Download Atoms

Bohr’s Atom
electrons in orbits
nucleus
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ charge
1
neutron
No charge
1
electron
- charge
nil
ATOMIC STRUCTURE
He
2
4
Atomic number
the number of protons in an atom
Atomic mass *
The atom’s mass –
A Weighted average of the
isotopes – (protons + neutrons)
* * number of electrons = number of protons * *
Atomic Number
Atomic Number -- is the number of
protons in the nucleus of the atom.
This carbon atom’s
atomic number is 6.
The number of protons (atomic
number) determine the identity
of an element.
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
Atoms have NO overall electrical charge
so, an atom must have as many
electrons as there are protons
in its nucleus.
# of electrons = # of protons
Isotopes
Isotopes are atoms of an element that have
the SAME number of protons,
but a DIFFERENT number of neutrons.
Isotopes remain the same element,
because the number of protons doesn’t
change.
The mass changes, but the element doesn’t!
Two Common Isotopes
Carbon has 6 protons
6 neutrons
7 neutrons
8 neutrons
Identified by the mass # Number of protons + neutrons
Properties of Isotopes
• Isotopes of an element share most of the
same properties – both chemical and
physical!
• However -- Some isotopes of an element
have special properties because they are
“unstable” (the nucleus will change over
time).
• This would be a radioactive isotope that will
spontaneously “fall apart” over time, giving
off small particles/ energy as they do.
Identifying Isotopes
• Isotopes are identified by their mass number
• Mass number is the sum of the protons and
neutrons (electrons not included – too small
to have an effect on mass)
Boron - 10
Boron - 11
All atoms which contain 17 protons
are called chlorine atoms
Chlorine (Cl) has 24 isotopes
Examples: Chlorine-35 and Chlorine-37 are both
isotopes of the element chlorine
Chlorine - 35 contains 18 neutrons
(17 protons + 18 neutrons = 35 particles in the nucleus)
Chlorine - 37 contains 20 neutrons
(17 protons + 20 neutrons = 37 particles in the nucleus).
Atomic Mass
The atomic mass of an element is the
weighted average of the masses of all
of the naturally occurring isotopes of
that element.
Chlorine – 35:
Chlorine – 37:
76% of all chlorine in nature
24% of all chlorine in nature
35 x .76 = 26.6
37 x .24 = 8.88
26.6
+ 8.8
35.48 amu
Ions
Ion – An atom that LOSES or GAINS an
electron
Loses an electron: + Positively charged ion
Gains an electron: – Negative ion
 Missing an electron
 A lower energy
 Attractive to ions with
a negative charge
SUMMARY
1. The Atomic Number of an atom = number of
protons in the nucleus. Id’s the element!
2. The Mass Number of an atom = number of
Protons + Neutrons in the nucleus.
3. The Atomic Mass = the weighted average of isotopes
4. The number of Protons = Number of Electrons –
Atoms have NO overall electrical charge
5. Electrons orbit the nucleus in shells.
6. Each shell can only carry a set number of electrons.
7. Ion – An atom that loses or gains an electron
8. Isotopes are atoms of an element that have the
SAME number of protons, but a DIFFERENT
number of neutrons.
9. Isotopes are identified by their mass number;
Mass number is the sum of the protons and neutrons
10. The atomic mass of an element is the weighted
average of the masses of all of the naturally
occurring isotopes of that element.