atoms

• Atoms are the smallest particles that can exist independently.
• Protons have a positive charge, while electrons have a negative charge.
• THALES OF MELLITUS- Was the first important Greek scientist of record to speculate about the composition of matter. He noted that in both the synthesis, during life and the decomposition after death, water appeared to be the most importantly involved. He therefore assumed that water was the essence of all things, that it was the primary element.
• DEMOCRITUS - The father of atomic theory. He believed that everything is made up of tiny indivisible particles called "atoms".
• ANAXIMENES - Chose air as his primary element.
• HERODOTUS - Thought it was a fire
• PYTHAGORAS - Forsook the concept of a single primary element for one involving all three: water, air, fire plus a fourth, earth.
• EMPEDOCLES - Who develop this concept, that matter was composed of four elements – earth, air, water and fire.
• ARISTOTLE - Endorsed and advanced the theory of Empedocles. said there was no limit to division of matter.
• LEUCIPPE OF MILET - The first person recorded to believe that all matter consisted of atoms. He proposed that if one were to cut a piece of any element into smaller and smaller bits, it would eventually yield “uncuttable” particles called atomos (from where the word atom was derived meaning uncut or indivisible).
• PIERRE GASSENDI - Freed the atomism from atheism saying that atoms move not by themselves but as a gift of God. He believed that atoms form groups which he called molecule and holding together the group are mechanical forces.
• JOHN DALTON - An English school teacher who began the modern atomic theory. ❑ He used his knowledge of gases in the atmosphere as a model for the atom of his experiments. ❑ He concluded that all atoms of an element have the same size and weight and the atoms of elements unite chemically in simple numerical ratios to form compounds.
• dalton's model - solid sphere model or bowling ball model
• Joseph John Thompson’s Model - Plum Pudding Model
• Joseph John Thomson - an english scientist who provided the first evidence for the existence of the electron.
• ERNEST RUTHERFORD's model - nuclear model
• Niels bohr - proposed that electrons orbit the nucleus in shells.
• Niels bohr's model - planetary model
• Erwin schrodinger - quantum model
• Louis de Broglie - Proposed that the electron (which is thought of as a particle) could also be thought of as a wave.
• Erwin Schrodinger - used the idea of de Broglie (that electrons are wave particles) to develop a mathematical equation to describe the probable location of an electron around the nucleus
• Werner Heisenberg - discovered that for a very small particle like the electron, its location cannot be exactly known. This is called the Uncertainty Principle
• Johann Dobereiner - a German chemist who formed the triads of elements with similar properties. • made the first attempt to group similar elements in triads or three. He observed that the properties of the groups of elements were alike in many ways. • He observed that certain appropriate numerical relationship exists among atomic weight of elements having similar properties, when arranged in increasing atomic weight: the middle element is almost equal to the average of the atomic weight of the first and the last element
• Julius Lothar Meyer; Dimitri Ivanovich Mendeleev - both came up with periodic tables that showed how elements should be grouped.
• Henry Moseley - an English physicist observed that the order of the x-ray frequencies emitted by elements follows the ordering elements by atomic number.
• nucleus - central part of atom
• ATOMIC NUMBER - Represents the number of protons in the nucleus. It was determined by Henry Mosely.
• ATOMIC MASS/WEIGHT - a measurement of the total number of particles in an atom’s nucleus. The atomic weight is actually a weighted average of all naturally occurring isotopes of an element. All you need to find is the mass number.
• MASS NUMBER - The sum of the number of protons and the number of neutrons in an atom. • (number of protons + number of neutrons)
• IONS - If electrons are removed from or added to a neutral atom, it is therefore a charged particle of the same element
• CATION • a positively charge ion is formed when an electron is removed from the atom (+).
• ANION • a negatively charged ion is formed when an electron is added to the atom. (-).
• Electron Configuration • The distribution of electrons among the orbitals. • The summary of where the electrons are around a nucleus.
• Aufbau Principle • It says that the electrons fill the orbitals one at a time, starting with the lowest energy orbital then proceeding to the one with higher energy. • The higher the number of the main energy levels, the higher the energy. • The relative energies of the sublevels are not simple step ladder increase, there are overlaps. For example, the 3d orbitals have higher energy than the 4s orbital.
• Pauli’s Exclusion Principle • States that two electrons may occupy an orbital and they must have opposite spins. • The two spins orientations are loosely designated as clockwise and counter clockwise spins. They are also represented by an arrow pointing up and arrow pointing down. The arrows represent the electrons. Arrows pointing in opposite directions designate the opposite spins of the electrons.
• Hund’s Rule • States that the electrons occupy separate orbitals on the same subshell with parallel spins first before pairing.