Life10e Ch02 Lecture-Small Molecules and the Chemistry of Life

Electron

negligible mass; negative charge

Protons

have mass; positive charge

Neutrons

have mass; no charge

Element

pure substance containing only one

kind of atom.

atomic number

Number of protons

The number of protons

identifies an element.

Atoms have

volume and mass.

Mass of atoms consist of

one proton or one neutron

1 atomic mass unit (amu)

1 dalton, or 1.7 × 10–24 grams

Mass of electron

ne electron = 9 × 10–28 (negligible and usually ignored)

protons and electrons determine what

how an element behaves

in chemical reactions.

periodic table

how Elements are arranged

About 20–25% of the 92 elements

are essential to life (essential

elements)

Bulk elements: Carbon, hydrogen,

oxygen, and nitrogen make up

96%

Atomic Number

number of protons

Chemical symbol

He

Atomic weight

proton + neutrons

Mass number

number of protons +

number of neutrons/daltons

Isotopes

forms of an element with

different numbers of neutrons, and

thus different mass numbers

Example:

12C has 6 neutrons

13C has 7 neutrons

14C has 8 neutrons

Atomic weight

(relative atomic mass):

average of mass numbers of isotopes

in their normally occurring proportions.

Radioisotopes

give off energy in the form of alpha,

beta, and gamma radiation from the nucleus.

radioactive decay

transforms the atom,

sometimes resulting in a change in the number of

protons.

Molecule

stable association of atoms

Radioisotopes

useful in research and in

medicine, but radiation can damage cells

and tissues.

Radiation is sometimes

used to treat cancer

atoms will interact

The number of electrons determines how

Chemical reactions

Changes in the distribution of electrons between atoms.

Orbital

region where an electron is

found at least 90% of the time.

shapes

and orientations

can be

occupied by two electrons.

electron shells

First shell: one s orbital (holds 2

electrons). Second shell: 1 s and 3 p orbitals

(holds 8 electrons). Additional shells: 4 orbitals (each holds

8 electrons).

valence

shell

outermost electron shell, determines how the atom

behaves.

stable

outermost shell is full;’ wont interact with other atoms.

unpaired

electrons

are reactive atoms, in their outermost shell

Reactive atoms

an share electrons, or

lose or gain electrons, resulting in

atoms being bonded together to form

molecules.

Octet rule

Tendency of atoms to form

stable molecules resulting in 8

electrons in their outermost shell