Download I Examen II trim Science

Science Summary
I Exam, II Trimester
1. Describe the structure of atoms.
All matter is made up of atoms. An Atom is the smallest particle
into which an element can be divided and still be the same
substance.
Atoms of the same element are identical, and atoms from different
elements are different. The atom itself has sub-atomic particles
with different electrical charge. These are:
Protons (P+): Positively charged sub-particles that are located in
the nucleus (central part of the atom).
Electrons: (e-): Negatively charged sub-particles that move around the nucleus
in energy levels. Electrons are found likely in the electron clouds.
Neutrons: (n): Sub-particles located in the nucleus, with no electrical charge.
The n and the P+ determine the atom´s mass.
The e- determines the volume of the atom.
2.



Define these terms:
(# = number)
Atomic #: Number of P+
Mass #: Number of n plus number of P+
Atomic mass: Isotope X Abundance / 100
Example: Boron-10 has an abundance of 20%, what is the atomic mass?
10 X 20 / 100 = 2 a.m.u.
 Isotopes: are atoms that have the same # of protons but different number
of neutrons.
 Ion: an atom that has different number of electrons.
 Anion: ion that gains electrons, so the atom gains a negative charge.
 Cation: ion that loses electrons, so the atom gains a positive charge.
3. Compare the Mendeleev’s and the current arrangement of the periodic
table.
Dmitri Mendeleev was a Russian chemist who arranged the elements in the
increasing atomic mass. Some elements that had similar properties were also
arranged in periods.
Then, there was a problem, some elements didn’t fit in this arrangement, so
Henry Moseley re-arranged this organisation with the atomic number, so all
the elements could fit in Mendeleev’s pattern. A
TOMIC NUMBER GIVES THE IDENTITY OF THE ELEMENT, AND
PROPERTIES CHANGE ACROSS THE PERIODIC TABLE.
4. Explain what data of elements can be found in the periodic table:
Periodic Table: A table in which elements are arranged taking into account
different properties. The mass number is not shown because of isotopes.
28
Ni
Nickel
58.71
Atomic Number
Chemical Symbol
Name of the Element
Atomic Mass
5. Determine # of: Protons, electrons and neutrons.
Mass #
In neutral atoms:
Atomic number = Number of Protons
12
6𝐶
Number of Protons = Number of electrons
Number of Neutrons= Mass number - Atomic number.
Atomic #
Ions
Atomic number= Number of Protons
Number of Neutrons = Mass number - Atomic number.
Number of Electrons = Atomic Number (plus or minus) the number next to
the chemical symbol.
If the symbol following the element is a - , add the number next to it. (Anion)
It the symbol following the element is a +, subtract the number next to it.
(Cation)
Examples: Cl- x the “–“represents a negative charge, so it gained 1 electron
so, Atomic number plus x.
Cl+ x the “+” represents a positive charge, so the atom lost an electron so,
Atomic number minus x.
6. Determine atomic masses of isotopes
To determine the atomic mass of an isotope, multiply the isotope and the
abundance and divide it into 100. If there is more than one isotope, do the
same but add them all at the end.
Example: Calculate the atomic mass of Rubidium-85, which occurs at 72%
and Rubidium-87 which occurs at a 28%.
85 X 72 / 100 = 61.2
87 X 28 / 100= 24.36
61.2 + 24.36 = 85.56 a.m.u
7. Identify the location and names of the groups of metals.
1. Alkali Metals
2. Alkaline Earth
Metals
3-12. Transition
Metals
13. Boron Group
14. Oxygen Group
14. Carbon Group
15.Halogens
15. Nitrogen Group
16.Noble Gases
8. Explain the development of the atomic
theory
Democritus
Atom (Aristotle said we
couldn’t reach the atom)
Dalton
All substances are made of
atoms, which can´t be neither created nor
destroyed. Atoms of the same element are the
same
Thomson
Discovered electrons
(Cathode-Ray Tube)
Rutherford
Bhor
Discovered the nucleus, P+ and n.
Discovered energy levels
Schrodinger (Modern Theory)
Electron Clouds
9. Explain the three types of radioactive decay.
The nucleus of all atoms (with the exception of hydrogen) contains one or
more protons and one or more neutrons. The nucleus of most carbon atoms,
for instance, contains six protons and six neutrons. In most cases, the nuclei of
atoms are stable; that is, they do not undergo changes on their own. A carbon
nucleus will look exactly the same a hundred years from now as it does today.
