Matter takes up space and has mass Everything composed of matter Any biological process, function or structure can be broken down to its chemical level.

Matter takes up space and has mass Everything composed of matter

Any biological process, function or structure can be broken down to it’s chemical level -> molecules/atoms

Atoms and Molecules Element-substance that cannot be broken down

chemically to simpler substances with different properties

There are 92 naturally occurring elements, 25 of which are essential to life

O - 65% C - 18.5 % H - 9.5 % N - 3.3 %

C, H, O found in carbs, proteins, lipids and nucleic acids

N found in proteins, nucleic acids P found in nucleic acids S

Ca, P, K, S, Na, Cl, Mg = ~4 %

Few elements exist pure (alone) in nature - they are part of compounds

Compounds-substance containing two or more elements in a fixed ratio

Atomic structure Protons and

neutrons located in the nucleus at the center of the atom

Electrons found outside nucleus in orbitals, electron shells, or energy levels

Atomic number - the # of protons in an element, gives it it’s unique properties - all atoms of a particular element have the same # of protons

Atomic mass =

Atomic Symbols Each element represented by unique atomic symbol

One or two letters First letter capitalized Superscripted number before:

• Represents mass number

•

Subscripted number before• Represents to atomic number

• Number of protons in nucleus

MassMassNumberNumber

AtomicAtomicNumberNumber

AtomicAtomicSymbolSymbol

126

Carbon

C

Periodic Table Elements grouped in periodic table based on

characteristics Horizontal rows = periods; larger and larger

1

H1.008

3

Li6.941

11

Na22.99

19

K39.10

4

Be9.012

12

Mg24.31

20

Ca40.08

5

B10.81

13

Al26.98

21

Ga69.72

6

C12.01

14

Si28.09

22

Ge72.59

7

N14.01

15

P30.97

23

As74.92

8

O16.00

16

S32.07

24

Se78.96

9

F19.00

17

Cl35.45

25

Br79.90

10

Ne20.18

18

Ar39.95

26

Kr83.60

2

He4.003

II

IIII IIIIII IVIV VV VIVI VIIVII

VIIIVIII

11

22

33

44

Groups

Periods

Isotopes

Isotope - same # of protons (same element), different # of neutrons (different atomic mass)

Radioactive isotopes (radioisotopes) -

Radioisotopes

Tracers-monitor fate of atoms Useful in medical diagnosis (PETscans) Exposure to high levels can damage

molecules (DNA) harming organisms and causing cancer

Electrons and Bonding

Electrons determine how atoms behave when contacting other atoms-this is the single most important factor in the chemistry of living things

The # of electrons in the outermost shell (valence) determines chemical properties of atoms

Atoms with incomplete outer shells tend to interact with other atoms

Atoms want to have their outermost energy level filled

They can fill it by sharing electrons, or by giving electrons to or receiving electrons from another atom

Compounds and Molecules

When atoms of two or more elements chemically bond together, a compound is formed

The shapes of molecules are important in the structural and functional roles they play in living things

Chemical Bonds Sharing of

electrons forms a covalent bond

Giving and receiving electrons form ionic bonds

Covalent bond between atoms form molecules

Ionic bond

One atom (Na) gives (donates) an electron

The other atom (Cl) receives an electron

The atom that gives up an electron becomes a positive ion

The atom that receives an electron becomes a negative ion

Opposite charges attract each other (electrostatic attraction) to form am an ionic bond

Electrons and energy levels

Excited state - when an electron absorbs additional energy to move up to the next energy level. Electrons return to original ground state by emitting extra energy

Plants use this brief energy increase (10-8 sec) during photosynthesis

Biologically Important Weak Bonds

Organisms need to be able to change to maintain homeostasis (chemical balance) to meet changing environment

Covalent bonds are too strong and cannot be broken easily and changed

Weak bonds of biological importance include: ionic bonds, hydrogen bonds, van der Waals interactions

Hydrogen Bonds

Electrostatic attraction between oppositely charged portions of nearby molecules

Hydrogen bonds form between molecules that have no net overall electrical charge (are neutral)

Ionic bonds form between oppositely charge atoms

Weak bonds play crucial role in stabilizing shape of large molecules like DNA, proteins

Covalent bonds = 50-110 kcal/mole

Ionic bonds = 10 kcal/mole

Hydrogen bonds = 4-5 kcal/mole

van der Walls = 1-2 kcal/mole