Summary Organic and inorganic matter

MATTER

SOLIDS → compact & have a definitive shape
LIQUIDS → definitive volume and take shape of their container
GASES → have neither a shape nor a volume

 All forms of matter are made of building blocks → chemical elements
 Elements → a substance which cannot be split into a simpler substance by using basic
chemical procedures
o 118 elements & 92 occur naturally on earth

CHEMICAL ELEMENTS
 26 different elements in human body
 Major elements → oxygen(O), carbon( C), hydrogen(H) & nitrogen(N)
o 96% of body mass
 Lesser elements → Calcium(Ca), Phosphorus(P), Potassium(K), Sulphur(S), Sodium(Na),
Chlorine(Cl), Magnesium(Mg), Iron(Fe)
o 3.6% of body mass
 Trace elements → make up 0.4% of body mass
o Iodine needed to make thyroid hormones
 All have important function in the body

ATOM
 Smallest chemical unit of a molecule
 Nucleus contains: protons(positive charge) & neutrons(no charge)
o Nucleons = protons & neutrons
 Electrons(negative charge) orbit around nucleus in an electron shell




 Atoms have net charge of zero
 Orbital → barrier(energy shell) preventing electron from passing beyond
→ can have multiple orbits, that set up further and further from nucleus
o 1st orbital (2 electrons), 2nd orbital (8 electrons), 3rd orbital (8 electrons), 4th orbital (18
electrons)

 Atomic number: number of protons in nucleus (= number of electrons)
o Used to identify element

,  Mass number: number of protons + neutrons (mass of nucleus)
 Atomic mass: average mass of all its naturally occurring isotopes

Isotopes
 When an atom exists as one or more species (same atomic number but differ in atomic
mass)
o Therefore different number of neutrons

Ion → formed when an element gains or loses an electron (positive or negative)
o Ionisation - process of losing or gaining electrons (e.g. Ca 2+)

Molecule → formed when > 2 atoms share electrons (e.g. H 2O)
Compound → substance that contains atoms of two or more different elements (e.g. H 2O)

CHEMICAL BONDS
→ forces that hold together the atoms of a molecule or a compound
o Dependent on valence electrons (electrons found in the other most orbital of the atom)

Ionic bonds
 Results when valence electrons from one atom are completely transferred to 2nd atom
(NOT sharing)
o Ions are formed
o Cations → positively charged & move towards negative pole (cathode)
o Anions → negatively charged and move towards positive pole (anode)
 Form ionic compounds
 Example: Na + Cl → Na+(cation) Cl- (anion)
 Easily dissociate(separate) & ions attracted to polar water molecules & hydration spheres
are formed
o These polar molecules are soluble
 In body → found in teeth & bones - give strength
 Electrolyte → an ionic compound which breaks apart in solution
o Most ions in body are dissolved in fluid as electrolytes

Covalent bonds
 Occur when atoms share valence electrons
 Found between identical atoms (e.g. O 2) - strongest because electrons are equally shared
 > No. of electron pairs shared, stronger the bond
 Most common chemical bond in body
 Non-polar molecules → electrons equally distributed between atoms
 Single (H2) , double (O2) or triple (N2) bonds can form between two atoms
 Polar molecules → when covalent bonds are formed between two different atoms
(electrons pulled towards atom with larger nucleus)
o Positive & negative side(end to which electron is pulled)
o Water is polar & serves as a solvent
o Polar covalent bonds are weaker & can ionise(unstable & breakdown)

HYDROGEN BONDS
 Found between polar molecules
 Usually form between slightly positive hydrogen with second electronegative atom (oxygen
or nitrogen)
 Weaker than covalent bonds