But some nuclei are unstable. An unstable nucleus is one that undergoes some
internal change spontaneously. In this change, the nucleus gives off a
subatomic particle, or a burst of energy, or both. As an example, an isotope of
carbon, carbon-14, has a nucleus consisting of six protons and eight (rather
than six) neutrons. A nucleus that gives off a particle or energy is said to
undergo radioactive decay, or just decay. Elements with a grater atomic
number of 82 (Above Lead) are radioactive. Radioactive elements emit three
types of radioactive decay:
A) Alpha Particles: The combination of 2 P+ and 2 N (nucleus of Helium)
are ejected from the nucleus. Alpha decay usually occurs in heavy
nuclei such as uranium or plutonium, and therefore is a major part of the
radioactive fallout from a nuclear explosion. These are very large.
Alpha particles are easy to stop; they can be stopped by a sheet of
paper. Double positive charge
B) Beta Particles: Beta Particles are ejected when there is beta decay. This
process occurs when a neutron in the nucleus turns into an electron. It is
hard to stop; it carries a negative charge and is very harmful for living
organisms.
C) Gamma Rays: Are high frequency
electromagnetic radiation, emitted from
radioactive elements. These beams are pure
energy. No mass or electric charge. Penetrate
through almost all materials.
10.Mention uses of isotopes:
a. Carbon dating: Used to determine the age of organisms that contain
Carbon.
b. In surface and ground water: To determine where water existed. To
explain the water cycle.
c. In Nutrition: Used as tracker to mark the absorption of nutrients in the
body.
d. In medical uses: Used in nuclear treatment, like cancer treatment.
e. Geology and Climatology: To determine the ages of rocks and tracker
for the environmental processes.
f. Smoke detectors: Detect the presence of smoke and heat.
g. Labelling Chemical Reactions: Study of chemical changes and its
process.
h. Pest Control: Regulation of species defined as pest.
i. Nuclear Weapons: Nuclear bombs
j. Agriculture: To improve crops in many ways.
k. Biological Tracing: To trace elements in humans or animals.
11.Nuclear Fusion and Fission, and Einstein’s Theory.
Nuclear Fission (Division):
• Uranium has not enough
nuclear forces
• Stretches into an elongated
shape
• Electric forces push it into an
even more elongated shape
• Electric forces > strong
nuclear forces
• The nucleus splits
• U-235 released energy (kinetic ENERGY, ejects a neutron and gamma
radiation)
• Creates a chain reaction within each nucleus separating.
• Nuclear energy is an important source, this works by nuclear fission.
• They use Uranium as fuel.
• Example: Atomic Bomb
Nuclear Fusion:
• Is the opposite to nuclear fission, it is a
combination of nuclei
• Energy is released as smaller nuclei
fuse. Less mass is obtained
• For a fusion reaction to occur, the
nuclei must collide at a very high speed in
order to overcome the mutual electric
repulsion
• Examples: Sun and other stars and the
hydrogen bomb
Einstein’s Formula: E= mc2
E= Potential Energy
M= mass
C= speed of light
C2= constant of energy and mass
This formula is very important to understand how and why energy is
released in nuclear reactions. If you increase the energy, you increase the
mass. When you have a bigger atom, there is enough energy.
13. What is the half-life of an element?
The half life of an element is the rate of decay for a radioactive isotope; half
the time is needed to an element to decay.
The shorter the half life is, the faster it disintegrates.
12. Differentiate between natural and artificial transmutation. Give
examples. THESE ARE EXAMPLES, BUT WHAT IS IMPORTANT IS
TO UNDERSTAND THE PROCESS
Transmutation is the process into which a radioactive nucleus emits an alpha
or beta particle. There is a change in the atomic number, so the element
changes.
Natural Transmutation
Artificial Transmutation.
Rutherford was the first in succeeding
Happens in Uranium-238
Alpha particle is ejected
Uranium-238 turns into Thorium- He bombarded Nitrogen with alpha
particles.
234
The Nitrogen turned into Oxygen
Kinetic Energy is released
The mass of the atom is affected.
When a beta particle is ejected, the These experiments are made to create
some synthetic elements.
number changing is the atomic
number
13.Explain the relation between the repulsive charges and the strong
nuclear force.
The strong nuclear force: Is the force that holds together the nucleus.
This force acts only in short distances. When there are two much
protons, the protons want to escape the nucleus.
The neutrons hold together the protons, but in nucleus with more of 82
protons, the neutrons can no longer retain the protons, so radiation is
emitted.
14.Benefits/Disadvantages of nuclear power.
Benefits
Disadvantages
A source of electricity, instead of fossil Radioactive wastes that pollute rivers
fuels.
and others.
Science progress
Mutation causes by the radioactivity,
for example one extra finger, or a
missing finger