AHSGE: Science Introduction to Chemistry

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AHSGE Science Introduction to Chemistry

• The Atom

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The Atom

• In this section you will
• Construct a Model of the Atom
• Determine Properties of the Subatomic Particles
• Differentiate Between Energy Levels and Orbitals

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Construct a Modelof the Atom
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Home

• 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.

• This single particle is called an atom.
• An atom is the smallest unit of matter that
  retains the properties of the original substance.

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Construct a Modelof the Atom
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• There are approximately 92 naturally occurring
  atoms.

• What makes one atom different from another?
• To answer this question we need to look inside
  the atom.

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Construct a Modelof the Atom
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• Atoms are composed of 3 subatomic particles.

• The protons and neutrons are located in a small
  area in the the center of the atom called the
  nucleus.

• Electrons move around the nucleus in much the
  same way planes circle an airport waiting to land.

Proton
Nucleus
Neutron
Electron
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Construct a Modelof the Atom
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Home

• 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.

• In the next section, we will look at the
  properties of the individual particles in more
  detail.
• Three key properties of subatomic particles are
  mass, charge, and number.

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Determine Properties of the Subatomic Particles
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Mass

• 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 AMUs to equal 1 gram.
  You can see an AMU is extremely small.

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Determine Properties of the Subatomic Particles
Mass

• Protons and Neutrons each have a mass of 1 AMU.

• Electrons have no mass 0 AMU

• Electrons actually do have some mass. They are
  so much lighter than protons and neutrons that,
  by comparison, their mass is negligible.

Proton
Neutron
Electron
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Determine Properties of the Subatomic Particles
Mass

• Where in an atom is most of the mass located?

• Protons and neutrons have a mass and are located
  in the nucleus. The electrons have virtually no
  mass.

Nucleus
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Determine Properties of the Subatomic Particles
Mass

• Protons and neutrons each have a mass of 1 AMU
  and electrons have essentially no mass.

• So, the mass of the entire atom can be found by
  adding the number of protons and neutrons.

Protons Neutrons Atomic Mass
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Determine Properties of the Subatomic Particles
Mass

• What is the mass of the atom shown below.

2 Protons (1AMU each) 2 AMU
2 Neutrons (1AMU each) 2 AMU
4 AMU
Atomic Mass
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Determine Properties of the Subatomic Particles
Mass

• 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 AMUs
52 AMUs
14 AMUs
231 AMUs
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Determine Properties of the Subatomic Particles
Mass

• Complete the table below then click for answers.

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10
31
50
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Determine Properties of the Subatomic Particles
Charge

• 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.
• A Proton has a positive charge 1
• A Neutron has a neutral charge 0
• An Electron has a negative charge -1

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Determine Properties of the Subatomic Particles
Charge

• Is the nucleus of an atom positively or
  negatively charged?

• The nucleus is positively charged since it is
  composed of positively charged protons and
  neutral neutrons.

Proton 1
Neutron 0
Electron -1
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Determine Properties of the Subatomic Particles
Charge

• 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
2 Electrons (-1 each) - 2 charge
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Determine Properties of the Subatomic Particles
Charge

• 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 cant 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 charge.

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Determine Properties of the Subatomic Particles
Charge

• A proton has a positive charge 1

• An electron has a negative charge -1

• A neutron is neutral. It wont affect overall
  charge.

• One positive proton will cancel out one negative
  electron leaving an overall charge of Zero

Overall Charge 0
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Determine Properties of the Subatomic Particles
Charge

• Complete the table below then click for the
  answers.

5
0
- 5
0
16
0
- 16
0
19
0
- 19
0
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Determine Properties of the Subatomic Particles
Charge

• 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?
• Will the atom still be neutral (overall charge
  0)?
• Take a look at the next slide to see.

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Determine Properties of the Subatomic Particles
Charge

• Consider an atom with 2 protons and 2 electrons.

Gained 1 Electron 2 Protons 2 3 Electrons
- 3 Overall Charge - 1
Lost 1 Electron 2 Protons 2 1 Electrons
- 1 Overall Charge 1
2 Protons 2 2 Electrons - 2 Overall
Charge 0
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Determine Properties of the Subatomic Particles
Charge

• 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
- 2
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Determine Properties of the Subatomic Particles
Number

• 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.
• However, when the nucleus of an atom becomes too
  large it will become unstable.

