matter. origins of the idea democritus (~400 bce) –matter is composed of atoms –atoms are...
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Matter
Origins of the Idea
• Democritus (~400 BCE)– Matter is composed of atoms– Atoms are eternal, invisible, indivisible,
and incompressible• Greeks believed in 3 phases or
states of matter– Solid, liquid, gas– We now add plasma as the fourth
phase
Matter in the Universe
• 99% of the known matter in the universe is Hydrogen and Helium
• The majority of the known matter is in the form of a plasma in stellar interiors
• The average density of the known matter in the universe is such that 1 gram would occupy a volume 30 x that of Earth
• The location and characteristics of most of the matter in the universe is unknown – dark matter
Antimatter
• A 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.
Elements
• Fundamental forms of matter
• Can’t be broken apart by normal
means
• 92 occur naturally on Earth
• They are the same everywhere
What Are Atoms?
• Smallest particles that retain the distinguishing
physical and chemical properties of an element
• Made up of subatomic particles:– Protons (+)
– Electrons (-)
– Neutrons (no charge)
Hydrogen Helium
electron
proton
neutron
Examples of Atoms
Chemical Bonds, Molecules, & Compounds
• Bond is union between electron structures of atoms
• Atoms bond to form molecules
• Molecules may contain atoms of only one element - O2
• Molecules of compounds contain more than one element - H2O
Atomic Number
• Number of protons
• All atoms of an element have the same atomic number
• Atomic number of hydrogen = 1
• Atomic number of carbon = 6
6C12 6C13 6C14
Mass Number
Number of protons
+Number of neutrons
Isotopes vary in mass number
6C12 6C13 6C14
Isotopes
• Atoms of an element with different numbers of neutrons (different mass numbers)
• Carbon 12 has 6 protons, 6 neutrons
• Carbon 14 has 6 protons, 8 neutrons
6C12 6C13 6C14
Chemical Origins
• Most chemical elements were created after the Big Bang in subsequent generations of stars.
Nucleosynthesis:
primordial (H, He, Li)
stellar (He -> Fe)
explosive (Co -> …)
Radioisotopes - Radioactivity• Have an unstable nucleus that emits energy and
particles a particles – 2 protons and 2 neutrons b particles – an electron g rays – a high energy photon
• Radioactive decay transforms radioisotope into a different element
• Decay occurs at a fixed rate
• Because decay happens at a fixed rate, you can use it for age dating! (C14 has a half-life of 5,700 years.)
The 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 rock
Dating of rocks on Earth, on the Moon, and meteorites all give ages of ~ 4.6 billion years.