Basic concepts

Atom

What are Atoms

• Atoms are building blocks of matter thatmake up everyday objects.

• A desk, air and even you are made up ofatoms.

• There are 90 naturally occurring kinds ofatoms.

Subatomic particles

subatomic particle is a particle smaller than an atom:

it may be elementary or composite.

• Protons – carry a positive charge

• Neutrons- carry no charge

Protons and neutrons join together and form nucleus.

• Electrons - carry negative charge and circle the nucleus.

Isotopes

• Isotopes are atoms with the same number of protons , but differing numbers of neutrons . Isotopes are different forms of a single element .

• For example, the most common isotope of hydrogen has no neutrons at all; there's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.

Hydrogen Deuterium Tritium

Orbit

• Unlike planets orbiting the Sun, electrons cannot be at any arbitrary distance from the nucleus; they can exist only in certain specific locations called allowed orbits.

How do the electron orbits work?• Each orbit around the nucleus represents an energy level, and electrons

cannot exist in between orbits. Orbits closer to the nucleus have lower energy.

• If energy is added, an electron can be "excited" to jump to a higher energy level and orbit farther from the nucleus. Eventually, though, the electron will return to its original state, and the atom will give off energy equal to the difference between the two orbits.

Orbital versus Orbit

• The definition of orbital is "a wave function describingthe state of a single electron in an atom (atomic orbital)or in a molecule (molecular orbital)." and also "the wavefunction of an electron in an atom or molecule,indicating the electron's probable location.“

• The definition of orbit is "Physics. (in Bohr theory) thepath traced by an electron revolving around the nucleusof an atom.

Shell

• An electron shell may be thought of as an orbit followed by electrons around an atom nucleus.

• Shell Basics

• Let's cover some basics of atomic shells:1. The center of the atom is called the nucleus.2. Electrons are found in areas called shells. A shell is sometimes called an energy level.3. Shells are areas that surround the center of an atom.4. Each of those shells has a name (K, L, M...).

How many electrons fit in each shell

around an atom?• The maximum number of electrons that can occupy a specific energy level can

be found using the following formula:

Electron Capacity = 2n2

• The variable n represents the Principal Quantum Numberthe number of the energy level in question.

Energy Level• (Principal Quantum Number) Shell Letter Electron Capacity• 1 K 2• 2 L 8• 3 M 18• 4 N 32• 5 O 50• 6 P 72

Subshell

• Definition: A subshell is a subdivision of electron shells separated by

electron orbitals.

Subshells are labelled s, p, d, and f in an electron configuration.

Subshell label Max es- shells containing it History

s 2 Every shell sharp

p 6 2nd shell and higher principal

d 10 3rd shell and higher diffuse

f 14 4th shell and higher fundamental

g 18 5th shell and higher (next in alphabet

(theoretically) after f)

Conductors

• Conductors are made of materials that electricity can flow through easily.These materials are made up of atoms whose electrons can move away freely.

• Examples:

copper Aluminum Gold

insulators

• Insulators are materials opposite of conductors. The atoms are not easily freed and are stable, preventing or blocking the flow of electricity.

Examples:

Glass Rubber Plastic

Electron theory

• Electricity is the movement of electrons through a conductor. Electrons areattracted to protons. Since we have excess electrons on the other end of theconductor, we have many electrons being attracted to the protons. Thisattraction sort of pushes the electrons toward the protons. This push is normallycalled electrical pressure. The amount of electrical pressure is determined bythe number of electrons that are attracted to protons.

• The electrical pressure or electromotive force (EMF) attempts to push anelectron out of its orbit and toward the excess protons. If an electron is freedfrom its orbit, the atom acquires a positive charge because it now has one moreproton than it has electrons. The unbalanced atom or ion attempts to return toits balanced state so it will attract electrons from the orbit of other balancedatoms. This starts a chain reaction as one atom captures an electron andanother releases an electron. As this action continues to occur, electrons willflow through the conductor. A stream of free electrons forms and an electricalcurrent is started.

Electron theory

• So far we have described current as the movement of electrons through a

conductor. Electrons are negatively charged particles that move toward

something that is positively charged. Electrons move because of this

potential difference. This describes one of the common theories about

current flow.

• The electron theory states that since electrons are negatively charged,

current flows from the most negative to the most positive point within an

electrical circuit. In other words, current flows from negative to positive.

This theory is widely accepted by the electronic industry.

Electron theory

Two theories describe current flow:

1- The conventional theory, commonly usedfor automotive systems, says current flowsfrom (+) to (-) ... excess electrons flow froman area of high potential to one of low potential

(-).

2 -The electron theory, commonly used forelectronics, says current flows from (-) to(+) ... excess electrons cause an area ofnegative potential (-) and flow toward an arealacking electrons, an area of positive potential(+), to balance the charges.

References

• http://education.jlab.org/atomtour/

• http://education.jlab.org/qa/electron_number.html

• http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Electron_shell.html

• http://www.chem4kids.com/files/atom_orbital.html

• http://autolabscopediagnostics.com/electron.htm