Atom theory

• Atom model is the model used to describe the structure of an atom
• Model is the three-dimensional representation of a person or thing
• the atomic model has changed throughout the centuries, starting in 400 BC, when it looked like a billiard ball
• Democritus is a greek Philosopher who conceived the idea of indivisible units called atoms
• Democritus' theory was ignored and forgotten\ for more than 2000 years
• Leucippus of Miletus is the teacher of Democritus
• Democritus' Theory

  1. All matters are composed of atoms, which are bits of matter too small to be seen. These atoms cannot be further split into smaller portions.
  2. There is a void, which is an a spaceempty space between atoms.
  3. Atoms are completely solid
  4. Atoms are homogeneous, with no internal structure
• "Atomos means "Atom" in Greek, as proposed by Democritus
• Empedocles proposed that matter is made up of four elements which are earth, water, air, and fire
• Aristotle rejected the idea of atoism of matter. He also believed that there is not limit to subdividing matter.
• Joseph John Thomson discovered electrons through cathode ray tube experiment
• In 1803, John Dalton proposed generalizations about atoms:

  1. Atoms are the smallest particles of matter. They cannot be divided into smaller particles.
  2. all atoms of an element are identical, but they differ from atoms of other elements in terms of mass, size, and properties.
  3. In chemical reactions, atoms cannot be created or destroyed. They simply combine, separate, or rearrange.
  4. Atoms of two or more elements combine to form compounds in ratios of simple whole numbers.
  5. atoms of the same element can unite in more than one ratio to form more than one compound.
• Isotopes are atoms of an element that have the same atomic number but different mass.
• Nuclear charge is the total charge of all protons in the nucleus. Has the same value as the atomic number.
• Henry Mosely discovered or proposed the idea of atomic number in 1913.
• The three laws of matter are:

  1. Law of Conservation of Mass
  2. Law of Definite Proportion
  3. Law of Multiple Proportion
• Law of Conservation of Mass is when the total mass of substances present at the end of a chemical reaction is the same as before the process.
• The law of Definite Proportion is when a chemical compound always contains the same elements combined thein the same proportion by mass.
• The law of Multiple proportion is when two elements can combine to make more than one compoundproportions
• Atom has two regions: Nucleus and Electron Cloud
• Nucleus is the center of the atom that contains most of the mass
• Electron Cloud surrounds the nucleus and takes up most of the space
• Inside the nucleus there are: Protons and Neutrons
• Inside the Electron Cloud we find: Electrons
• Protons are positively charged subatomic particles
• Neutrons are neutrally charged subatomic particles
• Electrons are negatively charged subatomic particles and relatively no mass.
• Atomic Number is the number of protons in the nucleus of an atom
• in a neutrally charged atom, the number of protons is equal to the number of electron inside the atom
• Mass number of the nucleus of an atom is equal to the number of protons and neutrons
• IUPAC stands for International Union of Pure and Applied Chemistry
• Atomic Mass of an atom expressed in atomic mass unit (amu)
• One amu is defined as a mass equal to 1/12 the mass of the single carbon-12 atom
• Atomic Weight is the ratio of the average atomic mass in different isotopes of that particular element