CSET Practice Test Subtest II Science

Subatomic Particles

The first subatomic particle to be identified was the 
electron, in 1898. Ten years later, Ernest Rutherford 
discovered that atoms have a very dense nucleus, 
which contains protons. In 1932, James Chadwick 
discovered the neutron, another particle located 
within the nucleus. 

And so scientists thought they had found the smallest 
atomic building blocks. This changed in 1963 when 
Murray Gell-Mann proposed his quark theory. Gell-Mann 
believed that each proton and each neutron is made up 
of three even smaller particles -- particles he named 
quarks. 

Physicists have learned a great deal over the past 100 
years. For instance, it is now known that in each atom 
of carbon12, there are a set number of subatomic 
particles: six electrons, six protons, and six neutrons. 
The atom's nucleus and electrons are held together by 
the electromagnetic force -- the positive charges of the 
protons balances the negative charges of the electrons. 
Neutrons have no charge. 

An atom consists of a nucleus of protons and neutrons 
surrounded by electrons. Typically a model is used which 
has the electrons "orbiting" the nucleus.

Protons, neutrons, and electrons

Elements make up compounds, and are considered the 
basic building blocks of matter. You cannot break down 
elements into smaller parts, but you can classify the 
different parts within the element. Within the element 
are protons, neutrons, and electrons. The neutron, a 
chargeless particle, can be found in the nucleus along 
with the proton, which is a particle only slightly smaller 
than the neutron but positively charged. Electrons are 
negatively charged and are found circling the nucleus 
(much like the sun and the planets in our solar system). 

Within the atom, one can find a nucleus. The nucleus, 
which does not move around like electrons, contains 
both neutrons and protons. Both neutrons and protons 
have mass, and these two contribute almost 100% of 
the atomic mass of an element. Electrons, on the other 
hand, have almost no mass. Most calculations assume 
a mass of zero for electrons. Electrons, being so small, 
can move around very quickly around the nucleus. 
Protons and neutrons can also be broken down into 
quarks, but you won't learn about those petit particles 
in this chemistry year. 

A common demonstration to show how little space the 
electrons and nucleus take up in the atom is with the 
football field analogy. If a football stadium was 
considered to be an atom, a feather on the 50 yard 
line would be the nucleus. That is how much empty 
space there is within an atom! 

Elements

As mentioned before, an element's mass is determined 
by its protons and neutrons. The electrons, having 
almost no mass, do no contribute to the mass of an 
element. An element is defined by the number of protons 
and electrons it has. The number of nuetrons an element 
has, however, can vary from atom to atom.

Atomic Structure 
A. Atomic Number Equals Electrons or Protons 
Each element has an atomic number. The atomic numbers 
are listed along with the names and symbols of the 
elements on the inside cover of the text. The atomic 
number equals the charge on the nucleus. It therefore 
also equals the number of protons in the nucleus and also 
equals numerically the number of electrons in the neutral 
atom. The atomic number has the symbol Z. 

Different elements have different atomic numbers; 
therefore, atoms of different elements contain different 
numbers of protons (and electrons). Oxygen has the 
atomic number 8; its atoms contain 8 protons and 8 
electrons. Uranium has the atomic number 92; its atoms 
contain 92 protons and 92 electrons. 

B. Mass Number Equals Protons plus Neutrons 
Each atom also has a mass number, denoted by the 
symbol A. The mass number of an atom is equal to the 
number of protons plus the number of neutrons that it 
contains. In other words, the number of neutrons in 
any atom is its mass number minus its atomic number. 

Number of neutrons = mass number - atomic number 
or 
Mass number = number of protons + number of neutrons 

C. Isotopes 
Although all atoms of a given element must have the 
same atomic number, they need not all have the same 
mass number. For example, some atoms of carbon 
(atomic number 6) have a mass number of 12, others 
have a mass number of 13, and still others have a 
mass number of 14. These different kinds of the same 
element are called isotopes. Isotopes are atoms that 
have the same atomic number (and are therefore of 
the same element) but different mass numbers.

Plate Tectonics

According to the plate tectonic model, the surface of 
the Earth consists of a series of relatively thin, but rigid, 
plates which are in constant motion. The surface layer 
of each plate is composed of oceanic crust, continental 
crust or a combination of both. The lower part consists 
of the rigid upper layer of the Earth's mantle. The rigid 
plates pass gradually downwards into the plastic (soft) 
layer of the mantle, the astenosphere. The plates may 
be up to 70 km thick if composed of oceanic crust or 
150 km incorporating continental crust. Plates move at 
different velocities, The African plate moves about 
25 mm per year, whereas the Australian plate moves 
about 60 mm per year. 

Most of the Earth's tectonic, seismic and volcanic 
activity occurs at the boundaries of neighbouring plates. 
There are three type of plate boundaries: divergent, 
convergent and transform boundaries. 

Divergent plate margins 

At this type of boundary new oceanic crust is formed in 
the gap between two diverging plates. Plate area is 
increased as the plates move apart. Plate movement 
takes place laterally away from the plate boundary, 
which is normall marked by a rise or a ridge. The ridge 
or rise may be offset by a transform fault. Presently, 
most divergent margins occur along the central zone of 
the world's major ocean basins. The process by which 
the plates move apart is referred to as sea floor spreading. 
The Mid-Atlantic Ridge and East Pacific Rise provide good 
examples of this type of plate margin. 

The rate at which each plate moves apart from a 
divergent margin varies from less than 50 mm per year 
to over 90 mm per year and can be determined from 
the pattern of magnetic anomalies either side of a 
spreading ridge. Either side of a spreading centre, weak 
magnetic anomalies 5-50 km wide and hundreds of 
kilometres long can be identified. molten rock cools 
between diverging plates the magnetic minerals present 
align themselves with the orientation of the Earth's 
magnetic field at that time. The polarity of the Earth 
has changed at regular intervals throughout geological 
time. Magnetic north has alternated between the Arctic 
(normal polarity) and the Antarctic (reversed polarity). 
As a result of this, sections of crust formed during a 
period of normal polarity have a paleomagnetic remnance 
which is oriented towards today's magnetic north, while 
a section of crust formed during a period of reversed 
polarity does not. These long linear strips of magnetic 
anomalies form a symmerical pattern either side of a 
spreading centre. A record of the changes in the Earth's 
magnetic polarity has been established and dated for the 
Cenozoic and is the basis for magnetostratigraphy. This 
record, in conjunction with the magnetic stripes found 
either side of a spreading ridge, allows the rate and 
pattern of sea floor spreading to be examined. 

Convergent plate boundaries 

At a convergent boundary two plates are in relative 
motion towards each other. One of the two plates slides 
down below the other at an angle of around 45 degrees 
and is incorporated into the Earth's mantle along a 
subduction zone. The path of this descending plate can 
be found from analysis of deep earthquakes and the initial 
point of descent is marked on the surface by a deep 
ocean trench. Plate area is reduced along the subduction 
zone. When two plates of oceanic crust collide a volcanic 
island arc may form. As one of the plates is subducted 
beneath the other it begins to melt at a depth of 
between 90 and 150 km and the resulting magma rises 
to the surface above the subduction zone to form a 
chain or arc of volcanoes. The edge of the plate which 
is not descending is therefore marked by a chain of 
volcanic islands. 

Conservative or transform margins 

The San Andreas fault system is the most famous 
example of this type of boundary. Here two plates move 
laterally past each other and oceanic crust is neither 
created nor destroyed.