Structure of an atom Review Stuff
Structure of an atom
 An atom is the smallest unit of matter that can exist while still retaining the
properties/identity
 Consists of two different regions – Nucleus & electron Cloud
o Nucleus
 Located in the center of the atom
 Made up of Protons and Neutrons
 Overall charge of the nucleus is positive (+)
 Protons
o Positively charged (p+)
o The # of protons is the same as the atomic #
o The # of protons = the # of electrons
 The charges need to balance each other out so
that the atom has an overall charge of zero
o Protons help make up the mass of the nucleus (they
have mass)
o Protons (atomic #) can never change because they
serve as DNA to atom
 Mass Number
o The mass number is a WHOLE number –(it is the atomic
mass rounded to a whole number)
o Mass number = protons + neutrons
 Neutrons
o Neutrons have no charge, they are neutral (n0)
o Located in the nucleus
o The number of Neutrons can vary based on the existing
isotope
o To find neutrons: Mass # - atomic # =neutrons
o Electron Cloud/ Electron Orbital
 Located around the nucleus
 Contains electrons
 Electrons
o # of electrons are = # of protons
o Electrons move rapidly inside their electron cloud
o Electrons have a negative charge (e-)
o Electrons do not have a relative mass, they do take up
space and have a volume
o Periodic Table
 Groups- columns on the periodic table represent GROUPS
 There are 8 groups on the periodic table
 The group # represents the number of v.e- in an element
o Valence Electrons-are the electrons that are used for
bonding

o The maximum amount of v.e- that can exist are 8
(because there are only 8 groups)
Lewis Dot Symbol
o The dots around the element represent the number of
valence electrons
o Lewis dot symbol- represents electrons for a single
atom
o Lewis Dot Structure- represents electrons for a
molecule (more than one atom)
o