Molecular Shape & Bonding Flashcards
Why do chemical bonds form?
They lower the potential energy between charged particles that constitute atoms.
What is the difference between a pure covalent bond and a polar covalent bond? And which is more electronegatively different?
Pure= electrons equally shared, polar= electrons shared unequally.
Polar bond more electronegatively different
Which is more electronegatively different an ionic bond or a covalent bond?
Ionic
What happens in an ionic bond? And what holds this bond together?
Metal loses electron becoming a cation (due to metals having low ionisation energy- does not take a lot of energy to remove an electron)
Non-metal gains an electron becoming an anion (because it has a high electron affinity)
Ions held together by electrostatic attraction
What are the main properties of an ionic bond?
-ionisation energy & electron affinity
-structure
-heat of formation is
The ionisation energy (energy used to remove an electron) to form the cation is endothermic
The acceptance of an electron (electron affinity) by the non metal is exothermic
Forms a highly structured crystal lattice, means that the heat of formation is a large exothermic value
What are valence electrons?
The outermost electrons of an atom
What is Lewis Theory?
The valence electrons are held most loosely and hence are used in bonding.
Elements in a column of periodic table have the same properties because they have the same amount of valence electrons
What does Lewis theory say about ionic bonding?
Electrons are transferred from one atom to another atom- forming ions.
One atom needs to lose a valence electron(s) whilst another must gain an extra electron(s) into its valence shell.
What is the octet rule?
Aka rule of 8, represents a very stable configuration for some atoms. Corresponds to the nearest inert-gas configuration.
What would you describe an element with a low ionisation energy as?
Electropositive e.g Na
What are the main properties of ionic compounds?
High melting and boiling points
Solids at room temp
The larger the ion the weaker the attraction so has lower lattice energy
The larger the charge the stronger attraction so higher lattice energy
What does Lewis theory say about covalent compounds?
Octet rule applies, achieve octet by sharing electrons
The bond consists of a shared pair of electrons
What are the electrons that are not shared in the covalent bond called?
Lone pairs of electrons
What is the formula for the assignment of a formal charge?
Number of valence electrons - (no. of lone pair electrons + 1/2 no. bonding electrons)
What is a single unpaired electron called?
A free radical
What is the definition of electronegativity?
The ability of an atom to pull bonding electrons towards itself
What is a polar covalent bond and why does one form?
Covalent bonding between atoms which have different electronegativities, causes electrons to be shared unequally.
Creates polarity (one atom has a slightly negative charge, other has slightly positive)
Occurs because one atom is more electronegative so pulls electrons towards it
Give some examples of polar covalent bonds and how do you know they are polar?
HCl, H2O, NH3
They have a dipole
What are the most and least electronegatively atoms?
Fluorine-most (halogens are very electronegative)
Cesium- least (metals are not very electronegative)
How do you work out the size of a dipole?
Indicated by dipole moment (D)
D= e x d
e=magnitude of charge of an atom
d=distance between the two charges
