Technical Science
Introduction to Chemistry
The Atom
●
In this section you will…
– Construct a Model of the Atom
– Determine Properties of the Subatomic Particles
Construct a Model
of the Atom
● This single particle is called an atom.
● An atom is the smallest unit of matter that retains the properties of the original substance.
● The ancient Greeks reasoned that a pure substance could be divided down to a point where you would have only one particle of that substance left.
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Construct a Model
of the Atom
●
What makes one atom different from
another?
●
To answer this question we need to look
inside the atom.
●
There are approximately 92 naturally
occurring atoms.
Construct a Model
of the Atom
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● Atoms are composed of 3 subatomic particles.
Proton Neutron
Electron
● The protons and neutrons are located in a small area in the the center of the atom called the nucleus.
Nucleus ● Electrons move around the nucleus in much the
Construct a Model
of the Atom
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● Our model of the atom is a representation of the most current information about atoms.
● It places the protons and neutrons in a small dense nucleus in the center with the electrons moving
around the outside.
Home
● In the next section, we will look at the properties of the individual particles in more detail.
● Three key properties of subatomic particles are
Determine Properties of
the Subatomic Particles
Mass
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● To measure the mass of a subatomic particle, we first need an appropriate unit of measure. To this point, we have measured mass in grams.
● The problem is that grams are much to large to
measure something as small as a subatomic particle. We need a much smaller unit of measure.
● This unit is called the Atomic Mass Unit (AMU). ● One AMU is approximately 1.67 x 10-24 grams.
● It takes about 6 x 1023 AMU’s to equal 1 gram. You can see an AMU is extremely small.
Determine Properties of
the Subatomic Particles
Mass
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● Protons and Neutrons each have a mass of 1 AMU.
1 AMU
Proton Neutron
1 AMU
Electron
1 AMU
● Electrons have no mass 0 AMU
1 AMU
● Electrons actually do have some mass. They are so much lighter than protons and neutrons that, by
Determine Properties of
the Subatomic Particles
Mass
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● Where in an atom is most of the mass located?
Α Protons and neutrons have a mass and are located
in the nucleus. The electrons have virtually no mass.
Determine Properties of
the Subatomic Particles
Mass
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● So, the mass of the entire atom can be found by adding the number of protons and neutrons.
Protons + Neutrons = Atomic Mass
Determine Properties of
the Subatomic Particles
Mass
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● What is the mass of the atom shown below.
2 Protons (1AMU each) = 2 AMU
2 Neutrons (1AMU each) = 2 AMU
Determine Properties of
the Subatomic Particles
Mass
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● What is the atomic mass of an atom with…
4 protons and 5 neutrons =
24 protons and 28 neutrons =
7 protons and 7 neutrons =
91 protons and 140 neutrons =
9 AMU’s
52 AMU’s
14 AMU’s
Determine Properties of
the Subatomic Particles
Mass
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● Complete the table below then click for answers.
Protons Neutrons Atomic Mass
35 65
10 20
39 70
39 89
30
10
31
Determine Properties of
the Subatomic Particles
Charge
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● A second property of subatomic particles is charge. ● Charge is the electrical state of the particle.
● There are three types of charge:
Positive (+), Negative (-), and Neutral (0) ● Opposite charges attract each other.
Proton +1 Neutron 0
Electron -1
Determine Properties of
the Subatomic Particles
Charge
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● Is the nucleus of an atom positively or negatively charged?
Α The nucleus is positively charged since it is
Determine Properties of
the Subatomic Particles
Charge
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● What is the charge on all the protons, the neutrons, and the electrons in the atom below.
2 Protons (+1 each) = + 2 charge
2 Neutrons (0 each) = 0 charge
Determine Properties of
the Subatomic Particles
Charge
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● Now that you know the charges on each of the
subatomic particles you can calculate the charge on the entire atom.
● This is not quite as easy as calculating atomic mass. We can’t just add up all the particles that have
charge because there are different kinds of charge. ● Positive charges will cancel out negative charges. ● Neutral charges will have no effect on the overall
Determine Properties of
the Subatomic Particles
Charge
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● A proton has a positive charge +1
+1
● An electron has a negative charge -1
-1
● A neutron is neutral. It won’t affect overall charge.
0
● One positive proton will cancel out one negative electron leaving an overall charge of Zero
Determine Properties of
the Subatomic Particles
Charge
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● Complete the table below then click for the answers.
Atom Charge Protons Charge Neutrons Charge Electrons Overall Charge 5 protons 6 neutrons 5 electrons 16 protons 16 neutrons 16 electrons 19 protons 20 neutrons 19 electrons
+ 5 0 - 5 0
+ 16 0 - 16 0
Determine Properties of
the Subatomic Particles
Charge
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● As you saw, when the number of protons equals the number of electrons the overall charge is zero.
● What do you think would happen if an atom gained or lost electrons?
Determine Properties of
the Subatomic Particles
Charge
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2 Protons = + 2
2 Electrons = - 2
Overall Charge = 0
Gained 1 Electron
2 Protons = + 2
3 Electrons = - 3
Overall Charge = - 1
Lost 1 Electron
2 Protons = + 2
1 Electrons = - 1
Overall Charge = + 1
Determine Properties of
the Subatomic Particles
Charge
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● Consider an atom with 6 protons and 6 electrons. What would be the overall charge if the atom…
Lost 1 Electron =
Lost 2 Electrons =
Gained 1 Electron =
Gained 2 Electrons =
+ 1
+ 2
- 1
Determine Properties of
the Subatomic Particles
Number
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● A third important property of an atom is the number of subatomic particles that compose it. ● The more protons and neutrons the greater the
mass of the atom.
