Atom - MedFriendly.com

WHAT IS THE NUCLEUS MADE OF?

The nucleus is made up of particles known as protons and neutrons. Together, protons and neutrons are

known as nucleons. Protons are positively charged particles, whereas neutrons have no electric charge.

To the right is a drawing of a nucleus, with the protons and neutrons shown.

WHAT IS GOING ON IN THE SPACE OUTSIDE OF THE NUCLEUS?

Outside of the nucleus, there are areas of space that contain moving electrons (negatively charged

particles). These areas of space are called electron shells. Atoms can have up to seven electron shells.

The electron shell closest to the nucleus is known as the K shell. As the shells move out from the center,

they are known as the L shell, the M shell, the N shell, the O shell, the P shell, and the Q shell, in that

order.

Each electron shell can hold a certain number of electrons. For example, the K shell can hold 2 electrons,

the L shell can hold 4 electrons, the M shell can hold 8 electrons, the N shell can hold 18 electrons, and

the O shell can hold 32 electrons. The farther away an electron shell is from the nucleus, the more energy

its electrons have. The outer shell is the last shell with electrons in it. This can be any of the shells (K

through Q), it just depends on how many shells are in the atom. If the outer shell has 8 electrons or is full

of electrons, the atom is considered very stable (not changing).

CAN THE POSITIONS OF THE ELECTRONS IN THEIR ELECTRON SHELL BE DETERMINED AT A

GIVEN TIME?

No. The positions of the electrons in their electron shells cannot be exactly determined at any given time.

However, each electron shell is made up of areas known as orbitals (also known as probability clouds).

Orbitals are areas in which one or two electrons are likely to be found at a given time.

NOW THAT I READ ALL THAT, COMPARE PROTONS, NEUTRONS, AND ELECTRONS.

Protons have a positive electric charge, electrons have a negative electric charge, and neutrons have no

electric charge. Since protons and electrons have opposite electric charges, the charges cancel each

other out. By canceling each other out, atoms are electrically neutral (meaning they have no electric

charge).

Another comparison of protons, neutrons, and electrons, relates to size. As was mentioned earlier, an

electron is very small. Electrons are much smaller than protons and neutrons. Specifically, the mass of a

neutron is about 1,840 times that of an electron. The mass of a proton is about 1,836 times that on an

electron.

DO ALL ATOMS HAVE THE SAME NUMBER OF PROTONS AND NEUTRONS?

No. The number of protons and neutrons that atoms have differ depending on what element they come

from. Elements (such as oxygen or hydrogen) are identified by the number of protons that they have. The

number of protons in a nucleus is known as the atomic number (abbreviated as Z). The number of protons

is equal to the number of electrons. The number of neutrons in atoms of the same element can differ. The

number of neutrons in a nucleus is known as the neutron number (abbreviated as N). The number of

protons and neutrons in a nucleus is known as the mass number (abbreviated as A).

CAN THERE BE DIFFERENT FORMS OF THE SAME ELEMENT?

Yes. Different forms of the same element (such as oxygen or hydrogen) are known as isotopes. These

elements have the same number of protons but different numbers of neutrons as compared to the natural

form of the element. Every element has an isotope. Isotopes made by man are known as radioisotopes.

IS THERE ANYTHING SMALLER THAN PROTONS OR NEUTRONS?

Yes. Protons are made up of even smaller substances known as quarks. Quarks are only found in groups.

There are six types of quarks, each of which have their own special names: up quarks, down quarks, top

quarks, bottom quarks, charm quarks, and strange quarks. Protons are made of two up quarks and one

down quark. Neutrons are made of one up quark and two down quarks. When quarks come together to

form particles, these particles are known as hadrons. Protons and neutrons are types of hadrons.

As was mentioned earlier, electrons are smaller than protons and neutrons, but they do not make up the

protons and neutrons like the quarks do. Electrons belong to a class of particles known as leptons. There

are five other types of leptons besides electrons. They are known as the muon, the tau, and three types of

neutrinos. The muon and the tau both have negative electric charges. The three types of neutrinos have

no charge, and little, if any mass.

IS THERE ANYTHING SMALLER THAN QUARKS OR ELECTRONS?

Scientists now believe that quarks and electrons cannot be divided and that they are the fundamental

substances that all matter is made of. However, scientists are still investigating whether this is true. It is

possible that electrons and quarks are made up of smaller substances that have yet to be discovered.

Remember that at one point in time it was believed that atoms could not be divided.

WHAT IS ATOMIC WEIGHT?

Atomic weight (also known as atomic mass or relative atomic mass) is the amount of matter in an atom. In

other words, it is the amount of substance in an atom. Do not take the word "weight" literally, since it is

impossible to weigh an object as small as an atom. This is why the word "mass" is the best term to use

since it means the amount of substance in an atom.

