2 Atomic Mass - Nucleus of atom contains most of the mass Protons and neutrons arefar moremassive thanelectrons
3 Atomic MassAtomic mass unit (amu) – unit of measurement used for atomic particles Mass of a proton = 1 amu =mass of 1 neutron 1 amu ≈ 1/12 mass of acarbon atom containing 6p+and 6 n
4 Numbers Atomic number – number of protons in an atom Each element has a unique number of protons(atomic number)
5 Numbers- Mass number – the sum of the number of protons and number of neutrons in the nucleus- Mass # = Atomic # + # of neutrons
6 Isotopes – atoms of the same element with different number of neutrons Isotopes of an element have slightlydifferent properties- Examples:Carbon-12 (C-12) most common and stableCarbon-14 (C-14) unstable and radioactive- To identify isotopes, use the element name followed by the mass number Examples: Boron-10, Boron-11
7 - Average atomic mass – the weighted-average mass of the mixture of all isotopes of an element
8 Boron-11 80% (4/5) of all boron atoms are the isotope Boron-11 4/5 x (11 amu) + 1/5 x (10 amu) = 10.8 amu this is the average atomic mass ↑
9 ** The average atomic mass is always very close to the mass number of the most common (most abundant) isotope, and can be rounded to the nearest whole number when using mass numbers.