3. Bonding Flashcards
(23 cards)
Define ionic bonding
The electrostatic attraction between oppositely charged ions formed by electron transfer
How do metals ionic bond?
Lose electrons (become +ve cations) due to low electronegativity
How do non-metals ionic bond?
Gain electrons (become -ve anions) due to high electronegativity
Define covalent bond
The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms. Attraction of the electrons is greater than the repulsion between the nuclei.
Define bonding pair
Pair of electrons shared between 2 electrons
Define lone pair
Pair of unshared electrons in the outer shell of an atom
Define polyatomic ion
An ion containing more than one atom, held by covalent bonds eg SO4^2-
Define octet rule
When reacting, atom tends to gain, lose or share electrons to achieve right in its outer shell
Give examples of compounds that don’t follow the octet rule
BeCl2 (Be is electron deficient)
BF3 (B is electron deficient
PCl5 (P is expanded octet)
How do electron deficient atoms occur?
- element with less than 4 outer shell electrons usually lose electrons to form ions, but for small atoms, the relevant ionisation energies may be so high that covalent bonding occurs instead
- as there are less than 4 electrons available for sharing, there will be less than eight outer shell electrons per atom in the resulting compound
Describe how PCl5 is expanded octet
- elements in the third period can become expanded octet due to the presence of empty 3d orbitals
- phosphorus ground state has 3 unpaired electrons in 3p orbitals, in excited state one 3s electron is promoted to 3d orbital
- as this occurs in excited state, PCl5 tends to be unstable decomposing to PCl3 and Cl2
Define coordinate (dative) bond
A shared pair of electrons between two atoms with both electrons shared by one atom - formed between atoms when one of the atoms donates both electrons (lone pair) to the bond
Give an example of a compound with a dative bond
NH4
Define electronegativity
The extent to which an atom attracts the bonding electrons in a covalent bond
Define polar bond
A covalent bond in which there is unequal sharing of the bonding electrons, often due to differences in electronegativity between two atoms
Why does electronegativity decrease down a group?
Increasing size of atoms
Why does electronegativity increase across a period?
Increasing nuclear charge decreases size of atoms
What are the most electronegative elements?
Top right hand corner - Fluorine is most electronegative element
What is the name of the scale used to determine the electronegativity of elements?
Pauling scale
How does the difference in electronegativity dictate the degree of ionic character in covalent bonds?
0 difference = pure covalent eg H-H, C-H, Cl-Cl
>1.7 difference = predominantly ionic eg Na+ Cl-
<1.7 difference = polar covalent eg HCl
Define metallic bonding
Attraction between positive metal ions and delocalised negative electrons
Describe metallic bonding
- in a metal, the atoms are packed closely together in a regular lattice
- the outer electrons of the atoms are relatively easily removed. The valence electrons are no longer located in the outer shell of one particular metal atom but are attracted by a number of the surrounding nuclei
Why does the electrical conductivity of the metals increase from group 1 to 3?
Directly related to the number of delocalised electrons
