Parts of Atoms

Parts of AtomsMost of the mass of the atomis concentrated in a densenucleus.The nucleus is made up ofpositive protons and neutralneutrons.Electrons are NEVER in the nucleus.Instead electrons travel outside the nucleus inmostly empty space.

Atomic Numbers10NeNeon20.18Atomic NumberThe atomic number of anelement is equal to thenumber of protons in itsnucleus.We know that a neon atomhas 10 protons because neonhas an atomic number of 10.

What about Mass?Protons and neutrons eachweight about 1000 times asmuch as electrons.So we calculate atomicmasses by adding up onlyneutrons and protons.We ignore the masses of electrons becausetheir mass is so small compared to the mass ofprotons and neutrons

Isotopesmass 1 mass 2 mass 3Isotopes are members of a family of elementswith the same number of protons (same atomicnumber) but a different number of neutrons(different atomic mass).Isotopesofhydrogen1 proton but no neutrons (mass 1)1 proton and 1 neutron (mass 2)1 proton and 2 neutrons (mass 3)

Weighted Average100 lbs 200 lbs 300 lbs98 skinnies 1 fat 1 superfat98 x 100 = 98001 x 200 = 2001 x 300 = 300100 10300The weightedaverage10300 divided by 100 = 103 lbs

10NeNeon20.18On the Periodic TableAtomic masses are often notwhole numbers.atomic mass (a weightedaverage of more thanone isotope)The atomic mass for neon is the weightedaverage of a common isotope with a mass of 20and a less common isotope with a mass of 21.The weighted average of 20.18 shows up on thePeriodic Table for neon.

Calculating Neutrons10NeNeon20.18Round off the atomicmass to the nearestwhole number.So 20.18 is rounded offto 20, a whole number.Subtract the number of protons(10) from the rounded atomicmass (20).So neon has 10 neutrons.

Calculating Electrons10NeNeon20.18Atomic NumberAn atom that has neither lostnor gained electrons isneutral.In a neutral atom, thenumber of electrons equalsthe number of protons (thesame as the atomic number)Neon (atomic number 10) has 10 electrons