The atom is where chemistry begins. Everything in the class will be an extension, built on that basic information. Be sure you take the time to understand the material presented on atoms.
An atom is made of 3 parts. Those parts are neutrons, protons, and electrons. The center of the atom is called the nucleus. The nucleus is made up of neutrons and protons. Electrons are the particles that float around the exterior part of the atom, like planets circling the sun. [2] X Research source The size of an atom is incredibly small. To give some perspective, think about the largest sports arena you know about, maybe the Houston Astrodome. If you consider the Astrodome to be the atom, then the nucleus of that atom is about the size of a pea somewhere around the 50 yard line. [3] X Research source
The atoms of a specific element are always the same. This means that every element has a known, and unique, number of neutrons and protons in its atomic structure. [5] X Research source
You don’t have to calculate anything to know the number of protons in the nucleus of an element. That number is printed at the top of every squared box, for every element, in the periodic table.
Lewis structures are useful in drawing simple diagrams that identify bonds, such as covalent bonds, that are shared between elements in an atom or molecule. [8] X Research source
The diagram shows the stable arrangement of electrons, where they bond to the next element, and information about the strength of the bonds, like if the bonds are shared or doubled. Think about the octet rule, and picture the symbol for an element, perhaps C for carbon. Now place or picture 2 dots at each compass position, meaning 2 dots north of the C, east, west, and south. Now picture an H, representing a hydrogen atom on the other side of each of the 2 dots. This completed Lewis diagram means that the single carbon atom in the center is surrounded by 4 hydrogen atoms. The electrons are bonded in a covalent manner, meaning the carbon and hydrogen atoms share one of their electrons to bond to each other. [11] X Research source The molecular formula for this example is CH4, and is the formula for methane gas.
Talk to your professor, or members of your study group if the concepts about chemical bonding and Lewis diagrams are not clear.
Understanding the periodic table is critical to passing the first part of your chemistry class.
The atomic mass unit is printed for every element inside the square at the bottom, just under the name of the element. Remember, the only two things that are in the nucleus of an atom are protons and neutrons. The periodic table tells you the number of protons, and it tells you the atomic mass number. From that point, the math is simple. Subtract the number of protons from the atomic mass number, and that gives you the number of neutrons in the nucleus of every atom for that element. [15] X Research source
Since an atom has no overall charge, all the positive and negative charges contained in the atom must balance. Therefore, the number of electrons is equal to the number of protons. [16] X Research source
The format for a chemical equation consists of reactants on the left side of the equation, then an arrow in the direction of the products of the equation, then the products. The parts on one side of the equation have to balance the parts on the other. [18] X Research source For example, Reactant 1 + Reactant 2 → Product 1 + Product 2 Here is an example using the symbols for Tin, which is Sn, in its oxidized form, which is SnO2, combined with hydrogen gas, which is written as H2. SnO2 + H2 → Sn + H2O. But this equation is not balanced since the quantity of reactants must equal the quantity of products. The left side has one more oxygen atom than the right side. [19] X Research source Use basic math to balance the equation by indicating 2 hydrogen units on the left side of the equation, and 2 water molecules on the right. The final balanced equation looks like this: SnO2 + 2 H2 → Sn + 2 H2O . [20] X Research source
The equation gives you the ingredients, on the left side of the equation, but does not tell you how much to use of each ingredient. The equation also tells you what the products will include, but again does not tell you the quantity of the products. You have to figure that out. Using the previous example, SnO2 + H2 → Sn + H2O, consider why this equation, or recipe formula, won’t work. The Sn parts are equal on both sides, and the H2 parts are equal on both sides. But the left side has 2 oxygen parts, and the right side has only 1 oxygen. Change the right side of the equation to indicate the product will contain 2 H2O parts. The 2 in front of the H2O means all the quantities in that grouping are now doubled. So now the oxygen balances, but adding the 2 means there is more hydrogen on the right side of the equation than on the left. Go back to the left and change the H2 ingredient to be twice that, by putting a 2 in front of the H2. Now you have adjusted the ingredients on both sides of the equation. What goes into the recipe and what comes out, are equal, or balanced.
