How Atoms Differ October 2, 2014
Reading an Element A – Atomic Number: the number of protons in an atom (this identifies the element) B – Average Atomic Mass C – Chemical Symbol D – Chemical Name
Atomic Number - Z All atoms are neutral, the charges of the protons and electrons must cancel each other out Atomic Number = number of protons = number of electrons Fill in the table below. Element Atomic Number ProtonsElectrons Pb
Isotopes Isotopes are atoms with the same number of protons but different number of neutrons. The atomic number stays the same Mass will change, since neutrons have a relative mass of 1
Isotope Notation Mass Number – the sum of the atomic number(or number of protons) and neutrons in the nucleus These are both saying that the element is carbon, it has a mass number of 14, atomic number of 6 So 6 protons, 6 electrons, and 8 neutrons Carbon -14
Fill in the table below ElementMass #Atomic # Protons & Electrons Neutrons Isotope Symbol Neon2210 Calcium4620 Oxygen178 Iron5726 Zinc6430 Mercury20480
Atomic Mass An Elements mass is made up of protons (1 amu) and neutrons (1 amu) However an elements mass is usually never a whole number. Atomic Mass of an element is the weighted average mass of the isotopes of that element
Calculating Atomic Mass Chlorine – 35 has a mass of amu, a percent abundance of 75.78% Chlorine – 37 has a mass of amu, a percent abundance of 24.22% Calculate the mass contribution of each isotope Chlorine – 35: ( amu x 75.78%) = amu Chlorine – 37: ( amu x 24.22%) = amu Now add the isotopes mass contribution together to get your weighted average atomic mass ( amu amu) = amu The weighted average atomic mass should be the same or very close to what is on the periodic table.
Isotope Practice Boron has two naturally occurring isotopes: boron – 10 (abundance = 19.8%, mass = amu) and boron – 11 (abundance = 80.2%, mass = amu). Calculate the mass of boron. Identify the unknown element X, based on the information given in the table. Nitrogen has two naturally occurring isotopes, N -14 and N- 15. Its atomic mass is amu. Which isotope is more abundant? Explain. IsotopeMass (amu)Percent Abundance X – % X %