Tutor profile: Douglas C.
What's the difference between a covalent and an ionic bond, and how do they form?
Understanding how molecules form can throw many students for a loop the first time that they learn it. The confusion is understandable; we're talking about atoms, the smallest complete unit of matter, a thing that most of us will never actually see or truly interact with in our every day lives. So to make it clear, I'll use two items that most people are at least familiar with: magnets and a lifeguard's flotation device. When two atoms join together, we call that a molecule. Nearly every form of molecule is held together by either an ionic or a covalent bond. Those bonds are created by the electrons of the atoms in the molecule. You can think about atoms like picky eaters; they only want things a certain way. When it comes to the number of electrons they have around them, they REALLY want 8 electrons in their outermost electron layer, and they'll do anything to make that happen. Sometimes, they'll give away or straight up steal electrons to get that desirable eight. Other times, they'll share their electrons with another atom, so that in total, they both have eight. These two options will give us ionic and covalent bonds. The two types of bonds come down to either "give and take" or "cooperating". Ionic is the "give and take" approach, while covalent bonds are about "cooperating". Let's start with ionic bonds. If an atom has 9 electrons in its outermost, or valence, shell, it desperately wants to give it away. If another atom has 7, it's greedy for that last electron to satisfy its craving. If the two are near each other, Atom #1 will happily give its electron to Atom #2. But here's the thing: electrons have a negative charge, which means that they're like one side of a magnet. When Atom #1 gives away its electron, it's losing some of its negativity, making it more positive. When Atom #2 receives that electron, it's gaining negativity, making it more negative. And just like magnets, when you have a positive and a negative near each other, they'll stick tight together, bound by magnetism. That's an ionic bond! So whenever you need to remember how ionic bonds form, just think about two atoms stuck together like magnets. One is positive, one is negative, and they got that way by moving one or more electrons between them. Covalent bonds, on the other hand, are all about cooperation. Instead of giving or taking electrons completely, each atom donates one electron to a shared pair of electrons that travels around both atoms, binding them together. imagine the electron pair like a lifeguard's ring-shaped flotation device. If two people were drowning near each other, the lifeguard could throw them one single ring. Both people can grab onto it, and the ring will keep both of them above water until help arrives. While both are holding it, we can say that they're connected; each person is firmly attached to the other by the ring. The same is true of atoms in a covalent bond. Each atom needs the extra electrons, and since they're sharing that pair of electrons, they're connected to each other. So when you need to recall how covalent bonds form, remember one ring can save two swimmers and one pair of electrons can bring two cooperative atoms together!
Subject: World History
What was the biggest empire in the world?
Ah, the age-old siren song of competition. Who is the biggest? Who's the strongest? Whose dad is tougher? Well, there are two distinctly different correct answers for this question. First and foremost, the British Empire had the most territory spread out over the world. At their peak, they controlled over 13 million squares miles of land territory. 13 million! And that doesn't even consider all of the ocean that their ships dominated, essentially giving them control of global trade at the time. Now, they were pretty late to the party, in terms of history's empires. Since its formation out of the collapse of the Holy Roman Empire, the English had almost constantly been in conflict, either with itself or with its neighbors. There were wars with the French and with the Spanish, and more commonly with each other over religion, right to rule, and how to rule. They didn't really get their act together until the Age of Exploration, when most European countries began sending out ships to find faster routes to the Asian trade markets and accidentally stumbled across North and South America. Soon, the British were snapping up new land for colonies like kids in a candy shop, and when they defeated the French in the Seven Years War, they become the dominant colonizers in the world. In fact, their territory was so global that the expression "the sun will never set on the British empire" had two meanings: first, that the British empire would never fall (it did, after World War I) and second, that the sun was literally always shining on some territory the British owned! Even when it was bedtime in England, their colonies in India and Africa would still be catching rays. Pretty good, England. The other empire in the running was far less modern, but still just as impressive. The Mongols, using only horses, clever strategy, and ruthlessness, carved out an 11 million mile swath of Asia that stretched from China all the way across to the edges of Europe! It's the largest contiguous, or unbroken, land empire in history. It's larger than Alexandar the Great's territory, larger than Rome, and larger than the Ottomans! While history likes to discount the Mongols as nomadic savages, they were actually extremely disciplined and phenomenal strategists. They also knew how to use psychology against their enemies and to keep the peace in their territory. It was said that many cities on the Mongol war path would surrender before they even arrived, and that during their reign over Asia, "a man could safely walk across the continent with a golden plate on his head", meaning that the Mongols kept tight security and punished crime swiftly and severely. Unfortunately, they were also largely responsible for the spread of the Black Death plague which swept through Asia and nearly decimated Europe. They did such a good job preserving the safety and efficiency of trade that the plague was easily able to travel across their entire territory! So, if anyone asks what the biggest empire in history was, you'll have to ask for more detail. Do they want the one with the most territory or the one with the most connected land? Whether with ships or horses, the British and the Mongols both secured their place in history as the biggest kids on the block.
Why does the Hulk from Marvel Comics have the worst superhero origin story, according to biology?
Here's the thing about the Hulk: While he isn't the only superhero with a radiation-based origin , he is one of the few that the comic book world has gotten specific about. Those details tell us everything we need to know. According to science, Dr. Banner needs a hospital, not anger management lessons. Let's do the work. First of all, gamma radiation, the kind that Banner was exposed to, is certainly capable of producing mutations in living cells and the organisms they compose, but it's certainly not for the better. Gamma radiation is what is known as "ionizing radiation", a form of electromagnetic energy that can literally rip electrons of atoms. That makes molecules, two or more atoms held together by electrons, particularly vulnerable to damage or even complete breakdown. That includes "life's instruction manual", DNA. DNA is one of the most complex molecules in existence, and whenever there are changes to the code it contains, things can go south quickly. Now, mistakes do happen in nature itself; the body's DNA replication process naturally makes about one error per billion sequences of DNA, but those mutations are almost always benign. However, at the most basic level, cancer is caused by mutated DNA that get replicated consistently by the body instead of getting fixed. If the Hulk's origin story is massive, unprotected exposure to gamma radiation, one of the ionizing energies on the electromagnetic spectrum, his DNA would have sections of it broken off. With enough exposure, it could destabilize his entire DNA sequence, killing most of his cells and leaving the survivors unable to copy themselves! No more smashing for the Hulk. That being said, there are a few nifty, superhero-like mutations that real-world science can offer. For example, a certain mutation dubbed "the Hercules gene" limits a person's myostatin, a hormone that puts a cap on how much muscle a normal human can develop. Without myostatin holding them back, people and animals with this mutation have significantly more muscle and a greater ability to use it, making their strength significantly higher! No, they can't leap tall buildings in a single bound, but still, a cool example of mutation working in our favor! For those of us who don't live in a comic book, we want consistency in our DNA. After all, your DNA is what makes you unique and awesome, and in order to keep it that way, your cells need to keep on copying that code down to the last nucleotide. So if you want super-strength, stay away from the local nuclear power plant and hit up the gym. Trust me, your genes will thank you for it!
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