Green Pea AnalogySome Initial Concepts

How large is an atom? How many atoms are in the leads of 12 lead pencils? Pencil leads are made of carbon atoms. Carbon has an atomic mass of 12.

Atomic mass is the mass of an atom. It is calculated as the sum of the number of protons and neutrons in the atom, because protons and neutrons make up the majority of the atom's mass. Each proton and neutron is given an atomic mass of 1. Since carbon has six protons and six neutrons, its atomic mass is 12. Carbon also has six electrons, but these are extremely light compared to the protons and neutrons and do not contribute to carbon's integral atomic mass.

Atomic mass is so light (1 atomic mass unit (amu) 1.66 x 10∼ -24 g) that it is impractical to measure. Instead, scientists estimate atomic mass by measuring the mass of the element (in grams) which is equal in value to the number of protons and neutrons in an atom of the element. The amount of an element with this mass (in grams) is called a mole. An atom of carbon has an atomic mass of 12, so a mole of carbon weighs 12 grams. Placing 12 grams of carbon (pencil lead) beside 28 grams of silicon (sand) enables one to visually contrast the atomic mass of carbon (atomic mass 12) to that of silicon (atomic mass 28). (The comparison is not entirely visual, since element density influences the volume of a mole of an element.)

A mole of any element contains 602, 000, 000, 000, 000, 000, 000, 000 atoms of that element, that is 602 sexillion US, 602 trilliard UK or 6.02 x 1023 atoms. This number is called Avogadro's Number after Amedeo Avogadro (1776-1858) who discovered this number-of-atoms-in-a-mole relationship.What does this have to do with 12 pencil leads?Twelve pencil leads weigh approximately 12 grams, so have 6.02 x 1023 atoms in them.

But what does 6.02 x 1023 atoms mean?

100 = 1 One pea

101 = 10

10 peas - spoonful

102 =100 10 spoonfuls of peas - plateful

103 = 100010 platefuls of peas – a bag

104 = 10 000 10 bags of peas

105 = 100 000100 bags of peas - fridgeful

106 = 1 000 000 10 fridges full of peas - an average bedroom

107 = 10 000 000 Average house full from basement to attic with peas

109 = 1 000 000 000 100 houses full from basement to attic with peas - a small village

1012 = 1 000 000 000 000

100 000 houses full from basement to attic with peas - a small city

1015 = 1 000 000 000 000 000A large city like New York covered 1 m deep with peas

1018 = 1 000 000 000 000 000 000 A area like Kalimantan covered 1 m deep with peas

1020 = 100 000 000 000 000 000 000 The land mass of China covered 1 m deep with peas

1021 = 1 000 000 000 000 000 000 000The land mass of the world covered 1 m deep with peas

1023 =100 000 000 000 000 000 000 000

The entire surface of the earth plus 99 planets just like earth covered 1 m deep with peas

6.02 x 1023 = 602 000 000 000 000 000 000 000

= 1/18 the surface area of the Sun

= 602 earth sized planets covered 1 m

deep with peas

= 12 pencil leads

= one mole of carbon

atoms