The Atom – Modern Atomic Theory
Subatomic Particles:
symbol
location
Relative
charge
Relative mass
(amu)
Actual mass (g)
Proton
Neutron
Electron
In a neutral atom, the number of ________ is always the same as the number of
_________.
Why does the atom not fall apart?
How does the mass of the electron compare to the mass of the proton?
Heisenberg Uncertainty Principle:
The nucleus makes up most of the __________ of an atom.
The electron cloud makes up most of the ___________ of an atom.
Atomic Numbers:
Atomic Number – number of ________ in an atom – determines the atom’s identity (located
above element on periodic table.)
______________ found that each element has a different number of protons in its
nucleus.
T or F: The atomic number of an element can change. Why or why not?
An individual atom is electrically neutral, which means the number of protons equals the
number of electrons.
So, an element’s atomic number also indicates the number of electrons in a neutral atom.
Ions:
When an atom gains or loses electrons, it acquires a net electrical charge and is called an
ion.
Anion:
Cation:
Examples:
1.
A magnesium ion loses 2 electrons, what is the charge on a magnesium ion?
2. A fluorine atom gains 1 electron, what is the charge on the fluorine ion?
3. An iron atom loses 3 electrons, what is the charge of the iron atom?
Isotopes:
All atoms of a given element have to have the same number of __________ in their nucleus,
but not necessarily the same number of ___________.
One isotope of each element is more common than another.
In nature, elements are found as a mixture of isotopes.
For example, in a drop of water, 99.9844 % of the hydrogen isotopes are hydrogen – 1.
Example:
isotope name
* hydrogen
(hydrogen - 1)
deuterium
(hydrogen – 2)
tritium
(hydrogen – 3)
# of protons
1
# of neutrons
0
# of electrons
1
1
1
1
1
2
1
* indicates the most common isotope of H (look at its average atomic mass)
The major difference between isotopes of the same element is their mass. The more
neutrons an element has, the higher the mass of that element is.
Mass Number – sum of the _________ and ________ in an atom
Atomic Mass – average mass of all the ________ of a particular element
Isotope – atom of an element that has a different number of ________ in the nucleus
Isotopes are named by their mass numbers.
For example: All chlorine nuclei have 17 protons in their nuclei, but some have
18 neutrons
Mass # = ____
and some have
20 neutrons
Mass # = ____
What is the most common isotope of chlorine?
Examples:
1.
The chlorine isotope with 17 protons and 20 neutrons is called:
2. The chlorine isotope with 17 protons and 20 neutrons is called:
3. The symbol for chlorine – 35 is:
4. The symbol for chlorine – 37 is:
* mass # on top and atomic # on bottom
Because Atomic # = # of protons
And
Mass # = # of protons + # of neutrons
How do you find the # of neutrons in an isotope?