Download I can describe an atom and its components I can relate energy levels

Matter, part 2
● I can describe an atom and its components
● I can relate energy levels of atoms to the
chemical properties of elements
● I can define the concept of isotopes
Isotopes
● Atoms of the same element that have
different mass numbers
○ All atoms of the same element have the
same number of protons
○ The number of neutrons can vary
○ ex)Chlorine atoms have 17 protons but
can have 18 or 20 neutrons.
■ There are chlorine atoms with mass #s
of 35 and 37. (17+18=35, 17+20=37)
Isotopes
● Atomic mass- the average of
the mass numbers of the
isotopes of an element.
○ Most elements are mixtures
of isotopes
○ ex) Atomic mass of chlorine
is 35.453, the average of
the mass numbers of
naturally occurring
isotopes of chlorine-35 and
chlorine-37
Radioactive Isotopes
● Some isotopes are unstable and tend to
break down
○ The isotope emits energy in the form of
radiation
● The spontaneous process through which
unstable nuclei emit radiation is called
radioactive decay.
Radioactive Isotopes
● In radioactive decay, a nucleus can...
○ lose protons and neutrons
○ change a proton to a neutron
○ change a neutron to a proton
● Because the # of protons identifies an
element, decay changes the identity of the
element
Electron Energy Levels
● The exact position of
an electron cannot be
determined
○ Electrons occupy
areas called energy
levels
● The volume of an atom
is mostly empty space
● The size of an atom
depends on the number
and arrangement of its
electrons
Electron Energy Levels
● The first energy level
can hold 2 electrons
● The second energy
level can hold 8
electrons
● The third energy level
can hold 18 electrons
● The fourth energy
level can hold 32
electrons.
Valence Electrons
● Electrons in the outermost energy level
○ Determine the chemical behavior of the
different elements
● Elements with the same number of valence
electrons have similar properties.
○ ex) A sodium ion (atomic # 11) and a
potassium ion (atomic # 19) each have
one valence electron.
○ Both are highly reactive metals, and
easily combine with other elements
Valence Electrons
Ions
● An atom that gains or
loses an electron, and
has a net electric
charge
● An atom with fewer
than 4 valence
electrons will tend to
lose valence electrons
and become positively
charged.
○ ex) Na+
Ions
● An atom with more than 4 valence electrons
tends to gain electrons and form a
negatively charged ion.
○ ex) Cl-
Abundance of Elements
● The 2 most abundant elements
in the universe are hydrogen
and helium
● All other elements account
for less than 1% of all
atoms in the universe.
● 98.5% of Earth’s crust is
made of only 8 elements.