Notes
Section 2.1
The Nature of Matter
Why do we study chemistry in biology class?
Life depends on chemistry
Chemical reactions maintain life What is the study of chemistry in living
things called? biochemistry
Chemistry Basics
Matter: substance of which any physical
thing is composed. Basic unit of matter = atom
The word atom means “unable to be cut”
Named by Democritus
Atoms are composed of 3 main types of subatomic particles
1. Proton - positively charged particle
2. Neutron – neutral particle – no charge 3. Electron – negatively charged particle
Protons and neutrons are together in the nucleus Electrons orbit around the nucleus Why? They are attracted by:
the positive charge of the proton(s) the mass of the
nucleus
Interesting Tidbits
The charge of a proton (+) is equal to and
opposite the charge of an electron (-)
The mass of a proton is over 1800 times
larger than that of an electron
The neutron also has a mass similar to
that of the proton
More on the Atom
o Neutral Atom – equal # protons and
electrons o Atomic Number - # protons in nucleus o Mass Number - # protons and neutrons
Elements
Substance composed of only 1 type of
atom
Over 100 known About 2 dozen found in living things Represented by 1 – 2 letter symbols
C = carbon He = helium
Most Common Elements in Living Organisms
Oxygen Hydrogen Carbon Nitrogen
Isotopes
Atoms of same element with differing
numbers of neutrons
This alters the atom’s mass but NOT its chemical properties
Isotopes are distinguished by the mass number on their symbol 12C 13C 14C
Radioactive Isotopes
Unstable nuclei
Breakdown at constant rate Emit radiation Uses:
Determine the age of rocks and fossils Treat cancer Tracers in living tissue Kill bacteria in food
Chemical Compounds
2 or more elements chemically combined
in fixed amounts • Elements change properties when they combine in a compound!!! • e.g. NaCl = enhance the taste of food
• •
Na = explosive silvery metal Cl = poisonous green gas
Compounds are represented by formulas
Symbols of elements present and the
ratio in which they occur H2SO4 H2O
NaCl
Molecule = smallest unit of a compound
Chemical Bonds
Forces holding atoms together in
compounds
Formed by specific interactions of electrons
Two main types of chemical bonds:
1. Covalent (weak, and share electrons) 2. Ionic (strong, and transfer electrons)
Covalent Bonds
Sharing of electrons between atoms
o Single bond = sharing two electrons
Fluorine molecule = F2 o Double bond = sharing four electrons o Triple bond = sharing six electrons
o Example = H2O
Ionic Bonds
Transfer of 1 or more electrons Atom becomes electrically charged Charged atom = Ion Opposite charges hold atoms together in a compound Example: NaCl
Weak Chemical Bonds
Van der Waals Forces
Slight attraction between different molecular surfaces Due to positive and negative regions on the molecules
Geckos feet show Van der Waals forces at work in strong adhesion of two hydrophobic surfaces to adhere in air.
Chemistry Basics (cont’d)
Chemical Reactions – interaction of
molecules to yield new molecules
Reactants yield products Total # atoms of each element is the same on each side of the equation
A look at an atom
Neutrons are in red
A look at an atom
Periodic Table of Elements