8 th Grade Science

 Matter – has mass & takes up space  Examples: rocks, tables, computer, books  Non-matter: heat & light  Atoms - the smallest component of an element consisting of a nucleus containing neutrons, protons and electrons.

 Joined together in various combinations  Elements – made of only one type of atom and cannot be broken down into simpler form

 Democritus – 1 st proposed that matter is made of small particles; John Dalton expanded later  Protons – positive electrical charge  Neutrons – no electrical charge  Electrons – negative electrical charge

 Atomic number – number of protons in an atom  Mass number = protons + neutrons  Isotopes – same element but different numbers of neutrons  Atomic number=number of protons=number of electrons

Atoms

 Compounds – contain atoms of more than one element and are chemically bonded together  Sodium chloride (NaCl) – table salt  Chemical Properties – when one substance reacts with another  Iron oxide (Fe 2 O 3 )- rust

 Chemical bonds – forces that hold atoms together in a compound  Electrons in the highest cloud can form bonds  2  8  18  32  50  72

 Covalent bond – sharing outer electrons  Molecules – group of atoms connected by covalent bonds  Pg.41 figure 7  Ionic bond – atoms that combine with a negative or a positive charge  Ions – electrically charged atoms

 Metallic bonds – movement of electrons from one positively charged ion to another  Hydrogen bonds – can form without the interactions of electrons  Example – hydrogen & oxygen (H 2 O)

 Mixtures – 2 or more substances not chemically combined  Heterogeneous mixture – not mixed evenly & each part keeps its own properties  Homogeneous mixture – evenly mixed throughout A.k.a – solution  Mini lab pg. 43

Properties of Matter

 Density – measure of the mass of an object divided by its volume  D = M/V  g/cm 3  Density columns

 Solid  Liquid  Gas  Plasma  Pg. 49 (notes)  Pg.51 #5 Classify