Transcript CHEMISTRY - Falmouth Schools

Chemical Context of Life
Chapter 2
• Matter - anything that takes up
space, has mass.
• Element - substance cannot be
broken down by chemical reaction
(i.e. copper)
• Represented by a symbol (Cu)
http://www.dmturner.org/Teacher/Pictures/Matter.gif
• Compound - consists of 2+ elements
combined in fixed ratio.
• 92 natural elements, 25 essential.
• Carbon, oxygen, nitrogen, hydrogen,
phosphorus, sulfur included.
http://attrasoft.com/imagefinder60/image_abm60_12_12.jpg
• Atom - smallest unit of matter; still
has properties of original element.
• Composed of subatomic particles.
• Neutrons are neutral, protons
positive charge, and electrons
negative charge.
http://serc.carleton.edu/images/usingdata/nasaimages/atom-with-electrons.gif
• Protons and neutrons - found in
atomic nucleus; electrons orbit
nucleus.
• Atoms of one element have same
number of protons in nuclei (atomic
number)
• Protons and neutrons together mass number.
Negative charge
Positive charge
Neutral charge
http://www.bartleby.com/images/A4images/A4atom.jpg
• Mass # - atomic # = number of
neutrons.
• Atomic weight - total mass of atom.
• Electrons weigh very little; mass
number is approximation of atomic
weight of atom.
http://www.bbc.co.uk/schools/gcsebitesize/img/gcsechem_90.gif
Isotopes
• Isotopes - atoms of element have
different numbers of neutrons
(different weights)
• Element exists as mixture of
isotopes.
• Radioactive isotope (carbon-14) nucleus decays spontaneously and
gives off energy.
http://education.jlab.org/glossary/isotope.gif
Energy
• Energy - ability to do work.
• Potential energy - stored energy;
kinetic energy - energy of motion.
• Top of a hill, potential energy;
rolling down the hill, kinetic energy.
• Electrons change positions while
orbiting nucleus.
http://www.glenbrook.k12.il.us/gbssci/phys/Class/energy/u5l1b1.gif
• Positions around nucleus - electron
shells or energy levels.
• Move away from the nucleus,
energy levels increase.
• Electron absorbs energy as it
moves away from nucleus.
• Gives off energy as moves closer to
nucleus.
Bonding
• Atoms share or transfer atoms
(bonding)
• Atoms held together by electrons
they share or transfer.
• Covalent bonding - pair of electrons
shared.
• 2+ atoms held together by covalent
bond = molecule.
http://www.cem.msu.edu/~reusch/VirtTxtJml/Images/lewstrc1.gif
• Covalent bonds either polar or
nonpolar.
• Electrons shared equally - nonpolar.
• Electrons closer to 1 atom – polar (1
atom more electronegative than
other).
• Ionic bonds - 1 atom donates
electrons to other atom - form
compounds (i.e. salt).
• Ionic and covalent bonds - strong.
Sodium donates electron to
• Ionic bond
chlorine.
Polar covalent bond – electrons pulled closer to
• Polar bond
oxygen.
• There are weaker bonds that exist
briefly.
• Hydrogen bonds form when H+ atom
covalently bonds to one atom but
attracted to another atom.
• Occurs mostly with O2 (like in
water).
Reactions
• Chemical reaction - making and
breaking of chemical bonds.
• Starting materials – reactants;
ending materials - products.
• Concentration of reactants
determines how fast or slow
reaction will go.
Rusting is an example of a chemical reaction
http://www.oxygenkiosk.net/php-cgi/d/135-2/A_Chemical_reaction.jpg