LC CHEM - chemical bonding

valency of an element

number of atoms of hydrogen that the element can bond with

two types of bonding / two ways elements can combine to satisfy the octet rule

ionic / covalent

ionic bond definition

electrostatic attraction between a positive and negative ion

comment on the structure of ionic compounds

• ionic compounds dont form individual molecules

• each positive ion is surrounded by six negative ions, and each negative ion is surrounded by six positive ions

  • orderly arrangement of oppositely charged ions is called a crystal lattice structure

whats the shape of an ionic compound caled

crystal lattice structure-

melting/boiling points of ionic compounds? why?

• very high melting and boiling points

• electrostatic attractions between the oppositely charged ions are very strong and require a lot of energy to be broken

apaearence of ionic compounds at room temperature

• exist as solid crystalline structures (crystal lattice)

ionic compounds conduction of electricity

• do not conduct electricity in the solid state as ions are not free to move (held in crystal lattice structure)
  will conduct electricity only in a molten or dissolved state (when there are ions available and are free to move)

for a compound to conduct electricity, what are the conditions

• ions must be present

• must be free to move

three uses of ionic compounds

• different salts used on food to preserve them

• sodium chloride is spread on roads in wintoer to help melt ice and snow

• hydrated sodium carbonate is used in washing soda tablets to clean clothes and to remove hardness (limescale) from water

define a covalent bond

occurs when electrons are shared between atoms, normally occurs between non metal atoms

whats a molecule

two or more atoms chemically combined by covalent bonding

whats a sigma bond

formed by head on overlap of two orbitals

whats a pi bond

formed by the sideways overlap of p or d orbitals

differences between sigma and pi bonds

• sigma bonds are head on, stronger and involve overlap of any type of orbital

• pi bonds are sideways, weaker and only involve the overlap of p or d orbitals

properties of covalent compounds

• low melting and boiling points

• liquids or gases, or soft solids

• will not condunct electricity

why do covalent compounds have low melting and boiling points

• intermolecular forces between covalent molecules are generally weak and easily broken

why dont covalent compounds conduct electricty

• no ions available

what do atoms being localised mean

not free to move from one atom to the next, but are held between atoms

what can break a triple bond

• lightning

• nitrogen fixing bacteria

single bonds are what type of bonds

sigma bonds

double bonds consist of what

a sigma and two pi bonds

all triple bonds consist of what

a sigma and two pi bonds