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Course: Class 9 Chemistry (India) > Unit 3
Lesson 3: Molecules and ions- Introduction to ions
- Naming ions and ionic compounds
- Molecules and compounds
- Naming monatomic ions and ionic compounds
- Common polyatomic ions
- Naming ionic compound with polyvalent ion
- Worked example: Finding the formula of an ionic compound
- Worked example: Formula for an ionic compound
- Naming ionic compounds
- Find the formula for ionic compounds
- Predicting the formula of the given compound
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Naming ions and ionic compounds
Ionic compounds are neutral compounds made up of positively charged ions called cations and negatively charged ions called anions. For binary ionic compounds (ionic compounds that contain only two types of elements), the compounds are named by writing the name of the cation first followed by the name of the anion. For example, KCl, an ionic compound that contains K⁺ and Cl⁻ ions, is named potassium chloride.
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- At1:33...
"...the chlorine grabs an electron..."
What is this "grab"? Both the chlorine and the potassium were initially neutral, where the positive protons and negative electrons balanced each other and seemed happy. What is it that propels the electron over to Chlorine? It wouldn't seem to be an electrical force.(68 votes)- If you see the electronic configuration of Cl you will observe that it is just one electron short of a noble gas configuration which is the ultimate 'happy' state. Similar is the case for K which has 1 electron in excess so K gives its excess electron to Cl, both achieve a stable noble gas configuration and they live happily ever after. :D
In short the desire to achieve stability propels the atoms to lose,gain or share electrons(148 votes)
- why is chlorine ion named as chloride? Just because it is halide? What about potassium?(15 votes)
- For single-atom cations (positive ions) the name of the ion is the same as the name of the atom. For single-atom anions (negative ions) the name of the ion will have the -ide suffix.
So Li is "Lithium", Li+ is also "Lithium", but Li- is "Lithide".
HOPE THAT WAS HELPFUL(117 votes)
- What does the K mean for potassium(13 votes)
- K comes from kalium, the Mediaeval Latin word for potash, which contains potassium.(19 votes)
- I am having trouble getting this concept of ionic compounds. When I go to the practice section on this it asks me questions like, " What is the most stable monatomic ion formed from fluorine?" I am not seeing in the video on how to solve these problems. Maybe it is just me? Thank you! :)(22 votes)
- The most stable monatomic ion will occur when the atom's electron shells are all completely full. For example, fluorine will want 1 more electron to fill it's electron shell because it's one away from the closest noble gas. Thus, by adding one electron, it would become F-(8 votes)
- When K wants to give up an electron because it has 1 too many and Cl takes the electron because it wants to become like a noble gas...wouldn't they immediately break apart after the electron transfer is complete?(6 votes)
- Because after electron transfer takes place K ends up having a positive charge and Cl has a negative charge. Because opposite charges attract they stick together. :)(28 votes)
- Why is potassium chloride considered an "ionic" compound if the two atoms already neutralized each other?(8 votes)
- because potassium chloride exists as as ions of potassium(as K+) and chlorine(Cl-) and not as atoms who shared electrons like in NH3(ammonia)(14 votes)
- Alkali metals in Group one like to lose an electron and Halides like to have one more electron to have 8 electrons in the outer shell, so that they are more stable.
However, why is this configuration the most stable one? What makes it stable?(6 votes)- This question has already been answered below. If you want a more quantum mechanical explanation, I suggest you take a look here - https://www.quora.com/Why-do-8-electrons-form-a-stable-shell-Why-not-7-6-4-2.(4 votes)
- why does potassium go by "K" in the periodic table?(1 vote)
- The symbol for potassium, K, comes from the Arabic kali, which comes from the root word alkali, al-qalyah in Arabic, which means plant ashes.
In 1807, British chemist Humphry Davy isolated potassium by electrolysis and named it potassium which derived from the earlier name of pot ash (he added the –ium suffix because it’s a metal). The name potassium itself goes back to original Arabic meaning and the original way of obtaining potassium. The idea is that you would take plant ashes, like wood, and dissolve the water soluble potassium compounds in water in a pot, hence the name pot ash. The water solution with potassium compounds is slightly basic, which also explains the connection of alkali and basicity. The actual potassium salts are obtained by allowing the water to evaporate which leaves behind the salt.
In 1809 German chemist Ludwig Wilhelm Gilbert proposed the name Kalium as an alternative to Davy’s which was more in line with in earlier German chemist, Martin Klaprot, who proposed the name kali in 1797, again in reference to alkali. Nowadays English and French speaking countries primarily use potassium for the name, while other countries including Germany use kalium. The IUPAC allows both names, but chose K for the symbol in reference to the German kalium name.
