topic 2 - structure and bonding Flashcards
what is an ion
a positively or negatively charged atom
what is ionic bonding
the strong electrostatic force of attraction between oppositely charged ions formed by electron transfer
what does isoelectronic mean
same electronic structure
metal ions
lose electrons to form positive ions
non-metal ions
gain electrons to form negative ions
what are the physical properties of ionic compounds
- high melting points ( there are strong attractive forces between the ions )
- non-conductor of electricity when solid ( ions are held together tightly and can not move )
- conductor of electricity when in solution or molten (ions free to move )
- brittle/easy to cleave apart ( force of repulsion if ions move which pushes the layers apart )
- generally soluble in water ( water is very polar. it can disrupt the electrostatic force of attraction between the ions and break them up )
what is covalent bonding
a covalent bond is strong and is caused by the electrostatic attraction between the bonding shared pair of electrons and the two nuclei.
a shared pair of electrons with opposite spins to obtain full orbitals
what is a dative covalent bond
dative covalent bond forms when both electrons are donated by the same atom
where direction of the arrow go to in dative bonding
goes from the atom that is providing the lone pair to the atom that is deficient
what are the factors affecting the length of a covalent bond
- size of the atoms involved ( radius ), the bigger the atom the bigger the bond
- difference in electronegativity ( polarity ), polar covalent bonds are longer
- overall structure, size, number of atoms around central atom
what are bond lengths measured in
picometres (pm)
what is bond strength measured in
KJmol-1 ( how much energy released when they form / bond enthalpy )
what is the link between length and strength of covalent bond
the shorter a covalent bond, the stronger it is ( inversely proportional )
large atomic radius = pair of electrons are far away from the nucleus
what is electronegativity
the relative ability of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself
where does a permanent dipole-dipole force occur and what effect does that make to melting and boiling point
occurs between polar molecules
commonly compounds with C-Cl, C-F, C-Br, H-Cl, C–O bonds
polar molecules are asymmetrical and have a bond where there is a significant difference in electronegativity between the atoms
higher melting and boiling points
what is the strength of a dipole-dipole force compared hydrogen bonds and london forces
- weaker than hydrogen bonding
- stronger than london forces
where do london forces occur and what are its properties
they occur in all molecules and are the weakest intermolecular force of all ( but the strength does vary, bigger Mr=stronger london force because more electrons are involved )
this means it has an increased melting and boiling point so more energy needed to break intermolecular forces
where do induced dipole forces only occur
- monatomic elements, cannot be polar
diatomic elements , because they have the same electronegativity so no permanent dipole - larger non-polar molecules such as CO2, alkanes and AlCl3, because they are symmetrical with no obvious dipoles
where does hydrogen bonding occur
occurs between molecules that contain a hydrogen atom directly bonded to nitrogen, oxygen or flourine ( most electronegative elements )
it is the strongest intermolecular force ( essentially just a very strong dipole )
- hydrogen flouride , water and ammonia
have a much higher melting and boiling points
what is solubility
solubility of a solute in solvent is a complicated balance of energy required to break bonds in the solute and solvent against energy given out making new bonds between the solute and solvent
solubility is the maximum amount of a solute that can dissolve in a given quantity of solvent at a specific temperature and pressure, forming a saturated solution.
what is the solubility of simple alcohols
the smaller alcohols are soluble in water because they can form hydrogen bonds with water. decreases as the hydrocarbon chain length increases because the non-polar alkyl (hydrocarbon) part resists interaction with water.
