ATOMIC STRUCTURE

Current Model of Atomic Structure Nucleus: center of atom Very dense Contains protons and neutrons Electron cloud Areas around nucleus where electrons are likely to be Organized in levels Close to nucleus, less energy Each level can hold a certain number of electrons

The Subatomic Particles Protons Positive charge p+ Have mass of 1amu amu = atomic mass unit 1/12 a Carbon 12 atom

The Subatomic Particles Neutrons No charge n0 mass of 1 amu

The Subatomic Particles Electrons Negative charge e- very, very little mass (not counted)

Mass Only protons and neutrons have mass Each has a mass of 1 amu Mass Number = protons + neutrons Average Atomic Mass = weighted average of all isotopes of an element More on this later This is what is listed on the periodic table

Atomic Number Number of protons in an element Never changes! If you change the number of protons you would have a different element How does this compare to changing the number of neutrons?

Element Boxes Atomic Mass 16.00 O Chemical Symbol 8 Atomic Number

The boxes give lots of information… Atomic number is the number of protons Neutral atom (no positive or negative charge) Protons = electrons Use the MAN formula to get number of neutrons

What's the MAN Formula?!? Mass (rounded to a whole number!) -Atomic Number Neutrons

MAN example… 3 Li Lithium 6.941 Mass=6.941round to 7 Atomic Number=3 M - A = Neutrons 7 – 3 = 4 neutrons! 3 Li Lithium 6.941

What else do we know? 3 Li Lithium 6.941 Atomic Number=3 -3 protons -if it is neutral (which it is unless you are told it isn’t), than there are also 3 electrons 3 Li Lithium 6.941

A Note on Symbols… Capital and lower case letters are important! Co is the metal cobalt (one of the elements that can become a magnet and is associated with the color blue in some pigments) CO is a deadly gas! Carbon monoxide ALWAYS USE CAPITALS AND LOWER CASE LETTERS PROPERLY!!!

Isotopes Atoms of same element that have different masses same number of protons, but different neutrons Atomic mass is the average of the masses of the different isotopes not even numbers Sodium (Na) is 22.9 Depending on the context, you will either round to a whole number or use the exact number from the periodic table

Isotope and Symbolic Notation

Calculating Average Atomic Mass Percent abundance x isotope mass = mass contribution Add up the mass contribution of each element to get the average atomic mass Example: Mg has 3 isotopes, calculate the average atomic mass: 78.99% is 24 amu 10.00% is 25 amu 11.01% is 26 amu