BIOL 1003 Lecture Notes - Lecture 3: Nuclear Transmutation, Electromagnetism, Chemical Element

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22 Nov 2017
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An atom is the smallest constituent unit of ordinary matter that has the properties of a
chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized
atoms. Atoms are very small; typical sizes are around 100 picometers (a ten-billionth of a
meter, in the short scale).
Atoms are small enough that attempting to predict their behavior using classical physics
as if they were billiard balls, for example gives noticeably incorrect predictions due to
quantum effects. Through the development of physics, atomic models have incorporated
quantum principles to better explain and predict the behavior.
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The
nucleus is made of one or more protons and typically a similar number of neutrons. Protons
and neutrons are called nucleons. More than 99.94% of an atom's mass is in the nucleus.
The protons have a positive electric charge, the electrons have a negative electric charge,
and the neutrons have no electric charge. If the number of protons and electrons are equal,
that atom is electrically neutral. If an atom has more or fewer electrons than protons, then
it has an overall negative or positive charge, respectively, and it is called an ion.
The electrons of an atom are attracted to the protons in an atomic nucleus by this
electromagnetic force. The protons and neutrons in the nucleus are attracted to each other
by a different force, the nuclear force, which is usually stronger than the electromagnetic
force repelling the positively charged protons from one another. Under certain
circumstances, the repelling electromagnetic force becomes stronger than the nuclear
force, and nucleons can be ejected from the nucleus, leaving behind a different element:
nuclear decay resulting in nuclear transmutation.
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