Download Atomic Structure

Atoms
• Once believed to be the
smallest particles that
made up matter
• Nucleus: Protons and
Neutrons. ~same mass
• Protons and neutrons
are made of quarks.
• Electron Cloud:
Electrons. Much smaller
mass than protons and
neutrons.
• Protons are positively
charged
• Neutrons have no charge
• Electrons are negatively
charged
• Atoms are neutral since
they have the same number
of protons and electrons.
Atomic Structure
• The nucleus is located
in the center of the
atom.
• The electron cloud
which surrounds the
nucleus contains
electrons spinning
around the nucleus.
Current Atomic Model
• The smallest
particles of matter
are now believed to
be the quark and
the electron.
• Protons and
Neutrons are made
from quarks.
Electron Arrangements
• The electrons are arranged in energy levels within
the electron cloud.
• Each energy level or shell is labeled with a number or
letter. For example K-Shell or energy level 1
• Each energy level or shell can hold a maximum
number of electrons: #e- = 2n2 where n = energy
level. Level 1 holds 2 electrons.
• Electrons closer to the nucleus have the lowest
kinetic energy because of attractive forces between
the electrons and protons.
Atomic Structure Diagrams
• Elements are made up of atoms with a specific
atomic number (number of protons)
• For example, all Helium elements contain 2
protons (atomic number 2).
• Atomic structure diagrams show how the
electrons are arranged in the different energy
levels or shells within the electron cloud.
Atomic Structure Diagram
E
E
E
E
E
P
N
E
E
E
E
E
E
P= protons, N=
neutrons found in
nucleus.
How many protons
should this atom
have?
If its mass number
is 23, how many
neutrons should it
have?
Properties of Atoms
• Atomic radius – the distance from the nucleus to the
outer edge of the electron cloud.
• Ionization energy - The energy required to remove
the outermost (highest energy) electron from a
neutral atom in its ground state in order to form a
cation.
• Electron affinity - The energy given off when a
neutral atom in the gas phase gains an extra electron
to form a negatively charged ion.
• Electronegativity - a measure of the attraction of an
atom for the electrons in a chemical bond.
Ions
• If an atom gains or loses electrons, it forms an
ion.
• Cations – positively charged due to loss of
electrons.
• Anions – negatively charged due to gain of
electrons.
Isotopes
• An atom’s mass number is the total number of
protons and neutrons.
• When like atoms of the same element have
different number of neutrons, they are called
isotopes.
• Isotopes of one element all have the same
number of protons (atomic number, Z) but
different numbers of neutrons (thus different
atomic weights, A).
• Every element has several isotopes
Science Changes Over Time
• How did the following theories change
– Democritus thought that atoms were the smallest
particles that make up matter.
– Dalton thought that atoms could not be created,
divided, or destroyed.
– Dalton thought that all atoms of the same
element were exactly alike.
– Scientists accepted that protons, neutrons, and
electrons were the smallest subatomic particles.