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AP®︎/College Biology
Course: AP®︎/College Biology > Unit 1
Lesson 2: Elements of lifeElements and atoms
Elements are pure substances with specific properties. Atoms are the smallest units of elements that still retain the element's properties. Atoms contain electrons, neutrons, and protons. Each element is defined by the number of protons in its nucleus. Created by Sal Khan.
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- What are the 4 fundamental blocks of the life? Is Carbon one of them?(607 votes)
- The human body contains 65% oxygen, 18% carbon, 10% hydrogen, 3% nitrogen, 1.5% calcium, 1% phosphorus, 0.35% potassium, 0.25% sulfur, 0.15% sodium, 0.05% magnesium, and copper, zinc, selenium, molybdenum, fluorine, chlorine, iodine, manganese, cobalt, iron have a percentage of about 0.7%, and there are trace amounts of lithium, Strontium, aluminum, silicon, lead, vanadium, arsenic, bromine are in trace amounts.(1221 votes)
- Why is the protons so close together? Doesn't positive and positive repel.(384 votes)
- There is one fundamental force called the Strong Nuclear Force. This force holds protons together, otherwise the electric force would repel the protons away from each other.(433 votes)
- is there something smaller than a atom?(161 votes)
- Yes, there are indeed. An atom itself is consisted of a nucleus that is 'orbited' by electrons. Inside the nucleus are the protons and the neutrons. These subatomic particles must be 'smaller,' for they are the building blocks of an atom.
We can even have smaller. Quarks make up protons and neutrons. Gluons are the subatomic particles that 'bind' quarks and hold them together.
Here are some other particles that are also 'smaller' than an atom:
1) Photons (tiny particles of light. Though they are powerful packets of energy, they have no mass).
2) Neutrinos (another tiny particle. They are similar to electrons, though they do not have an electrical charge. Neutrinos are born from violent explosions, such as exploding stars and gamma ray bursts. They are nearly massless and are capable of traveling at almost the speed of light. However, they interact quite weakly with other particles).
Hope that helped! :o)(509 votes)
- What is an atom?(43 votes)
- An atom is a conglomeration of subatomic particles that were fused together under extreme heats and pressures many millions/ billions of years ago. Indeed the heavier elements were created in the supernovas of dying stars (we're all made of star dust! how special!) Anyways what conceptually separates an atom from the subatomic particles which comprise it is the fact that when these individual particle come together they assume properties that the particles would lack alone. And again, if you were to break an atom apart into its electrons, protons and neutrons, those building blocks would no-longer exhibit the behavior and properties that they exhibited as a combined mass. Much of these behaviors are due to the number of electrons (negatively charged particles). And the number of electrons is typically dictated by the number of protons, because protons have a nearly equal positive charge, in comparison to the aforementioned electrons. They attract because opposite charges of similar magnitude attract one another.(82 votes)
- Why does "lead" abbreviate to "Pb" ?(29 votes)
- The chemical symbol for lead is Pb, which comes from the Latin word plumbum, meaning "waterworks," referring back to ancient times when the metal was widely used in the construction of water pipes.(31 votes)
- What is the actual process used to determine the number of protons in an element?(34 votes)
- The numbers of a proton determines the atomic number and what exactly is this element. So, more or less, the different numbers protons are always there, and we are the ones who gives names to them. In a way, for example, we are the ones who named the atom with 8 protons "oxygen".(6 votes)
- so, if you can change one atom into another, could you get rich changing a lead atom into a gold or silver atom and then selling it for money?(17 votes)
- This indeed is a very good question, that is thousands of years old. The ability to transform base metals into Gold was one of the main goals of Alchemists in in Middle Ages and Renaissance Europe, and it was called Chrysopoeia. However, the final goal of the Alchemist was not the making of money... http://en.wikipedia.org/wiki/Alchemy#Overview(37 votes)
- dear sal sir
would the nucleus be a cluster or not a cluster(20 votes)- The Nucleus of an Atom is a grouping of Neutrons and Protons held tightly together by the Strong Nuclear Force(33 votes)
- Do you think that the element with an atomic number of 43 will turn up in nature? I know scientists have created Technetium, a man-made element with an atomic number of 43, but do you think a natural element with 43 protons will turn up?(10 votes)
- Technetium has already been found to occur in the Sun as well as trace amounts in the Earth's crust.(30 votes)
- this might be a dumb question but why is the periodic table shaped the way it is , is it in a specific order(10 votes)
- Not a stupid question at all, a very good one because some people might think the periodic table is arbitrarily shaped the way it is. There are specific reasons why it's shaped the way it is.
