Compounds and Molecules Chapter 6.1 Notes

Chemical Bonds A compound is made of two or more elements that are chemically combined Chemical bonds are the forces that hold atoms or ions together in a compound Bonds can bend, stretch, and rotate without breaking

Inside of the balloon there is hydrogen and oxygen gas (2 oxygen atoms are chemically combined together and 2 hydrogen atoms are chemically combined together) When heat is added, the bonds between the atoms are broken Atoms rearrange and form new chemical bonds (oxygen bonds with 2 hydrogen to form water)

Chemical Structure A compound’s chemical structure is the way the compound’s atoms are bonded Structures can be shown by various models Different models show different aspects of the compounds

Ball-and-Stick Model Atoms are represented by balls Bonds that hold the atoms together are represented by sticks True chemical bonds are not as rigid as the sticks, but this model makes it easy to see the bonds and the angles they form If this model was more accurate, the bonds would be shown as flexible springs

Bond Length and Bond Angle Bond length is the distance between the nuclei of two atoms that are bonded together If a compound has three or more atoms, the bond angle, or the angle formed by two bonds to the same atom, tells you which way the atoms point

Space-Filling Model Model that shows the relative sizes of atoms in a compound Does not show bond lengths Each hydrogen takes up less space than the oxygen atom

Structure and Properties The chemical structure of a compound determines the properties of that compound Compounds that have network structures are strong solids A network structure has bonds with the same bond angles and an arrangement of atoms that is the same everywhere in a compound Compounds with network structures have very high melting points and boiling points

Quartz—made of silicon and oxygen atoms bonded in a strong, rigid structure

Networks made of bonded ions Table salt, or sodium chloride (NaCl), is made of positively charged sodium ions and negatively charged chloride ions The strong attraction between opposite charges cause high melting points and high boiling points

Sodium chloride has regularly shaped crystals and a repeating network

Compounds made of molecules If we just look at salt and sugar, they both look very similar—their structures are very different Unlike salt, sugar is made of molecules Compounds made of molecules may be either a solid, liquid, or a gas

A molecule of sugar has carbon, hydrogen, and oxygen atoms that are joined by bonds Molecules of sugar attract one another to form crystals, but these attractions are much weaker

Quick Lab Melting Sugar and Salt Inquiry Lab