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Determine Properties of the Subatomic Particles
Number

• 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
• This means that the overall charge of an
  unreacted atom will always be zero.

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Determine Properties of the Subatomic Particles
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Number

• If an atom has 15 protons, how many electrons
  will it have before it reacts?

• 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?

• 9 Electrons. Mass of 19 AMU 10 neutrons 9
  Protons Protons Electrons in an unreacted atom.

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Differentiate Between Energy Levels and Orbitals
Home

• When we explored the model of the atom, all we
  said about the electrons is that they were
  outside the nucleus.

• While this statement is true, it is also
  incomplete.
• In this section, we will take a more detailed
  look at where electrons can be located.

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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.

• The goal of the air traffic controller is to use
  the air space around the airport efficiently and
  to insure that the planes dont collide.
• The same is true for the electrons in an atom.
• We want to use the space around the nucleus
  efficiently but we cant have two electrons in
  the same place at the same time.

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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.

• The Energy Level refers to the electrons
  distance from the nucleus.

Energy Level 4
Energy Level 3
Energy Level 2
Energy Level 1
Nucleus
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Differentiate Between Energy Levels and Orbitals

• Energy Levels represent an electrons distance
  from the nucleus.

• The first energy level is the closest and
  therefore the smallest level.
• Each subsequent level gets further away and
  therefore larger.
• The further an electron is from the nucleus,
  the more energy it will have.

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Differentiate Between Energy Levels and Orbitals

• In which energy levels could you put the smallest
  and largest number of electrons?

• Least Energy Level 1 Most Energy Level 4The
  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?

• Energy Level 1The closer to the nucleus the
  lower the energy.

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Differentiate Between Energy Levels and Orbitals

• Energy Levels represent an electrons distance
  from the nucleus but that isnt the only factor
  to consider when positioning electrons in an atom.

• 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.
• The flight pattern is the path the plane would
  follow while it is flying at a given distance.

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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.

• 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.
• Keep in mind the larger the energy level the more
  room there is for more orbitals.

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Differentiate Between Energy Levels and Orbitals

• Energy Levels and Orbitals

Nucleus
Level 1
Level 2
Level 3
Level 4
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Differentiate Between Energy Levels and Orbitals

• Remember, Energy Levels determine an electrons
  distance from the nucleus.

• 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
  electrons that can be placed in each energy level.

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Differentiate Between Energy Levels and Orbitals

• 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
Sixteen 1 S, 3 P, 5 D, and 7F Orbitals
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Differentiate Between Energy Levels and Orbitals

• How many electrons can fit in the first Energy
  Level? (Remember, a maximum of 2 electrons can
  fit in a single orbital)

• Two There is only 1 orbital in the first energy
  level.

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Differentiate Between Energy Levels and Orbitals

• How many electrons can fit in the P orbitals of
  the second Energy Level? (2 electrons/orbital
  max)

• Six There are 3 P orbitals in the second energy
  level.

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Differentiate Between Energy Levels and Orbitals

• How many electrons can fit in the D orbitals of
  the third Energy Level?

• Ten There are 5 D orbitals in the third energy
  level with a maximum of 2 electrons in each.

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Differentiate Between Energy Levels and Orbitals

• How many electrons can fit in the F orbitals of
  the fourth Energy Level?

• Fourteen There are 7 F orbitals in the fourth
  energy level with a maximum of 2 electrons in
  each.

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Differentiate Between Energy Levels and Orbitals

• How many electrons are in each energy level?
• Level 1
• Level 2
• Level 3
• Level 4

Two 1 Orbital 2 electrons/orbital
Eight 4 Orbitals 2 electrons/orbital
Eighteen 9 Orbitals 2 electrons/orbital
Thirty Two 16 Orbitals 2 electrons/orbital
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Differentiate Between Energy Levels and Orbitals
Home

• Why do the electrons stay in the energy levels
  and orbitals? (Why dont they just fly off into
  space?)

• 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.

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AHSGE Science Introduction to Chemistry

• You have Completed
• The Atom