Chemical elements The periodic table The periodic table is a very useful invention for chemists the scientists who study the substances around us It is a chart containing all the known chemical elements It even has spaces for elements not yet discovered To understand the periodic table how it was invented and why it is needed by chemists it is important to know about atoms and elements Inside an atom Nucleus containing protons and neutrons Neutron Proton Electron Atoms Books birds buildings and all the other things around you are made from tiny things called atoms You are made from atoms too Atoms are so small that a million of the biggest ones would make a pile less than half a millimeter high We cannot see atoms even with a microscope It can be difficult to believe that something invisible exists Just over a hundred years ago a few scientists still did not believe in atoms but the results of many experiments show that atoms are real Not only that they are made from even smaller things called subatomic particles Inside an atom There are three main types of subatomic particle Protons and neutrons are the heaviest They join together to make a 6 This is a diagram of a lithium atom Its nucleus is surrounded by three electrons and it contains three protons and four neutrons cluster in the middle of the atom called the nucleus Electrons are much lighter subatomic particles and clouds of them surround the nucleus THAT’S A FACT The nucleus of an atom is around 100,000 times smaller than the atom as a whole and most of an atom is empty space The name atom comes from the Greek word atomos meaning something that cannot be split
Elements A chemical element is a substance made from one type of atom Some elements such as gold and iron have been known for thousands of years Others have been discovered much more recently Helium often used in balloons was discovered in 1895 Americium used in smoke alarms was discovered only in 1944 Scientists continue to discover new elements today The atomic number proton number of an atom is the number of protons it contains All the atoms of an element have the same atomic number Hydrogen and Everything is made from atoms even you Oxygen atoms make up 65 percent of your body and carbon atoms make up 18 percent of it Hydrogen atoms make up most of the rest along with small percentages of many other elements carbon are two different elements Every hydrogen atom contains just one proton but every carbon atom contains six protons There are over a hundred different elements and no two elements have the same atomic number The periodic table helps chemists understand all the different elements and what they do 7