Elements which occupy the same column (or group) have the similar reactivities based on how many valance electrons they have. So for example on the far right in group 18 are the noble gases which, while greatly different in size, all are common in that they are very unreactive. To the left of them in group 17 are the halogens which are still greatly different in size but are very reactive now still thanks to their valance electrons.
The rows (or periods) tell you broadly how many electrons are in the energy levels (or shells) of elements. So elements in the first row (hydrogen and helium) can have 2 valence electrons because they only have access to the first energy level which only holds 2 electrons. Elements in the second row can have 8 valence electrons now since the second energy level can hold up to 8 electrons. And so on.
Side note The two rows at the bottom are sometimes confused as separate rows from the rest of the periodic table, but are actually part of the 6th and 7th rows which fit in-between groups 3 and 4 (or groups 2 and 3, there is some disagreement exactly where the break is). They're often shown separate because to include them would make the periodic table rather long and difficult to print onto papers and textbooks so they condense it as such.
Hope that helps.(28 votes)
Video transcript
We humans have known,
for thousands of years, just looking at our
environment around us, that there are
different substances. And these different
substances tend to have different properties. And not only do they have
different properties, one might reflect
light in a certain way, or not reflect light, or
be a certain color, or at a certain temperature, be
liquid or gas, or be a solid. But we also start
to observe how they react with each other in
certain circumstances. And here's pictures of
some of these substances. This right here is carbon. And this is in
its graphite form. This right here is lead. This right here is gold. And all of the ones that I've
shown pictures of, here-- and I got them all from this
website, right over there-- all of these are in
their solid form. But we also know that
it looks like there's certain types of air, and
certain types of air particles. And depending on what
type of air particles you're looking at, whether it
is carbon or oxygen or nitrogen, that seems to have different
types of properties. Or there are other things
that can be liquid. Or even if you raise the
temperature high enough on these things. You could, if you raise
the temperature high enough on gold or lead, you
could get a liquid. Or if you, kind of, if
you burn this carbon, you can get it to
a gaseous state. You can release it
into the atmosphere. You can break its structure. So these are things that we've
all, kind of, that humanity has observed for
thousands of years. But it leads to a
natural question that used to be a
philosophical question. But now we can answer
it a little bit better. And that question is, if you
keep breaking down this carbon, into smaller and
smaller chunks, is there some smallest chunk, some
smallest unit, of this stuff, of this substance, that still
has the properties of carbon? And if you were
to, somehow, break that even further,
somehow, you would lose the properties
of the carbon. And the answer is, there is. And so just to get
our terminology, we call these
different substances-- these pure substances that
have these specific properties at certain
temperatures and react in certain ways-- we
call them elements. Carbon is an element. Lead is an element. Gold is an element. You might say that
water is an element. And in history, people
have referred to water as an element. But now we know that water is
made up of more basic elements. It's made of oxygen
and of hydrogen. And all of our elements
are listed here in the Periodic
Table of Elements. C stands for carbon-- I'm just
going through the ones that are very relevant to humanity,
but over time, you'll probably familiarize
yourself with all of these. This is oxygen. This is nitrogen. This is silicon. Au is gold. This is lead. And that most basic unit, of any
of these elements, is the atom. So if you were to keep
digging in, and keep taking smaller and
smaller chunks of this, eventually, you would
get to a carbon atom. Do the same thing over
here, eventually you would get to a gold atom. You did the same thing
over here, eventually, you would get
some-- this little, small, for lack of a
better word, particle, that you would call a lead atom. And you wouldn't be
able to break that down anymore and still
call that lead, for it to still have
the properties of lead. And just to give you an idea--
this is really something that I have trouble
imagining-- is that atoms are
