Learning Task One Flashcards
1
Q
What is matter?
A
Matter is anything that occupies space or has mass.
2
Q
What are the three states of matter?
A
Solid, liquid, gas.
3
Q
What are substances?
A
Substances are categories of matter with different physical properties.
4
Q
What are the two general groups of substances?
A
Elements and compounds.
5
Q
What is an element?
A
An element contains atoms of only one type.
6
Q
How many known elements are there?
A
A little over 100 known elements.
7
Q
How many elements occur naturally?
A
92 elements occur naturally.
8
Q
Give examples of elements.
A
- Oxygen
- Hydrogen
- Carbon
- Copper
- Silver
9
Q
What is a compound?
A
A compound contains atoms of more than one type.
10
Q
What are examples of compounds?
A
- Water (H2O)
- Sugar (C6H12O6)
11
Q
What is an atom?
A
The smallest unit into which an element can be broken and still possess the properties of that element.
12
Q
What is a molecule?
A
The smallest independent unit into which a substance can be broken while still possessing the properties of that substance.
13
Q
What is the letter symbol for sodium?
A
Na.
14
Q
What is the letter symbol for sulfur?
A
S.
15
Q
What is the letter symbol for carbon?
A
C.
16
Q
What is the difference between an atom and a molecule?
A
A molecule can be an independent unit of a compound or element, while an atom can only be the smallest unit of an element.
17
Q
True or False: A molecule must be independent.
A
True.
18
Q
Fill in the blank: The smallest independent particle of the element oxygen contains ______ linked atoms.
A
two
19
Q
What happens to an atom of oxygen when it is broken down?
A
It retains its properties but will not remain as a single atom for any length of time.
20
Q
The atom
A
21
Q
The atom is composed of a dense e nucleus surrounded by revolving electrons (rather like our sun
A
22
Q
surrounded by the planets). It is held together by electric forces. The properties possessed by
A
23
Q
elements are determined by the makeup of the atom.
A
24
Q
Al the atoms of a given element contain the same number of protons in their nucleue The
A
25
atomic number of any element is always equal to the number of protons in its nucleus The
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RmE of aach of the different elements contaln a difterent number of protons in their nucleus
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So
each element has a different atomic number.
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For example
all hydrogen atoms contain one proton in their nucleus
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29 protons
and all carbon atoms contain six protons.
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Figure 1 shows a model of a carbon atom.
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Nucleus.
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Proton
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with four electrons.
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Neutron
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The nucleus of the carbon atom contains six protons
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number of carbon is six. As well
there are six electrons
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Figure 1Carbon atom
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10
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This outer orbital is referred to as the valence
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interact
is used because the electrons in
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and six
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a carbon atom. The first or inner orbital contains two electrons. The outer orbital is half-filled
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Valence
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orbit
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Electron
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neutrons. Thus
the atomic
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which revolve around the nucleus of
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e orbital. The term
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this orbit interact
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valence
which means ability to
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with the electrons in the valence
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orbits of other atoms. In fact
the behaviour of electric circuits is quite dependent on the
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behaviour of these valence electrons
as you will see later
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er in this Learning Task.
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A-1
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CONSTRUCTION AND INDUSTRIAL ELECTRICIAN IAPPRENTICESHIP PROGRAM: LEVEL 1
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LEARNING TASK 1
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Orbital motion
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From the orbital motion of the electrons around the nucleus it can be deduced that:
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Electrons
like any other body
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velocity of a moving object are connected by the equation
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E=
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my²
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2
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Ihe mass of the electrons must be a fraction of the mass of the nucleus (otherwise
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nucleus and electrons would be moving a similar amount).
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Ihere is a force of attraction between the nucleus and the electrons that holds the
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electrons in orbit.
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The orbital motion of electrons can be compared to swinging in a circle a rock attached to an
70
elastic band:
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• If the rock is not given any energy
it will stay stationary.
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If the rock is given energy and starts moving
it will revolve around your hand the way the
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electrons revolve around the nucleus.
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. If the rock were heavier than you
it is likely that as you exerted a force you would move
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rather than the rock. Similarly
if the electron were heavier than the nucleus
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nucleus would revolve around the electron.
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A-1
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. If the elastic band were to break
the rock would no longer revolve around your hand
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would fly off in a straight line. This would also happen to an electron if there were no force
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of attraction between it and the nucleus.
