Chemical Bonding Flashcards
What are the Nobel gases?
Helium
Neon
Argon
Krypton
Xenon
Radon
Key properties of the Nobel Gases
8e- in outer shell
very stable
most unreactive of all elements
monatomic
don’t usually form bonds with other elements
fulfil Lewis Octet rule
8 e- in valence shell (8e- in s and p orbitals)
define: valence shell
outermost occupied shell of an atom
highest principle quantum umber
e- are most likely to participate in bonding
atoms with valence shell not will form chemical bonds
types of e-
core e-
valence e- (only important in bonding)
define: ionic bond
electrostatic attraction forms between oppositely charged ions
arises from transfer of e- between atoms
define: covalent bond
shared pair of e- between atoms
ionic bonding; losing e-
more H+ than e-
positive charge
called positive ions or cations
generally s & d block elements
ionic bonding; gaining e-
more e- than H+
negative charge
called negative ions or anions
generally p block elements
Example of ionic compound
Sodium Chloride
Ions held together by electrostatic forces
contains one cation and one anion - neutral charge
ionic compounds have neutral charge
toral charge of anions and cations must be equal
ionic compounds form giant 3D structures called ionic lattices
covalent bonding
many elements exist as molecules
held together by a covalent bond
simple diatomic molecules
Different elements combine to form covalent bonds
Represented by lines or wedges
covalent bonding: fluorine
requires 1e- for full outer shell
forms diatomic fluorine
single F-F bond
covalent bonding: chlorine
requires 1e- for full valence shell
forms diatomic chlorine
single cl-cl bond
covalent bonding: oxygen
requires 2e- for full outer shell
forms diatomic O2
double O=O bond
covalent bonding: nitrogen
requires 3e- for full outer shell
forms diatomic N2
Triple N-N bond
define: electronegativity
describes the power of an atom in a molecule to attract e- towards itself
has no units
high electronegativity = pulls e- more strongly towards itself
low electronegativity = pulls e- more weakly towards itself
what are the most electronegative element?
nitrogen
oxygen
fluorine
chlorine
periodic property
electronegativity dependent on position of an element in periodic table
nuclear charge
atomic radius
e- shielding
atom has higher electronegativity if it has?
higher nuclear charge
small atomic radius
low amount of shielding
how to predict bond ionic or covalent
calculate difference in values of electronegativity
predict ionic?
difference has to be GREATER than 1.7
predict covalent?
difference has to be LESS than 1.7
Polar bonds - hydrogen chloride
special case
gaseous- H and Cl are covalently bonded - polar covalent bond
aqueous- ionises completely H+ and Cl-
electronegativity difference 0.9
covalent or ionic scale of bonding
ionic or covalent tend to have different properties
can predict via:
boiling point
melting point
solubility in water
electrical conductivity
further ionic bonding
some atoms behave as a single entity when they are a compound:
phosphate -3
sulphate -2
carbonate -2
nitrate -1
hydroxide -1
ammonium +1
further covalent bonding
not all e- need to be covalently bonded to fill valence
unbounded pairs of e- are lone pairs
lone pairs can be shared with ions
forming dative covalent bonds
what is a dative covalent bond?
a bond where a lone pair of e- is shared with an ion
describe why atoms form chemical bonds
unfilled valence orbitals will form chemical bonds with other atoms
to fulfil octet rule with 8e- in valence shell
predict type of bond formed between atoms depending on?
position of elements in periodic table
difference in electronegativity (ionic or covalent)
electronic configuration (single, double, triple covalent)
