what is an atom? what are atoms made of? what is an element? how many elements are there? what is...
TRANSCRIPT
What is an atom?
What are atoms made of?
What is an element?
How many elements are there?
What is the difference between a compound and a molecule?
What is an atom? What are atoms made of?
Atoms are the basic building blocks of ordinary matter. Atoms can join together to form molecules, which in turn form most of the objects around you.
Atoms are composed of subatomic particles.
What is an atom? What are atoms made of?
The 3 basic subatomic particles:
Protons, abbreviated p+, have a positive charge.
Neutrons, abbreviated n (or n0), have no charge.
Electrons, abbreviated e-, have a negative charge.
What is an atom? What are atoms made of?
All atoms are electrically NEUTRAL in their standard state.
In a neutral atom, all positive charges are "cancelled out" by an equal number of negative charges. In other words, there are equal numbers of protons and electrons in a neutral atom.
Here's an example of a Carbon (C) atom in its neutral state:
The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons 'orbit' the nucleus.
A particular atom will have the same number of protons and electrons and most atoms have at least as many neutrons as protons.
Protons carry a positive electrical charge, electrons carry a negative electrical charge and neutrons carry no electrical charge at all.
An element is a substance that is made entirely from one type of atom.
For example, the average atom of nitrogen contains 7 protons, 7 neutrons and 7 electrons. If you change the number of protons an atom has, you change the type of element it is.
What is an element? How many elements are there?
Isotopes
If you had very, very good eyes and could look at the atoms in a sample of hydrogen, you would notice that most of the hydrogen atoms would have no neutrons, some of them would have one neutron and a few of them would have two neutrons.
These different versions of hydrogen are called isotopes. All isotopes of a particular element have the same number of protons, but have a different number of neutrons. If you change the number of neutrons an atom has, you make an isotope of that element.
A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements.
What is the difference between a compound and a molecule?
All compounds are molecules but not all molecules are compounds.
A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compounds.
What is the difference between a compound and a molecule?
Molecules
Compounds
Compound or molecule?
What kind of information does the periodic table of the elements contain ?
What is the periodic table of the elements?
How will I use the periodic table of the elements?
Carbon12.011
C6
Carbon12.011
C6
Element Name
Atomic Weight
Atomic Symbol
Atomic Number
Krypton is an element.
Krypton is one of the gases that makes up the earth's atmosphere.
There is very little krypton in the atmosphere. The earth's atmosphere is roughly 0.0001% krypton, or about one part per million.
Krypton is a colorless, odorless gas that rarely reacts with other elements. A container full of krypton gas looks just like a container full of air. It isn't very exciting.
Things become more interesting when an electric current is sent through a container of low pressure krypton. When this is done, krypton lights up in much the same way a fluorescent light bulb. This glowing gas is called a plasma.
Krypton83.80
Kr36
Element Name
Atomic Weight
Atomic Symbol
Atomic Number
How many protons, electrons and neutrons are in an atom of krypton, carbon, oxygen, neon, silver, gold, etc...?The atomic number is the number of protons in an atom of an element. In our example, krypton's atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus.
The interesting thing here is that every atom of krypton contains 36 protons. If an atom doesn't have 36 protons, it can't be an atom of krypton. Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of krypton creates an atom of bromine.
How many protons, electrons and neutrons are in an atom of krypton, carbon, oxygen, neon, silver, gold, etc...?By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.
Number of Electrons = Number of Protons = Atomic Number
An atom can gain or lose electrons, becoming what is known as an ion. An ion is nothing more than an electrically charged atom. Adding or removing electrons from an atom does not change which element it is, just its net charge.
Ions
Ions
For example, removing an electron from an atom of krypton forms a krypton ion, which is usually written as Kr+. The plus sign means that this is a positively charged ion. It is positively charged because a negatively charged electron was removed from the atom. The 35 remaining electrons were outnumbered by the 36 positively charged protons, resulting in a charge of +1.
Atomic Weight
The atomic weight is basically a measurement of the total number of particles in an atom's nucleus. In reality, it isn't that clean cut. The atomic weight is actually a weighted average of all of the naturally occurring isotopes of an element relative to the mass of carbon-12.
Carbon12.011
C6
Atomic Weight
If we know atomic number then we can determine the number of electrons and protons.
Krypton83.80
Kr36
Number of Electrons = Number of Protons = Atomic Number
How many neutrons are in an atom of krypton?
How many neutrons are in an atom of krypton?
To find out how many neutrons are in an atom of krypton we must first determine the mass number.
Unfortunately, the mass number isn't listed on the Table of Elements.
Krypton83.80
Kr36
Happily, to find the mass number, all you need to do is round the atomic weight to the nearest whole number. In our example, krypton's mass number is 84 since its atomic weight, 83.80, rounds up to 84.
Krypton83.80
Kr36
Atomic Weight
How many neutrons are in an atom of krypton?First, determine the mass number.
The mass number is a count of the number of particles in an atom's nucleus. Remember that the nucleus is made up of protons and neutrons. So, if we want, we can write:
Mass Number = Number of Protons + Number of Neutrons
For krypton, this equation becomes:
84 = Number of Protons + Number of Neutrons
How many neutrons are in an atom of krypton?
Hmmn.. if we only knew how many protons krypton has, we could figure out how many neutrons it has.
Wait a minute... We do know how many protons krypton has!
The atomic number equals number of protons!
How many neutrons are in an atom of krypton?
If we know the atomic number then we know the number of protons. The atomic number (36) is the number of protons in krypton. Putting this into the equation, we get:
84 = 36 + (Number of Neutrons)
What number added to 36 makes 84? Hopefully, you said 48. That is the number of neutrons in an atom of krypton.
Krypton83.80
Kr36 atomic number = number of
protons
How many protons, electrons and neutrons are in an atom of krypton, carbon, oxygen, neon, silver, gold, etc...?The interesting thing here is that adding or removing neutrons from an atom does not create a different element. Rather, it creates a heavier or lighter version of that element. These different versions are called isotopes and most elements are actually a mixture of different isotopes.
If you could grab atoms of krypton and count the number of neutrons each one had, you would find that most would have 48, others would have 47, some would have 50, some others would have 46, a few would have 44 and a very few would have 42. You would count different numbers of neutrons because krypton is a mixture of six isotopes.
Number of Protons = Atomic Number = 36
Number of Electrons = Number of Protons = Atomic Number = 36
Number of Neutrons = Mass Number - Atomic Number =84 - 36 = 48
For krypton:
In Summary...
For any element:
Number of Protons = Atomic Number
Number of Electrons = Number of Protons = Atomic Number
Number of Neutrons = Mass Number - Atomic Number
