Science-10

E.Brennan

Atomic Structure

·  is a counting number

·  equals the number of protons

·  is the identity of the element (all atoms of a given element have the same # of protons)

·  is a counting number

·  equals sum of protons + neutrons

·  (is not equal to 2 x protons since protons and neutrons do not always come in identical numbers)

·  is a calculated (think ‘decimal points’) number

·  approximately equal to sum of protons + neutrons (which make up essentially the mass)

1.  Within atoms of the same element, the number of ______will never vary from one atom to the next.

2.  Within atoms of the same element, the number of ______will vary from one atom to the next. These various form of the element are called ______.

3.  All the isotopes of a particular element have the same ______but they have different ______.

4.  ______elements exist naturally as a mix of isotopes, so the______number we use is just a way of indicating which isotope we mean.

5.  The ______is actually a weighted average of all naturally occurring isotopes (taking into account how frequently each is found).

6.  In a neutral atom the number of ______equals the number of ______.

7.  If the atom is charged it is because it gained or lost one or more ______. Example: charge of 2+ is the result of ______, while charge of 3- is the result of ______.

8.  Charged atoms have mass that is ______than their neutral counterparts.

All atoms in chart are neutral.

Symbol / Name / Atomic
Number / Atomic
Mass / Protons / Neutrons / Electrons / Mass
Number / Isotopic
Symbol
1 / B / 6
2 / 11 / 23
3 / 31 / 39
4 / 88.9 / 39
5 / 29 / 35
6 / Pb / 208
7 / 103 / 70
8 / 89
9 / Mo / 54
10
11
12

So, what’s up with all these isotopes anyway?

In nature elements are not made up of atoms that are all exactly the same!

Some will be heavier than others, even though they are still the same type of atom.

C-12 and C-14 are both Carbon, with all the usual Carbon properties, but the C-14 has two more neutrons, and is heavier.

Both Carbons exist in nature, but in different abundances. They are not 50/50 or else we would average the two weights and report a calculated Atomic Mass in the periodic table of 13. Because the reported Atomic Mass is very very close to 12, we know that almost all of the Carbon found in nature is C-12, with a teeny bit of C-14.

Look up Chlorine in the periodic table. In nature it consists of Cl-35 and Cl-37. Since its Atomic Mass is reported to be 35.45 we can conclude which isotope occurs the most (...... right?)

(You will look at the math behind these calculations in Chem11.)