Atomic Structure - Bellwork What experiment did Rutherford perform that identified positively charged nucleii in an atom? What do we call Thomson’s atomic model? Atoms are mostly made up of _____________. What are the other components? Hint: there’s three!

The Atom An atom is the smallest particle of an element that still retains the properties of the element.

Parts of an Atom  The nucleus is made up of protons and neutrons.  It is surrounded by electron orbits.  Protons have positive charges.  Electrons have negative charges.  Neutrons don’t have a charge.

Atomic Number The atomic number is the number of protons in the atom. These are specific to each element! Example: Carbon’s atomic number is ~6. This means it has 6 protons in its nucleus.

Atomic Mass What is the atomic number for Nickel? How many protons are in Nickel?

Nomenclature Sy Mass Number

Atomic Mass Unit (amu) The amu is a method of measuring the mass of an atom relative to the mass of a specific atomic standard (usually hydrogen)

Atomic Mass Unit (amu) 1 amu is equal to 1/12 the mass of a carbon-12 atom. Protons and neutrons generally have a mass of 1 amu

Atomic Mass The atomic masses on the periodic table have many decimals. This is because that number is the weighted average atomic mass of all the naturally occurring isotopes.

Isotopes Different atoms of the same elements have the same number of protons… HOWEVER They may have different numbers of neutrons! These are called ISOTOPES.

What to Remember Atomic Number = # of Protons = # of Electrons Atomic Mass = # of Protons + # of Neutrons # of Neutrons = Atomic Mass - # of Protons Protons + Electrons – Neutrons 0

Isotopes Normally, Carbon has 6 protons and 6 neutrons. The mass of each of those is 1 amu. Its atomic mass is then 12 (6 protons + 6 neutrons = 12) But sometimes it has 7 neutrons. Which makes the atomic mass increase to 13. That carbon isotope is then called 13 C, or “carbon-13.”

Isotope Abundances You can figure out how abundant a particular isotope is by analyzing that element’s mass.

Figuring Abundance Fluorine (F) has an atomic mass that is extremely close to 19 amu. If fluorine had a lot of fairly abundant isotopes, it’s atomic mass would probably not be so close to a whole number.

Calculating atomic mass You can calculate the atomic mass of any element if you know the number of isotopes, their masses, and their percent abundances.

Calculating atomic mass Isotope 6 X Mass: % Abundance: 7.59% Mass contributions: x 7.59% = Isotope 7 X Mass: % Abundance: 92.41% Mass Contributions: x 92.41% = Weighted atomic mass = sum of the mass contributions of all isotopes ( ) = 6.94 amu What element do you think this is?

Radioactivity Remember: Chemical reactions only involve an atom’s electrons However, atoms can decay by losing nuclear parts (p or n). This is called a nuclear reaction.

Radioactivity The particles emitted from the atom are called radiation. Unstable atoms will release particles until they become stable atoms – as a different element!

Types of Radiation Alpha α Beta β Gamma γ

Types of Radiation Alpha Radiation – Made up of alpha particles – An alpha particle is made up of 2 protons and 2 neutrons – Has a 2 + charge – Is basically the same thing as a Helium atom – Represented as 4 He or α

Types of Radiation Alpha Radiation U → 4 2 He Th Atomic Mass Atomic Number

Types of Radiation Beta Radiation – Made up of beta particles – A beta particle consists of one electron – Has a 1 - charge – Also called “positrons”

Types of Radiation