Chapter 6 Shape of Molecules and Intermolecular Forces Flashcards
What is the electron-pair repulsion theory?
Electron pairs surrounding a central atom determine the shape of the molecule or ion.
Electron pairs repel one another so that they are arranged as far apart as possible
Arrangement of electron pairs minimises repulsion and holds the bonded atoms in a definite shape.
What is the strength of electron pairs?
bonded-pair/bonded-pair<bonded-pair/lone-pair<lobe-pair/lone-pair
What affect does the number of lone-pair electrons have on the bond angles?
Decreases the bond angle by 2.5 for each lone pair, as they repel more strongly than bonded-pairs.
What is electronegativity?
The attraction of a bonded atom for the pair of electrons in a covalent bond
What is Pauling electronegativity values?
Indicating the strength of the electronegativity.
Electronegativity increases across and up the table
What are non-polar bonds?
A bonded electron pair is shared equally between the bonded atoms. When bonded atoms are the same or have similar electronegativity
What are polar bonds?
Bonded electrons pair is shared unequally between the bonded atoms.
What are intermolecular forces?
Weak interactions between dipoles of different molecules.
Responsible for physical properties
What are induced dipole-dipole interactions (London forces)?
Weak intermolecular forces that exist between all molecules, whether polar or non-polar
How does induced dipole-dipole interaction work?
Movement of electrons produces a changing dipole in a molecule.
Instantaneous dipoles exist but the position is constantly changing, inducing a dipole on neighbouring molecules, attracting one another
What is the effect of electrons on London forces?
The more electrons in each molecule, the larger the instantaneous and induced dipoles, the stronger the attractive forces, more energy needed to overcome intermolecular forces, increasing boiling point.
What is permanent dipole-dipole forces?
Interactions between permanent dipoles in different polar molecules
What are simple molecular substances?
Made up of simple molecules- small units containing a definite number of atoms with a definite molecular formula.
What is the structure of simple molecular substances?
Simple molecular lattice, molecules are held by weak intermolecular forces, atoms within each molecule are bonded together strongly by covalent bonds
What are the properties of simple molecular substances?
Low melting and boiling point, which only the intermolecular forces break, the covalent bonds don’t.
Intermolecular forces break and dissolve in non-polar solvent. insoluble in polar solvents
Do not conduct electricity
What is hydrogen bonding?
Special type of permanent dipole-dipole interaction found between molecules containing an electronegative atom with a lone pair of electrons or a hydrogen atom attached to an electronegative atom.
Strongest type of intermolecular attractions.
How does hydorgen bond work?
Acts between a lone pair of electrons on an electronegative atom in one molecule and a hydrogen atom in a different molecule
Why is ice less dense than water?
Hydrogen bonds hold water apart in open lattice structure, which water molecules in ice are further apart than in water, so ice is less dense than water.
Why does water have high boiling point?
Have hydrogen bonds over and above London forces, which requires high energy to overcome the forces.
What is the property of hydrogen bonds?
High surface tension
High viscosity