Hope that helps.(11 votes)
- Does this naming system work for all ionic compounds?
I'm confused about when exactly you would keep the cation name and add the -ide to the anion element. Is it only for ionic compounds with a metal, like potassium?(4 votes)- It does get more complicated than this and it takes an entire book to cover all the rules. But in simple terms, when an element such as potassium forms a cation (K+) then it is still called potassium - there is no change of name. It is the atoms that form the anions that change names, so chlorine becomes chloride (Cl-). Hence the ionic compound formed between potassium and chlorine is called potassium chloride.
But not all anions end in "ide". If there is oxygen involved as well, then they end in "ite" or "ate". For example, sodium sulfate (Na2SO4, made of Na+ and SO4^2- ions).(5 votes)
- When the halogens are mentioned, it seems like they are characterized by having 7 electrons. My question is... do all atoms with an odd number of electrons "want" an even number of electrons? In1:20, Sal says that the halogens would love to have 8 electrons.
Also, how does Sal get 7 electrons in the first place? For a neutral atom (if it is one), I thought there would be, for example, 17 electrons for Chlorine.
I think I'm missing something. I'd appreciate it if someone would help me :)(3 votes)- The other replier is correct; Sal is referring to valence electrons. Yes, an atom like chlorine has more than seven electrons, but only the valence electrons are responsible for chemical bonding and so we’re only interested in those (as opposed to the core electrons).
An atom like chlorine prefers to have eight valence electrons, not so much because eight is an even number, but rather because it is trying to follow the octet rule. The octet rule is a general rule which says that many elements achieve stability by having eight valence electrons. There are atoms with even valence electrons as neutral atoms, and not eight (like oxygen), which also try to achieve eight valence electrons following this octet rule.
Hope that helps.(6 votes)
Video transcript
- [Instructor] Let's get
some practice now thinking about how ions typically form, how they might form compounds and how we name those compounds. So let's start with
something in group one. In this first column, this
first column is often known as alkali metals. So let's start with potassium. K is the symbol for potassium. Now things in group one here, one way to think about
is their outermost shell has one electron in it. So they wouldn't mind
losing that electron. So when they ionize, they
tend to lose an electron and become a cation, a positive ion. And so let's look at a situation
where I have some potassium that has been ionized. I could write it just like this, we've seen that in previous videos and we can refer to this
just as a potassium ion, we could refer to this
as potassium one plus. We could refer to this
as a potassium cation. Now let's go on to the other
side of the periodic table. Things that would really
love to grab an electron. So things in group, in the halides, which is this column right over here. So these are the halides. They have seven electrons
in their outermost shell. They would love to have eight, so they tend to be really
good at grabbing electrons. And so let's say we're
dealing with chlorine, and chlorine is able to ionize. So it's able to grab an electron. When chlorine grabs an electron, it will be a negatively charged ion, so you could write it
as Chlorine one minus, but the way that we
generally refer to an anion, a negatively charged ion, instead of just calling
this the chlorine anion, we would call this chloride. So this we would refer to as Chloride. Now as you can imagine
with potassium having a positive one charge or one plus charge and this having a negative charge, they're going to be
attracted to each other and they can actually
form an ionic compound. The ionic compound they
would form, we would write as, you'd write your positive ion first and then you would
write your negative ion. And this right over
here would be described as potassium chloride. Let me write that down. Potassium, potassium chloride. Now you might be saying, "Well, I just," Let me rewrite the whole thing. So you know the chloride
part, you say okay, this is going to be an anion because instead of writing chlorine which is the name of this element, I wrote this IDE at the end to say, "Hey, this is an anion," so I know that this is the
chlorine anion, this is chloride, why didn't I do something
similar for potassium? Well, the way the convention works is if someone says potassium chloride, you know you're dealing
with an ionic compound and if the chlorine has
a negative one charge, an ionic compound, the whole thing is gonna be neutral. So if this one over here is one minus, then you know this over
here is just one-for-one, this is going to be one plus so you know that you're
dealing with a potassium cation and you could say and a chloride
ion or a chlorine anion. You could refer to it various ways, but this is potassium chloride. You have a positively charged potassium and you have a negatively
charged chlorine, which we would call a chloride. In the next few videos I'll
do many, many more examples of this and ones that will be
a little bit more complicated.