

Smallest unit of matter
Three subatomic particles



Protons
Neutrons
Electrons




Positively charged
Are part of the nucleus
Have a mass of 1 amu
Number of protons = atomic number

Defines the atom




Have a neutral charge
Also part of the nucleus
Have a mass of 1 amu
neutrons + protons = atomic mass




Have a negative charge
Moving around the nucleus
Have little mass
Number of electrons = number of protons

Variant forms of an atom


Atoms with same number of protons (C = 6) have
different number of neutrons 12C has 6 protons and
6 neutrons; 14C has 6 protons and 8 neutrons.
Some isotopes (radioactive) are unstable and decay
into more stable atoms
 Used to date rocks and fossils
 Used as tracers to follow atom through reactions or
through body


Radioisotopes are radioactive isotopes
They are not stable
Emit particles and energy as they decay spontaneously
into other elements


Decays at a constant rate into the same products
 Example: 14C → 14N

Tracer


Molecule with a detectable substance attached
PET scans




Electrons & Energy Levels
Full Shells = Happy Shells
Unfilled Shells = Reactive
Atoms  Molecules


Electrons are attracted to protons but are
repelled by other electrons
Orbitals are volumes of space around nucleus
where electrons are found


Each orbital hold 2 electrons
Shells



Are levels or orbitals
Closest to nucleus = 1 orbital = 2 electrons
Next shell = 4 orbitals = 8 electrons


Any atom with a vacant orbital will tend to fill
it by forming a bond with other atom(s)
Chemical bonds are unions between electron
structures of atoms

May give up , gain, or share electrons


Chemical bond
Distribution of electrons changes if the atom gives
up, gains, or shares electron(s)

Molecules


“2 or more atoms of
the same or different
elements join in
chemical bond”
One element



Oxygen
Hydrogen
Nitrogen

Compound

2 or more elements
 H2O = Water
 CO2 = Carbon dioxide

Mixture

Blend without
chemical bond
 Sugar water



Ionic Bond
Covalent Bond
Hydrogen Bond

Electrons are transferred



Forms ions atoms with a net electrical charge
+/


Gained
Lost
Gain electrons = - charge
Lose electrons = + charge
Positive and negative ions attract each other



NaCl
HCl
KBr
Sodium ion
Chloride ion
a
A crystal of table salt is
a cubic lattice of many sodium
ions and chloride ions.
b
The mutual attraction of
opposite charges holds the
two kinds of ions together
closely in the lattice.
Fig. 2.8, p. 23


Electrons shared
Non-polar covalent


Equally shared
Polar covalent



Unequally shared
Slight positive & negative charge to opposite “poles”
of the molecule
Charge areas attract
 Hydrogen bond

Form between a hydrogen atom and an
electronegative atom


Each with separate polar covalent bonds
Are not chemical bonds



Do not make atoms into molecules
Individually weak
Collectively stabilize structures of large molecules

Water molecules are polar
Form hydrogen bonds with other polar molecules
 Hydrophilic substances (water-loving)
 Hydrophobic substances (water-dreading)


Polarity gives liquid water unique properties
that make life possible:



Resistance to temperature changes
Internal cohesion
Dissolves polar and ionic substances



Absorbs heat without changing temperature
Evaporation = cooling
Freezing hydrogen bonds resist breaking

Crystal structure is less dense than water

Hydrogen bonding


Cohesion (stickiness)
Cohesion pulls water through plants

Capillary action



Solvent is a substance, usually liquid, that
dissolves other substances
Solutes are dissolved substances
Water is an excellent solvent



Will dissolve most polar molecules
Is the most nearly universal solvent
Form spheres of hydrogen
 Clusters of water molecules around a solute
 A substance is said to be dissolved after solvent
molecules cluster around its ions or molecules & keep
them disapersed



Arrange substances from acid to base 0-14
7 = Neutral
Power of hydrogen (negative exponent)

Acids 0-7 on pH scale
(Protons) H+ ions
 Red in litmus
 Sour taste
 React with metals


Bases 7-14 on pH scale



OH- ion
Blue in litmus
Bitter taste

Weak acid and the base that forms in water



H2CO3  HCO3- + H+
Carbonic acid  Bicarbonate
Prevents swings in pH.

Form from an acid and a base
Hydrochloric acid + Sodium hydroxide = Sodium
chloride + water
 HCl + NaOH  NaCl + H2


Useful ions in solution