Studied by 9 people
Aristotle assumed..
All substance was made up by the four elements, fire, air , earth and water.
John Dalton described atoms as..
Indestructible, small, sphere-shaped, solid particles with a fixed shape.
Antoine Lavoisier
Father of modern chemistry, law of conservation of matter based on his investigations.
Joseph Louis Proust (JLP)…
Law of definite proportions, states elements combine to form compounds in already defined proportions.
Law of Multiple Proportions
Postulated by Dalton. States elements can be combined in more than one proportion.
Dalton’s postulates of his atomic theory…
All elements made of atoms.
Atoms of same element are identical, if element is different so is atom.
Atoms in an element are not created nor destroyed during a chemical reaction, they are reorganized.
ATOM MODEL 1: DALTON - 1803
First atom model, simplest.
ATOM MODEL 2: JJ THOMSON’S - 1904
Carried experiments with cathode rays and magnetic fields. He discovered atoms have charges, electrons. He invented first mass spectrometer.
He called electrons corpuscles, electrons distributed evenly in atom. Atom is neutral due to balance of positive and negative charge, conceived atom as a compact invisible particle.
ATOM MODEL 3: E. RUTHERFORD - 1911
He used radioactivity to determine atomic structure.
He established atom has 2 regions, a shell and a nucleus, with a positive charge and, electrons (negative charge) that surround the nucleus.
Named positive particles protons and declared the amount of electrons and protons inside the atom is equal.
Nucleus conforms most of atom mass, its volume is mostly empty space.
ATOM MODEL 4: N. BOHR’S - 1913
Interested in knowing function of electrons, did experiments to measure the energy of electrons. He exposed a hydrogen atom to energy, witnessed an emission of light and proposed an explanation.
assumed electrons were divided in orbits with a different amount of energy each, called them energy levels.
Stated that electrons can change of energy level by absorbing energy and acquire an excited state.
When electrons jump between orbit levels, a photon is emitted or absorbed, and its energy is the difference of energy between levels.
(Energy levels symbolized with letter n, n: 1, 2, 3…)
WAVE THEORY
One of the most valuable contributions to the knowledge of the atom.
Based on Christian Huygens’s theory, that considers light an electromagnetic wave, and Isaac Newton’s proposal about light being composed of corpuscles which explains the phenomena of refraction and reflection of light.
Dual behavior of light, as a WAVE and as a PARTICLE.
Planck’s Quantum Theory…
Max Planck discovered that atoms and molecules emit energy in form of energy packets or quanta. This discovery marked the beginning of the study of modern physics
WAVELENGHT
Distance between 2 adjacent crests or troughs.
FREQUENCY
Number of wavelengths that pass through a given point every second.
AMPLITUDE
Vertical distance from the middle line of a wave to its crest.
ELECTROMAGNETIC SPECTRUM
It is the energy that travels as waves. There are different types of energies and they differ by their frequencies and wavelengths.
The radio waves have longer wavelengths and a low frequency, while the gamma ray waves have shorter wavelengths and high frequency.
In the electromagnetic spectrum, these are on opposite sides, the radio, on the left side and with the lowest energies, and the gamma ray on the right side with the highest energies.
The higher the frequencies, the more dangerous they are to humans.
PRINCIPLE OF DUALITY 1924
By Louis de Broglie, explained that matter behaves just as light does, relationship between the atom and light.
UNCERTAINTY PRINCIPLE
By Werner Heisenberg, postulates that it is impossible to know simultaneously the speed and position of an electron.
WAVE EQUATION - Schrödinger
The probability function of finding an electron at a certain point in space, these probability spaces around the nucleus are called atomic orbitals.
(In terms of the wave behavior of the electron)
An atomic orbital..
Is a region in space around the nucleus where the electron can most likely be found and where the energy in this region is constant.
Each of the orbitals has a different shape.
AMQ (Angular momentum quantum) or SECONDARY QUANTUM NUMBER relationship with principal quantum number.
Spin quantum number (ms)
Refers to the two possible spins of the electron, one clockwise and one counterclockwise.
PAULI’S EXCLUSION PRINCIPLE
There cannot be 2 electrons in the same orbital (atom) that have the same values of n, l and m.
ELECTRON CONFIGURATION
Most stable arrangement of electrons with the ground energy within an atom.
In order to make an electron configuration you need the atomic number of the element (on top of the letter of the element, amount of protons).
ATOM
Basic unit of a substance that cannot be broken down chemically, so small that it cannot be seen through any microscope. Made up of protons, electrons and neutrons.
Electrons..
Discovered by JJ Thomson through cathode rays, negative charged particles.
Protons..
Described by Rutherford through experiment with gold foil, positive charged particles.
Neutrons..
Described by Chadwick through bombarding boron atoms, no charge because of lack of electrical charge.
ATOMIC NUMBER
Represents the identity of the element. Indicates amount of electrons in the element. Amount ELECTRONS = amount PROTONS.
ATOMIC MASS
Sum of neutrons and protons in the nucleus.
ELEMENTS IN EARTH AND HUMAN BODY
118 elements currently known, 90 are found naturally.
96% of human body mass is formed by carbon, hydrogen, oxygen and nitrogen. Contains more oxygen than any other element.
