Why the Formation of Ionic Compounds Is Exothermic

Why the Formation of Ionic Compounds Is Exothermic Have you ever wondered why the formation of ionic compounds is exothermic? The quick answer is that the resulting ionic compound is more stable than the ions that formed it. The extra energy from the ions is released as heat when ionic bonds form. When more heat is released from a reaction than is needed for it to happen, the reaction is exothermic. Understand the Energy of Ionic Bonding Ionic bonds form between two atoms with a large electronegativity difference between each other. Typically, this is a reaction between metals and nonmetals. The atoms are so reactive because they do not have complete valence electron shells. In this type of bond, an electron from one atom is essentially donated to the other atom to fill its valence electron shell. The atom that loses its electron in the bond becomes more stable because donating the electron results in either a filled or half-filled valence shell.  The initial instability is so great for the alkali metals and alkaline earths that very little energy is required to remove the outer electron (or 2, for the alkaline earths) to form cations. The halogens, on the other hand, readily accept the electrons to form anions. While the anions are more stable than the atoms, its even better if the two types of elements can get together to solve their energy problem. This is where ionic bonding occurs. To really understand whats going on, consider the formation of sodium chloride (table salt) from sodium and chlorine. If you take sodium metal and chlorine gas, salt forms in a spectacularly exothermic reaction (as in, dont try this at home). The balanced ionic chemical equation is: 2 Na (s) Cl2 (g) → 2 NaCl (s) NaCl exists as a crystal lattice of sodium and chlorine ions, where the extra electron from a sodium atom fills in the hole needed to complete a chlorine atoms outer electron shell. Now, each atom has a complete octet of electrons. From an energy standpoint, this is a highly stable configuration. Examining the reaction more closely, you might get confused because: The loss of an electron from an element is always endothermic (because energy is needed to remove the electron from the atom. Na → Na 1 e- ΔH 496 kJ/mol While the gain of an electron by a nonmetal is usually exothermic (energy is released when the nonmetal gains a full octet). Cl 1 e- → Cl- ΔH -349 kJ/mol So, if you simply do the math, you can see forming NaCl from sodium and chlorine actually requires the addition of 147 kJ/mol in order to turn the atoms into reactive ions. Yet we know from observing the reaction, net energy is released. Whats happening? The answer is that the extra energy that makes the reaction exothermic is the lattice energy. The difference in the electrical charge between the sodium and chlorine ions causes them to be attracted to each other and move toward one another. Eventually, the oppositely charged ions form an ionic bond with each other. The most stable arrangement of all the ions is a crystal lattice. To break the NaCl lattice (the lattice energy) requires 788 kJ/mol: NaCl (s) → Na Cl- ΔHlattice 788 kJ/mol Forming the lattice reverses the sign on the enthalpy, so ΔH -788 kJ per mole. So, even though it take 147 kJ/mol to form the ions, much more energy is released by lattice formation. The net enthalpy change is -641 kJ/mol. Thus, the formation of the ionic bond is exothermic. The lattice energy also explains why ionic compounds tend to have extremely high melting points. Polyatomic ions form bonds in much the same way. The difference is that you consider the group of atoms that forms that cation and anion rather than each individual atom.

