Atom: the smallest part of an element that maintains the properties of that element Element: a substance that is composed of one type of atom Parts of an Atom: Proton: positively charged (nucleus) Electron: negatively charged (electron cloud) Neutron: no charge (nucleus) The number of protons and electrons in most atoms are equal giving the atom a net charge of zero. Periodic Table – the periodic table of elements is used to group elements according to their characteristics. Each element has a number and a symbol. Atomic number Element symbol Elemen t name Atomic mass The atomic number tells you the number of protons The atomic mass is equal to the number of protons + the average number of neutrons In some atoms, called isotopes there are more or less neutrons. Isotopes usually have slightly different properties than their parent atoms. Symbol Nitrogen Oxygen Carbon Atomic Number Atomic Mass Protons Neutrons Electrons Number of Protons Number of Neutrons Atomic Mass Properties Carbon - 12 6 6 12 Typical Carbon Carbon – 14 6 8 14 Radio isotope, can be used for carbon dating and as a marker element Almost all of the mass of an atom is found in the nucleus. ◦ Protons and Neutrons are given the same mass values (1 amu) ◦ AMU = atomic mass unit If an atom gains or losses electrons, it becomes an ion ◦ Ions have positive or negative charges ◦ Losing electrons gives an atom a more positive charge ◦ Gaining electrons gives an atom a more negative charge ◦ Positively and negatively charged ions are attracted to one another Forces that hold atoms together are called bonds. The outermost electrons of an atom determine its bonding abilities The different orbits of an atom hold different numbers of electrons. The first orbit holds two electrons. Each orbit after that holds 8. Atoms without full orbits bond readily with other atoms to fill their orbits Filling outer orbits stabilizes the atoms and forms compounds or molecules. Ionic bonds form between oppositely charged ions to fill their orbits. One atom loses and electron and the other atom gains it. Covalent Bonds form when two or more atoms share electrons. Carbon atoms can create bonds with up to four other atoms, making it a very versatile atom. It is also able to form double and triple bonds, which are strong, because they are sharing two or three electrons.