2 History of the AtomDemocritus argued that atoms were the smallest particles of matter.The atom comes from the Greek word atomos that means “not able to be divided”.
3 John Dalton Dalton proposed the first atomic theory. 1) All matter is made of atoms. Atoms are indivisible and indestructible.2) All atoms of a given element are identical in mass and properties3) Compounds are formed by a combination of two or more different kinds of atoms.4) A chemical reaction is a rearrangement of atoms.
4 J.J. ThomsonThomson discovered negatively charged particles called electrons.Designed the “plum pudding” model.
5 Ernest RutherfordRutherford discovered that atoms contain a small, dense, positively charged center called the nucleus.
6 Niels BohrBohr suggested that electrons (which have a negative charge) moved around the nucleus at certain fixed distances.ElectronsNucleusElectrons
7 According to the current atomic theory, electrons are most likely to be found in the electron cloud around the nucleus.Electron Cloud
8 Dmitri MendeleevRussian chemistCreated the periodic table
15 CompoundsA substance made of two or more elements chemically combined form a compound.Example: NaCl, H2O, CO2
16 Parts of the AtomProton: a positively (+) charged particle of the nucleus.Neutron: a neutral particle of the nucleus.Electron: a negatively (-) charged particle around the nucleus.
17 Electron (Shell) Cloud (levels or orbitals) Neutron (neutral)Nucleus(98% of the mass of atoms)Proton (+)Electron (Shell) Cloud (levels or orbitals)
18 Atomic Mass Unit (amu): the SI unit for the masses of particles in atoms. Atomic Number: the number of protons in the nucleus of an atom.Mass Number/Atomic Mass: the number of protons and neutrons in an atom.Atomic Mass: the weighted average of the masses of all the naturally occurring isotopes of an element.