EARTHS CYCLES in ACTION THE nitrogen cycle By Diane Dakers A nitrogen atom Electron Neutron P Proton CRABTREE Publishing Company www crabtreebooks com
CHAPTER 1 Why Care About Nitrogen Every known living thing plant and animal contains nitrogen About three percent of your body is nitrogen That means if you weigh 100 pounds 45 kilograms you contain about three pounds 1 4 kg of nitrogen That’s about how much a large guinea pig weighs A nitrogen atom E N Electron Neutron Proton Tiny Building Blocks Everything in the world is made up of atoms and molecules Atoms and molecules are submicroscopic This means they are so small that they cannot be seen with an ordinary microscope Atoms are individual building blocks and molecules are combinations of those building blocks The Periodic Table of Elements lists the 118 known types of atoms For example one of those atoms is nitrogen represented on the periodic table as N P Every living thing contains nitrogen including you 4
Another is oxygen represented by the letter O When one nitrogen atom combines with two oxygen atoms they form a molecule called NO2 This is nitrogen dioxide a brown gas that is sometimes seen hanging over big cities In combination with other toxic gases this brown haze is also called smog The atoms that combine to form the most important molecules in the human body are carbon C hydrogen H phosphorus P oxygen O and nitrogen N In the center of each atom is a nucleus which contains protons and neutrons Surrounding the nucleus is a cloud of electrons The number of electrons is the same as the number of protons in an atom Nitrogen has seven protons and seven electrons Charting the Atoms The Periodic Table of Elements shows all the chemical elements known to exist Each element is made up of atoms of that type of element For example the element nitrogen consists of nitrogen atoms Some elements occur naturally and others are developed in laboratories and are therefore synthetic or human-made The periodic table lists them in order of increasing atomic number or the number of protons in the atom’s nucleus Nitrogen is number 7 in the table 5 Periodic Table of Elements
