Download Modem Atomic I fleoly Bohr`s Model of Atom

4.2 Structure at Atom
Subatomic Particles: protons, electrons, and neutrons
Protons
o Rutherford concluded that amount of positive charge varies with elements
o Positively charged (1+)
o Found in nucleus
o Every atom of an element has the same number of protons (“Atomic Number”)
Electrons
o Particles that Thomson detected
o Negatively charged (1– )
o Found outside of nucleus
o 1/1836 of mass of proton or neutron (has mass, but very little)
o Every atom of an element has the same number of electrons (equal to the number of
protons).
Neutrons
o 1932 Chadwick discovered
o Neutral charge (0)
o Found in the nucleus
o Mass (almost exactly) equal to proton
o Most (but NOT ALL) atom of an element has the same number of neutrons.
Particle
Proton
Electron
Neutron
Symbol
Charge
Relative Mass
(Proton = 1)
Location
p+
Positive
1
In nucleus
e-
Negative
1
1836
Outside nucleus
n
Neutral
1
In nucleus
The Atomic Number of an element equals the number of protons in an atom of that
element.
o Each element has a unique one
o Also equals the number of electrons
The Mass number equals the sum of protons and neutrons
o Number of neutrons equals mass number minus atomic number
Isotopes
o Atoms of same element with different numbers of neutrons (so also
different mass number).
o Same atomic number
o Different mass number
o For most elements it is hard to notice any differences in the physical or
chemical properties of isotopes. (Hydrogen is the exception.)