Chapter 6 - Shapes Of Molecules And Intermolecular Forces Flashcards
(33 cards)
What is the electron-pair repulsion theory?
- electrons repel one another
- electron pairs surrounding a central atom determines the shape of the molecule/ion
- electron pair repel to be as fair apart as possible
- arrangement of electron pair minimises repulsion holding the bond in a specific shape
- different number of electron = different shape
What are three-dimensional shape s used to represent molecules 3D shape?
- a straight line = bond IN plane of the page
- a triangle filled = bond is coming OUT the page
- a triangle made out of multiple lines = bong going INTO the page
The shape of molecules depend on …………………………………….
Number of pairs of electrons
What must be included for a molecule to have a LINEAR shape?
- 2 electron pairs
* 180° between each bond
What must be included for a molecule to have a TRIGONAL PLANAR shape?
- 3 electron pairs
* 120° angles between each bond
What must be included for a molecule to have a TETRAHEDRAL shape?
- 4 electron pairs
- 109.5° between each bond
- 0 lone-pairs
What must be included for a molecule to have a OCTOHEDRAL shape?
- 6 electron pairs
* 90° between each bond
How do lone pairs effect the shape of a molecule?
- it is closer to the central atom and occupies more space
- higher repulsion decreases the bond angle
- bond angle reduce by 2.5° for each lone pair bench changing the shape of the molecule
What must be included for a molecule to have a pyramidal shape?
- 3 bond pairs
- 1 lone-pair
- 107 ° between bonds
What must be included for a molecule to have a non-linear shape?
- 2 bond pairs
- 2 lone-pairs
- 104.5° between each bond
What’s electronegativity?
The attraction of a bonded atom for the pair of electrons in a covalent bond
How is electronegativity measured?
Depends on the position of the periodic table
Increases across and increase up the periodic table
Complete the graph
Bond type Electronegativity difference
Covalent a)
Polar covalent b)
Ionic C)
a) 0
b) 0 to 1.8
c) greater than 1.8
Complete the sentence:
•if electronegativity are the same the ……………………….
•if the electronegativity are vastly different …………………… occurs
•if the electronegativity are slightly different ………………………. exists
•different electronegativity causes a ………………
- molecules is non-polar
- ionic bonding
- a polar molecule
- permeant dipole
What is a non-polar bond?
The bonded electron pair is shared equally between the bonded atoms
What molecules of elements have a pure covalent bond?
Hydrogen, oxygen and chlorine etc
What’s a polar covalent bond?
The bonded electron pair is shared unequally and have different electronegativity values
What’s a dipole?
Separation of opposite charges
Why are water molecules polar?
Each O-H bond has induced dipole which act in different directions and do not oppose directly
Why is carbon non-polar?
The double bond between C and O has a permanent dipole which act in different directly and exactly oppose. Hence, cancels out the dipole making the dipole 0
Complete the sentence:
Ionic solutes dissolve in ……
• polar solvents
What properties do covalent bonds have?
- intermolecular forces
* very strong
What are the three types do intermolecular forces? And in order of strength from lowest to highest
- induced dipole-dipole interaction ( known as London Forces)
- permeant dipole-dipole interactions
- hydrogen bonds
Outline the intermolecular force known as LONDON FORCES
- weakest intermolecular forces
- exists in all molecules
- at the beginning, there is an even distribution, the movement of electrons forming a dipole known as instantaneous dipole
- it is constantly changing
- the instantaneous dipole induces a dipole in another
- only temporary
