Transcript The Structure of the Atom

The Structure of the Atom
Modern Concept of Atomic Theory
1. Atom consists of a tiny nucleus
2. Electrons move in an area directly
surrounding the nucleus which is called an
ORBITAL.
NUCLEUS
•Contains protons
—Positively charged
—Relative mass = 1836 amu
•Contains neutrons
—No charge
—Relative mass = 1839 amu
•Protons and neutrons are about the same mass
NUCLEUS
•The nucleus accounts for only a small portion
of the atom’s volume
BUT
•Contains the majority
of the atom’s mass
ORBITAL
• Contains electrons
—Negatively charged
—Relative mass = 1 amu
• The orbital accounts for the majority of the
atom’s volume
BUT
• Contains only a small portion of the atom’s
mass
Electrons
• Electrons move randomly
• Electrons cannot be shown to be at any one
location at any one time
• Electrons can only be shown to be in a
probability map of where they could be
• Negatively charged electrons tend to stay
close to the nucleus because of their
attraction to the protons positive charge
Atomic Chemical Properties
• Atoms have different chemical properties
because of the number and arrangement of
the electrons
– Electrons are the parts of the atoms that combine
with other atoms to form molecules
Atomic Number
• Is basically the number of the element on the
periodic table
• It also determines the number of protons in
the nucleus
Number of protons = atomic number
Atomic Mass
• The mass of the atom
• This is calculated by averaging the exact weight
of every naturally-occurring stable isotope of
that atom in nature based on the percent
abundance of that atom in nature.
Example: Carbon
Mass Number
Exact weight
% abundance
12
12.000000
98.90
13
13.003355
1.10
(12.000000)(0.9890) + (13.003355)(0.0110) = 12.011 amu
Mass number
• The rounded form of the atomic mass
• Gives the amount of protons & neutrons
combined
• Using the atomic number as well, you can
calculate the number of neutrons in the
nucleus
Number of neutrons = Mass number – atomic number
Nuclear Symbol
• By knowing the element symbol, atomic
number, and mass number, you can write the
nuclear symbol of an element