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Electron orbitals
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Flectrons revolve at high speed in their orbits around the atom's nucleus. Because of their areat
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speed. centrifugal force tends to pull the electrons out of their orbit. Electrostatic forces. which
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vou will learn about in Learning Task 2
keep the electrons from breaking away. However
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sufficient outside force is applied to an electron to aid the centrifugal force
the electron can be
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freed from the atom.
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Al electrons do not possess the same amount of energy. Electrons farther from the nucleus
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bavo more eneray than electrons closer to the nucleus. If they all possessed the same energy
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they would all be in the same orbit. In the previous analogy
if more energy is supplied to the
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rock. the rock speeds up
the centrifugal force increases
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revolves in a larger orbit.
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The fact that electrons closer to the nucleus have less energy than electrons in the valence orbit
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means that the electrons in the inner orbits are difficult to free from the atom
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Therefore
you can neglect the electrons in the inner orbits and concern yourself only with those
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in the outer valence orbit when you consider removal of electrons from the atom.
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cONSTRUCTION AND INDUSTRIAL ELECTRICIAN APPRENTICESHIP PROGRAM: LEVEL 1
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11
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LEARNING TASK 1
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Electrons fill the orbits in a very definite pattern:
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The inner shell fills to a maximum of two electrons.
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The next orbit fills to a maximum of eight electrons.
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. The third orbit can holda maximum of 18 electrons.
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The fourth can hold a maximum of 32 electrons
and so on.
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The general formula is that the nth shell can in principle hold up to 2 x n squared electrons
105
Although that formula gives the maximum in principle
in fact
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(by known elements) for the first four shells (K
L
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electrons in any one shell.
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The outer valence orbit can never fill to more than eight electrons.
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Figure 2 shows the maximum numbers of electrons for each orbit.
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Freeing electrons
111
12
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N -
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L
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M-
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K
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2 8 18 32 50
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Maximum number of electrons
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Figure 2-Electron orbitals
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A-1
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As energy is given to the rotating rock
its velocity increases and the centrifugal force increases.
121
The elastic band stretches and the size of the orbit increases. Eventually the centrifugal force is
122
too great for the elastic band
and it breaks
123
Ine orbiting electron is similar: as more eneray is provided to the electron
its centritugal TorcCe
124
increases until finaly it breaks free from the electrostatic force between itself and the nucleus.
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When this happens
the electron becomes a free electron.
126
AOms become stable if they have eight electrons in their valence orbit. This is calleda stable
127
AOms automatically adjust to the mOst stable state possible. Those atoms with tewer
128
than four valence electrons give them up
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electrons attract more electrons from
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relatively easily.
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their surroundings to complete a stable octet.
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Atoms with more than four valence
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CONSTRUCTION AND JNDUSTRIAL ELECTRICIAN APPRENTICESHIP PROGRAM: LEVEL 1
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LEARNING TASK 1
135
Any energy added to the electrons in the valence orbit is distributed equally among all those
136
electrons. This means that less energy is required to remove an electron from its orbit if it is the
137
only electron in the orbit. More energy is required if there are other electrons in the same orbit.
138
The more electrons there are in the valence orbit
the more energy is required to free an electron.
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Conductors
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A-1
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Materials that have electrons that are easily freed are called conductors of electricity. Atoms
142
that have one to three valence electrons are conductors. However
what makes one conductor
143
better than another is the number of free electrons per unit volume of the material. The greater
144
the number of free electrons per unit volume
the better electrical conductor the material is. For
145
example
a cubic centimetre of copper contains approximately 8.5 x 10" free electrons. Silver
146
has about 5% more free electrons per unit volume and is about 5% better as a conductor than
147
copper. Most metals are good conductors.
148
Insulators
149
Insulators are materials from which electrons are very difficult to free. Atoms that have five to
150
eight valence electrons are insulators. To free electrons
much mnore energy must be supplied to
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insulators than to conductors. Examples of elements that are insulators are the inert gases
such
152
as helium.
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Semiconductors
154
Semiconductors are those elements that are neither good conductors nor good insulators. They
155
are the elements with exactly four valence electrons. Examples are carbon
silicon
156
tin and lead. Later in yur studies you will learn that adding impurities to semiconductors can
157
produce some very useful electrical attributes.
