Examples - Carbon and Lead
Carbon is an extremely important element with unique chemical properties, without which life could not exist. It is an essential element in life chemistry and it is the base element of organic compounds. In combination with oxygen, in carbon dioxide (CO2), carbon is found in the earth's atmosphere and dissolved in all water bodies.
Figure 1: Left: Ultrapure carbon as graphite, (original size: 1 x 3 cm) [http://images-of-elements.com/carbon.php]. Right: Rough diamond [this photo is public domain, extracted from http://images-of-elements.com/carbon.php].
The element carbon carries the symbol C. Its atomic number is 6. Consequently, a carbon atom has 6 protons and 6 electrons.
The atomic weight of carbon is 12.01. Carbon's key isotopes are 12C, 13C and 14C. The most common isotope of carbon is 12C. Its nucleus consists of 6 protons and 6 neutrons while the isotope 13C contains 7 neutrons and 14C contains 8 neutrons.
Of carbon’s 6 electrons, 2 electrons go into the first energy level (the lowest energy level, aka the 1s orbital). The remaining 4 electrons go into the second energy level (2 electrons go into the 2s orbital and 2 electrons go into the 2p orbital). This results in an electron configuration of carbon is 1s22s22p2. As there are 4 electrons at the outermost energy level, carbon has 4 valence electrons. The valence electrons are important because they are the ones involved in chemical bonds.
Lead is a toxic heavy metal. Lead is for example used in construction and lead-acid batteries.
The element lead carries the symbol Pb. Its atomic number is 82. Consequently, a lead atom has 82 protons and 82 electrons.
The atomic weight of lead is 207.2. Lead's key isotope is 208Pb. Its nucleus consists of 82 protons and 126 neutrons. Other lead isotopes are 204Pb, 206Pb, and 207Pb.
Once there are as many electrons in an atom as in the lead metal the arrangement of electrons gets quite complicated. (The electron configuration of lead is [Xe] 4f145d106s26p2, where [Xe] is an abbreviation for the electron configuration of xenon. Xenon has the atomic number 54 and its electron configuration is already quite long.)
Figure 2: Ultrapure lead bead (original size 1.5 x 2 cm) [http://images-of-elements.com/lead.php]