unbelievably small, really unimaginably small. So for example, carbon. My hair is also
made out of carbon. In fact, most of me
is made out of carbon. In fact, most of all living
things are made out of carbon. And so if you took my hair--
and so my hair is carbon, my hair is mostly carbon. So if you took my
hair-- right over here, my hair isn't yellow,
but it contrasts nicely with the black. My hair is black,
but if I did that, you wouldn't be able to
see it on the screen. But if you took my
hair, here, and I were to ask you, how many
carbon atoms wide is my hair? So, if you took a cross
section of my hair, not the length, the
width of my hair, and said, how many carbon
atoms wide is that? And you might
guess, oh, you know, Sal already told me
they're very small. So maybe there's 1,000 carbon
atoms there, or 10,000, or 100,000. I would say, no. There are 1 million
carbon atoms, or you could string 1
million carbon atoms across the width of
the average human hair. That's obviously
an approximation. It's not exactly 1 million. But that gives you a sense
of how small an atom is. You know, pluck a
hair out of your head, and just imagine
putting a million things next to each other,
across the hair. Not the length of the hair,
the width of the hair. It's even hard to see
the width of a hair, and there would be a
million carbon atoms, just going along it. Now it would be pretty
cool, in and of itself, that we do know that there
is this most basic building block of carbon, this most basic
building block of any element. But what's even neater is
that, those basic building blocks are related
to each other. That a carbon atom is made
up of even more fundamental particles. A gold atom is made up even
more fundamental particles. And depending-- and
they're actually defined by the arrangement of
those fundamental particles. And if you were to change the
number of fundamental particles you have, you could change the
properties of the element, how it would react, or you could
even change the element itself. And just to understand
it a little bit better, let's talk about those
fundamental elements. So you have the proton. And the proton is actually
the defining-- the number of protons in the
nucleus of an atom, and I'll talk about the
nucleus in a second-- that is what defines the element. So this is what
defines an element. When you look at the
periodic table right here, they're actually written
in order of atomic number. And the atomic
number is, literally, just the number of
protons in the element. So by definition,
hydrogen has one proton, helium has two protons,
carbon has six protons. You cannot have carbon
with seven protons. If you did, it
would be nitrogen. It would not be carbon anymore. Oxygen has eight protons. If, somehow, you were to
add another proton to there, it wouldn't be oxygen anymore. It would be fluorine. So it defines the element. And the atomic
number, the number of protons-- and
remember, that's the number that's
written right at the top, here, for each of these
elements in the periodic table-- the number of protons is
equal to the atomic number. And they put that
number up here, because that is the defining
characteristic of an element. The other two constituents
of an atom-- I guess we could
call it that way-- are the electron
and the neutron. And the model you
can start to build in your head-- and this model,
as we go through chemistry, it'll get a little bit more
abstract and really hard to conceptualize. But one way to
think about it is, you have the protons
and the neutrons that are at the center of the atom. They're the nucleus of the atom. So for example, carbon,
we know, has six protons. So one, two, three,
four, five, six. Carbon-12, which is
a version of carbon, will also have six neutrons. You can have versions
of carbon that have a different
number of neutrons. So the neutrons can change,
the electrons can change, you can still have
the same element. The protons can't change. You change the protons, you've
got a different element. So let me draw a carbon-12
nucleus, one, two, three, four, five, six. So this right here is
the nucleus of carbon-12. And sometimes, it'll
be written like this. And sometimes, they'll actually
write the number of protons, as well. And the reason why we
write it carbon-12-- you know, I counted
out six neutrons-- is that, this is
the total, you could view this as the total number
of-- one way to view it. And we'll get a
little bit nuance in the future-- is that this
is the total number of protons and neutrons inside
of its nucleus. And this carbon, by definition,
has an atomic number of six, but we can rewrite
it here, just so that we can remind ourselves. So at the center of a carbon
