Download Dalton`s Atomic Theory

Modern View of Atomic
Structure
Atoms consist of a tiny, positively charged nucleus
(containing protons and neutrons) surrounded by a
“cloud” of negatively charged electrons
Relative charge of electron: −1
Relative charge of proton: +1
Neutrons carry no charge (electrically neutral)
Atoms contain an equal number of electrons and
protons, so atoms have no net electrical charge
The nucleus is extremely small in comparison to the
volume of the atom (Rutherford!)
The majority of the atom’s volume is the space in
which the electrons reside
The electrons are attracted to the protons in the
nucleus (electrostatic attraction between opposite
charges)
Atoms have very small masses - the heaviest known
atom is about 4 x 10−22 g
Therefore, atomic mass unit (amu) is used to
describe the mass of an individual atom
The proton and neutron have nearly identical mass,
and are much heavier than the electron (1 proton
has same mass as 1836 electrons)
Atomic Number, Mass Number,
and Isotopes
The atoms of each element have a characteristic
number of protons
This is known as the atomic number
For neutral atoms, the number of electrons must
equal the number of protons
Every carbon (C) atom contains 6 protons and 6
electrons
Every neon (Ne) atom contains 10 protons and 10
electrons
Atoms of a given element can differ in the number of
neutrons they contain and consequently in mass
Most C atoms have 6 neutrons, although some have
more and some have less
The mass number is the total number of protons
and neutrons in the nucleus
Mass number
Atomic number
12
6
C
Symbol of element
The atomic number is often omitted when chemical
symbols are used.
Carbon-12 can be represented simply as
12
C
Atoms that contain 6 protons and 8 neutrons would
have the following symbol
14
C
Atoms with identical atomic numbers but different
mass numbers are called isotopes of one another
Various carbon isotopes include
11
C
12
C
13
C
14
C
Identify the subatomic particles in the following:
121
Sb
192
Os
163
Dy
94
Mo