To pass chemistry, you will need to know how to solve equations that involve chemical reactants, products, and the introduction of some other influence that alters either the reactants, products, or both. [22] X Research source
Common types of chemical reactions you can expect to learn about include synthesis, analysis, substitution, double displacement, acid-base, oxidation-reduction, combustion, isomerization, and hydrolysis. [23] X Research source The types of reactions presented in your chemistry class may vary, depending on the goals of each class. High school chemistry may not provide the same level of detail as that of chemistry taken at a college or university.
Understanding the changes that happen with different types of chemical reactions can be confusing. Understanding what happens during specific chemical reactions can be a challenging section of your chemistry class.
For example, you already know what happens when you combine 2 hydrogen atoms with 1 oxygen atom, you get water. So if you put that water you just made into a pot, and put it on the stove using heat, something changes. You created a chemical reaction. If you put that water into the freezer, same thing. You introduced a change that altered the original reactant, water in this case. Go over each type of reaction one by one until you understand it, then move on to the next type. Focus on the energy source that drives the reaction, and the primary changes that result. If you are having trouble in this area, make a list of what is confusing to you, and go over it with your professor, your study group, or someone that knows chemistry well.
If possible, work on nomenclature before you actually begin the class. Many workbooks are available for purchase or through online access.
The superscript numbers follow a pattern found in the periodic table, and indicate the overall charge of the element or chemical compound. Review the periodic table to see elements in vertical rows that share the same superscript numbers. Subscript numbers are used to identify the quantity of each identified element that is part of the chemical compound. As previously discussed, the subscript of 2 in the molecule H2O tells you that there are 2 hydrogen atoms as a part of that molecule.
One of those reactions is the oxidative-reduction reaction. This reaction involves the process of either gaining or losing electrons. An easy way to remember the process is to remember the phrase “LEO the lion says GER”. This stands for Lose Electrons in Oxidation, and Gain Electrons in Reduction. [26] X Research source
To make a neutral charge, the positively charged ion, called a cation, must be balanced by an equal charge from a negative ion, called an anion. The charges are identified as superscripts. [27] X Research source For example, the magnesium ion carries a +2 cation charge, and the nitrogen ion has a -3 anion charge. The +2 and -3 would be indicated as superscripts. To properly combine the two elements to arrive at a neutral charge, 3 magnesium atoms are used for every 2 nitrogen items. [28] X Research source The nomenclature that identifies this uses subscripts, and is written as Mg3N2. [29] X Research source
The alkaline earth metals found in the second column form 2+ cations, such as Mg2+ and Ba2+. [31] X Research source Elements in the seventh column are called halogens, and form -1 anions, such as Cl- and I-. [32] X Research source
In other words, magnesium is always represented as Mg, and always carries a cation charge of +2. [34] X Research source
It would be so much easier to understand if everything was visible, right in front of you. But in addition to comprehending all the chemistry that is happening, you also have to understand the language used to record and represent everything to do with chemistry. If understanding chemistry is difficult for you, realize that you are not alone, but don’t let it beat you. Talk with your professor, your study group, a teaching assistant, or someone that is really good at chemistry. You can learn all this, but it may help if it can be explained in a way that makes sense to you.
Memorize a helpful phrase. The phrase, “Please Excuse My Dear Aunt Sally” tells you what applications to perform first. The first letter of each word indicates the order to be used. Anything in Parentheses is done first, then Exponentiation, Multiplication or Division, the lastly Addition or Subtraction. Complete the calculation 3 + 2 x 6 = ___, by ordering your steps according to the phrase. The answer to the equation is 15.
Know where to round up or down. If the digit next in the series is a 4 or less, then round down, and if it is a 5 or greater round up. For example, consider the number 6. 66666666666666. You are asked to round your answer to the second decimal place. The answer is 6. 67. [37] X Research source
In other words, you no longer consider positive or negatives, just the distance to zero. For example, the absolute value of -20, is 20. [38] X Research source
Measures of matter are expressed in moles (mol). Temperature is expressed in degrees Fahrenheit (°F), Kelvin (K), or degrees Celsius (°C). Mass is expressed in grams (g), kilograms (kg), or milligrams (mg). Liquid measures are expressed in liters (L), or milliliters (mls).
