Structure and Bonding Flashcards
What do substances with high and low melting points have?
substances with high melting points have strong forces of attraction between atoms and low melting point shave weak forces of attraction between molecules
What are the strength of forces and arrangements of particles in solids, liquids and gases
giants solids- with ionic and covalent bond are solids with high melting points. particles r in a fixed arrangement, do not move and vibrates.
molecular solids- have low melting points but forces r strong between molecules. particles r in a fixed arrangement, do not move and vibrates.
liquids- have low melting points but forces r strong between molecules. particles r close tgt but r arranged randomly, they slide over each other
gases- hv low melting and boiling points. particles r far apart and move randomly.
What is a covalent bond?
a covalent bond is the force of attraction between the nuclei of two neighbouring atoms and a pair of electrons shared between them. they r very strong takes a lot of energy to break them apart.
Describe covalent bonding
formed by the overlap of atomic orbitals. each orbital which combines contributes an unpaired electron to the bond, the joined orbital is called a molecular orbital. the greater the overlap of the atomic orbital, the stronger the covalent bond is
What is a sigma bond?
a sigma bond is the overlap of atomic orbitals about a line drawn between the two nuclei. electron density is found symmetrically about a line drawn joining the two nuclei
What is a pi bond?
a pi bond is the sideways overlap of p orbitals. electron density is not found symmetrically about a line drawn joining the two nuclei.
How is a single bond represented?
a shared pair of electrons in a single bond is represented by a single line
What are lone pairs?
are electron pairs in the outer shell that do not take part in bonding
What do dot and cross diagrams show?
show how electrons are paired together in a molecule or ion
What are electron deficient molecules and expanded octet
are atoms in a compounds that have less that 8 electron in the outer shell. expanded octet has more than 8 electrons in the outer shell.
What is coordinate/ dative covalent bond
is where one atom provides both electrons for the covalent bond. for it to occurs need the first atom with lone pair of electrons and second with an unfilled orbital.
What does displayed formula show?
shows the coordinate bond with an arrow. the head of the arrow points away from the atoms which donates the lone pair
Explain ionic bonding
ions are formed by gaining or losing electrons, usually have a full outer shell. ionic bonding is the net attractive force between positive and negative ion. the net attractive force results in a giant ionic structure. the structure is arranged into a 3 dimensional lattice. electrostatic attractive force between ion acts in all directions and the bond is very strong
Explain metallic bonding
is a lattice of positive ions in a sea of delocalised electrons. delocalised electrons are not associated with atoms or ions. they move freely between metals
What is electronegativity? Where does it increase and decrease?
is the ability of an atom in a covalent bond to attract electrons in the bond to itself, it increases across a period from group 1-7, decreases down any group
What are polar and non polar molecules? also speak about its polarity
if electronegative values in a covalent bond are the same its non polar, also if positive n negative coincide its non polar
if electronegative values in a covalent bond are different then its polar, if the positive and negative values do not coincide its polar
What’s the degree of polarity measured by?
degree of polarity is measure using dipole movement
What are the 3 types of intermolecular forces?
permanent dipole- dipole force
van der Waals forces
hydrogen bonding
Describe the 3 intermolecular forces
permanent dipole- dipole- is the weak attractive force between the positive of a molecule and negative of another neighbouring molecule
van der Waals- partakes in temporarily induced dipoles
hydrogen- permanent form of dipole bonding, it required one molecule with a H atoms covalently bonded to an f, n or o atom, a second molecule with f, n or o atom with a lone pair of electrons.
What is a lattice?
is a regular 3 dimensional arrangement of particles.
What are giant structure and their 3 types?
are lattices with strong bonds between the particles
3 types:
ionic- sodium chloride, magnesium oxide
covalent- diamond, silicon dioxide
metallic- copper, iron
What are the properties of ionic, covalent and metallic structures?
ionic:
high melting n boiling points
soluble in water
conduct electricity when molten or dissolved in water
brittle
covalent:
high melting n boiling points
insoluble in water
apart from graphite, does not conduct electricity
apart from graphite, hard
metallic:
high melting n boiling points
insoluble in water
conduct electricity when solid or molten
malleable and ductile
Describe the properties of simple molecular substances
have low melting and boiling points because they have weak intermolecular forces
solubility depends of if its polar or non polar
also cannot conduct electricity
