Atoms and Atomic Structure
by Owen Borville
September 12, 2019 updated 10/9/22
Learning, Physical Science, Chemistry, Physics
Atomic Models in History
Ancient Greeks=400 B.C. Democritus=believed matter was composed of tiny, indivisible particles.
Aristotle=the competing model=believed matter could be subdivided unlimited times
18th century= John Dalton=based on experimental evidence from the law of definite proportions believed:
=elements are made of atoms
=atoms are indivisible
=atoms of an element are alike
=atoms of different elements are different
=atoms combine chemically in small, whole number ratios=law of definite proportions
Discovery of the Electron=1904=JJ Thompson discovered the electron, thus proving that the atom is not indivisible=negative charges electrons surrounding a positively charged nucleus=the plum pudding model=cathode ray tube
Nuclear Model=1911=the discovery of the nucleus in the center of the atom was the framework of the nuclear atomic model. The famous gold foil experiment showed that alpha particles were deflected from the center of the atom represented by a gold foil=the nucleus was predicted to be a small, dense, positively charged center surrounded by mostly empty space. Neutron particles were also discovered to occupy the nucleus along with similar sized proton particles to form the mass of the nucleus.
The Bohr Model=1913=The atomic model proposed by Niels Bohr included spherical orbital energy levels that electrons existed and travelled through around the nucleus. The energy level that the electron travelled through depended on how much energy the electron had and that electrons could jump from one energy level to another. Energy is emitted in the form of photons when an electron loses energy.
Quantum Mechanical Atomic Model=1926
Further research indicated that electrons did not travel in perfect circular orbits around the nucleus as Bohr envisioned, but rather in more complicated orbital patterns that differ in shape and direction. The orbital patterns describe where the electrons are likely to be found. All of the orbitals together form the "electron cloud" of the atom. The quantum mechanical model is still the atomic model used today.
An atom is the smallest unit of an element that has certain chemical properties.
An element is one specific type of atom that has certain chemical properties.
A compound is a substance containing two or more atoms chemically bonded together.
A molecule is the smallest unit of a compound that has defined chemical properties.
An ion is an atom or group of atoms bonded together that has an electric charge. Cations are positively charged ions and anions are negatively charged ions.
A proton is a positively charged sub-atomic particle located in the nucleus, or central portion of the atom.
A neutron is a subatomic particle with no charge that is located in the nucleus.
An electron is a negatively charged subatomic particle that orbits or rotates around the nucleus of the atom and has a mass much less than protons and neutrons. Atoms can have several electrons orbiting around the nucleus.
The Atomic Number is the number of protons in one atom.
The Atomic Mass Number is the number of protons and neutrons in an atom.
An isotope of an atom is an atom with same atomic number (protons) but different number of neutrons.
by Owen Borville
September 12, 2019 updated 10/9/22
Learning, Physical Science, Chemistry, Physics
Atomic Models in History
Ancient Greeks=400 B.C. Democritus=believed matter was composed of tiny, indivisible particles.
Aristotle=the competing model=believed matter could be subdivided unlimited times
18th century= John Dalton=based on experimental evidence from the law of definite proportions believed:
=elements are made of atoms
=atoms are indivisible
=atoms of an element are alike
=atoms of different elements are different
=atoms combine chemically in small, whole number ratios=law of definite proportions
Discovery of the Electron=1904=JJ Thompson discovered the electron, thus proving that the atom is not indivisible=negative charges electrons surrounding a positively charged nucleus=the plum pudding model=cathode ray tube
Nuclear Model=1911=the discovery of the nucleus in the center of the atom was the framework of the nuclear atomic model. The famous gold foil experiment showed that alpha particles were deflected from the center of the atom represented by a gold foil=the nucleus was predicted to be a small, dense, positively charged center surrounded by mostly empty space. Neutron particles were also discovered to occupy the nucleus along with similar sized proton particles to form the mass of the nucleus.
The Bohr Model=1913=The atomic model proposed by Niels Bohr included spherical orbital energy levels that electrons existed and travelled through around the nucleus. The energy level that the electron travelled through depended on how much energy the electron had and that electrons could jump from one energy level to another. Energy is emitted in the form of photons when an electron loses energy.
Quantum Mechanical Atomic Model=1926
Further research indicated that electrons did not travel in perfect circular orbits around the nucleus as Bohr envisioned, but rather in more complicated orbital patterns that differ in shape and direction. The orbital patterns describe where the electrons are likely to be found. All of the orbitals together form the "electron cloud" of the atom. The quantum mechanical model is still the atomic model used today.
An atom is the smallest unit of an element that has certain chemical properties.
An element is one specific type of atom that has certain chemical properties.
A compound is a substance containing two or more atoms chemically bonded together.
A molecule is the smallest unit of a compound that has defined chemical properties.
An ion is an atom or group of atoms bonded together that has an electric charge. Cations are positively charged ions and anions are negatively charged ions.
A proton is a positively charged sub-atomic particle located in the nucleus, or central portion of the atom.
A neutron is a subatomic particle with no charge that is located in the nucleus.
An electron is a negatively charged subatomic particle that orbits or rotates around the nucleus of the atom and has a mass much less than protons and neutrons. Atoms can have several electrons orbiting around the nucleus.
The Atomic Number is the number of protons in one atom.
The Atomic Mass Number is the number of protons and neutrons in an atom.
An isotope of an atom is an atom with same atomic number (protons) but different number of neutrons.
