The structure of the atom. Chemistry The structure of the atom.

The Atomic Theory: All matter is made of atoms, which are particles too small to be seen. Each element has its own kind of atom.

The evolution of the atomic Theory: Dalton Rutherford’s gold foil experiment Bohr models Quantum Mechanics All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the different elements coming together.

Sub Atomic Particles + 1 1 - Subatomic Particle Charge Mass (Amu) Atomic mass units Where it is located in an atom Proton Neutron Electron Inside the nucleus + 1 1 Inside the nucleus - Basically 0 Orbiting outside the nucleus

The Modern Theory of Atomic Structure: Atomic number: The number of protons in the nucleus of an atom of that element. Gives the number of electrons in a neutral element. Gives the order of elements on the periodic table If an atom gains or loses a proton it not only changes its atomic number, it also becomes a new element.

The Modern Theory of Atomic Structure: Mass number: is the total number of protons and neutrons in the nucleus of an atom How do we find the number of Neutrons? (mass number) - (atomic number) =# of neutrons

Bohr’s Model of Electrons: Suggested that electrons move around the nucleus of an atom in orbits or shells. Each orbit is a certain distance from the nucleus and contains a definite number of electrons. The orbits are filled in a routine way: First orbit: 2 electrons Second orbit: 8 electrons Third orbit: 8 electrons

Bohr model of Nitrogen: Check your periodic table for Nitrogen 7 -3 N Nitrogen 14.0

Bohr model for Magnesium:

Bohr Model for Argon

Isotopes Atoms of the same element that have different numbers of neutrons Two ways to recognize isotopes: Isotope Name: Chemical name – mass # Example: Carbon -11, Carbon -12, Carbon -13 Isotope Symbol: Example: Chemical Symbol of element Mass number X atomic number

Isotopes: The Isotope symbol makes it easy to find the number of neutrons

Atomic mass: The weighted average of the mass an element’s naturally occurring isotopes. A “weighted average” means you take into account the % of each isotope that is present in an ordinary sample of the element.

Example: A particular sample of carbon has 10% carbon-11, 80% carbon-12, and 10% carbon-13. Calculate the atomic number of this sample of carbon.