2Origins of the Idea Democritus (~400 BCE) Matter is composed of atomsAtoms are eternal, invisible, indivisible, and incompressibleGreeks believed in 3 phases or states of matterSolid, liquid, gasWe now add plasma as the fourth phase
3Matter in the Universe99% of the known matter in the universe is Hydrogen and HeliumThe majority of the known matter is in the form of a plasma in stellar interiorsThe average density of the known matter in the universe is such that 1 gram would occupy a volume 30 x that of EarthThe location and characteristics of most of the matter in the universe is unknown – dark matter
4AntimatterA matter particle and an antimatter particle are the same with the exception of charge and magnetic properties (which are opposite).Naturally formed and man-made.When matter and antimatter particles collide, they annihilate each other.
5Elements Fundamental forms of matter Can’t be broken apart by normal means92 occur naturally on EarthThey are the same everywhere
7What Are Atoms?Smallest particles that retain the distinguishing physical and chemical properties of an elementMade up of subatomic particles:Protons (+)Electrons (-)Neutrons (no charge)
8Examples of AtomselectronprotonneutronHydrogenHelium
9Chemical Bonds, Molecules, & Compounds Bond is union between electron structures of atomsAtoms bond to form moleculesMolecules may contain atoms of only one element - O2Molecules of compounds contain more than one element - H2O
10Atomic Number 6C12 6C13 6C14 Number of protons All atoms of an element have the same atomic numberAtomic number of hydrogen = 1Atomic number of carbon = 6
11Isotopes vary in mass number 6C12 6C13 6C14Number of protons+Number of neutronsIsotopes vary in mass number
12IsotopesAtoms of an element with different numbers of neutrons (different mass numbers)Carbon 12 has 6 protons, 6 neutronsCarbon 14 has 6 protons, 8 neutrons6C12 6C13 6C14
13Chemical OriginsMost chemical elements were created after the Big Bang in subsequent generations of stars.Nucleosynthesis:primordial (H, He, Li)stellar (He -> Fe)explosive (Co -> …)
14Radioisotopes - Radioactivity Have an unstable nucleus that emits energy and particlesa particles – 2 protons and 2 neutronsb particles – an electrong rays – a high energy photonRadioactive decay transforms radioisotope into a different elementDecay occurs at a fixed rateBecause decay happens at a fixed rate, you can use it for age dating! (C14 has a half-life of 5,700 years.)
15The Age of the Solar System Ages of rocks can be measured through radioactive dating:Measure abundance of a radioactively decaying element to find the time since formation of the rockDating of rocks on Earth, on the Moon, and meteorites all give ages of ~ 4.6 billion years.