Atoms

Atoms Elements are made of individual particles called atoms Every atom is made of 3 parts: Protons Neutrons Electrons

Atoms (cont.) Protons: positive charge Nucleus Neutrons: neutral, no charge Electrons: negative charge Travel around the nucleus, creating a cloud Nucleus

Protons All atoms have a specific number Identifies the element Change the number, change the element Proton # = Atomic # Shown on periodic table

Add them together = atomic mass Use atomic # to find # of protons Write this down! Protons and Neutrons Add them together = atomic mass Use atomic # to find # of protons Use atomic mass to find number of neutrons

# of electrons = # of protons Electrons are so small, they do not really contribute to the mass

Bohr suggested that electrons orbit the nucleus in levels Bohr Model Bohr suggested that electrons orbit the nucleus in levels This is not technically correct. It is used more as a representation.

Another view

Energy Levels First level = 2 electrons Second level = 8 electrons Third level = 18 electrons Fourth level = 32 electrons Outer level has greatest effect on properties - called Valence electrons Outer level can never have more than 8 electrons

Chemical symbols used to represent elements First letter = CAP Second letter = lower case

Same element - different number of neutrons Changes the atomic mass Isotopes Same element - different number of neutrons Changes the atomic mass

Example of Isotopes - Carbon