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Atomic structure
Subject classification: this is a physics resource.
An Atom is a small part of element that takes part
in chemical reactions. It is made up of three subatomic structures
called Protons, Neutrons, and Electrons.
Subatomic structures:
__________________________________
Particle: Charge:
Mass:
Proton +1
1 *u
Neutron 0
1 *u
Electron -1
1 / 1836*u
Atomic theoryPositron +1.
1 / 1836*u
The Nucleus, in the center of the atom, consists of protons and
neutrons. Orbiting around the nucleus are the electrons.
The nucleus, in the center of an atom, consist of protons and
neutrons. Orbiting around the nucleus are the electrons. Each unique
element has an Atomic Number equal to the number of protons it
contains. There are 94 naturally occurring elements (1-94) and
others which have been artificially created (95+..) Each element has
an Atomic Weight for the most commonly found isotope. Atomic
Weight = number of protons + number of neutrons. See: The
Periodic table In a stable uncharged atom the number of electrons
Model of a Lithium atom
Atomic Structurewill equal the number of protons. If the number of electrons is
changed the atom will become ionized and gain either a positive
(fewer electrons) or negative (greater electrons) charge.
The same element can exist in different forms, each form having the
same atomic number, but different mass numbers. These forms are
called isotopes. Isotopes that cannot decay during a defined period
are called stable isotopes. And isotopes that can decay during a
defined period are called unstable (or radioactive) isotopes. For
example :
1
2
3
1H
1H 1H
Protium. Deuterium.
Tritium.
Tritium is an unstable isotope of hydrogen.
IsotopesBohrs model Electrons are considered to move around the nucleus
in fixed shells (orbits), at various energy levels. These levels may be
designated K L M N shells ........ or 1 2 3 4 ........... Orbits . The first
level contains only 2 electrons. The second level can hold
6electrons. The number of maximum electrons that can occupy one
shell s defined by the formula of 2nî or 2 n square , where n is the
number of the shell
When the electrons are excited, then they can transfer between the
shells. As we move away from the nucleus, the energy levels
increase.electrons have their own energy and the energy increases
with increasing the n value or orbit
The configuration of electrons occupying the least amount of space
(Bohrs model) is called the ground state. But when electrons are
excited (by getting electricity, heat), they jump to a higher level.
This condition of the atom is called an excited state. When the
electrons return to the ground state they give off energy.
All energy levels contain sublevels known as s p d f.
Excited state of atom
Levels and sublevelsS sub level can contain 2 electrons. (One pair.)
P can contain 6 electrons. (Three pairs.)
D can contain 10 electrons. (Five pairs.)
F can contain 14 electrons. (Seven pairs.)
The first shell has only the sublevel s and therefore has only 2
electrons The second shell has both the sublevel s & p and can hold
8 electrons The third shell has the sublevel s,p & d and can hold 18
electrons The fourth and the last shell has the sublevel s,p,d & f and
can hold 32 electrons.
The regions around a nucleus where the probability of finding an
electron of a particular energy level is highest are called orbitals.
An Orbital can hold only two electrons. They are spinning opposite
ways. They are called orbital pairs. 'n' represents principal
quantum number or simply the number of the shell. So nth shell
contains n^2 number of orbitals hence 2*n^2 number of electrons.
The shape of orbital depends on the sublevel.
Valence electrons revolve in valence shells.
Orbital
ValenceElectrons that can enter into a reaction are only at the last level.
These electrons are called valence electrons. The maximum
number
of valence electrons is 8. The Valence determines how many
electrons the atom has to borrow or lend. All parts of atoms except
the last orbit are called a kernel.
The electron dot formula represents the valence electrons.
Examples: . .
. N . The dotted formula of
the nitrogen.
.
Ionization energy is the amount of energy needed to remove or add
an electron from a gaseous atom or ion. Ionization energy depends
on the number of protons in the nucleus and the shielding
(screening) of the inner electrons.
Radioactivity
Structure of The Atom
Ionization energy
See alsoContent is available under CC BY-SA 3.0 unless otherwise noted.
"The Three Isotopes of Hydrogen - Video & Lesson Transcript |
Study.com" . study.com. Retrieved 2018-09-18.
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