Atomic Structure – Chemistry

00:00 So first, let's take a look at general atomic structure. We have protons, neutrons, electrons.

00:08 You've probably all heard of those.

00:10 To review protons and neutrons, they're found in the nucleus of an atom.

00:14 And electrons are found in the periphery. Protons and neutrons have some mass.

00:21 And electrons have barely any mass at all, which is why they float around essentially in electron cloud around the central nucleus of protons and neutrons.

00:34 Protons are found in the nucleus. They're positively charged and they weigh one atomic mass unit.

00:44 Neutrons are also found in the nucleus and weigh one atomic mass unit whereas electrons weigh barely anything. Their weight is essentially negligible.

00:57 And they're found in a cloud surrounding the protons and neutrons in the nucleus and have a negative charge.

01:04 So proton's positive, electron's negative, neutrons neutral.

01:10 Atomic number is what defines an element. So let's say we're looking at carbon, it has atomic number 6.

01:18 It means it has 6 protons. And any atom with 6 protons is called carbon.

01:25 We may see some variants in the number of neutrons and electrons, we'll take a look at some example shortly.

01:31 But atomic number definitely defined by the number of protons and that defines what the element is called.

01:39 We have also atomic mass. When we add the protons and the neutrons in the nucleus together, that gives us the atomic mass.

01:47 Again, each of them is one atomic mass unit, and thus our atomic mass for standard carbon, the most prevelant form of carbon is 12 atomic mass units.

01:58 As I mentioned, we could have a varying number of neutrons. They are less common forms.

02:04 But isotopes are the name we gave for a varying numbers of neutrons.

02:09 Again, here we have carbon. It has 6 protons. It will always have 6 protons.

02:14 But we could have carbon-13, which you've probably heard of in carbon dating. Carbon-14.

02:21 We have 6 protons. We subtract that from 13 means we have 7 neutrons.

02:27 We might even see in variant instances, carbon-14, in which case we actually have 8 neutrons and the atomic mass of 14.

02:39 We can also see variation in electrons. When we have either more or less electrons, we have ions.

02:47 For example, if we look at sodium, in its natural state, we have a balanced number of electrons and protons.

02:55 However, we'll often see sodium as a postive ion, so Na+, in which case we have one less electron We take away a negative charge, but we still have the same number of positive charges, so we end up with a positive ion.

03:13 In the example below we see, we have chlorine. Chlorine is in its balanced state where we have equal number of electrons and protons.

03:22 However chlorine sometimes likes to gain an electon, in which case we have an additional negative charge and so there's not balance, we'll see Cl-.

03:33 And we'll see later in the next lecture, how sodium and chloride might interact with each other because of these positive and negative charges.

03:43 So once again, to emphasize, proton number is not going to change, at least in biology.

03:50 And proton number is going to define what element we're looking at.