Atomic Structure Atomic number the number of protons

Atomic Structure

§ Atomic number – the number of protons in the nucleus of an atom ( ID of element ) § Mass number– sum of protons and neutrons in an atom. § Actual mass- what an atom actually weighs.

Actual atomic mass § Mass of a proton = 1. 0 x 10 -23 g § Mass of a neutron = 1. 0 x 10 -23 g 1( 1. 0 x 10 – 23 ) g 2( 1. 0 x 10 – 23 )g 3 ( 1. 0 x 10 – 23 )g

Relative atomic mass – the mass of an atom compared to a standard. § if we say protium is one, then deuterium is two and tritium will be three. R-ATM 1 R- ATM 2 R- ATM 3

The real standard is carbon-12 § a Protium atom is 1/12 the weight of a carbon-12 atom, so it still works out that the relative atomic mass is still one.

Atomic Mass § If each element has several isotopes with their own relative atomic masses, what number is put on the periodic table? § Atomic mass ( atomic weight, old school) is the weighted average of all the naturally occurring isotopes of that element.

Do the math § Symbol R-atm X % = product § 35 Cl 34. 969 x 75. 53 = 26. 41 § + 37 Cl 36. 966 x 24. 47 = 9. 045 Atomic mass of Cl = 35. 46 amu § Move the decimal in the % 2 places to the left before you enter it into the calculator.

Alternate set up § (R-atm x %) + (R-atm x %)= atomic mass § (34. 969 x. 7553) + (36. 966 x. 2447) =35. 46 § Repeat for as many isotopes that there are for that element.