The role of chemistry in biology

Matter

Anything that takes up space and has mass

Element

A substance that can't be broken down into other substances by chemical reactions

Compound

A substance made of two or more different elements combined in a fixed ratio

Essential elements

Elements an organism needs to live and reproduce

Atom

The smallest unit of matter that still has the properties of an element

Three key subatomic particles

Protons (+), electrons (-), neutrons

Where are protons and neutrons located in an atom?

Packed together in the atomic nucleus

Atomic number

The number of protons in an atom's nucleus; the bottom number

Mass number

The total number of protons and neutrons in an atom's nucleus

Isotopes

Atoms of same element with same number of protons, different number of neutrons

Radioactive isotopes

An isotope whose nucleus decays spontaneously, releasing particles and energy

Half-life

The time it takes for 50% of a radioactive isotope to decay

Electron shell

A fixed energy level at which electrons orbit the nucleus

How does electron energy relate to distance from nucleus?

Electrons farther from nucleus have higher potential energy

What happens when an electron absorbs energy?

It moves to a higher electron shell

What happens when an electron loses energy?

It falls to a lower electron shell and releases energy lost as heat

Valence elections

The electrons in an atom's outermost shell

Valence shell

The outermost electron shell of an atom

What determines an atom's chemical reactivity?

The number of electrons in its valence shell (unpaired/incomplete = reactive)

Inert (unreactive) elements

Elements with a full valence shell

Maximum electrons per orbital

2 electrons

Maximum electrons in first electron shell

2 electrons (one s orbital)

Maximum electrons in second electron shell

8 electrons (one s orbital & three p orbitals)

Covalent bond

Chemical bond formed by 2 atoms sharing a pair of valence electrons

Single vs double covalent bond

Single bond = one shared electron pair

Double bond = two shared electron pair

Molecule

Two or more atoms held together by covalent bonds

Valence (of an atom)

The number of covalent bonds an atom can form, usually equal to it unpaired valence elections

Electronegativity

How strongly an atom pulls shared pair of electrons towards itself in a covalent bond

Nonpolar covalent bond

A bond where electrons are shared equally (atoms have similar electronegativity)

Polar covalent bond

A bond where elections are shared unequally, giving partial charges (atoms differ in electronegativity)

Why is water a polar molecule?

Oxygen is more electronegative than hydrogen, pulling shared electrons towards itself

Ion

An atom that has gained or lost electrons, giving it an electrical charge

Cation

A positively charged ion - formed by losing electrons

Anion

A negatively charged ion - formed by gaining an electron

Ionic bond

The attraction between oppositely charged ions

Ionic compound (salt)

A compound formed by ionic bonds between cations and anions e.g. NaCl

Are ionic bonds stronger dry or dissolved in water?

Stronger when dry; weaker (partially shielded) when dissolved in water

Hydrogen bond

A weak attraction between a hydrogen atom (with a partial + charge) and an electronegative atom (O or N) on another molecule

Van Der Waals interactions

Weak attractions between molecules caused by ever-shifting regions of partial charge

Which bonds are strongest; covalent, ionic (dry), hydrogen or Van Der Waals?

Covalent & ionic strongest

Hydrogen & Van Der waals weakest

Why does molecular shape matter biologically?

Shape determines how molecules recognise and bind to each other

Shape of a water molecule

Bent/V-shaped,

bond angle of 104.5°

Shape of a methane (CH4) molecule

Tetrahedral

Bond angle of 109.5°

Chemical reaction

A process that makes or breaks chemical bonds, changing the composition of matter

Reactants vs products

Reactants are the starting substances, bonds broken

Products are the substances formed by the reaction, bonds formed