Download Atomic Structure

Atomic Structure
What is an atom?
• Atom: the smallest unit of matter
that retains the identity of the
substance
• First proposed by Democritus
Atomic Structure
• Atoms are composed of 2 regions:
• Nucleus: the center of the atom that
contains the mass of the atom (majority)
• Electron cloud: region that surrounds
the nucleus that contains most of the
space in the atom
Electron
Cloud
Nucleus
What’s in the Nucleus?
• The nucleus contains 2 of the 3
subatomic particles:
• Protons: positively charged subatomic
particles
• Neutrons: neutrally charged subatomic
particles
What’s in the Electron Cloud?
• The 3rd subatomic particle resides
outside of the nucleus in the electron
cloud
• Electron: the subatomic particle with a
negative charge and relatively no mass
How do these particles
interact?
• Protons and neutrons live compacted
in the tiny positively charged nucleus
accounting for most of the mass of
the atom
How do these particles interact?
The negatively charged electrons are small
and have a relatively small mass but occupy a
large volume of space outside the nucleus
Relative Weights of Sub-Atomic
Particles
How do the subatomic particles
balance each other?
• In a neutral atom:
• The protons equal the electrons
• If 20 protons are present in an atom then 20
electrons are there to balance the overall
charge of the atom—atoms are neutral
• The neutrons have no charge; therefore
they do not have to equal the number of
protons or electrons
How do we know the number of
subatomic particles in an atom?
• On the Periodic Table
Atomic Number
Symbol
Name
Atomic Mass
(Mass Number)
How do we know the number of
subatomic particles in an atom?
• Atomic number: this number indicates the
number of protons in an atom
• Ex: Hydrogen’s atomic number is 1
• So hydrogen has 1 proton
• Ex: Oxygen’s atomic number is 8
• So oxygen has 8 protons
**The number of protons identifies the atom.
Ex. 29 protons = which element???
How do we know the number of
subatomic particles in an atom?
• Atomic #- 8 (protons) • Since it has 8 protons
• Mass #: the number of it must have 8 neutrons
protons and neutrons in
(16-8)
the nucleus
• Ex: oxygen has a
mass of 16.
• # of neutrons =
mass # - atomic #
Determining the number of
protons and neutrons
• Li has a mass number of 7 and an
atomic number of 3
• Protons = 3 (same as atomic #)
• Neutrons= 7-3 = 4 (mass # - atomic #)
• Ne has a mass number of 20 and an
atomic number of 10
• Protons = 10
• Neutrons = 20 - 10= 10
What about the electrons?
• The electrons are equal to the
number of protons
• So e- = p = atomic #
• Ex: O has a mass # of 16 and an
atomic # of 8
• p+ = 8
• no = 8
• e- = 8
Determine the number of
subatomic particles in the
following:
Cl has a mass # of 35
and an atomic # of 17
• p+ = 17,
• no = 18,
• e- = 17
• P+ = 19,
• no = 20
• e- = 19
How exactly are the particles
arranged?
• Bohr Model of the atom: Electron levels
All of the
protons and
the neutrons
The 3rd ring
can hold up
to 18 eThe 4th ring
and any after
can hold up to
32 e-
The 1st ring can
hold up to 2 eThe 2nd ring can
hold up to 8 e-
What does carbon look like?
Mass # = 12
The second
electron shell
can hold how
many
electrons?
8
6 p and 6 n live
in the nucleus
Carbon has
four of the 8 .
p+ = 6
atomic # = 6
no = 6
Therefore, carbon
has 4 VALENCE
ELECTRONS
(the # of electrons
found in the
outermost shell)
e- = 6
Your Turn
• Bohr Models
• Hydrogen
• 1 valence
Beryllium
2 valence
Nitrogen
5 valence
A quick word about ions
• Ions- a charged particle that forms when
an atom (or group of atoms) gains or
loses one or more electrons.
• + Ions: have lost one or more electrons
• - Ions: have gained one or more
electrons
Some examples…
…and some jokes