chem bonding Flashcards
what is electronegativity?
the measure of an atom’s ability to attract electrons in a covalent bonds to itself
what is the trend of electronegativity down a group? explain.
down a group, electronegativity decreases - effective charge increase, shielding effect increase, no. of quantum shells increase, hence outermost electrons are further away from nucleus so nucleus of the atom has a weaker attraction for electrons of another nucleus
what is the trend of electronegativity across the period?explain.
across a period, electronegativity increases - effective nuclear charge increase, shielding effect remains unchanged, hence nucleus of atom has higher attraction for electrons of another nucleus
what is a covalent bond?
the electrostatic force of attraction between the positively charged nucleus of both atoms and their shared electrons
what are the factors affecting the strength of a covalent bond?
- bond length - bond length increase, covalent bond strength decrease
- bond order - no. of covalent bonds between a pair of atoms - bond order increase, bond strength increase
what is a sigma bond and a pi bond?
head on overlap and side on overlap. a sigma bond must exist first for a pi bond to exist
what is a metallic bond?
the electrostatic force of attraction between a lattice of metal cations and sea of delocalised valence electrons
what are the factors affecting the strength of a metallic bond?
- charge and radius of cation - charge increase, radius decrease, charge density increase, hence strength increase
- no. of valence electrons contributed per atom - ~ increase, no. of delocalised electrons increase, hence strength increase
what are alloys? what are the properties of alloys?
they are mixtures of metals (with small quantities of other elements). they make metals harder as the atoms of different sizes disrupt the orderly arrangement of the main metal atoms so they cannot slide over each other easily when force is applied.
what is an ionic bond?
it is the electrostatic force of attraction between oppositely charged ions in a giant ionic lattice
what are the factors affecting the strength of ionic bonding?
- ionic charge (greater impact)
2. ionic radius
what is lattice energy?
the heat evolved when 1 mole of pure ionic solid is formed from its constituent gaseous ions
what are the types of intermolecular forces of attraction?
- dispersion forces/ instantaneous dipole-induced dipole attraction
- permanent dipole-permanent dipole attraction
- hydrogen bonding
when do dispersion forces occur?
non polar molecules/atoms
what are the factors affecting the strength of dispersion forces?
- no. of electrons - ~increase, size of electron cloud increase, polarisability increase, dispersion forces form more easily, hence strength increase
- surface area of of contact - ~increase, s.a for electron cloud to be distorted increase (for molecules with a similar no. of electrons)
what are the factors affecting the strength of pd-pd attractions?
net dipole moment - ~increase, strength increase
when do pd-pd attractions occur?
polar molecules
what are the conditions for hydrogen bonding to occur?
- one molecule must contain a hydrogen atom bonded to F, O or N
- the other molecule must have F, O or N with lone pair of electrons
what is a giant molecular compound
a network of covalent solids which do not consist of discrete molecules. the atoms are held together by covalent bonds in a giant covalent lattice structure
what is the structure of diamond?
each c atom is covalently bonded to 4 other c atoms and form a tetrahedral structure
what are the properties of diamond?
hard, high mp/bp/insoluble in any solvent
what is the structure of graphite?
each c atom is covalently bonded to 3 other c atoms
what is the structure of quartz/sand?
each si atom is covalently bonded to 4 other o atoms and each o atom is covalently bonded to 2 other si atoms
what makes an ionic compound soluble in water?
ion-dipole interactions - occurs between an ion and the oppositely charged end of a dipole, is weaker than ionic bonding but stronger than hydrogen bonding, pd-pd and dispersion forces
how do you explain the solubility/ miscibility of a substance in a given solvent?
- identify type of interaction holding solute particles together and solvent particles together
- identify type of interaction that can occur between solute and solvent particles
- compare relative strength
- since the energy released from solute-solvent interactions is greater than or comparable to the energy required to overcome solute-solute interactions and solvent-solvent interactions, X is soluble/ miscible in Y
what is dative bonding?
when one of the atoms provides both bonding electrons
what are the conditions for a dative bond to form?
- donor atom must have a lone pair of electrons
2. acceptor atom must contain an empty orbital in its valence shell
what is an electron deficient species?
an atom/molecule that requires fewer than the number of electrons required for maximum stability
why does expansion of octet occur?
elements from period 3 onwards can utilise their d orbitals in covalent bonding as d orbitals are energetically accessible
why are some elements unable to undergo expansion of octet?
their 3d orbitals are not energetically accessible as 3d orbitals are in a different outer quantum shell, which is at a much higher energy level than its valence shell
