The Chemical Level of Organization

Atoms• Atomic Structure• Electron Shells, losing/gaining electrons• Ions

Molecules, their formation through bonds• Chemical Bonds (how, why, and types)

Macromolecules• 4 major macromolecules

Elements & Atoms

ElementsDifferent kinds of matter (material) that have distinct (chemical) properties

Examples:

• gold• carbon• hydrogen• sodium• nitrogen• calcium• oxygen

many different object/pictures

5 basic shapes

Atoms

Smallest unit/piece of an element (matter) that still has the properties of that element.

The structure and components of an atom

--Neutral

--positive

--negative

Electron

Neutron

ProtonElectron Shell (orbital)

NucleusElectron Shell (orbital)

2p, 2e, Helium 4p, 4e, Beryllium3p, 3e, Lithium

Different elements are made of atoms with different numbers of protons and electrons—that is why each element has its own unique set of properties

Element Number of protons

Number of electrons

% of Body by Weight

Hydrogen 1 1 9.5

Carbon 6 6 18.5

Nitrogen 7 7 3.3

Oxygen 8 8 65.0

Sodium 11 11 0.2

Sulfur 16 16 0.3

Chlorine 17 17 0.2

Valence Shellsoutermost shell of atom = valance shell

• Atoms are most stable when the outer shell is filled, or emptied.

Valance shells

Electron shells of common elementsValance in red

1st shell 2nd shell 3rd shell 4th shell

Hydrogen 1

Carbon 2 4

Nitrogen 2 5

Oxygen 2 6

Sodium 2 8 1

Chlorine 2 8 7

Potassium 2 8 8 1

calcium 2 8 8 2

Behavior of atoms and outer electron shells

Atoms “want” to have completely emptied or completely filled outer electron shells.

Atoms will gain, lose, or share electrons to fill or empty their outer shells.• This is the basis for chemical bonds and the

formation of ions

electron shell = orbital = valence shell = regions that hold electrons

Formation of ions

Gaining or Losing Electrons

Gaining ElectronsIf the outer shell is almost full, gaining electrons is likely to happen

Losing ElectronsIf the outer shell is almost empty, losing electrons is likely to happen

Note that both of these events will result in the creation of an ion.

1- 1+

Atoms lose an electron and become a positive ion.

Atoms gain electrons and become a negative ion.

4 protons: 4+ 3 electrons: 3- Charge: 1+

4 protons: 4+ 5 electrons: 5- Charge: 1-

(not from your text)

Functions of Ions

Generate Electricity (membrane potentials) • e.g., neurons of your brain and nervous system (sodium,

potassium, and calcium)

Regulate/initiate cellular events• e.g., help initiate muscle contraction, release of

neurotransmitters, expression of DNA, activate enzymes (calcium), blood clotting

Building materials• e.g., Calcium (and phosphate) is part of bones

Regulate pH/acidity • HCO3- (bicarbonate ion)

CHEMICAL BONDING AND MOLECULES

CHEMICAL BONDING

Two or more atoms can bind together to form a molecule.

There are 3 major types of chemical bonds• Ionic Bonds• Covalent Bonds• Hydrogen Bonds

Create molecules

do NOT create molecules

Ionic Bonds

Formation of an Ionic Bond

Covalent Bonds

When an electron pair is shared, both atoms get to “count” the other atom’s electron as if it was part of their own valance shell.

Covalent Bonds:• Atoms share electrons

• Strength:

Polar and Non-polar Bonds/Molecules

Non-Polar = electrons are shared equally • the entire molecule is neutral and uniformly charged.• Tends to mix well with other non-polar substances• Don’t mix well with water

Polar = electrons are not shared equally• then entire molecule is neutral overall, but has

regions/areas that are + or – charged• Tends to mix and dissolve well with other polar things• LIKES WATER/mixes with water

Polar (and charged)

HydrophilicWater soluble

nonpolar

HydrophobicNot water soluble

(lipid soluble)

Hydrogen bonds

Hydrogen BondsAre attractive forces between a hydrogen and an oxygen or a hydrogen and a nitrogen

• NOT based on electron transfer or sharing

Hydrogen bonds can exists between:1. two different molecules--resulting in their being held together.

2. two different parts of the same molecule— resulting in the bending/folding of the

molecule.

But hydrogen bonds don’t create molecules the way that a covalent or ionic bond does.

Comments on H-bonds

individual hydrogen bonds are weak, the collective influence of many hydrogen bonds can be significant• The bending of molecules with hydrogen bonds creates

the final 3D shape of proteins• Form between water molecules• Hold DNA strands together

H-bonds are weak bond formed between two polar molecules based on opposite charges attracting (not based on electron sharing)