CHAPTER 3
Section 1
Dmitri Mendeleev
A Russian scientist who was able to
organize the elements in a pattern according
to their properties.
Atomic Mass – average mass of one atom
of the element.
Periodic Table – chart of the elements
showing the repeating pattern of their
properties.
-Patterns appeared when arranged in
order of increasing atomic mass
Inside an Atom
Nucleus – core of an atom containing
protons and usually neutrons.
-Protons – small positively charged
particles.
-Neutron – small particles with no
charge.
-Electrons – negatively charged
particle that moves around the nucleus of an
atom.
Atomic Mass Unit (amu) – unit used to
measure the mass of particles in an atom.
-Ex. Protons and Neutrons are 1 amu
Atomic Number – the number of protons
in the nucleus of an atom.
Reading the Periodic Table
Chemical Symbol – one or two letter
representations of an element.
Ex. C – Carbon, Na - Sodium
Groups or Families – elements that are
arranged in a column.
Period – elements arranged in a
horizontal row.
Why the Table Works
Valence Electrons – one of the electrons
farthest away from the nucleus. These
electrons are involved in a chemical reaction.
-The elements in each group of the
periodic table have the same number and
arrangement of valence electrons.