so this video is a quiz for those of you who need to review basic atomic structure the structure within an atom so let's start with this question which of the following particles is found outside of the nucleus is it the electrons the neutrons the protons or is it a combination of two of the three answer choices listed here well let's talk about the structure of the atom in the center of the atom which is known as the nucleus you have the protons which i'm going to write in red and the neutrons which i'm going to put in brown outside of the nucleus are the electrons the electrons are orbiting the nucleus and so the electrons form the electron cloud but the nucleus consists of the protons and the neutrons now the atom is mostly empty space even though this picture doesn't show it to scale this nucleus is relatively small to the electron cloud and so a lot of matter like high energy particles can go straight through an atom because an atom is mostly empty space 99 of the mass is concentrated in the nucleus of the atom protons and neutrons are almost more than 1800 times more massive than an electron so going back to this question the particles that are found outside of the nucleus are the electrons a is the right answer to this problem now let's move on to this problem number two which of the following subatomic particles carries a positive charge is it the electrons the neutrons or the protons neutrons are electrically neutral they don't have a charge think of n for neutral protons carry a positive charge think of p for positive and electrons carry a negative charge but you have to just know that by elimination so the answer for this one are the protons they carry the positive charge so c is the right answer now going back to the structure of the atom i have some questions for you so we said that at the center we have the protons which carry a positive charge and the neutrons which carry a neutral charge or no charge at all and the electrons which orbit it and they carry a negative charge now perhaps you've taken physics and you know that opposite charges attract so if you have a positive charge and a negative charge there is an electrostatic force of attraction that accelerates them toward each other so therefore the electrons are attracted to the nucleus so why don't the electrons just fall into the nucleus what keeps them in orbit around the nucleus it turns out that their speed keeps them in orbit they're moving pretty fast whenever you have an object that's moving in one direction and if there's a force that's perpendicular to the motion of the object the force doesn't change the speed of the object rather it changes the direction of the object so the electron at this point wants to fly outside of the atom but the electrostatic force between the electrons and protons help keep it in orbit so the electron doesn't fly out of the atom or doesn't really fall into nucleus as long as it maintains the right energy now if an electron absorbs a photon and gets a lot of energy sometimes its kinetic energy might be high enough where it can fly off and leave an atom if it has the right energy and there are times where an electron actually can fall in the nucleus and a nuclear reaction can occur but that's a whole another topic but for the most part electrons tend to stay in their orbit the combination of the electrostatic force and their tangential velocity keeps them in orbit now when the electron does fall into the nucleus that process is known as electron capture you can actually look it up and when that happens the chemical identity of the substance actually changes the element changes from one element to another and so the electron sometimes can fall into nucleus and other times if it gains a lot of energy it could fly away from the atom turning into an ion and an ion is basically a particle with unequal numbers of electrons and protons but these things are not the norm for the most part an atom is electrically neutral under standard conditions and electrons tend to maintain in their orbits so they don't always just leave just like that now here's another question for you if like charges i mean if opposite charges attract then that means that like charges must repel each other so if we put two protons next to each other they should feel a force that will accelerate them away from each other inside a nucleus you have two protons that are very very close to each other so therefore the electrostatic force has a tendency to pull them apart so what keeps the nucleus together what what keeps the protons so close to each other when we know that like charges they repel and it turns out there's another type of force within the nucleus of an atom it's known as the strong nuclear force it's very powerful much stronger than electrostatic force and it keeps the nucleus together it prevents the protons from flying apart and as you've seen nuclear reactions are far more powerful than chemical reactions the straw nuclear force it's a lot stronger than electrostatic force number three which particle has the greatest amount of mass the mass of a proton is 1.672 times 10 to the negative 27 kilograms is very very small and the mass of a neutron is 1.6749 times 10 to the minus 27. so a neutron is slightly heavier than a proton now the mass of an electron is a lot smaller it's 9.11 times 10 to the minus 31. now you might be wondering what do these numbers mean in terms of atomic mass units a proton is approximately one atomic mass unit the same is true for a neutron now neutron is slightly more heavier than a proton but in terms of atomic mass units these two are very close to each other and they're approximately one the electron is a lot lighter than the proton or the neutron and it's about point zero zero zero five four nine atomic mass units so the atomic mass of an element is based on the number of protons and neutrons because the electron is so light relative to a neutron and a proton the mass of the electrons within an atom is considered to be negligible so the particle with the greatest amount of mass in this problem is the neutron it's slightly more heavier than a proton number 4 what is the net charge of an ion with 12 protons and 9 electrons to calculate the net charge it's simply equal to the sum of the charges of the protons and the electrons just keep in mind a proton bears a positive charge and an electron bear is a negative charge so we have 12 protons each with a charge of plus one so it's going to be plus 12 since there are 12 protons and we have 9 electrons so it's going to be plus negative 9. therefore the net charge of this ion is going to be positive 3. it has a positive charge because there's more protons than electrons if it has more electrons it would have a negative charge and so the answer for this one is e number five which of the following is not true regarding atoms and ions so let's look at a atoms are electrically neutral is that true it turns out it is this is an example aluminum 27. aluminum has an atomic number of 13 and a mass number of 27. and in periodic table you might see it like this it might have a 13 on top and a 26.98 on the bottom which i'm going to round to 27. the larger of the two numbers is always the mass number the smaller one is the atomic number now the number of protons is always equal to the atomic number which is 13. the number of neutrons is the difference between a mass number and the atomic number so 27 minus 13 is 14. the number of electrons is equal to the atomic number which is 13 minus the charge so there's no charge in this case so it's 13 minus zero so there are 13 electrons now an atom is electrically neutral because it has an equal number of protons and electrons so a is a true statement which means c is also true now an ion would look something like this you would literally see a net charge aluminum has a positive 3 charge so the number of protons is still 13 the neutrons is the same but the electrons is going to be the atomic number minus the charge so 13 minus 3 is 10. so electrons i mean ions rather have unequal number of protons and electrons so d is a true statement and ions do carry a positive or negative charge as we see here atoms don't carry a charge they're neutral a positively charged ion is known as a cation so this is a cation a negatively charged ion like the fluoride ion is an anion now the last statement has to be false by default ions have equal numbers of protons and neutrons that's not always true some ions may have that but the majority of ions have different numbers of protons and neutrons so e is the answer it's the false statement that we're looking for you