Notesale: Turn your study into money

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ATOMIC
STRUCTUR
Great idea of science

An atom is the smallest constituent unit of ordinary matter that has the
properties of a chemical element
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Atoms are very small; typical sizes are around 100 pm
(a ten-billionth of a meter, in the short scale)
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Atoms are small enough that classical physics give noticeably incorrect results
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Every atom is composed of a nucleus and one or more electrons bound to the
nucleus
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Protons and neutrons are called
nucleons
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94% of the atom's mass is in the nucleus
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If the number of protons and electrons are
equal, that atom is electrically neutral
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atom

Electrons of an atom are attracted to the protons in an atomic nucleus by this
electromagnetic force
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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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The number of
neutrons defines the isotope of the element
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Atoms can attach to one or more
other atoms by chemical bonds to form chemical compounds such as molecules
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Not all the matter of the universe is composed of atoms
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First evidence-based theory
In the early 1800s, John Dalton used the concept of atoms to explain
why elements always react in ratios of small whole numbers (the law of
multiple proportions)
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1% tin and 11
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7% tin and 21
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This means that 100g
of tin will combine either with 13
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13
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This common pattern in
chemistry suggested to Dalton that elements react in whole number
multiples of discrete units—in other words, atoms
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[4]
Dalton also believed atomic theory could explain why water absorbs
different gases in different proportions
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[5]
Dalton hypothesized this was due to the differences in mass and
complexity of the gases' respective particles
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The radius of a nucleus is
approximately equal to 1
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[37] This is much smaller than the radius of the atom, which is
on the order of 105 fm
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At distances
smaller than 2
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[38]
Atoms of the same element have the same number of protons, called
the atomic number
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The total number of
protons and neutrons determine the nuclide
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[39]
The proton, the electron, and the neutron are classified as fermions
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Thus, every proton in the nucleus must occupy
a quantum state different from all other protons, and the same applies
to all neutrons of the nucleus and to all electrons of the electron cloud
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[40]
For atoms with low atomic numbers, a nucleus that has more neutrons
than protons tends to drop to a lower energy state through radioactive
decay so that the neutron–proton ratio is closer to one
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Thus, there are
no stable nuclei with equal proton and neutron numbers above atomic
number Z = 20 (calcium) and as Z increases, the neutron–proton ratio of
stable isotopes increases
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5)
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Nuclear fusion occurs when multiple atomic particles join
to form a heavier nucleus, such as through the energetic collision of
two nuclei
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[41] Nuclear fission is
the opposite process, causing a nucleus to split into two smaller
nuclei—usually through radioactive decay
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If this modifies the number of protons in a nucleus, the atom
changes to a different chemical element
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This deficit
is part of the binding energy of the new nucleus, and it is the nonrecoverable loss of the energy that causes the fused particles to remain
together in a state that requires this energy to separate
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[45] It is this energy-releasing process
that makes nuclear fusion in stars a self-sustaining reaction
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That means fusion processes producing nuclei that have

atomic numbers higher than about 26, and atomic masses higher than
about 60, is an endothermic process
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[
Electron cloud
Main articles: Atomic orbital and Electron configuration

A potential well, showing, according to classical mechanics, the
minimum energy V(x) needed to reach each position x
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The electrons in an atom are attracted to the protons in the nucleus by
the electromagnetic force
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The closer an electron is to the nucleus, the greater the
attractive force
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Electrons, like other particles, have properties of both a particle and a
wave
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This behavior is

atom

defined by an atomic orbital, a mathematical function that
characterises the probability that an electron appears to be at a
particular location when its position is measured
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[47]
Orbitals can have one or more ring or node structures, and they differ
from each other in size, shape and orientation

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