The Chemical Compounds of Life Basic chemistry

Matter Anything that has mass and takes up space is matter. There are about 103 naturally occurring different types “building materials” of matter; we call these types elements.

Atoms The smallest particle of an element that has all the properties of that element and that can’t be broken down by ordinary physical or chemical means.

Atom structure

Protons Atomic number gives the number of protons in an atom. The number of protons in an atom determine its essential character. Changing the number of protons changes the element.

Neutrons Neutrons are found in the nucleus with protons. The atomic mass number gives the number of neutrons PLUS the number of protons. Neutron number can vary somewhat.

Electrons Electrons carry a tremendous amount of energy. # of electrons is usually equal to # of protons. Arrangement of electrons determines how an atom will interact with other atoms.

Building an atom cience/terc/content/investigations/es050 1/es0501page05.cfmhttp:// cience/terc/content/investigations/es050 1/es0501page05.cfm om.htmhttp:// om.htm Practice!

Isotopes An isotope is an atom with an unusual number of neutrons. Different elements have different numbers of possible isotopes. Carbon has 4 isotopes.

Isotopes of carbon Nonradioactive carbon-12Nonradioactive carbon-13Radioactive carbon-14 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 8 neutrons 6 electrons 6 protons 7 neutrons

Valence electrons Atoms “want” to have a filled valence and will interact with other atoms to get it. May gain or lose electrons – ionic bond May share electrons – covalent bond

Ions An ion is an atom with an electrical charge. Created by gaining or losing electrons. Cation – positively charged ion. Anion – negatively charged ion.

Ionic bonds ps=20&sf=&sa=0&sq=&dm=0&p=781E1B 35841F6F4C Sodium atom (Na)Chlorine atom (Cl) Transfer of electron

Ionic bonds Sodium atom (Na)Chlorine atom (Cl)Sodium ion (Na + )Chloride ion (Cl - ) Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1

Ionic bonds Transfer of an electron leaves the Na atom as a positive ion (Na + ) and the Cl atom as a negative ion (Cl - ). What happens to particles with opposite charges? Resulting substance is called a compound, and we can write a chemical formula for it: NaCl

Ionic bonds Remember that each atom wants to have a filled valence. Consider Magnesium (atomic # 12) and Chlorine (atomic # 17): describe the bond that forms.

Covalent bonds Two atoms may come close enough to share electrons. Each atom “feels” like it has a full valence. Formation of the bond releases energy and the resulting substance acts like a single unit. Creates molecules.

A water molecule Covalent bond

Hydrogen bonds Weak attractions between polar molecules that contain hydrogen atoms. Important in forming complex shapes in large molecules. More on these later…