atom, we have this nucleus. And carbon-12 will have six
protons and six neutrons. Another version of
carbon, carbon-14, will still have six
protons, but then it would have eight neutrons. So the number of
neutrons can change. But this is carbon-12,
right over here. And if carbon-12 is neutral--
and I'll give a little nuance on this word in a second
as well-- if it is neutral, it'll also have six electrons. So let me draw those six
electrons, one, two, three, four, five, six. And one way-- and this is
maybe the first-order way of thinking about
the relationship between the electrons
and the nucleus-- is that you can imagine the
electrons are, kind of, moving around, buzzing
around this nucleus. One model is, you
could, kind of, thinking of them as
orbiting around the nucleus. But that's not quite right. They don't orbit the
way that a planet, say, orbits around the sun. But that's a good
starting point. Another way is, they're kind
of jumping around the nucleus, or they're buzzing
around the nucleus. And that's just
because reality just gets very strange at this level. And we'll actually have
to go into quantum physics to really understand what
the electron is doing. But a first mental
model in your head is at the center of this
atom, this carbon-12 atom, you have this nucleus,
right over there. And these electrons are
jumping around this nucleus. And the reason why these
electrons don't just go off, away from this nucleus. Why they're kind of
bound to this nucleus, and they form part
of this atom, is that protons have
a positive charge and electrons have
a negative charge. And it's one of these properties
of these fundamental particles. And when you start
thinking about, well, what is a
charge, fundamentally, other than a label? And it starts to
get kind of deep. But the one thing
that we know, when we talk about
electromagnetic force, is that unlike charges
attract each other. So the best way
to think about it is, protons and
electrons, because they have different charges,
they attract each other. Neutrons are neutral. So they're really just sitting
here inside of the nucleus. And they do affect the
properties, on some level, for some atoms of
certain elements. But the reason why we have the
electrons not just flying off on their own is
because, they are attracted towards the nucleus. And they also have an
unbelievably high velocity. It's actually hard for-- and
we start touching, once again, on a very strange
part of physics once we start talking about what
an electron actually is doing. But it has enough, I
guess you could say, it's jumping around enough that
it doesn't want to just fall into the nucleus, I guess is
one way of thinking about it. And so I mentioned,
carbon-12 right over here, defined by the
number of protons. Oxygen would be defined
by having eight protons. But once again, electrons can
interact with other electrons. Or they can be taken
away by other atoms. And that actually forms a lot of
our understanding of chemistry. It's based on how many
electrons an atom has, or a certain element has. And how those electrons
are configured. And how the electrons of
other elements are configured. Or maybe, other atoms
of that same element. We can start to predict
how an atom of one element could react with another
atom of that same element. Or an atom of one element,
how it could react, or how it could
bond, or not bond, or be attracted, or
repel, another atom of another element. So for example-- and we'll
learn a lot more about this in the future-- it is possible
for another atom, someplace, to swipe away an
electron from a carbon, just because, for
whatever reason. And we'll talk about certain
elements, certain neutral atoms of certain elements,
have a larger affinity for
electrons than others. So maybe one of those swipes
an electron away from a carbon, and then this carbon
will be having less electrons than protons. So then it would have five
electrons and six protons. And then it would have
a net positive charge. So, in this carbon-12,
the first version I did, I had six protons,
six electrons. The charges canceled out. If I lose an electron, then
I only have five of these. And then I would have
a net positive charge. And we're going to talk
a lot more about all of this throughout the
chemistry playlist. But hopefully, you
have an appreciation that this is already
starting to get really cool. Once we can already
get to this really, fundamental building
block, called the atom. And what's even neater is that
this fundamental building block is built of even more
fundamental building blocks. And these things
can all be swapped around, to change the
properties of an atom, or to even go from an
atom of one element to an atom of another element.