The Chemistry of Life, Atoms and Elements Atoms and Atomic Structure

atom

smallest unit of matter that retains original properties

subatomic particles

made up of even smaller structures

Electron shells

regions
surrounding atomic nucleus
where electrons exist; each can
hold a certain number of electrons

1st shell

closest to the nucleuscan
hold 2 electrons

2nd shell

 can hold 8 electrons

3rd shell

can hold 18 electrons but “satisfied” with 8

Some atoms may have more than 3 shells

Matter

 can be combined physically to form a mixture – atoms of two or more elements physically intermixed without changing chemical nature of atoms themselves

suspensions, colloids, solutions

There are 3 basic types of mixtures

Suspension

mixture containing two or more components with large, unevenly distributed particles; will settle out when left undisturbed

Colloids

two or more components with small, evenly distributed particles; will not settle out

Solutions

two or more components with extremely small, evenly distributed particles; will not settle out; contain a solute dissolved in a solvent

Solute

substance that is dissolved

Solvent

substance that dissolves solute

 chemical bonds

Matter can be combined chemically when atoms are combined by

Molecule of an element

 formed by chemical bonding between two or more atoms of same element

Compound 

formed when two or more atoms from different elements combine by chemical bonding 

valence electrons of atoms interact

Chemical bonds are formed when 

octet rule 

states that an atom is most stable when it has 8 electrons in its valence shell   

Ionic bond 

formed when electrons are transferred from a metal atom to a nonmetal atom; results in formation of ions: cations and anions 

Anion

negatively charged ion; forms when nonmetal gains one or more electrons

The attraction between opposite charges bonds ions to one another forming a compound called a salt

Salt

any metal cation and nonmetal anion held together by ionic bonds

electrolytes

Salts can dissolve in water to form cations and anions called

Na+, k+, Ca2+, Mg2+, H+, Cl-, HCO-3, PO₄^3-

Important Ions in the Human Body

covalent bonds

strongest bond; form when two or more nonmetals share electrons 

single bond

Two atoms can share one

electronegativity

All elements have protons that attract electrons; property known as

fluorine

An element’s electronegativity increases from the bottom left to the upper right of the periodic table making

nonpolar

covalent bonds result when two nonmetals in a molecule with similar or identical electronegativities pull with equal force; therefore share electrons equally 

Nonpolar molecules occur in 3 situations

polar

 covalent bonds form polar molecules when nonmetals with different electronegativities interact resulting in an unequal sharing of electrons 

higher

atom with… electronegativity becomes partially negative as shared electrons are pulled toward other atom 

lower

Atom with…electronegativity becomes partially positive as shared electrons are pulled toward other atom 

dipoles 

Polar molecules with partially positive and partially negative ends are known as

surface tension

Hydrogen bonds are responsible for a key property of water

Water (H₂O)

makes up 60–80% of mass of human body and has several key properties vital to our existence

High heat capacity

able to absorb heat without significantly changing temperature itself

Carries heat with it when it evaporates (when changing from liquid to gas)

Cushions

and protects body structures because of relatively high density

lubricant

acts as... between two adjacent surfaces (reduces friction)

universal solvent

Water serves as body’s primary solvent; often called the

Oxygen pole – partially negative (δ⁻) 

Hydrogen pole – partially positive (δ⁺) 

 Water is a polar covalent molecule

hydrophilic solutes

Water is only able to dissolve

hydrophobic

Solutes that do not have full or partially charged ends are…do not dissolve in water; includes uncharged nonpolar covalent molecules such as oils and fats

 hydrogen ion (H⁺) 

The study of acids and bases is really the study of the

positively charged hydrogen ions (H⁺) and negatively charged hydroxide ions (OH⁻)

Water molecules in solution may dissociate (break apart) into

Acid

hydrogen ion or proton donor; number of hydrogen ions increases in water when acid is added 

Base (alkali)

hydrogen ion acceptor; number of hydrogen ions decreases in water when base is added

pH = – Log [H⁺]

Literally the negative logarithm of the hydrogen ion concentration:

buffer

chemical system that resists changes in pH; prevents large swings in pH when acid or base is added to a solution

7.2

Intracellular pH is

Carbohydrates, Lipids, Proteins, Nucleic Acids

Organic Compounds