shapes of molecules and intermolecular forces chp 6 Flashcards
what is electron-pair repulsion theory used for
The electron-pair repulsion theory is a model used in chemistry for explaining and predicting the shapes of molecules and polyatomic ions
what are the main ideas behind electron-pair repulsion theory
- number of electron pairs arround central atom determine shape of molecule
- electron pairs repel eachother as far away as possible
- static shape of molecule is where repulsion between pairs is minimised
when drawing a molecule is 3D what does a solid line represent
represents a bond in the plane of the paper
when drawing a molecule in 3D what does a dotted wedge represent
represents a bond going into the plane of the paper
When drawing a molecule in 3D what does a solid wedge represent
it represents a bond coming out of the plane of the paper
why do lone pairs have a stronger repulsive force than bonded pairs
A lone pair of electrons is slightly closer to the central atom, and occupies more space than a bonded pair. This results in lone pairs repelling more strongly.
what is the trend in repulsion between pairs of different kinds
what is the shapes table
bonded pairs on left, lone pairs on right side
what actually is the bond angle
the angle between the bonded pair of electrons
what are some examples of ions with a trigonal planar strcuture
what is an example of an ion that has a tetrahedral structure
what is electronegativity
electronegativity is a measure of an atoms ability to attract electron towards it in a covalent bond
on what scale is the electronegativity measured
the pauling scale
what is the trend in electronegativity across the periodic table
increases up and across the peridoic table
if the pauling value is high does that mean the element is highly electronegative or barly electronegative
it means its highly electronegative
what are the most electronegative elements
- nitrogen
- oxygen
- fluroine
- chlorine
what are the least electronegative elements
- group 1 metals
what differences do there need to be in the pauling value of atoms for different types of bonding to occur
how are electrons shared in a non-polar bond
in a non-polar, the bonded electron pair is shared equally between the bonded atoms
when will a bond be non-polar
-if the bonded atoms are the same
-the bonded atoms have the same or similar electronegativity
what is a pure covalent bond
a covalent bond that forms between two atoms of the same element and so the electrons are shared between the atoms equally.
what is a polar bond
- bonded electron pair is shared unequally between bonded atoms
- polar when pauling values differing by 0.4
what is a dipole
- a charge separation due to uneven electron sharing in a covalent bond,
what are the characteristics of a dipole on a non-polar molecule
- a dipole on a non-polar molecule will be an induced dipole brought about my nucleo/electrophiles
how can multiple permenant dipoles within a molecule effect the overall features of the molecule
- if acting in opposite directions can cancel out
- may reinforce one another producing larger dipole
what are intermolecular forces
- weak interactions between dipoles of different molecules
what are the 3 main categories of intermolecular forces
- induced dipole-dipole intertactions (london forces)
- permanent dipole-dipole interactions
- hydrogen bonding
what are characteristics that intermolecular forces are largely responsible for
responsible for physical properties such as melting and boiling points, whereas covalent bonds determine the identity and chemical reactions of molecules
what is the trend in intermolecular force strength within the 3 main categories
what are london forces
London forces are weak intermolecular forces that exist between all molecules, wether polar or non-polar, They act between induced dipoles in different molecules.
How are induced dipoles formed
-movement of electrons produces a changing dipole in a molecule
-at any instant, an instantaneous dipole will exist, but its position is constantly shifting
-The instantaneous dipole induces a dipole on a neighbouring molecule
-The induced dipole induces further dipoles on neighbouring molecules, which then attract one another
what determines the strength of an induced dipole
the number of electrons in the molecule
what do more electrons in a molecule mean for the induced dipole
the more the electrons in each molecule:
-the larger the instantaneous and induced dipoles
-the greater the induced dipole-dipole interactions
-the stronger the attractive forces between molecules
How does the number of electrons and therefore the characteristics of the induced dipole within a molecules affect the boiling point of the molecule
-larger numbers of electrons mean larger induced dipoles
-more energy is then needed to overcome the intermolecular forces, increasing the boiling point
what is a simple molecular substance
A simple molecular substance is made up of simple molecules (small units containing a definite number of atoms with a definite formula).
what is the structure of simple molecular substances when in a solid state
simple molecules form a regular structure called a simple molecular lattice
what are the features of a simple molecular covlanet lattice
low melting and boling point with varying solubility depending on the polarity
what explains the low melting and boiling point in a simple molecular substance
- Intermolecular forces: Weak forces (van der Waals, dipole-dipole, hydrogen bonding) between molecules
- Molecular size: Smaller molecules experience weaker london forces
- Polarity: Nonpolar molecules have lower melting and boiling points compared to polar molecules due to weaker intermolecular forces.
what occurs when a simple molecular substance is melted
only the weak intermolecular forces break, the covalent bonds are strong and do not break
what is the solubility of non-polar simple molecular substances in non-polar solvents
- compounds are soluble
- interactions between solvent and compound which causes compound to dissolve
what is the solubility of non-polar simple molecular substances in polar solvents
- they are insoluble
^intermolecular bonding within polar solvent is too strong to be broken
^little interaction between substances
what is the solubility of polar simple molecular substances
-Polar covalent substances may dissolve in polar solvents as the polar solute molecules and the polar solvent molecules can attract each other(process is similar to dissolving ionic compounds).
what determins the solubility of polar simple molecular substances
the solubility depends on the strength of the dipole of each atom of each element within the polar simple molecular substances.
Can a substances dissolve in both polar and non-polar solvents
compounds containing both polar and non-polar parts in their structure such as ethanol can dissolve in both polar and non-polar solvents
Are simple molecular compounds electrically conductive
- no charge carriers so no matter if solid, molten or aqeous will not conduct electricity
covalent bonding
what is a Hydrogen bond
a hydrogen bond is a special type of permanent dipole-dipole interaction found between molecules containing:
-an electronegative atom with a lone pair of electrons
-a hydrogen atom attached to an electronegative atom
Are hydrogen bonds strong or weak
strong, they are the strongest type of intermolecular attractions
How does hydrogen bonding affect the density of solid water
- Hydrogen bonds hold water molecules apart in an open lattice structure
- the water molecules in ice are further apart than in water
- solid ice is less dense than liquid water floats
How does hydrogen bonding affect the melting and boiling points of water
- it increases the boiling/melting point
^high quantity energy needed to melt/boil water than if just had london forces
