ATI TEAS 7 I COMPLETE CHEMISTRY REVIEW Part 1 I

and they are not called molecules in their natural form. The natural form refers to the elements that appear directly on the periodic table, so I must emphasize that this is in its natural form because they are able to create a molecule which is when they combine with other elements, when they combine like in the second set of examples, they fit the description of a molecule, so the first set of examples are molecules of the same type of atom and the second set of examples are molecules with different types of atoms if you need a picture of the second set, it will I'll give one in a minute so that this second set of examples that are locked in here can be described in more detail as compounds, a compound consists of two or more different types of atoms. so we can clearly see that this second row of molecule examples can also fit the description of a compound, therefore these molecules can also be called compounds.

Let's take an expanded look at these compounds. Take for example nacl, we see a sodium atom bonded to a chlorine atom. and this together is equivalent to a molecule which is also called a compound, it is a molecule because it is made of two or more atoms and it is a compound because it is made of two different types of atoms, both sodium and chlorine atoms, and this sums up the relationship. between subatomic

part

icles atoms elements molecules and compoundsThe periodic table shows the 118 known elements. Every element we know is made up of a unique type of atom and because each element is made up of a unique type of atom, no two are the same, so we can conclude that each one will have different properties or properties.

Characteristics There are several ways to put these elements into categories, but we are going to go over the most important and most common ways to categorize them, so first the elements are arranged in order from the lowest atomic number to the highest atomic number, so starting from top left to bottom right, so our lowest atomic number is hydrogen with an atomic number one and going down the row we have helium with an atomic number two lithium with an atomic number three beryllium with an atomic number four boron with an atomic number five and as we go down the list or rows from left to right, we will eventually reach our last element with the largest atomic number, 118.

Next, we have columns going down the periodic table, at Referred to as groups or families there are 18 groups in total, the elements in the same group share similar properties, so next we have the horizontal rows and they are known as periods. There are seven periods in total, so you may be looking at the bottom two rows and wondering where they are. Well, actually they are

part

of rows six and seven. Some periodic tables will put them at the bottom here just to save some space and make the periodic table look more compact, but if we look closely we see that in row 6 there is a gap. here it says atomic numbers 57 and 71.

So this space is reserved for elements that have atomic numbers 57-71 and if you look here, this atomic number of lanthanum is 57, so this row starting with lanthanum fits here too if we look in row 7 there is a space left here for atomic numbers 89 to 103 and that is exactly where this bottom row goes. We can also separate these elements by metals, non-metals and metalloids, very important if we look at the top left corner where there is a Hydrogen star is below and you will notice that this hydrogen is not a metal, however, what is it doing in the other side with metals?

Well, it's there because it shares the same properties with the one in group 1a, so all the elements here in group 1a will have similar properties, that's why hydrogen is there even though it's considered a non-metal, so Let's look at the properties of metals, nonmetals, and metalloids, starting with metals. so these metals have a brilliant shine, they are excellent conductors of heat and electricity, for example we have the metal in our cables that we use to transfer and conduct electricity, they are ductile and that means they can be compressed into a cable, they are malleable. which means they are flexible without breaking so this guy here is hammering his metal and reshaping it and it doesn't splinter and the metals that break are very dense and have a high melting and boiling point which means they require very hot. energy to bring them to a melting or boiling point, finally, they have a tendency to form cations or, in other words, positively charged atoms.

Nonmetals are more or less the opposite of metals. First, instead of being bright, they are dull, poor in terms of heat and electricity. Conductors are usually brittle and easy to break and have a low density. They also have a low melting and boiling point, so it doesn't take much energy to bring them to a boiling or melting point. Furthermore, they finally form cations and anions. Metalloids are like a fusion of metals and non-metals, so they share properties of both. Just remember that these metalloids are found on what looks like a ladder on the periodic table that divides the metals on the left side and the nonmetals on the right. side, so I made this graph here with some other important metal-related properties about metals and metalloids.

I made it in graph form so you can see the differences side by side, so you can go ahead and stop this video if you want and check it out, we can also classify our elements by transition metals and main group elements. The transition metals are known as group b, which we're not going to go over in this video because it's not relevant and then we have our main group elements. which are known as group a, so the elements in our main group, group a is everything you see highlighted in purple and outside of these groups there are four very important ones that you need to remember, group 1a is your alkali metals, the group 2a are your alkaline earth metals and then if we jump to the other side and skip 3a4a5a and 6a, we will go to group 7a, which are the halogens, and group 8a, which are the noble gases, so each of these groups, as mentioned above it has different properties from each other so if we look at our group 1a alkali metals the most notable property is that they are highly reactive and reactive just means that they interact well with other atoms.

They also form cations with a positive charge, which means that all of the elements in this group 1a in Below Alkali Metals are going to form cations with a positive charge. Alkaline earth metals are also highly reactive, but not as much as alkali metals, forming cations with two more charged halogens. The most important thing you should remember about these is that they are diatomic elements and remember diatomic means that in the natural form of the element it is made up of two atoms, halogens also form anions with a negative charge, lastly our noble gases are the most stable and least reactive as well.

They are called inert gases and what This means that less reactive and more stable is that their outer valence shell is

complete

ly filled with electrons, making them stable and

complete

. First of all, when you look at the periodic table, keep in mind that these are all elements in their neutral form, meaning they have no charge if you look closely at one of these elements, say carbon, for example, in the center is the symbol of the element, in this case it is c for carbon, at the top you will find the atomic number, this number represents the number of protons in the atom.

The atomic number is also the identification, so to speak, for an atom, each element has a different atomic number and this number does not change. Next at the bottom we have the atomic mass, this is the average number of protons and neutrons for all the isotopes formed by this atom the atomic mass is similar to the mass number the mass number is the number of protons and neutrons in the atom this number is an integer to get the mass number you just have to round the atomic mass to an integer so for carbon we have We can round it to 12 and 12 is our mass number this is how it shows the element on the periodic table, but you will most likely be asked to write or show the element's symbol on a test.

This is how we do it by using carbon again. as an example we write the elemental symbol first on the top left we write the mass number and on the bottom left we write the atomic number so you can see here things are a little bit reversed and there you have it this is the correct way to write. Discover the element carbon, so what is a neutral atom or what makes an atom neutral? Neutral atoms are those found in the periodic table, they have the same number of protons as electrons and have no charge, they are neutral, let's take this carbon for example, what makes this carbon neutral, we know that it has six protons because we can see that it has an atomic number of six and since it is neutral, it has the same number of electrons as protons, the positive and negative charges cancel each other and what is it?

On the left is a neutral atom, let's look at another example in an exam, you will most likely see something worded like this where you are asked to find the number of protons, electrons and neutrons in an atom with this information provided here, the information provided is The element calcium we know that it has 20 protons because it has an atomic number of 20. We know that it has 20 electrons because it is a neutral atom the same number as the protons and now to find the number of neutrons we take the atomic mass and subtract the atomic mass number because the atomic mass is the number of protons and neutrons and the atomic number is the number of protons, so we are left with the total number of neutrons, which also happens to be 20.

In this case, let's do another example using aluminum as given information . given the atomic number we know that aluminum has 13 protons and 13 electrons because it is neutral now round the mass to 27 and subtract 13 we have 14 neutrons left by the way can you find the atomic mass and the mass number remember the mass? The number is an integer and is the number of protons and neutrons, while the atomic mass is a little more complicated, it is a decimal number and is the average of the protons and neutrons in the isotopes, so the atomic mass is 26.9 and is given in the periodic table. table and the mass number simply rounds up to 27. so we've

review

ed neutral atoms now let's

review

ions what is an ion an ion is a charged atom an atom gets a charge when it gains or loses electrons an ion or has more protons than electrons, in which case it is called a positively charged cation, or it has more electrons than protons, in which case it is called a negatively charged anion.

The golden rule that you should never forget about ions is that ions always have the same number of protons as the atomic number, in other words, the number of protons never changes, you can only change the number of electrons because remember that in the definition that I mentioned, an atom becomes an ion, either by gaining or losing electrons, so we are only manipulating the electrons, not the protons, so let's say we have an atom here and the plus sign represents protons because they have positive charges and the negative represents electrons, so this atom here has six protons and four electrons, these pairs are crossed out and we are left with two additional protons that make this atom a cation with a charge plus two.

Then we have an atom here with four protons and seven electrons, these pairs are crossed out and we are left with three additional electrons making this atom an anion with a negative charge of three, the following example is how you will probably see it on an exam. They give you information about the number of protons, electrons and neutrons or just protons and electrons, because neutrons are not very relevant here and then you have to find the charge of the ion, given the following information write the charge of the next ion, so here we have 12 protons 90 electrons and again the number of neutrons has no relevance to this question so you could forget about it, the pairs are crossed out and we are left with three extra protons making this a cation with one charge plus three .

Next, we are given the following: Write the charge for the following ion. We already have 9 protons and 10 electrons. We can say it will be an anion because it has more electrons than protons, we are left with an anion with a negative charge or you can just put negative, the one is always implied so you don't necessarily have to have the one that is there, so lastly I just want to leave you with uh the trends of the ions on the periodic table so quickly that group 1a, where you see the one plus or the positive over all of these elements, will form a one plus charge, so it includes hydrogen, lithium, sodium , potassium and everything else in that row, group uh. 2a will form cations with a charge of two plus and that includes everything in that row and then the transition metals, it varies, this is more than likely higher division

chemistry

so don't worry about that and so on, like thiswhich is very important for you to know.

This is a general guide to which ions. Sorry, what elements make up these ions, so there are some exceptions to this rule, but this is a good start to remembering the ion numbers at the top of the periodic table because this can seriously save your life. in an exam, remember that in these numbers at the top and of course they are negative or positive charges, atoms lose gain or share electrons, this is what forms a bond between two atoms. Atoms form bonds to satisfy the octet rule. The octet rule states that elements combine in such a way that each atom has eight electrons filling its valence shell for this to happen each atom must give up, gain or share electrons.

We know that the valence shell refers to the outermost shell. of an atom and the valence shell Electrons are all the electrons in that valence shell, so 80 electrons filling the valence shell will make these atoms very, very happy. The elements highlighted here are our noble gases and all elements strive to become like the noble gases they admire. noble gases because these noble gases are the most stable elements because they naturally have a complete valence shell, they naturally have eight electrons filling their valence shell with one exception, that exception is helium, it only has two electrons in its valence shell and no Strive to be like all other elements, it is perfectly fine for only two metals to lose electrons because they have fewer electrons in their outer shell, so since they have fewer electrons in their outer shell, it is easier for them to lose a pair.

You gain a lot, you will see this clearly once you see some examples, so here we have potassium as an example and potassium has 19 electrons in total. Note that you only have one valence electron in that valence shell, so since potassium is a metal, it is going to lose this valence electron, once that electron is lost the shell is now empty, therefore , potassium doesn't really need this shell and will basically disappear once that shell is gone, the shell underneath actually has eight electrons and this will now be the new valence. Because potassium lost one electron, that means it now has not 19 but 18 electrons total, so potassium with 19 protons and 18 electrons creates a cation with a charge plus one, so the conclusion here is that Metals lose electrons because they have fewer electrons in their outer shell.

Metals also form cations which are positively charged ions. Non-metals, on the other hand, gain electrons because they have more electrons in their outer valence shell. For example, we have fluorine here. and it has nine electrons in total. it has seven valence electrons here we have this atom floating around and it has one valence electron actually it will give this valence electron to fluorine and now fluorine will have a full valence shell it has eight electrons or eight valence electrons in its outer shell and now fluorine is happy, so just like we did with metals, now we have to look at the total number of electrons and adjust for it.

Fluorine has gained one electron, so it now has a total of 10 electrons, not nine. Fluorine has nine protons and again that's it. It will never change because remember the number of protons will never change in an atom, but now it has 10 electrons, so this creates an anion with a negative charge. The conclusion here is that nonmetals gain electrons because they have more electrons on the outside. Shell nonmetals also form anions, which are negatively charged ions, so note that this is exactly the opposite of the characteristics of metals. Now that we understand how metals and non-metals work when they create a bond, let's look at exactly how they create ionic bonds.

Ionic bonds will have a metal and a non-metal bonded together, the atoms forming ionic bonds will lose or gain electrons and this is known as electron transfer. Here we have sodium and chlorine atoms. Sodium is our metal. Chlorine is our non-metal, so we automatically know that we have an ionic bond because we have a metal and a non-metal bonding. Now you know that if you ever see a metal and a non-metal together, you will automatically know that it will be an ionic bond. Our sodium has 11 protons and 11. electrons and our chlorine has 17 protons and 17 electrons sodium would look a little like this and chlorine would look like this notice sodium our metal has only one electron in its valence shell and our chlorine does not Metal has seven electrons in its valence shell so again our metal is going to lose its electron and our non-metal is going to gain electrons during this ionic bond, this little guy is going to get there and that is a one electron transfer.

Now notice that sodium has a shell that has no electrons in it so it doesn't need the shell it will lose it completely and underneath it it has eight electrons in that new valence shell so sodium is happy and so is chlorine It is happy because it also has eight electrons in its valence shell. There is one last thing we need to adjust after filling these valence shells into the metal. We have lost one electron, so now sodium does not have 11 electrons, it now has 10. This sodium becomes a cation with a charge more one than chlorine. it gained an electron, so it's no longer 17, it's 18.

Chlorine is now an anion with a negative charge, so sodium is our positively charged atom and chlorine is our negatively charged atom, since we know that opposites attract, so this is what keeps the ionic. comes together is that the attraction of opposite charges metals are generally less electronegative and non-metals are more electronegative because non-metals are more electronegative it means they are better at attracting electrons to them so non-metals will always attract electrons from metals, that's why they gain electrons and metals are the ones that lose electrons, so let's go ahead and move on to covalent bonds.

Here we are going to work with two non-metals that join together. Atoms that form covalent bonds share electrons, so there is no electron transfer. Here an atom will not lose or gain electrons, but these atoms share these electrons. One important thing to remember is that all diatomic molecules have covalent bonds between the same atoms and if you need a reference, remember that these are all of your diatomic molecules listed. here, for example, here we have nitrogen and let's say another nitrogen shows up and that nitrogen says, "Hey, I want to get together, so we both have a full valence shell.

Hell yeah, let's get together and become diatomic molecules, so by coming together They become diatomic molecules and They will both live happily ever after. All these diatomic molecules will look very similar to this nitrogen. They will form a covalent bond between them. Let's look at an example of covalent bonds that are not between diatomic molecules. , for the sake of simplicity, I'm just going to draw the valence shell with the valence electrons, so I just want to let you know that so you don't get confused, not all the electrons will be drawn in these atoms. So here we have the valence shell. of carbon and these are our two valence shells of oxygen.

Notice that oxygen has six electrons in its valence shell and carbon has four electrons in its valence shell. Remember that these atoms have one goal in mind and that is to fill your valence shell. valence shell with eight electrons so carbon will take two electrons and share them with oxygen and oxygen will also take one of its electrons and share it with carbon so now this is all rearranged and we will notice that oxygen now It has eight electrons filling its valence shell and carbon also has eight electrons filling its valence shell, so all atoms are happy with filled shells.

Now let's look at how electronegativity relates to covalent bonds. In a covalent bond, one atom will always be slightly more negative than the other and of course that means that the other atom will be a little more positive now the key word here is slightly because if they were completely negative or completely positive that would make them have charges and that would mean they were ionic the atom that is more electronegative will be the more negative atom, this atom of course attracts more electrons around it and in case you need to refresh your memory this is the electronegativity trend on the periodic table , remember that fluorine is our most electronegative atom as we go from left to right or towards fluorine the electronegativity increases and as we go up the periodic table the electronegativity also increases.

Using our example of the hydrogen and chlorine bond, if we look up both atoms on the periodic table, we'll notice that chlorine is obviously more electronegative, therefore. It attracts more electrons around it and this makes chlorine partially negative. Let's represent this partially negative with a delta sign and a negative sign after it. By the way, delta means slightly, so slightly negative and hydrogen is less electronegative, it has fewer electrons around it. this makes hydrogen partially positive and we're going to represent this with the delta sign again and a positive sign, so slightly positive, let these delta signs be a reminder that these atoms are not ionic, they are not completely positive or negative , are only slightly positive. and slightly negative remember delta means slightly when the electronegativity difference between two atoms is equal to or greater than 0.5, this is called polar covalent bond so let's use our example of hydrogen and chlorine normally the electronegativity value will be given here hydrogen has a value of 2.1 and chlorine has a value of 3.0, so this is how we calculate the difference between the two values.

Basically, we just subtract them and we'll end up with 0.9. 0.9 is the total difference in electronegativity between hydrogen and chlorine to be able to do this. To be a polar covalent bond, the difference in electronegativity between the two atoms must be equal to or greater than 0.5, just as the difference in electronegativity between hydrogen and chlorine is 0.9. The two atoms form a polar bond or a polar covalent bond if the electronegativity is less than 0.5 the covalent bond is non-polar, although there is still one atom that is a little more positive and the other is a little more negative, the difference is still not significant enough to call it polar, take for example these atoms of hydrogen, the electronegativity value is 2.1 and of course it is the same value for both atoms because they are exactly the same atoms because the electronegativity between both atoms is the same there is an equal exchange of electrons between the two this applies to any molecule diatomic like oxygen and fluorine and all the other diatomic molecules that you will use we have a non-polar covalent bond let's go ahead and finish with some practice problems here we have hydrogen bonded to another hydrogen is this an ionic bond a polar covalent bond or a covalent bond non-polar the first thing we want to see is the automatic rule let's find out if this is an ionic bond if it is an ionic bond it will be a metal and a non-metal hydrogen is a non-metal so it is actually a non-metal and a non-metal so it is not ionic it is covalent now let's determine if it is a polar or non-polar covalent bond because it is a diatomic molecule and it is exactly the same atom bonded together which means the electronegativity is exactly the same so this is a covalent bond non-polar, how about carbon and hydrogen with values ​​of 2.5? and 2.1 this is a non-polar covalent bond because if we look at the difference between the two electronegativity values ​​we get 0.4 remember that polar is any difference of 0.5 or more, because it is only 0.4 makes this bond non-polar how about calcium and sulfur?

Metal and sulfur are non-metals, therefore we automatically know that we have an ionic bond. What happens to oxygen and hydrogen with values ​​of 3.5 and 2.1? If we find the difference of the two values, we get 1.4, which will make it a polar covalent bond. What happen with the water? Now I added a few extra things here just to make it seem a little more complicated, but that's the reality. You may see something like this on your exam. Focus on the electronegativity values ​​and find the difference of the values. The electronegativity difference here. is 1.4, so that will make h2o a polar covalent bond.

By the way, we automatically rule out ionic bonding because hydrogen and oxygen are nonmetals. I also want to introduce this symbol here called the dipole moment, the arrow points in the direction of the The most electronegative atom in this case both arrows point in the direction of oxygen. Then we have nitrogen bonded to nitrogen. We know it is a diatomic molecule, therefore we automatically know it is a non-polar covalent bond. Then we have Nacl. Sodium is our metallic chlorine. It's our non-metal, so we have an ionic bond, how about magnesium oxide again? Magnesium is our metal, oxygen is our non-metal, so again we have a bondweak.

Now how do we know that sour acid is an acid? Of course, we can know that it is an acid by its name, but what if we just saw its chemical formula. What would happen if we solved this chemical equation and not a label on acetic acid? How would we know that it is actually an acid? Note that acetic acid lost a hydrogen ion in its solution and, according to Bronson Larry's theory, an acid is one. that loses a hydrogen ion, so one last thing I want to mention using this exact same example is to notice these double arrows going in opposite directions, this means that the chemical equation is reversible if a solution can be reversed, let's assume it is a weak solution. strong solutions are not reversible, so finally, what does all this have to do with the ph scale?

Well, the basics of the ph scale state that anything below 7 is an acid and anything above 7 is a base and of course 7 itself is neutral. The higher you go on the scale and the higher the number, the stronger the base will be and the further down the scale and the lower the number, the stronger the acid will be. ph means potential of hydrogen, however I like to think of it as a concentration of hydrogen because the concentration helps me better understand the definition in greater depth, it really means the concentration of hydronium ions and hydroxide ions because a solution will have more hydronium ions o will have more hydroxide ions, meaning it will be more acidic or more basic, its basic solutions will have a higher concentration of hydroxide ions, and its acidic solutions will have a higher concentration of hydronium ions.

Okay, let's look at an example using hydrochloric acid, so here we have a flask with some water molecules and let's go. to add some hydrochloric acid represented by these molecules, remember that these molecules represent our sample here because hydrochloric acid is an acid that we expect to create a high concentration of hydronium ions in the solution, so if we look closely we will notice that h2o is actually attracting that hydrogen atom away from the hcl, so the hydrogen will actually separate from the chlorine and make its way and attach itself to the h2o and obviously this will create h3o plus or hydronium ions, so h3o Plus or hydronium is formed and now we are going to have a high concentration of h3o plus ions in this solution because hydrochloric acid is such a strong acid that we know it will dissociate completely, so it will look a lot like this in the solution, so that was an example of an acid, let's look at an example of a base using sodium hydroxide.

Here again we have a flask and again we have some water molecules inside and we are going to introduce some sodium hydroxide because sodium hydroxide is a base. we expected to create a high concentration of hydroxide ions in the solution. If we look closely at the sodium hydroxide, we will notice that oh it is actually going to dissociate or separate from the sodium and basically the sodium and oh are going to separate and we are going to form free ions, the result is a high concentration of hydroxide ions because sodium hydroxide is such a strong base that it will actually dissociate completely within the solution, so it will look a lot like this, so there is one last thing I want to mention here that is very important, I wrote here that acids have a higher concentration of hydronium ions, however, if you remember, our cat mentioned that hydrogen ions are practically the same as hydronium ions because hydrogen ions when in a solution become hydronium ions.

Again, although technically it's not the same, it's pretty much the same and I just wanted to mention it because if you look at another resource and they tell you the definition of ph, they might say that acids have a higher concentration of hydrogen ions, but you know that everything will be fine because you know that hydrogen ions and hydronium ions are pretty much the same thing, so we've seen an example of an acid using hydrochloric acid and we've seen an example of a base using sodium hydroxide. and we know that ph means hydrogen potential in other words we can also say that it is the concentration of hydrogen ions or hydronium ions, the same and the concentration of hydroxide ions.

This sums up this video. I hope you learned something new and thank you very much. for staying guys until next time