Download Atomic mass number

Unit 3 Notes –Isotopes
Learning Check
An atom has 14 protons and 20 neutrons.
A. Its atomic number is 14
B. Its mass number is
C. The element is
Mass Number = p + n
34
Silicon
Element Notation
Element Notation:
mass number
Charge
23 Na
11
atomic number
Practice 1
Mass number
59
28
Atomic Number
Name of Element?
Nickel
# of protons? 28
# of electrons? 28
# of neutrons? 59 = 28 + n = 31
Charge? Neutral or No Charge
Ni
Practice 2

Write the element notation for an ion with
17 protons, a charge of -1 and a mass of
37
37
17
Cl
-
IONS - Atoms of the same element but with a
charge (different # of electrons).
Ions with a positive charge
If a neutral atom loses one or more electrons
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
Ions with a negative charge
If a neutral atom gains one or more electrons
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
Ions
+
27
3
How many protons and electrons are in 13 Al ?
13 protons, 10 (13 – 3) electrons
2- ?
Se
How many protons and electrons are in 78
34
34 protons, 36 (34 + 2) electrons
Isotopes

Atoms of the same element but different
mass number (different # of neutrons).

To write: element name – Mass Number
Boron-10
 Boron-11

has 5 p and 5 n
has 5 p and 6 n
11B
10B
Example: Carbon

Normally carbon is: Carbon-12


These carbon atoms have 6 neutrons
Some carbon atoms may have 7 or 8
neutrons
Carbon-13
 Carbon-14


These atoms are still carbon, but we call
them isotopes
Mass Number

Mass number= number of protons + neutrons
Slightly different than Atomic Mass
 Refers to one specific atom (isotope)
(not all of that type)


Atomic mass number –
number of protons + neutrons
 an average of all the different isotope’s masses

Atomic Mass Number

Calculated by how many atoms of each type
there are in the universe
 For Carbon:




lot of Carbon-12
Some Carbon-13
Few Carbon-14
When you average out all of the masses you
get 12.011
Isotopes?
Which of the following represent isotopes of
the same element?
What is the name of the element?
1.
234
92
3.
2.
X
234
93
X
235
92
4.
X
238
92
X