Atomic Theory of Matter
All About Matter
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composed of molecules and made up of atoms.
defined as anything that occupies space and has mass.
can exist in any one of three states: solid, liquid and gas.
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Elements, compounds and mixtures
Compounds
Mixtures
Elements
substance that cannot be reduced to a simpler form by chemical means
formed when two or more elements are chemically combined
separated by chemical means and not by physical means
Elements and compounds which exist in another combination
separated by physical means and not by chemical means
Atoms and Molecules
Atoms
Molecules
smallest particle of an element and retains all the characteristics of that element
have sub-atomic particles, known as electrons, protons, and in most cases, neutrons.
electrons
negatively charged
protons
positively charged
neutrons
no charge
form the heavy and positively charged nucleus of each atom
revolve or orbit the nucleus
classified numerically
number of protons in the nucleus of an atom determines its atomic number
All atoms within an element, in its neutral state, will have an equal number of protons and electrons
chemical combination of two or more atoms, into which a pure substance can be divided whilst still retaining its composition and chemical properties.
Types of chemical bonding
Ionic
Covalent
occurs between a metallic element and a non-metallic element
results in the transfer of electrons from a metal to a non-metal to obtain a full valence shell for both atoms
occurs only between two non-metallic elements
results in the sharing of electrons allows each atom to attain the equivalent of a full valence shell
Energy levels
An electron in an atom has mass and revolves in motion about the nucleus. As it is moving around the nucleus, an electron has kinetic energy and due to its position in space, it also has potential energy.
electron’s total energy (kinetic and potential energies) determines the radius of the electron orbit. According to Newton’s Laws of Motion, it must not lose or gain energy for it to remain in its original orbit. But at the sub-atomic level, electrons are always losing or gaining energy, so they will be moving from orbit to orbit
If light (tiny packets of energy called Photons) is shone at an atom and if a photon of sufficient energy collides with an orbital electron, the electron will absorb some or even all the photon’s energy. As a result, the electron will jump to a new orbit, further away from the nucleus.
Once an electron has been elevated to an energy level higher than the lowest possible state, the atom is said to be in an “excited state”
But, an electron does not remain in the “excited state” for more than a fraction of a second before it releases the excess energy and returns to a lower energy orbit
Atomic shells and sub-shells
When an element is in a stable state, the electrons reside in a collection of orbits called shells. These shells are elliptical and arranged in steps that correspond to fixed energy levels
Using Pauli’s exclusion principle, each shell will contain a maximum of 2n2 electrons, where “n” corresponds to the shell number, starting with the one closest to the nucleus
The shells, starting with the shell closest to the nucleus and progressing outward, are labelled 1 to 7 or K to Q respectively. Each of the shells, K to Q, is a major shell and can be divided into one of four (4) sub-shells (s, p, d, and f).
Ionization
An atom becomes ionized when it loses or gains an electron.
An atom, which gains an electron, will have a resultant negative charge, and is called an anion (negatively charged ion).
An atom, which loses an electron, will have a resultant positive charge, and is called a cation (positively charged ion).
Conductors, semiconductors and insulators
Conductors
Semiconductors
Insulators
very low resistance to the flow of electric current
can conduct electricity very easily
extremely high resistance to the flow of electric current
cannot conduct electricity easily
atoms making up the crystal structure are tightly packed together
valence electrons can move freely from atom to atom
high mobility of electrons results in good electrical conductivity
very few free electrons
break down and conduct electricity
can be manipulated to be either a conductor or an insulator
conductive state of a semiconductor can be made to vary with temperature or by adding impurities to the semiconductor crystal
Intrinsic and extrinsic
Intrinsic
Extrinsic
usually made of pure crystals
conductivity rises with temperature
conductivity depends on introducing impurities into intrinsic semiconductors and the process is known as doping
Static electricity
A body of matter, if wholly composed of neutral atoms, will be electrically neutral and is said to have a zero charge.
When the matter comes into contact with other neutral bodies, electrons will not be gained or lost.
If a matter loses any electron from its atoms, there will consequently be more protons than electrons and it will become electrically positive. When this positively charged body come into contact with another matter having a negative charge, an electric current will flow between them.
The electrons from the negatively charged body will leave it and enter the positively charged body to achieve neutrality
When two bodies having opposite charges are placed near each other but not touching, a force is exerted between them. Their charges cannot equalize since the two bodies are not in contact and a current cannot flow. This force is known as an electrostatic force and is the basis for static electricity
The fundamental law of physics and electricity: Like charges repel, unlike charges attract.
Friction
one of the easiest ways to introduce a static charge
Electrons can be transferred from one body to another during the process of rubbing
for good conductors of electricity
difficult to detect a net gain or net loss in charge since an equalizing current flows easily between the conductors
for bad conductors of electricity
difficult for an equalizing current to flow between them. Therefore, a net gain or net loss in charge can be easily obtained
Electrostatic discharge
sudden and momentary electric current flow between two bodies of different electric potential
can seriously damage integrated circuits and can potentially cause immediate or latent failures