PS 3 Atomic Structure
PS 3 Atomic Structure

• The atom is the basic building block of matter and consists of subatomic particles (protons (+), neutrons, electrons (-), and quarks) it has an overall neutral charge

• Protons, electrons and neutrons differ in their location, charge, and relative mass.

• Protons and neutrons are made up of smaller particles called quarks and they are found inside the nucleus of an atom

• Size at the atomic level is measured on the nanoscale

• Scientists use models to help explain the structure of the atom

• The understanding of the structure of the atom continues to evolve

• There are 2 commonly used models-the Bohr model and the “electron cloud” model

• Electrons are found only in certain zones around the nucleus called electron shells. The outermost shell, the valence shell, has the electrons used for the bonding.

• Electrons: have a negative (-) charge. They are in rapid, continuous motion around the nucleus.

• The proton has a positive (+) charge. The number of protons determines the atomic number.

• The nucleus is the tiny, dense cluster of protons and neutrons in the center of the atom and has a positive charge

• Neutrons are neutral (no charge). The # of neutrons plus the # of protons is the atomic mass.

• The mass of an electron is smaller than the mass of a proton.

• The outermost electrons in an atom are called valence electrons

• Most of the mass of an atom is found in the nucleus

• The electron cloud makes up most of an atom’s volume

• The electron orbit refers to the travel of electrons around the nucleus of an atom

• The outer rings are the energy levels

Democritus
• Greek idea of an atom
• His term atomos became atoms

John Dalton
• Atom is a solid sphere like balls or marbles
• First person to propose an atomic theory
• Matter seemed to consist of particles
• All elements are made up of atoms
• Atoms of the same element are identical
• Compounds are made from joining two atoms
• Atoms are too small to see
• Atoms of different elements had different masses/properties

JJ Thomson
• Plum pudding model
• Discovered electrons
• Positively charged material/sphere with negative particles embedded within

Earnest Rutherford
• Gold foil experiment-decided electrons orbited a positive center
• Atom has a nucleus
• Atom is an empty space with a dense positively charged nucleus and electrons orbit the nucleus

Niels Bohr
• Atom has a nucleus
• Planetary model
• Electrons could only orbit at certain distances from the nucleus/electrons move in definite orbits
• Electrons in a fixed shell
• Atom absorbs or gives off specific amount of energy when electrons move from one shell to another
• Large sphere in the middle with a positive charge and negatively charged electrons revolving around the center

Modern Model (Schrodinger and other scientists)
• Atoms have a nucleus and it is positively charged
• Negatively charged cloud of electrons giving the atom its size
• Attempts to show the three dimension shape of an atom, but location of electrons is not known
• Arrangement of electrons are different from Bohr’s model