions from solution. Equal amounts of equally strong acids and bases neutralize each other, producing water and a salt.
Chemistry 101 - Oxidation - Reduction Reactions
Chemistry 101 defines oxidation - reduction reactions as chemical reactions involving the transfer of electrons. In the oxidation of iron reaction we studied previously, solid iron metal was oxidized, which means it lost electrons and oxygen was reduced, meaning it gained the electrons that iron lost.
4Fe(s) + 3O2(g) --> 2Fe2O3(s)
Electricity is the movement of electrons from higher concentration to lower concentration. Since there is a movement of electrons from one substance to another in oxidation-reduction reactions, oxidation-reduction reactions are the basis of batteries. The oxidation and reduction reactions are separated from each other, and the transfer of electrons from the oxidation to the reduction are pushed along a wire, or some other external pathway In this way, chemical energy is converted to electrical energy. Oxidation-reduction reactions can be reversed with the application of an external energy source in order to plate metals, such as copper-plating and gold-plating.
Chemistry 101 - Thermochemistry
Chemistry 101 teaches thermochemistry, which describes the heat of reactions. In chemical reactions, energy is neither created nor destroyed. This is known as the law of conservation of energy. Some chemical reactions require a net input of energy, known as endothermic reactions. Others produce a net output of energy, known as exothermic reactions. Chemical cold and hot packs you buy in the pharmacy are examples of endothermic and exothermic reactions, respectively. Adding heat to a substance increases its energy. The particles move more with this added energy, which is measured as temperature. Sometimes, this heat is used to change the phase or state of a substance, such as melting ice. Different substances have different specific heats, meaning that they require different amounts of energy to raise their temperature. For example, water has a high specific heat. It takes a lot of energy to raise the temperature of water. This is why bodies of water tend to maintain their temperature. Metals have a low specific heat, meaning it doesn't take much energy to raise their temperature. I would much rather put my hand in a cup of water that was on the stove for 5 minutes than a metal object that was on the same stove.
Chemistry 101 - Rates of Reaction and Equilibrium
Chemistry 101 also teaches reaction rates and equilibrium. Reaction rate is a measure of the change in concentration of reactants (left side of the balanced chemical equation) or change in concentration of products (right side of the balanced chemical equation) over time. Reaction rate can be increased by increasing the concentration of reactants, increasing the temperature, surface area of the reactants and the addition of a catalyst. A catalyst is a substance which speeds up the rate of a reaction, without being used up in the reaction. Enzymes are biological catalysts.
Some chemical reactions are reversible. In that case, when the rate of the forward reaction is equal to the rate of the reverse reaction, the reaction is said to be in equilibrium. A system in equilibrium resists changes to its equilibrium state. This is known as Le Chatelier's Principle. For example, if more reactants are added, the system will move to create more products. If more heat is added, the system will move to reduce the amount of heat.
Chemistry 101 - Stoichiometry
A study of Chemistry 101 is not complete without a discussion of stoichiometry. Stoichiometry is the quantitative basis of chemistry. Chemical reactions occur on the atomic level, but we measure them on the macroscopic level, assigning the value of 1 mole to any 6.02 x 1023 particles of a pure substance. A mole of carbon contains 6.02 x 1023 atoms and weighs 12 g. Whereas we cannot measure atoms because we cannot see them, we can measure 12 g of carbon.
C6H12O6 + 6O2 --> 6CO2 + 6H2O
In the reaction above, 1 molecule of glucose reacts with 6 molecules of oxygen to produce 6 molecules of carbon dioxide and 6 molecules of water. Since we cannot see molecules, we can interpret this reaction in terms of moles. Remember that a mole is equal to 6.02 x 1023 particles. In this case, 1 mole of glucose reacts with 6 moles of oxygen to produce 6 moles of each carbon dioxide and water. We can obtain the weight of a mole of any atom from the periodic table.
Glucose, C6H12O6, consists of 6 moles of carbon, each weighing 12 g, 12 moles of hydrogen, each weight 1 gram and 6 moles of oxygen, each weighing 16 grams. 1 mole of glucose weighs 180 grams. By mixing 180 grams of glucose with 6 moles of O2, or 6 x 2 x 16 grams = 192 grams of oxygen, we will generate 6 moles of each carbon dioxide and water.
Chemistry is a quantitative science which requires dedicated study and practice. It is a worthwhile endeavor, as matter is the basis of all living and non-living things. Visit http://chemin10.com to learn Chemistry 101, first-year chemistry, in easy-to-learn 10 minute videos, with quizzes, forum and live online tutoring. Learn Chemistry 101 with Chem in 10.
