Atomic number, atomic symbol, mass number, isotopes Atomic properties Atomic number, atomic symbol, mass number, isotopes

HOW DO WE DESCRIBE AN ATOM What makes up an atom Proton (positive charge) Neutron (neutral charge0 Electron (negative charge) Now we need to find a way to describe the properties of an individual atom

Nucleus Protons and Neutrons are located in the atom’s nucleus. Electrons- orbit around the nucleus

DESCRIBING THE ATOM Let’s take a look at the periodic tables around the room. On each periodic table are several things Symbol for the element Name of the element Numbers that describe the element

HOW DO WE NAME AN ELEMENT The first thing we will examine is the naming of elements Finding the names of elements is like doing a giant word search EXAMPLE: What is the name of the element with the symbol He?

ANSWER He is the symbol for the element HELIUM

TRY THESE Br Li Zn B Ag K

ANSWERS Br - Bromine Li - Lithium Zn - Zinc B - Boron Ag - Silver K – Potassium Let’s look at #5 and #6

FIND THE SYMBOL FROM THE NAME It’s usually easier to find the name of the element when you have the symbol. It’s harder to find the symbol when you have the name. Try these: Mercury Xenon Iron

REMINDER: For your periodic table ANSWERS Mercury - Hg Xenon - Xe Iron – Fe REMINDER: For your periodic table You may use this on your quizzes You must fill in your own information

WHAT DEFINES AN ATOM One particle defines what an atom (or element is) This particle is the PROTON The number of protons in an atom tells us what element it is.

ATOMIC NUMBER Atomic number: the number of protons in an atom Example: Find Hydrogen (H) on your periodic table The atomic number of hydrogen is 1. What is the atomic number for He?

ATOMIC NUMBER The periodic table is arranged in order of increasing atomic number. Find the atomic number for these: Sulfur Uranium Gold

ATOMIC NUMBER Sulfur - 16 Uranium - 92 Gold – 79 If you ever change the number of protons, you change the atom into a different element.

MASS NUMBER Mass number: the sum of an element’s protons and neutrons. Remember, electrons don’t have an atomic mass On your periodic table, this is found below the symbol of the element EXAMPLE: The mass number for H (hydrogen) is 1.008

UNITS The unit for the mass unit is the atomic mass unit (amu) Therefore: Hydrogen has a mass number of 1.008 amu

FIND THE MASS NUMBER Find the mass number for the following: Cl Pd Sr

Shells/ Orbitals/ Energy Levels The electrons orbit around the nucleus of the atom These area are called: shells, or orbitals, or energy levels

Valence Electron Valence electrons are the electrons in the outer most shell(energy level/ orbital) of an atom.

End of 1st Day

MASS NUMBER AND ISOTOPES Notice that not all the mass numbers are whole numbers A lot of them have decimals WHY?

Average Atomic Mass To calculate the average atomic mass, multiply the fraction by the mass number for each isotope, then add them together. 

Average Atomic Mass Average atomic mass = f 1M 1 + f 2M 2 + ... + f nM n where f is the fraction or decimal representing the natural abundance of the isotope and M is the mass number (weight) of the isotope.. 

Average Atomic Mass To calculate the average atomic mass, multiply the percentage in decimal form by the mass number for each isotope, then add them together. 

Average Atomic Mass (12.000000) (0.9890) + (13.003355) (0.0110) Example: (12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu mass number exact weight percent abundance 12 12.000000 98.90 13 13.003355 1.10

ISOTOPES The reason is that not every atom in an element has the same number of neutrons ISOTOPE: atoms of the same element with different numbers of neutrons Ex: C-12 and C-14 Isotopes of atoms is what is responsible for radiation The mass number is an average of all the different isotope masses

SYMBOLS How do we show how many protons and neutrons are in a symbol. EXAMPLE: An element has 10 protons and 10 neutrons, how do we show it? First, what is the element?

Number of protons + neutrons SYMBOLS Ne Number of protons + neutrons 20 10 Number of protons

WRITE THE SYMBOL FOR THESE 35 protons and 45 neutrons 40 protons and 51 neutrons 78 protons and 117 neutrons

HOW MANY PROTONS AND NEUTRONS 40Ar 18 56Fe 26 238U