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 The atom can be broken down into even smaller parts.
 The Proton is a positively charged particle that resides in
the nucleus of an atom.
 The Neutron is a neutrally charged particle that adds
mass to the nucleus.
 Electrons are negatively charged particles that orbit the
nucleus in the electron cloud.
 Elements are groups of atoms that are all the same.
 Elements are defined by how many protons are in their
 The element with 6 protons is known as Carbon.
 The number of protons is also called the Atomic
Number of an element.
The atomic number of
Einsteinium is 99. This
means there are 99
protons in an atom of
Note: There are the same number
of electrons as protons in every
 Another important part of Chemistry is Chemical
 Chemical Symbols are abbreviations used to identify the
different elements.
 Some give clues to what the element is
 E.g. C-Carbon, He-Helium, F-Fluorine
 While others are derived from other languages
 E.g. Na-Sodium, W-Tungston, Pb-Lead
 Chemical symbols always have the first letter
capitalized and the second letter is lower cased.
 The Atomic Mass Number of an element is the atomic
mass rounded to a whole number
 It represents the number of protons plus the number of
 The Atomic Mass is the weighted average of all the
isotopes of an element
 It is measured in atomic mass units (amu)
 Note: An isotope is an element with the same number of
protons, but a different number of neutrons.
Atomic Number
Chemical Symbol
Atomic Mass
*So, the atomic mass
number for Carbon
would be 12
 Isotopes- Calculating the number of neutrons
 Isotopes have different numbers of neutrons in
elements that have the same number of protons.
 To find the number of neutrons subtract the number
of protons from the mass number.
 Mass number–number of protons = number of neutrons
 E.g. How many neutrons in Carbon-12 and Carbon-14?
12-6= 6 neutrons
14-6= 8 neutrons
Both are carbon, but they do not have the same number of
 Calculating the atomic mass
 Atomic mass can be calculated for an atom by
multiplying the mass of each isotope by its percent
abundance, then adding the results.
 E.g. The element neon has three isotopic forms: Neon20 (90.92%), Neon-21 (0.257%), and Neon-22 (8.82%).
What is the atomic mass of neon?
Amu= atomic
mass units
(.9092 x 20) + (0.00257 x 21) + (0.0882 x 22) = 20.2 amu
Note: Make sure to change your percentage to a decimal.
 During chemical changes, atoms sometimes lose or
gain electrons to form charged particles called ions.
 Atoms that gain electrons have a negative charge.
 These are called cations
 Depicted with a + sign and a number.
 E.g. Li+, Ca+2, Al+3
 Atoms that lose electrons have a positive charge.
 These are called anions
 Depicted with a – sign and a number
 E.g. Cl-, O-2, N-3