● There is really no theoretical limit on the number of protons and neutrons in an atom.
Determine Properties of
the Subatomic Particles
Number
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● There is an important relationship between the number of protons and electrons.
● The number of proton equals the number of electrons in an unreacted atom.
● So, to start with, Protons = Electrons
Determine Properties of
the Subatomic Particles
Number
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● If an atom has 15 protons, how many electrons will it have before it reacts?
Α 15 Electrons.
Protons = Electrons in an unreacted atom.
● If an atom has an mass of 19 AMU & 10 neutrons, how many electrons will it have before it reacts?
Α 9 Electrons.
Mass of 19 AMU – 10 neutrons = 9 Protons Protons = Electrons in an unreacted atom.
Differentiate Between
Energy Levels and Orbitals
● When we explored the model of the atom, all we said about the electrons is that they were outside the nucleus.
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Home
● While this statement is true, it is also incomplete. ● In this section, we will take a more detailed look at
Differentiate Between
Energy Levels and Orbitals
● Locating electrons in an atom is similar to an air traffic controller keeping planes in holding patterns around an airport.
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● The goal of the air traffic controller is to use the air space around the airport efficiently and to insure that the planes don’t collide.
● The same is true for the electrons in an atom. ● We want to use the space around the nucleus
Differentiate Between
Energy Levels and Orbitals
● The first way to position electrons is to subdivide the space around the nucleus into discrete distances called Energy Levels.
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Nucleus
Energy Level 1 Energy Level 2 Energy Level 3 Energy Level 4
Differentiate Between
Energy Levels and Orbitals
● Energy Levels represent an electron’s distance from the nucleus.
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Nucleus
Energy Level 1 Energy Level 2 Energy Level 3 Energy Level 4 ● The first energy level is the closest and therefore
the smallest level.
● Each subsequent level gets further away and therefore larger.
Differentiate Between
Energy Levels and Orbitals
● In which energy levels could you put the smallest and largest number of electrons?
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Nucleus
Energy Level 1 Energy Level 2 Energy Level 3 Energy Level 4
Α Least = Energy Level 1 Most = Energy Level 4
The further an energy level is from the nucleus the larger it is so it can hold more electrons.
● Which energy level contains electrons at the lowest energy states?
Α Energy Level 1
Differentiate Between
Energy Levels and Orbitals
● Energy Levels represent an electron’s distance from the nucleus but that isn’t the only factor to consider when positioning electrons in an atom.
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● Remember our airport analogy where air traffic controllers are placing planes in holding patterns. ● In addition to assigning a plane a distance at which
to fly (energy level), the controller would also have to assign the plane a flight pattern.
Differentiate Between
Energy Levels and Orbitals
● For an electron this “flight pattern” is called an
Orbital. It is a way of subdividing an energy level.
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● An Orbital is the path that an electron follows within a given Energy Level.
● There are 4 types of orbitals: S, P, D, and F
● S orbitals are simplest paths while F orbitals are the most complex .
● The following diagram shows the types of orbitals that are available at each energy level.
Differentiate Between
Energy Levels and Orbitals
● Energy Levels and Orbitals
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Nucleus
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Differentiate Between
Energy Levels and Orbitals
● Remember, Energy Levels determine an electron’s distance from the nucleus.
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● Orbitals are subdivisions of energy levels and they determine the position of an electron within an
energy level. (2 electrons can fit in each orbital.) ● The diagram on the previous slide shows the
number and types of orbitals in the first 4 energy levels.
● On the next slide you will refer to that diagram to answer questions regarding the number of
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Differentiate Between
Energy Levels and Orbitals
Nucleus *
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Level 4 S P P P D D D D D F F F F F F F ● How many orbitals are in each Energy Level?
● Level 1 =
● Level 2 =
● Level 3 =
● Level 4 =
One: 1 S Orbital
Four: 1 S and 3 P Orbitals
Nine: 1 S, 3 P, and 5 D Orbitals
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Differentiate Between
Energy Levels and Orbitals
Nucleus *
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Level 4 S P P P D D D D D F F F F F F F
● How many electrons can fit in the first Energy
Level? (Remember, a maximum of 2 electrons can fit in a single orbital)
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Differentiate Between
Energy Levels and Orbitals
Nucleus *
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Level 4 S P P P D D D D D F F F F F F F
● How many electrons can fit in the P orbitals of the second Energy Level? (2 electrons/orbital max)
Α Six: There are 3 P orbitals in the second energy
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Differentiate Between
Energy Levels and Orbitals
Nucleus *
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Level 4 S P P P D D D D D F F F F F F F
● How many electrons can fit in the D orbitals of the third Energy Level?
Α Ten: There are 5 D orbitals in the third energy
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Differentiate Between
Energy Levels and Orbitals
Nucleus *
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Level 4 S P P P D D D D D F F F F F F F
● How many electrons can fit in the F orbitals of the fourth Energy Level?
Α Fourteen: There are 7 F orbitals in the fourth
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Differentiate Between
Energy Levels and Orbitals
Nucleus *
Level 1 S
Level 2 S P P P
Level 3 S P P P D D D D D
Level 4 S P P P D D D D D F F F F F F F ● How many electrons are in each energy level?
● Level 1 =
● Level 2 =
● Level 3 =
● Level 4 =
Nucleus
Energy Level 1 Energy Level 2 Energy Level 3 Energy Level 4
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Differentiate Between
Energy Levels and Orbitals
● Why do the electrons stay in the energy levels and orbitals? (Why don’t they just fly off into space?)
Α Electrons are negatively charged while the protons
in the nucleus are positively charged. Opposite
charges attract. So, the positively charged nucleus pulls the negatively charged electrons.