Atomic weight or atomic mass is not measured in pounds, of course, so what is the unit of measurement

for an atomic weight/atomic mass? The surprising answer is that they are unitless! That is, we do not

know how to find the mass of an individual atom by itself. What we can do is find the mass of a whole

bunch of atoms by comparing them to the mass of another bunch of atoms. This is where the term relative

atomic mass comes in, because the mass of atoms are measured by comparing one bunch of atoms

relative to (in relation to) another bunch of atoms, of the same sizes. This is easy to do if the same

numbers of atoms are in each bunch.

To make this easier to understand, let's pretend that paperclips the same thing as atoms (after all,

paperclips are pretty small). Let's also assume that we have two types of paperclips: white paperclips and

red paperclips. The two types of paperclips are in two piles. Let's also assume that we have the same

amount of paperclips in each pile and that the paperclips are the same sizes.

If we put one paperclip on a scale, it would be very hard to weigh it because the scale would probably not

be sensitive enough. However, if we put a whole bunch of paperclips on the scale, then we would be able

to weigh them. So let's say we put a whole bunch of white paperclips on one scale and a whole bunch or

red paperclips on another scale.

Now let's say that the white paperclips weighed 2 grams and that the red paperclips weighed 10 grams. A

gram is a very small unit of weight (you would need 453.359237 grams just to get one pound!) Now we

can compare the weight of the red paperclips to the weight of the white paperclips. To do this, we just

divide 10 (the weight of the red paperclips) by two (the weight of the white paperclips), and we get 5. We

can create a name for the units of weight for the paperclips (let's call them relative paperclip mass units).

So now we can say that the red paperclips have 5 relative paperclip mass units. The relative paperclip

mass units of the white paperclips would be 1. This is because two divided by two equals one.

Can we do the same type of equation as the one above with two different types atoms? Yes. All you need

to do is have some way of knowing that you have the same amount of atoms for each type of atom. But

how can we do this if we can't even see atoms? It requires believing in a hypothesis (an uncertain

assumption) put forth by a scientist named Lorenzo Romano Amedeo Carlo Avogadro di Quareqa e di

Carreto. Let's just call him Avogadro. The hypothesis is known as Avogadro's hypothesis and it says that

the same volumes (amounts of space occupied by something) of gases at the same temperature and

pressure contain the same numbers of molecules. Molecules are the smallest naturally occurring particles

of a substances and are made of any number of atoms, from one to thousands.

Keeping Avogadro's hypothesis in mind, let's say we have two containers of gas: one container has

hydrogen in it while the other container has oxygen in it. The hydrogen and oxygen are both at room

temperature and have the same pressures. If we believe in Avogadro's hypothesis, this means that the

number of molecules in each container is the same.

We have techniques to measure the weight of gases, so let's say that the hydrogen weighs .23 grams and

the oxygen weighs 3.68 grams. Now we can compare the weight of the oxygen gas to the weight of the

hydrogen gas. To do this, we just divide 3.82 (the weight of the oxygen gas) by .23 (the weight of the

hydrogen gas), and we get 16. We can create a name for the unit of weight for the gasses (let's call it

relative gas mass unit). So now we can say that the oxygen gas has 16 relative gas mass units.

We can also say that an oxygen atom is 16 times heavier than a hydrogen atom because atoms make up

the gas. In other words, since the oxygen gas is 16 times heavier than the hydrogen gas, the oxygen

atoms must be 16 times heavier than the oxygen atoms too. The official name for the units of mass for an

atom is called unified atomic mass units (abbreviated as u). The unified atomic mass units for hydrogen

would be 1. This is because .23 divided by .23 equals one.

If you look in a textbook, you will see that the relative mass of hydrogen equals 1.00794 u. Why not just

1? There are two main reasons:

1. As was mentioned earlier, atoms have isotopes (different forms of the same element due to different

numbers of neutrons). The atomic number that you see in textbooks for an element is the average of the

atomic masses for the natural element and its isotopes.

2. All elements are compared to an element known as carbon-12. It is called carbon-12 because it has 6

protons and 6 neutrons. The atomic mass of carbon-12 is equal to 12. Since all elements have their

weights divided by 12, it worked out that no other atomic masses came out to a whole number.

WHAT FIELDS OF SCIENCE DEALS WITH THE STUDY OF ATOMS?

Atoms are typically studied in chemistry (the science of elements, combinations of elements, the structure

of elements, and the interaction of different types of matter) and physics (the study of matter and energy,

especially as they relate to motion and force).

WHAT IS THE ORIGIN OF THE TERM, ATOM?

Atom comes from the Greek word "atomos" meaning "indivisible." The ancient Greeks believed that all

matter was made up of tiny particles called atoms.