SAT Cost, ACT Cost, and How to Save Money

SAT Cost, ACT Cost, and How to Save Money SAT / ACT Prep Online Guides and Tips If you're deciding between taking the SAT and the ACT and you have a tight budget, this guide will help. We'll cover the registration costs, reporting costs, and how you can save money no matter what test you choose. All Registration Costs for the SAT and ACT (Updated for 2019-2020) Let's first look at the cost of registering for the test, and extra fees. Fee Type What is this? SAT Cost ACT Cost Registration Fee The normal fee for each administration of the test you register for $64.50 ($49.50 without essay) $67($50.50 without essay) Late Fee Charged if you register after the regular deadline but before the final late deadline $30 $30 Waitlist Fee Charged if you register after the late registration deadline and are seated on test day. $53 $53 (standby testing) Change Fee Charged if you change the test center, test date, or test type $30 $30 Question and Answers An optional service that sends you the test questions and correct answers (useful for seeing what mistakes you made) $18 $20 International Fees Charged additionally if you're taking the test outside of the United States $43 to $53 $99.50 Sources: College Board and ACT, Inc The costs between the SAT and ACT are similar for registrations for U.S. students. If your schools require the essay section, taking the SAT saves you $1 per test. Clearly both tests charge through the nose for extra fees, punishing lack of planning ahead. As we'll cover below, planning early can represent a huge cost savings to you. All Reporting Costs for the SAT and ACT Once you take the test, you'll have to send your test scores to colleges. Each college you apply to will require its own SAT or ACT score report. If you apply to 12 colleges, you'll need to send 12 score reports. This is where the policies for the SAT and ACT really differ. Fee Type What is this? SAT ACT Free Score Reports The number of free reports you get when registering for the test 4 free reports, within 9 days after test 4 free reports, by the Thursday after the test Cost per School Charged for each report you send to a school outside of your free reports. $12 per school $13.00 per test per school Rush reporting Expedited sending of score reports $31 per school $16.50 per test per school Sources: College Board and ACT, Inc. Here's an elaboration. When you take the SAT or ACT, both tests allow you to send your scores to four schools for free. You will specify these four schools when registering for the test. The SAT gives you nine days after the test to decide those four schools, while the ACT only gives you six days. Outside of the free reports, both tests will charge you for sending score reports. This can happen if you're too late in specifying your free reports, or if you exceed the four free reports per test. The SAT and the ACT differ here in a significant way. The SAT can send all your College Board test scores to a school in a single report. This includes all SAT and SAT Subject Test administrations. The ACT, however, requires $13.00 per test per school. For example, if your school uses 'Superscoring', you might want to send two or three tests to combine the highest score.This can really rack up the cost really quickly.For example, if you're applying to ten colleges and you want to send three test scores, this will mean $13 x 10 x 3 = $390, just to send your scores to schools. All this money starts adding up. It pays to be proactive and to plan ahead. Here are four strategies to save as much money as possible on the SAT and ACT. 5 Tips to Save Money on the SAT and ACT If you're on a budget, you can save a lot of money by planning ahead. Here are important ways to get money back. #1: Apply for a Fee Waiver If You Qualify Both the College Board and the ACT know that low-income families find it difficult to pay for these expensive tests. Applying for a fee waiver can save you hundreds of dollars. With a fee waiver, both tests give you free registration for tests and free score reports. How do you qualify for a fee waiver? You qualify if any of the below is true: You're enrolled in or eligible for the federal Free and Reduced Price Lunch program You're enrolled in a federal, state, or local program that aids students from low-income families (like Upward Bound) Your family receives public assistance You live in public housing, a foster home, or are homeless. Your household income level falls below USDA levels for Reduced Price lunches To get a fee waiver, you MUST go through your school counselor. You cannot apply directly through the College Board or ACT, Inc. This takes time, so make sure you do this well before you plan to register for the test. Contact your school counselor as soon as possible if you qualify for a fee waiver. #2: Register Early The late fee for registration is around half the test of the cost itself, causing a 50% increase in the test cost if you're late to register. If you have a test date set in mind, register months in advance so you don't forget. Make sure you get a confirmation by e-mail so you have no surprises come test day. Even worse than paying the late fee is missing the test date registration altogether. If you've been prepping for a specific date, this will cause you to lose momentum from your test prep and lower your score. #3: Use the FREEScore Reports Both the SAT and ACT give you free score reports to send to schools of your choosing. Make sure you specify schools before registration so you don't forget. Once the ACT test date passes, you won't be able to specify any more colleges to receive your test scores. The only reason you may want to not specify a college for the free score report is if you're not sure you're going to do better, and you want to make sure the college receives only your top scores. For all other cases, send it to colleges that are on your application list. #4: Self-Report Scores When Possible In an attempt to lower the barrier to applying even further, some of the top schools in the country now allow students to self-report their SAT and ACT scores on their applications; you'll only have to submit official SAT/ACT score reports if you're accepted. Prestigious national universities that allow self-reporting of SAT/ACT scores include Stanford, Columbia, Johns Hopkins, Northwestern, Caltech, Rice, WashU in St. Louis, and Emory. Most of the top liberal arts colleges also have adopted this policy, including Williams, Amherst, Wellesley, Swarthmore, Middlebury, and Pomona. For all schools allowing self-reported SAT/ACT scores, make sure to check their policy on superscoring/score choice so that you're maximizing your standardized testing profile. Also, while this should go without saying, don't lie when self-reporting your SAT/ACT scores on your application. Don't write a score you plan to get on the February ACT or March SAT before admissions decisions go out (unless the school you're applying to accepts February ACT scores) and don't lie about doing better than you did. This will most likely result in your admission being rescinded not just because you didn't do as well as you said you did, but because you lied; institutions of higher learning generally aren't super keen to welcome academically dishonest students into their community. #5: Use Your SAT/ACT Score to Qualify for Scholarships Many states and schools have scholarships where the major qualification is your SAT/ACT score. By doing well on the test, you can make back well more than it cost to take the test. Take the time to research these scholarships and apply for them if you qualify. What's Next? Now that you know how much the SAT and ACT cost, let's read more resources to learn more about these tests. Want a super high SAT score or ACT score? I teach you how to get a perfect SAT/ACT score, based on my own experiences. What are good ACT scores or good SAT scoresfor college? Is the SAT or ACT easier? Find out which you should take. Want to improve your SAT score by 160 points or your ACT score by 4 points?We've written a guide for each test about the top 5 strategies you must be using to have a shot at improving your score. Download it for free now: