Saltar navegación

Activa JavaScript para disfrutar de los vídeos de la Mediateca.

Binary Compounds

Ajuste de pantalla

El ajuste de pantalla se aprecia al ver el vídeo en pantalla completa. Elige la presentación que más te guste:

Subido el 13 de febrero de 2016 por Enrique G.

12 visualizaciones

Más información Transcripción

Descargar la transcripción

Hello tiny scientists! In this video you're going to learn how to make binary compounds which are 00:00:01
compounds of two elements from the periodic table. I need you to remember the octet rule 00:00:07
because we're going to use it to explain how atoms combine with others making compounds. 00:00:12
Finally you will learn how to write the formula of a compound in the right order. The octet rule 00:00:18
is a very simple way to explain how atoms combine. Basically it says that every atom from the predict 00:00:27
table wants to have eight electrons in the last shell becoming like the closest noble gas. 00:00:33
Notice that all noble gases except helium which is too small all noble gases have eight electrons 00:00:40
in their last shell. There are some exceptions. Let's apply the octet rule to some elements to 00:00:47
see if we can predict the behavior of atoms when they combine for example chlorine which is the 00:00:55
closest let's apply the octet rule to some elements to see if we can predict the behavior 00:01:02
of atoms when they combine for example chlorine which is the previous element to argon has 00:01:12
seven electrons in the last shell and eight electrons in the previous one so if chlorine 00:01:20
wants to become a noble gas if he wants to have eight electrons in the last shell 00:01:26
he can do two things he can lose these seven electrons to become neon if you take 00:01:34
these electrons from chlorine then it would be exactly like neon or he can obtain 00:01:42
one extra electron from another atom and then become argon as you can imagine 00:01:49
it's much easier for chlorine to accept to gain one extra electron than to lose seven of them 00:01:57
so the general tendency of chlorine is to obtain one extra electron which is represented by its 00:02:07
oxidation number negative one means that he wants to accept one electron and this tendency 00:02:16
is the same for all halogens in the same group that than chlorine now let's see what happens to 00:02:24
sodium for example sodium has one electron in the last shell and eight electrons in the previous one 00:02:33
so if he wants to become a noble gas he can do again two things he can lose this electron and 00:02:41
remain with the eight in the previous cell or he can accept seven electrons to complete the last 00:02:49
cell as you can imagine again it's much easier to lose one electron than to obtain seven so the 00:02:57
tendency of sodium is always to give this last electron and that's why he has 00:03:04
positive one as an oxidation number and this is the tendency of all the first 00:03:12
group in the predictable all of them wants to give this last electron that 00:03:18
they have except for the hydrogen which is a exception that has oxidation 00:03:23
numbers of positive one and negative one which we're going to explain now one 00:03:28
last example. Let's see what happens to magnesium. Magnesium has two electrons in 00:03:35
the last cell and eight electrons in the previous one. Again to become a noble 00:03:41
gas he can lose these two electrons and remain with these eight in the last cell 00:03:47
or he can obtain or accept six electrons from other atoms. It's again much easier 00:03:52
to lose two electrons than to accept six so the tendency of magnesium always is to lose these two 00:04:01
electrons in the last shell to become a noble gas and this is the same tendency as the as for all 00:04:09
the elements in the second group they all want to lose these two electrons that have in the last 00:04:16
shell. That's why they have all oxidation number of positive 2. Notice that there 00:04:23
are some elements that don't have a clear tendency. For example we have 00:04:33
spoken about hydrogen which has positive 1 and negative 1 as oxidation number. 00:04:37
This means that hydrogen can lose the only electron that it has 00:04:46
or he can accept one electron to have two electrons in the last shell because 00:04:53
the closest noble gas to hydrogen is helium which has two electrons in the 00:05:00
last shell so hydrogen depending on which it combines two it can lose the 00:05:05
electron or accept one electron now let's try to understand what happens 00:05:15
when two atoms of different elements combine. In this first video we're going to study elements 00:05:22
with hydrogen called metallic hydrates or hidruro-metallicos in Spanish. They are the 00:05:27
combination of hydrogen with a metal from the periodic table. Remember the metals in the 00:05:33
periodic table are the ones to the left of this line. All metals in the periodic table have 00:05:39
something in common they have positive oxidation numbers which means that they prefer to give 00:05:48
electrons than to accept them okay so all of the metals of the project table wants to give 00:05:57
electrons because of their positive oxidation numbers in metallic hydrates hydrogen uses the 00:06:03
oxidation number of negative one always because he's combining with metals that always have 00:06:12
positive oxidation numbers so if metals want to give electrons then hydrogen chooses to accept 00:06:20
them the general rule to combine atoms is that electrons must not be free this is if an element 00:06:29
wants to give one electron there must be another element to accept it. The sum of 00:06:37
given and accepted electrons must be zero. Let's see an example. Imagine we 00:06:42
want to combine hydrogen with lithium. We have learned that lithium wants to give 00:06:50
one electron and that's why he has positive one as oxidation number. 00:07:01
remember that hydrogen uses its negative oxidation number which means that 00:07:08
hydrogen wants to accept one electron so if lithium wants to give one electron 00:07:18
and hydrogen wants to accept it then that's it we have one 00:07:24
electron one given electron and one accepted electron and we sum up these 00:07:33
two electrons then it's equal zero and then we can write the formula for the 00:07:41
combination of hydrogen lithium which is lithium hydride or either the lithium 00:07:54
let's see another example now we want to combine hydrogen with beryllium for 00:07:59
example from the oxidation numbers we know that beryllium wants to give to 00:08:12
electrons is that what what the oxidation number of plus 2 means and we 00:08:22
said that hydrogen we in metallic hydrates in idrurus metallicus always 00:08:29
acts with negative 1 that's it that's it hydrogen always want to obtain or to 00:08:37
accept one electron now we have a problem because we told that no electrons can be 00:08:45
free so if a beryllium wants to give two electrons we cannot write beryllium and 00:08:52
hydrogen like this because one accepted electron and two given electrons have 00:09:02
assumed are assumed like a not equal to zero so this cannot be like this instead 00:09:12
if beryllium needs to give two electrons but hydrogen only can accept one then we 00:09:21
need two hydrogens and then one of the hydrogen accept one of the electron and 00:09:33
the other hydrogen accept another electron so this hydrogen accept one the 00:09:43
beryllium gives two and this hydrogen except one and they sum all zero so the formula for the 00:09:54
compound with hydrogen beryllium must be beryllium hydrogen two because we need two hydrogens two 00:10:04
atoms of hydrogen for each one of the atoms of beryllium because of beryllium wants to give 00:10:12
two electrons and hydrogen can only accept one. So this is the formula for 00:10:18
beryllium hydride or hydrurode beryllium. In our last example we're going to learn 00:10:24
what happens when an element has more than one oxidation number. Let's try for 00:10:33
example to combine hydrogen with iron. As you already know iron has two possible 00:10:38
oxidation numbers plus two or plus three this means that iron wants to give 00:10:47
electrons but he can give two electrons or it can give three electrons depending 00:10:54
on the conditions so if iron wants to give two electrons then we need two 00:11:05
hydrogens to accept these two electrons of course so one is for this 00:11:17
hydrogen and this goes to this hydrogen and this way we have accepted 00:11:24
an electron, two given electrons and one accepted which is a sum of zero and so 00:11:32
we have a compound with two atoms of hydrogen for each atom of iron but we 00:11:41
can have another possibility which is that iron gives three electrons so in 00:11:50
this case we need three hydrogens three atoms of hydrogen to accept these three 00:11:57
electrons and then three electrons plus one plus minus one and plus negative one 00:12:09
then it's equal to zero so this compound is iron hydride three which is 00:12:20
hydrido de hierro as well as this one but they are different compounds with 00:12:30
different properties in nature we can found these two compounds of course they 00:12:37
have different formula because they have different proportions of hydrogen and 00:12:43
iron and this is all caused by the two possibilities of the oxidation numbers 00:12:48
of iron which are plus two and plus three the last thing we're going to 00:12:56
learn in this video is to write the symbols in a formula in the correct 00:13:04
order. To write the formula for binary compound we compare the positions of 00:13:08
both elements in this diagram. The leftmost element is written first and 00:13:13
then the rightmost. For example, in the previous examples we wrote the 00:13:17
combination of iron and hydrogen. We had two possibilities due to the two 00:13:27
oxidation numbers of iron but in both of the cases in both the compounds that we 00:13:37
got we wrote first the iron and then the hydrogen and not first the hydrogen and 00:13:43
then the iron this is incorrect and this is incorrect why do we do this because 00:13:53
when we combine iron with hydrogen in this table in this diagram we find iron 00:14:03
to the left of hydrogen then we write first high iron and then hydrogen 00:14:10
another example if we want to for example write the formula for water 00:14:17
which is a combination of hydrogen and oxygen as we find hydrogen to the left 00:14:23
of oxygen then we have to write first hydrogen and then oxygen and not oxygen 00:14:32
and then hydrogen this is incorrect okay another example for example if we want 00:14:40
to write the formula of ammonia ammonia co in Spanish which is a combination of 00:14:47
nitrogen and hydrogen again we write first nitrogen which is at the left and 00:14:52
then hydrogen with the corresponding number according to the proportions in 00:15:00
which nitrogen and hydrogen combines this is correct and the other possibility to 00:15:07
write first the nitrogen and then the nitrogen is incorrect okay this is the 00:15:13
correct order in which we write symbols and we can apply this general rule to 00:15:18
any combination of two elements in this diagram for example let's say we want to 00:15:25
combine potassium with sulfur then if potassium is on the left we have to 00:15:30
write first potassium and then sulfur and then the number corresponding to the 00:15:37
proportions in this case to number two in potassium okay this is correct and 00:15:43
the other possibility to write first sulfur and then potassium is incorrect 00:15:50
Subido por:
Enrique G.
Licencia:
Reconocimiento - No comercial - Compartir igual
Visualizaciones:
12
Fecha:
13 de febrero de 2016 - 13:31
Visibilidad:
Público
Duración:
15′ 58″
Relación de aspecto:
1.78:1
Resolución:
1280x720 píxeles
Tamaño:
55.56 MBytes

Del mismo autor…

Ver más del mismo autor

EducaMadrid, Plataforma Educativa de la Comunidad de Madrid

Plataforma Educativa EducaMadrid