1. Atoms and their structure

2. The Modern Model The modern atom is composed of two regions:
1. Electron cloud- Most of the volume of an atom and is the region where the electron can be found (extranuclear)
2. The nucleus – with protons and neutrons so that it has a Positive charge and almost all the mass

3. Major Subatomic Particles
Name
Symbol
Charge
Relative Mass (amu)
Actual Mass (g)
Electron e- -1
1/1840
9.11x10-28
Proton p+ +1 1
1.67x10-24
Neutron no
Atoms are measured in picometers, meters
Hydrogen atom, 32 pm radius
Nucleus is tiny compared to atom
If the atom were a stadium, the nucleus would be a marble
Radius of the nucleus is on the order of m
Density within the atom is near 1014 g/cm3

4. Nuclear Symbols
Every element is given a corresponding symbol which is composed of 1 or 2 letters (first letter upper case, second lower), as well as the mass number and atomic number E A Z
elemental symbol
mass number
atomic number

5. Elemental Classification
Atomic Number (Z) = number of protons (p+) in the nucleus
Determines the type of atom
Li atoms always have 3 protons in the nucleus, Hg always 80
Mass Number (A) = number of protons + neutrons [Sum of p+ and nº]
Electrons have a negligible contribution to overall mass
In a neutral atom there is the same number of electrons (e-) and protons (atomic number)

6. W F Br 184 74 19 9 80 35 Find the number of protons number of neutrons
number of electrons
atomic number
mass number W
184 74 F 19 9 Br 80 35

7. If an element has 91 protons and 140 neutrons what is the:
If an element has an atomic number of 34 and a mass number of 78 what is the:
number of protons in the atom?
number of neutrons in the atom?
number of electrons in the atom?
complete symbol of the atom?
If an element has 91 protons and 140 neutrons what is the:
atomic number?
mass number?
number of electrons?
complete symbol?

8. Isotopes
Atoms of the same element can have different numbers of neutrons and therefore have different mass numbers
The atoms of the same element that differ in the number of neutrons are called isotopes of that element H 1
Protium 2
Deuterium 3
Tritium

9. Naming Isotopes
When naming, write the mass number after the name of the element
Examples:
carbon- 12
carbon -14
uranium-235

10. Review:
Write the nuclear symbols ( ) and name including mass for three isotopes of oxygen in which there are 8, 9, and 10 neutrons respectively.

11. Ions
When atoms gain or lose electrons they form something called IONS. Energy is released when this happens.
Ions are electrically charged atoms. (positive or negative)

12. Cations (+)
CATIONS: are positively charged ions. Cations are formed when an atom loses electrons.
Metals and Hydrogen form cations
Ex: Na lose 1 electron
 Na1+

13. Anions (-)
ANIONS: are negatively charged ions. Anions are formed when atoms gain electrons.
Most non-metals form anions.
Ex: Cl gains one electron
 Cl1-

14. Charges of Ions Group 1  loses 1 electron = +1
Group 2  loses 2 electrons = +2
Group 13  loses 3 electrons = +3
Group 15  gains 3 electrons = -3
Group 16  gains 2 electrons = -2
Group 17  gains 1 electron = -1
Group18  has a full outer shell
= very stable 

15. Noble Gases Group 8A (He, Ne, Ar, etc.)
Have a full valence shell (complete octet)
They neither want to gain or lose electrons
Therefore, DO NOT form IONS
********Handout  chemical familes  discuss

16. (+) charge = subtract electrons from # protons
Only the number of electrons can change:
(+) charge = subtract electrons from
# protons
(-) charge = add electrons from

17. How many protons and electrons do each of the following have?
Br-1
Ca+2
Se-2
e) Mg+2
f) Au3+
g) P-3
h) Mn+4

18. Average Atomic Mass
Did you ever notice that the mass number on the periodic table is not a whole number?
There are the decimal numbers on the periodic table.
**This is because it is an average mass for all the isotopes of each atom

19. How heavy is an atom of oxygen?
There are different kinds of oxygen atoms (different isotopes)
16O, 17O, 18O
We are more concerned with average atomic masses, rather than exact ones
Based on abundance of each isotope found in nature
We can’t use grams as the unit of measure because the numbers would be too small
Instead we use Atomic Mass Units (amu)
Standard amu is 1/12 the mass of a carbon-12 atom
Each isotope has its own atomic mass

20. Calculating Averages
You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks?
Total mass = x 50 g + 1 x 60 g = 260 g
Average mass = (4 x 50 g + 1 x 60 g)/5 = (260 g)/5
= (4 x 50 g)/5 + (1 x 60 g)/5 = 260 g/5

21. Calculating Averages Average mass = 0.8 x 50 + 0.2 x 60
80% of the rocks were 50 grams
20% of the rocks were 60 grams
Average = (% as decimal) x (mass1) (% as decimal) x (mass2) (% as decimal) x (mass3) + …

22. Calculating Averages
Calculate the av atomic mass of copper if copper has two isotopes
69.1% has a mass of amu
The rest (30.9%) has a mass of amu
Magnesium has three isotopes
78.99% magnesium 24 with a mass of amu
10.00% magnesium 25 with a mass of amu
The rest magnesium 26 with a mass of amu
What is the atomic mass of magnesium?

23. Average Atomic Masses
If not told otherwise, the mass of the isotope is the mass number in amu
The average atomic masses are not whole numbers because they are an average mass value
Remember, the atomic masses the decimal numbers on the periodic table