THE CHEMISTRYOF

LIFE

Honors BiologyChapter 2

The Nature of Matter

Essential Question:How would you explain the relationship between atoms, elements, and compounds?

Atoms

smallest unit of matter

each element has its own unique # of protons

(atomic #)

Elements

Only ~ 24 elements found in living things

4 most abundant:1. Oxygen2. Carbon3. Hydrogen4. Nitrogen

Isotopes

atoms of same element with different # of neutrons

#p + #n = atomic mass

(mass #)

Radioactive Isotopes

some isotopes have unstable nuclei so they undergo “decay”

Chemical Cpds

compound: substance formed by chemical combination of 2 or more elements in definite proportions

cpd has different properties than elements alone had

Chemical Formulas

Chemical Bonds

Atoms form chemical bonds with other atoms to ________________.

The 2 main types of bonds are ________ and ____________.

Types of Bonds

Covalent Bonds Polar Covalent Bonds

share valence e-

unequal sharing e-

Chemical Bonds

Ionic bonds

transfer of e- atom with a charge (ion)

(+) ions = cations(-) ions = anionsopposite charges attract

charges must be balancedstronger bonds than covalent

van der Waals Forces

Because atoms do not share e- equally, there are polar bonds

This causes the (+) end of one molecule to be attracted to the (-) end of another molecule

This attraction is called van der waals forces Very weak compared to covalent bonds but are

still able to hold molecules together

Van der Waals Forces in action

What type of bond is shown here?