You may be asked to provide answers in units other than what was in the original question. For example, you may be given a temperature equation to solve in Celsius, and asked to give the final answer in Kelvin. Kelvin is the international standard for temperature measurements often used in chemical reactions. Practice changing from degrees Celsius to degrees Kelvin or Fahrenheit.
Look at the nutrition label on any food product. You will see calories per serving, per cent of RDAs, total fat, calories from fat, total carbs, and a breakdown of the different types of carbs. Practice by calculating different ratios and proportions using different categories for the bottom number. For example, calculate the amount of monounsaturated fat per the total amount of fat. Change this to a percent. Calculate how many calories are in the entire container by using the numbers provided for calories per serving and servings per container. Calculate how much sodium is contained in ½ of the full container. By practicing conversions like this, regardless of the units used, you will be much more comfortable exchanging these units of measure for chemistry measures, such as moles per liter, or grams per ml, etc.
For example, 0. 450 moles of Fe contains how many atoms? The answer is 0. 450 x 6. 022x10 23. [40] X Research source
Now answer the question, how many carrots are in a mole? Instead of multiplying by 12, you multiple using Avogadro’s number. So there are 6. 022 x 1023 carrots in one mole. Avogadro’s number is used to convert anything of substance, an atom, molecule, particle, or carrot, to how many of that thing is contained in one mole. If you know the number of moles of something, then the final value for the number of molecules, atoms, or particles present, is that number times Avogrado’s number. [41] X Research source Understanding how to convert particles to moles is an important part of passing chemistry. Molar conversions are a part of calculating ratios and proportions. This means the quantity of something in moles as a part of something else.
Molarity is commonly used in chemistry to express the quantity of something in a liquid environment, or the amount of a solute contained in a liquid solution. Molarity is calculated by dividing the moles of solute by the liters of solution. Molarity is expressed as moles per liter. [42] X Research source Calculate density. Density is also a commonly used measure in chemistry. Density is the measure of mass per unit volume of a chemical substance. The most common expression for density is given in grams per milliliter, or grams per cubic centimeter, which are the same thing. [43] X Research source
This does not apply to molecular formulas since that type of description tells you the exact proportions of chemical elements that make up the molecule. [45] X Research source
A molecular formula is written in language that uses the abbreviation of the element(s), and how many atoms of each element, make up the molecule. For example, the molecular formula for water is H2O. This means every water molecule contains 2 hydrogen atoms and 1 oxygen atom. The molecular formula for acetaminophen is C8H9NO2. Every chemical compound is represented by its molecular formula.
As a common math procedure, you will need to convert grams to moles. The atomic mass unit of an element, in grams, is equal to one mole of that substance. For example, calcium has a mass of 40 atomic mass units. Therefore, 40 grams of calcium equals one mole of calcium. [47] X Research source
By working in groups, some members will find areas easier than others, and can help share their methods of learning with the group. Divide and conquer.
Go back to those parts later and take a fresh look. If they still seem confusing, talk with your study group, your professor, or a teaching assistant. Try to answer the questions at the end of the chapter. Most textbooks provide additional information that explains the correct answers in case anything is confusing to you. Textbooks use visual aids to get the major teaching points across. Look at the visuals, and pay attention to the captions. This may help to clear some of the confusion.
Try saying something like, “I find it easier to study if I can listen to the lecture over again while I review my notes. Would it be okay if I record your lectures so I can do that?”
Avoid just memorizing the answers. Chemistry is a subject you have to understand in order to answer that same question if it was worded differently.
Many professors have study guides available and open additional office hours for student help when needed. Keep a list of areas that are difficult, and ask your professor or teacher for help. This provides you with an opportunity to understand the difficult topics before the class moves on to the next section, and you get even more confused.
Break down areas that are difficult into describable terms. For example, be able to verbalize that you do not understand oxidation reactions, or how to combine elements with positive and negative charges. By verbalizing the areas you are having difficulty understanding, you may also find some reassurance in realizing there is much you have learned and do understand.
